Hiie Ivanova - Academia.edu (original) (raw)

Papers by Hiie Ivanova

Research paper thumbnail of Reduced activity of glycine decarboxylase: effects on photosynthesis and respiration in potato leaves

Research paper thumbnail of Regulation of the Photosynthetic and Respiratory CO2 Exchange in Leaves by External Factors in the Light

The problems of interrelation of photosynthesis and respiration are actual up today. It has been ... more The problems of interrelation of photosynthesis and respiration are actual up today. It has been shown that respiratory processes are functioning in parallel with photosynthesis in the light (1, 2, 3, 4). Respiratory activity of mitochondria may be suppressed or enhanced by light depending on availability of substrates and the adenylate status of the cell (5). Both the primary and stored photosynthates may be the substrates of the Krebs cycle and the rate of mitochondrial decarboxylations to great extent is determined by their availability in different environmental conditions. The substrate level may be regulated by the mitochondrial pyruvate dehydrogenase complex (mPDC) which activity is reduced under photorespiratory conditions (2). Photorespiratory decarboxylation of glycine is the main CO2-producing reaction in mitochondria of C3 plants under normal conditions. Respiratory reactions made 3-15% the total rate of the decarboxylation of primary photosynthates. Photorespiratory decarboxylation of stored photosynthates 3 to 5 times exceeded the rate of respiratory decarboxylation of these compounds (6). At present the mechanisms of the main reactions of CO2 exchange in photosynthesizing leaves are known but a question of their environmental control needs the further examination. In this work by the means of a radio-gasometric method the basic components of photosynthetic and respiratory CO2 fluxes under different environmental conditions were measured and possible regulatory mechanisms discussed.

Research paper thumbnail of Regulation of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase in vivo: Control by High CO<sub>2</sub> Concentration

Photosynthetica, Jun 1, 2004

High CO 2 concentrations (HC) in air induce partial deactivation of ribulose-1,5-bisphosphate car... more High CO 2 concentrations (HC) in air induce partial deactivation of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC 4.1.1.39). Under saturating irradiance, increase in [CO 2 ] to 1 200 cm 3 m-3 reduces the concentration of operating carboxylation centres by 20-30 %. At a further increase in [CO 2 ], the activity remained on the same level. Under limiting irradiance, the lowest activity was reached at 600 cm 3 (CO 2) m-3. The presence of oxygen diminished deactivation, but O 2 failed to stimulate reactivation under high CO 2. Conditions that favour oxygenation of ribulose-1,5bisphosphate (RuBP) facilitated reactivation. Even HC did not act as an inhibitor. HC induces deactivation of RuBPCO by increasing the concentration of free reaction centres devoid of the substrate, which are more vulnerable to inhibition than the centres filled with substrates or products.

Research paper thumbnail of Quantitative analysis of photosynthetic carbon metabolism in protoplasts and intact leaves of barley. Determination of carbon fluxes and pool sizes of metabolites in different cellular compartments

BioSystems, Feb 1, 2011

Rates of carbon fluxes and pool sizes of photosynthetic metabolites in different cellular compart... more Rates of carbon fluxes and pool sizes of photosynthetic metabolites in different cellular compartments of barley protoplasts were calculated from the time curves of their labeling in the medium of 14 CO 2. Using membrane filtration procedure, kinetics of 14 C incorporation into the products of steady-state photosynthesis was determined separately in chloroplasts, mitochondria and cytosol of barley protoplasts illuminated for different periods in the air containing 14 CO 2. To extract the quantitative information, analytical labeling functions P(t) describing the dependence of 14 C content in the primary, intermediate and end products of a linear reaction chain upon the duration of tracer feeding have been derived. The parameters of these functions represent pool sizes of metabolites and rates of carbon fluxes. The values of these parameters were determined by fitting the experimental labeling curves to the functions P(t) by means of non-linear regression procedure. To elucidate the possible effects of fractionation on the photosynthetic carbon metabolism, the parameters of protoplasts were compared with corresponding values in intact leaves of barley.

Research paper thumbnail of C2 photosynthesis generates about 3-fold elevated leaf CO2 levels in the C3–C4 intermediate species Flaveria pubescens

Journal of Experimental Botany, Jun 10, 2014

Formation of a photorespiration-based CO 2-concentrating mechanism in C 3-C 4 intermediate plants... more Formation of a photorespiration-based CO 2-concentrating mechanism in C 3-C 4 intermediate plants is seen as a prerequisite for the evolution of C 4 photosynthesis, but it is not known how efficient this mechanism is. Here, using in vivo Rubisco carboxylation-to-oxygenation ratios as a proxy to assess relative intraplastidial CO 2 levels is suggested. Such ratios were determined for the C 3-C 4 intermediate species Flaveria pubescens compared with the closely related C 3 plant F. cronquistii and the C 4 plant F. trinervia. To this end, a model was developed to describe the major carbon fluxes and metabolite pools involved in photosynthetic-photorespiratory carbon metabolism and used quantitatively to evaluate the labelling kinetics during short-term 14 CO 2 incorporation. Our data suggest that the photorespiratory CO 2 pump elevates the intraplastidial CO 2 concentration about 3-fold in leaves of the C 3-C 4 intermediate species F. pubescens relative to the C 3 species F. cronquistii.

Research paper thumbnail of The Effects of Cold Acclimation on the Photosynthetic Carbon Metabolism in Leaves of Winter Rye (Secale Cereale L.)

Research paper thumbnail of Night and daytime water relations in five fast-growing tree species: Effects of environmental and endogenous variables

Ecohydrology, Nov 17, 2017

Our aim was to investigate the responses of night and daytime water fluxes to environmental stimu... more Our aim was to investigate the responses of night and daytime water fluxes to environmental stimuli and endogenous drivers in five tree species with different water-use strategies. Data analysis revealed that air vapour pressure deficit (VPD) and wind speed (U) were the main drivers of night-time sap flux density (Fnight) in all studied species. For Populus × wettsteinii, Populus tremula, Betula pendula and Alnus glutinosa VPD was also the major driver of daytime sap flux density (Fday). In Alnus incana VPD explained less from the total variation in Fday than the photosynthetic photon flux density (QP). The Fday versus VPD regression slope decreased significantly (P < 0.001) in the following sequence P. × wettsteinii = P. tremula > B. pendula > A. glutinosa > A. incana. However, the Fnight versus VPD regression slope declined (P < 0.05) in sequence P. × wettsteinii > B. pendula > P. tremula > A. incana = A. glutinosa. P. × wettsteinii and B. pendula demonstrated highest net photosynthesis rates (Pn) among the all investigated species. Multiple regression analysis (independent factors: leaf dark respiration rate and sucrose, glucose and starch contents) revealed that sucrose content was the only factor, which explained variation (R 2 = 0.35; P < 0.01) in predawn leaf conductance (gpd). Our findings suggest that trees ability to open stomata and lose water at night does not depend directly on their daily water-use strategy, but is determined probably by species photosynthetic capacity, growth potential and nitrogen-use strategy.

Research paper thumbnail of Light- and CO2-saturated photosynthesis: enhancement by oxygen

Photosynthesis Research, Jun 1, 2006

Oxygen may enhance CO 2-saturated photosynthesis in intact leaves, which display the Warburg effe... more Oxygen may enhance CO 2-saturated photosynthesis in intact leaves, which display the Warburg effect when illuminated at the current atmospheric level of CO 2 and O 2 , of about 350 ll l)1 and 21%, respectively. The magnitude of the stimulation depends on irradiance. The K M (O 2) of the stimulation is 128 lM (10.6% O 2). Maximum enhancement in wheat leaves is 6.1 and 5.3 lmol m)2 s)1 under 27.9 and 18.7 mW cm)2 , respectively, corresponding to a 25-30% increase in the ribulose 1,5-bisphosphate (RuBP) turnover rate if compared with O 2-free ambient gas phase. The stimulation appears in 5-10 s after a sharp increase in O 2. In response to a decrease in O 2 , the new stabilized rate is reached in 5-7 min. The stimulation does not involve any increase in the activity of Rubisco. The effect correlates with increased concentration of RuBP. Oxygen enhances CO 2-saturated photosynthesis by acting as a terminal electron acceptor in the photosynthetic electron transport. The magnitude of the effect may be adopted as an index of the pseudocyclic photophosphorylation in vivo. Abbreviations: C a-ambient CO 2 concentration; C w-concentration of dissolved CO 2 ; E f-free reaction centers of Rubisco; E T-the total concentration of active carboxylation centers; ER-Rubisco-RuBP complex; R f-free RuBP; R s-RuBP synthesis rate; R T-total RuBP; Rubisco-ribulose-1,5-bisphosphate carboxylase/oxygenase; RuBP-ribulose 1,5-bisphosphate

Research paper thumbnail of Specificity factor of Rubisco: estimation in intact leaves by carboxylation at different CO<sub>2</sub>/O<sub>2</sub> ratios

Photosynthetica, Jun 1, 2012

The specificity factor of Rubisco (S f) was estimated in intact leaves from the carboxylation of ... more The specificity factor of Rubisco (S f) was estimated in intact leaves from the carboxylation of ribulose-1,5-bisphosphate (RuBP) at various CO 2 /O 2 ratios. As oxygenation is calculated by the difference of the 14 CO 2 uptake by RuBP in the absence and presence of oxygen, it is important to choose the optimum CO 2 /O 2 ratios. At high CO 2 concentration (1,000 cm 3 m-3 and higher) oxygenation consumes less than 50% RuBP but the difference of concentrations of CO 2 at cell walls (C w) and at the carboxylation centers (C c) is 2-5% and the influence of mesophyll resistance (r md) is of minor importance. To accumulate large endogenous pool of RuBP, the leaves were preilluminated in the CO 2-and O 2-free gas environments for 8 to 10 s. Thereafter the light was switched off and the leaves were flushed with the gas containing different concentrations of 14 CO 2 and O 2. The specificity factor of Rubisco was calculated from the amount of the tracer taken up under different 14 CO 2 /O 2 ratios by the exhaustion of the RuBP pool. Application of 14 CO 2 allowed us to discriminate between the CO 2 uptake and the concurrent respiratory CO 2 release which proceeded at the expense of unlabelled intermediates.

Research paper thumbnail of Components of CO<sub>2</sub> exchange in leaves of C<sub>3</sub> species with different ability of starch accumulation

Photosynthetica, Mar 1, 2008

Using a radiogasometric method the rates of photorespiratory and respiratory decarboxylations of ... more Using a radiogasometric method the rates of photorespiratory and respiratory decarboxylations of primary and stored photosynthates in the leaves of two groups of C 3 species, differing in the ability of starch accumulation, were determined. One group included starch-accumulating (SA) species with rates of starch synthesis on the average 38 % the rate of photosynthesis [Solanum tuberosum L., Arabidopsis thaliana (L.) Heynh, Helianthus annuus L., and Plantago lanceolata L.]. The second group represented starch-deficient (SD) species with rates of starch synthesis less than 8 % the rate of photosynthesis (Secale cereale L., Triticum aestivum L., Hordeum vulgare L., and Poa trivialis L.). In SA species the rate of respiration in the dark was significantly higher than in SD species. No differences were found in the rates of photosynthesis, photorespiration, and respiration under irradiation. Thus, the degree of inhibition of respiration by irradiation was in SA species higher than in SD species. It is concluded that starch does not provide substrates for respiratory and photorespiratory decarboxylations in irradiated photosynthesizing leaves.

Research paper thumbnail of Photorespiratory and respiratory decarboxylations in leaves of C<sub>3</sub>plants under different CO<sub>2</sub>concentrations and irradiances

Plant Cell and Environment, Dec 1, 2007

ABSTRACTWe used an advanced radiogasometric method to study the effects of short‐term changes in ... more ABSTRACTWe used an advanced radiogasometric method to study the effects of short‐term changes in CO2 concentration ([CO2]) on the rates and substrates of photorespiratory and respiratory decarboxylations under steady‐state photosynthesis and in the dark. Experiments were carried out on Plantago lanceolata, Poa trivialis, Secale cereale, Triticum aestivum, Helianthus annuus and Arabidopsis thaliana plants. Rates of photorespiration and respiration measured at a low [CO2] (40 µmol mol−1) were equal to those at normal [CO2] (360 µmol mol−1). Under low [CO2], the substrates of decarboxylation reactions were derived mainly from stored photosynthates, while under normal [CO2] primary photosynthates were preferentially consumed. An increase in [CO2] from 320 to 2300 µmol mol−1 brought about a fourfold decrease in the rate of photorespiration with a concomitant 50% increase in the rate of respiration in the light. Respiration in the dark did not depend on [CO2] up to 30 mmol mol−1. A positive correlation was found between the rate of respiration in the dark and the rate of photosynthesis during the preceding light period. The respiratory decarboxylation of stored photosynthates was suppressed by light. The extent of light inhibition decreased with increasing [CO2]; no inhibition was detected at 30 mmol mol−1 CO2.

Research paper thumbnail of Contribution of primary and stored photosynthates to photorespiration and respiration in the light and in the dark

Research paper thumbnail of Tree age-dependent changes in photosynthetic and respiratory CO2 exchange in leaves of micropropagated diploid, triploid and hybrid aspen

Tree Physiology, Jun 1, 2014

The growth rate of triploid European aspen (Populus tremula L.) and hybrid aspen (P. tremula × Po... more The growth rate of triploid European aspen (Populus tremula L.) and hybrid aspen (P. tremula × Populus tremuloides Michx.) significantly exceeds that of diploid aspen, but the underlying physiological controls of the superior growth rates of these genotypes are not known. We tested the hypothesis that the superior growth rate of triploid and hybrid aspen reflects their greater net photosynthesis rate. Micropropagated clonal plants varying in age from 2.5 to 19 months were used to investigate the ploidy and plant age interaction. The quantum yield of net CO 2 fixation (Φ) in leaves of young 2.5-month-old hybrid aspen was lower than that of diploid and triploid trees. However, Φ in 19-month-old hybrid aspen was equal to that in triploid aspen and higher than that in diploid aspen. Φ and the rate of light-saturated net photosynthesis (A NS) increased with plant age, largely due to higher leaf dry mass per unit area in older plants. A NS in leaves of 19-month-old trees was highest in hybrid, medium in triploid and lowest in diploid aspen. Light-saturated photosynthesis had a broad temperature optimum between 20 and 35 °C. Rate of respiration in the dark (R DS) did not vary among the genotypes in 2.5-month-old plants, and the shape of the temperature response was also similar. R DS increased with plant age, but R DS was still not significantly different among the leaves of 19-month-old diploid and triploid aspen, but it was significantly lower in leaves of 19-month-old hybrid plants. The initial differences in the growth of plants with different ploidy were minor up to the age of 19 months, but during the next 2 years, the growth rate of hybrid aspen exceeded that of triploid plants by 2.7 times and of diploid plants by five times, in line with differences in A NS of 19-month-old plants of these species. It is suggested that differences in photosynthesis and growth became more pronounced with tree aging, indicating that ontogeny plays a key role in the expression of superior traits determining the productivity of given genotypes.

Research paper thumbnail of Responses of respiratory and photorespiratory decarboxylations to internel and external factors in C3 plants

Publication of this thesis is supported by Estonian University of Life Sciences. This research wa... more Publication of this thesis is supported by Estonian University of Life Sciences. This research was supported by the EU through the European Regional Development Fund (Center of Excellence ENVIRON).

Research paper thumbnail of CO2 Exchange Of Potato Transformants With Reduced Activities Of Glycine Decarboxylase

Elsevier eBooks, 2000

Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in ph... more Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in photosynthesising leaves of potato ( Solanum tuberosum L., var. Desiree) control plants and of its transformants (P1 and P15) with limited expression of glycine decarboxylase have been determined under normal environmental conditions. The rate of true photosynthesis was highest in leaves of control plants (16.0 μmol CO 2 m - 2 .s - 1 ). In transformant P1 it was 2 times lower while P15 showed an intermediate value. The same relationship was found for the total rate of intracellular decarboxylation in the light: 2.6, 1.3 and 1.8 μmol CO 2 m - 2 .s - 1 in leaves of control plants, P1 and P15, respectively. No differences were detected in the relative rate of intracellular decarboxylation indicating that transformants did not have any advantage with respect to respiratory losses during photosynthesis in the light. In all varieties the main substrates of decarboxylation were primary photosynthates, the contribution of stored photosynthates varied in the range from 15 to 25% the total rate of decarboxylation. The rate of photorespiration exceeded the rate of respiration 7.5 times in control plants and 1.8-2.5 times in transformants. The rate of respiration in the dark was in leaves of control plants 30-40% higher than in leaves of transformants. Light severely, about 20 times, inhibited this component of respiration in control plants but only 1.5 times in P1 and 5.5 times in P15. The specificity of Rubisco, determined in intact leaves in vivo , had significantly higher values in transformants compared to control plants. It has been shown that in transformants a portion of glycine was not decarboxylated by glycine decarboxylase but transported out of the glycolate cycle which results in a change of the stoichiometry between RuBP oxygenation and photorespiration and in an apparent increase of Rubisco specificity. In leaves of transformants the content of non-protein glycine was 3-5 times higher and the content of non-protein serine 6-15 times lower than in leaves of control plants.

Research paper thumbnail of Regulation of the Photosynthetic and Respiratory CO 2 Exchange in Leaves by External Factors in the Light

The problems of interrelation of photosynthesis and respiration are actual up today. It has been ... more The problems of interrelation of photosynthesis and respiration are actual up today. It has been shown that respiratory processes are functioning in parallel with photosynthesis in the light (1, 2, 3, 4). Respiratory activity of mitochondria may be suppressed or enhanced by light depending on availability of substrates and the adenylate status of the cell (5). Both the primary and stored photosynthates may be the substrates of the Krebs cycle and the rate of mitochondrial decarboxylations to great extent is determined by their availability in different environmental conditions. The substrate level may be regulated by the mitochondrial pyruvate dehydrogenase complex (mPDC) which activity is reduced under photorespiratory conditions (2). Photorespiratory decarboxylation of glycine is the main CO2-producing reaction in mitochondria of C3 plants under normal conditions. Respiratory reactions made 3-15% the total rate of the decarboxylation of primary photosynthates. Photorespiratory dec...

Research paper thumbnail of Effects of O2 and irradiance on CO2 assimilation in phaseolus vulgaris

Research paper thumbnail of Reduced activity of glycine decarboxylase: effects on photosynthesis and respiration in potato leaves

Science Access, 2001

Photosynthesis, respiration and carbon metabolism in photosynthesizing leaves of potato (Solanum ... more Photosynthesis, respiration and carbon metabolism in photosynthesizing leaves of potato (Solanum tuberosum L., var. Desiree) control plants and of its transformants (P1 and P15) with limited expression of glycine decarboxylase (GDC, EC 2.1.2.10) have been

Research paper thumbnail of CO2 Exchange Of Potato Transformants With Reduced Activities Of Glycine Decarboxylase

Developments in Plant Genetics and Breeding, 2000

Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in ph... more Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in photosynthesising leaves of potato ( Solanum tuberosum L., var. Desiree) control plants and of its transformants (P1 and P15) with limited expression of glycine decarboxylase have been determined under normal environmental conditions. The rate of true photosynthesis was highest in leaves of control plants (16.0 μmol CO 2 m - 2 .s - 1 ). In transformant P1 it was 2 times lower while P15 showed an intermediate value. The same relationship was found for the total rate of intracellular decarboxylation in the light: 2.6, 1.3 and 1.8 μmol CO 2 m - 2 .s - 1 in leaves of control plants, P1 and P15, respectively. No differences were detected in the relative rate of intracellular decarboxylation indicating that transformants did not have any advantage with respect to respiratory losses during photosynthesis in the light. In all varieties the main substrates of decarboxylation were primary photosynthates, the contribution of stored photosynthates varied in the range from 15 to 25% the total rate of decarboxylation. The rate of photorespiration exceeded the rate of respiration 7.5 times in control plants and 1.8-2.5 times in transformants. The rate of respiration in the dark was in leaves of control plants 30-40% higher than in leaves of transformants. Light severely, about 20 times, inhibited this component of respiration in control plants but only 1.5 times in P1 and 5.5 times in P15. The specificity of Rubisco, determined in intact leaves in vivo , had significantly higher values in transformants compared to control plants. It has been shown that in transformants a portion of glycine was not decarboxylated by glycine decarboxylase but transported out of the glycolate cycle which results in a change of the stoichiometry between RuBP oxygenation and photorespiration and in an apparent increase of Rubisco specificity. In leaves of transformants the content of non-protein glycine was 3-5 times higher and the content of non-protein serine 6-15 times lower than in leaves of control plants.

Research paper thumbnail of The Effects of Cold Acclimation on the Photosynthetic Carbon Metabolism in Leaves of Winter Rye (Secale Cereale L.)

Photosynthesis: from Light to Biosphere, 1995

Research paper thumbnail of Reduced activity of glycine decarboxylase: effects on photosynthesis and respiration in potato leaves

Research paper thumbnail of Regulation of the Photosynthetic and Respiratory CO2 Exchange in Leaves by External Factors in the Light

The problems of interrelation of photosynthesis and respiration are actual up today. It has been ... more The problems of interrelation of photosynthesis and respiration are actual up today. It has been shown that respiratory processes are functioning in parallel with photosynthesis in the light (1, 2, 3, 4). Respiratory activity of mitochondria may be suppressed or enhanced by light depending on availability of substrates and the adenylate status of the cell (5). Both the primary and stored photosynthates may be the substrates of the Krebs cycle and the rate of mitochondrial decarboxylations to great extent is determined by their availability in different environmental conditions. The substrate level may be regulated by the mitochondrial pyruvate dehydrogenase complex (mPDC) which activity is reduced under photorespiratory conditions (2). Photorespiratory decarboxylation of glycine is the main CO2-producing reaction in mitochondria of C3 plants under normal conditions. Respiratory reactions made 3-15% the total rate of the decarboxylation of primary photosynthates. Photorespiratory decarboxylation of stored photosynthates 3 to 5 times exceeded the rate of respiratory decarboxylation of these compounds (6). At present the mechanisms of the main reactions of CO2 exchange in photosynthesizing leaves are known but a question of their environmental control needs the further examination. In this work by the means of a radio-gasometric method the basic components of photosynthetic and respiratory CO2 fluxes under different environmental conditions were measured and possible regulatory mechanisms discussed.

Research paper thumbnail of Regulation of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase in vivo: Control by High CO<sub>2</sub> Concentration

Photosynthetica, Jun 1, 2004

High CO 2 concentrations (HC) in air induce partial deactivation of ribulose-1,5-bisphosphate car... more High CO 2 concentrations (HC) in air induce partial deactivation of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC 4.1.1.39). Under saturating irradiance, increase in [CO 2 ] to 1 200 cm 3 m-3 reduces the concentration of operating carboxylation centres by 20-30 %. At a further increase in [CO 2 ], the activity remained on the same level. Under limiting irradiance, the lowest activity was reached at 600 cm 3 (CO 2) m-3. The presence of oxygen diminished deactivation, but O 2 failed to stimulate reactivation under high CO 2. Conditions that favour oxygenation of ribulose-1,5bisphosphate (RuBP) facilitated reactivation. Even HC did not act as an inhibitor. HC induces deactivation of RuBPCO by increasing the concentration of free reaction centres devoid of the substrate, which are more vulnerable to inhibition than the centres filled with substrates or products.

Research paper thumbnail of Quantitative analysis of photosynthetic carbon metabolism in protoplasts and intact leaves of barley. Determination of carbon fluxes and pool sizes of metabolites in different cellular compartments

BioSystems, Feb 1, 2011

Rates of carbon fluxes and pool sizes of photosynthetic metabolites in different cellular compart... more Rates of carbon fluxes and pool sizes of photosynthetic metabolites in different cellular compartments of barley protoplasts were calculated from the time curves of their labeling in the medium of 14 CO 2. Using membrane filtration procedure, kinetics of 14 C incorporation into the products of steady-state photosynthesis was determined separately in chloroplasts, mitochondria and cytosol of barley protoplasts illuminated for different periods in the air containing 14 CO 2. To extract the quantitative information, analytical labeling functions P(t) describing the dependence of 14 C content in the primary, intermediate and end products of a linear reaction chain upon the duration of tracer feeding have been derived. The parameters of these functions represent pool sizes of metabolites and rates of carbon fluxes. The values of these parameters were determined by fitting the experimental labeling curves to the functions P(t) by means of non-linear regression procedure. To elucidate the possible effects of fractionation on the photosynthetic carbon metabolism, the parameters of protoplasts were compared with corresponding values in intact leaves of barley.

Research paper thumbnail of C2 photosynthesis generates about 3-fold elevated leaf CO2 levels in the C3–C4 intermediate species Flaveria pubescens

Journal of Experimental Botany, Jun 10, 2014

Formation of a photorespiration-based CO 2-concentrating mechanism in C 3-C 4 intermediate plants... more Formation of a photorespiration-based CO 2-concentrating mechanism in C 3-C 4 intermediate plants is seen as a prerequisite for the evolution of C 4 photosynthesis, but it is not known how efficient this mechanism is. Here, using in vivo Rubisco carboxylation-to-oxygenation ratios as a proxy to assess relative intraplastidial CO 2 levels is suggested. Such ratios were determined for the C 3-C 4 intermediate species Flaveria pubescens compared with the closely related C 3 plant F. cronquistii and the C 4 plant F. trinervia. To this end, a model was developed to describe the major carbon fluxes and metabolite pools involved in photosynthetic-photorespiratory carbon metabolism and used quantitatively to evaluate the labelling kinetics during short-term 14 CO 2 incorporation. Our data suggest that the photorespiratory CO 2 pump elevates the intraplastidial CO 2 concentration about 3-fold in leaves of the C 3-C 4 intermediate species F. pubescens relative to the C 3 species F. cronquistii.

Research paper thumbnail of The Effects of Cold Acclimation on the Photosynthetic Carbon Metabolism in Leaves of Winter Rye (Secale Cereale L.)

Research paper thumbnail of Night and daytime water relations in five fast-growing tree species: Effects of environmental and endogenous variables

Ecohydrology, Nov 17, 2017

Our aim was to investigate the responses of night and daytime water fluxes to environmental stimu... more Our aim was to investigate the responses of night and daytime water fluxes to environmental stimuli and endogenous drivers in five tree species with different water-use strategies. Data analysis revealed that air vapour pressure deficit (VPD) and wind speed (U) were the main drivers of night-time sap flux density (Fnight) in all studied species. For Populus × wettsteinii, Populus tremula, Betula pendula and Alnus glutinosa VPD was also the major driver of daytime sap flux density (Fday). In Alnus incana VPD explained less from the total variation in Fday than the photosynthetic photon flux density (QP). The Fday versus VPD regression slope decreased significantly (P < 0.001) in the following sequence P. × wettsteinii = P. tremula > B. pendula > A. glutinosa > A. incana. However, the Fnight versus VPD regression slope declined (P < 0.05) in sequence P. × wettsteinii > B. pendula > P. tremula > A. incana = A. glutinosa. P. × wettsteinii and B. pendula demonstrated highest net photosynthesis rates (Pn) among the all investigated species. Multiple regression analysis (independent factors: leaf dark respiration rate and sucrose, glucose and starch contents) revealed that sucrose content was the only factor, which explained variation (R 2 = 0.35; P < 0.01) in predawn leaf conductance (gpd). Our findings suggest that trees ability to open stomata and lose water at night does not depend directly on their daily water-use strategy, but is determined probably by species photosynthetic capacity, growth potential and nitrogen-use strategy.

Research paper thumbnail of Light- and CO2-saturated photosynthesis: enhancement by oxygen

Photosynthesis Research, Jun 1, 2006

Oxygen may enhance CO 2-saturated photosynthesis in intact leaves, which display the Warburg effe... more Oxygen may enhance CO 2-saturated photosynthesis in intact leaves, which display the Warburg effect when illuminated at the current atmospheric level of CO 2 and O 2 , of about 350 ll l)1 and 21%, respectively. The magnitude of the stimulation depends on irradiance. The K M (O 2) of the stimulation is 128 lM (10.6% O 2). Maximum enhancement in wheat leaves is 6.1 and 5.3 lmol m)2 s)1 under 27.9 and 18.7 mW cm)2 , respectively, corresponding to a 25-30% increase in the ribulose 1,5-bisphosphate (RuBP) turnover rate if compared with O 2-free ambient gas phase. The stimulation appears in 5-10 s after a sharp increase in O 2. In response to a decrease in O 2 , the new stabilized rate is reached in 5-7 min. The stimulation does not involve any increase in the activity of Rubisco. The effect correlates with increased concentration of RuBP. Oxygen enhances CO 2-saturated photosynthesis by acting as a terminal electron acceptor in the photosynthetic electron transport. The magnitude of the effect may be adopted as an index of the pseudocyclic photophosphorylation in vivo. Abbreviations: C a-ambient CO 2 concentration; C w-concentration of dissolved CO 2 ; E f-free reaction centers of Rubisco; E T-the total concentration of active carboxylation centers; ER-Rubisco-RuBP complex; R f-free RuBP; R s-RuBP synthesis rate; R T-total RuBP; Rubisco-ribulose-1,5-bisphosphate carboxylase/oxygenase; RuBP-ribulose 1,5-bisphosphate

Research paper thumbnail of Specificity factor of Rubisco: estimation in intact leaves by carboxylation at different CO<sub>2</sub>/O<sub>2</sub> ratios

Photosynthetica, Jun 1, 2012

The specificity factor of Rubisco (S f) was estimated in intact leaves from the carboxylation of ... more The specificity factor of Rubisco (S f) was estimated in intact leaves from the carboxylation of ribulose-1,5-bisphosphate (RuBP) at various CO 2 /O 2 ratios. As oxygenation is calculated by the difference of the 14 CO 2 uptake by RuBP in the absence and presence of oxygen, it is important to choose the optimum CO 2 /O 2 ratios. At high CO 2 concentration (1,000 cm 3 m-3 and higher) oxygenation consumes less than 50% RuBP but the difference of concentrations of CO 2 at cell walls (C w) and at the carboxylation centers (C c) is 2-5% and the influence of mesophyll resistance (r md) is of minor importance. To accumulate large endogenous pool of RuBP, the leaves were preilluminated in the CO 2-and O 2-free gas environments for 8 to 10 s. Thereafter the light was switched off and the leaves were flushed with the gas containing different concentrations of 14 CO 2 and O 2. The specificity factor of Rubisco was calculated from the amount of the tracer taken up under different 14 CO 2 /O 2 ratios by the exhaustion of the RuBP pool. Application of 14 CO 2 allowed us to discriminate between the CO 2 uptake and the concurrent respiratory CO 2 release which proceeded at the expense of unlabelled intermediates.

Research paper thumbnail of Components of CO<sub>2</sub> exchange in leaves of C<sub>3</sub> species with different ability of starch accumulation

Photosynthetica, Mar 1, 2008

Using a radiogasometric method the rates of photorespiratory and respiratory decarboxylations of ... more Using a radiogasometric method the rates of photorespiratory and respiratory decarboxylations of primary and stored photosynthates in the leaves of two groups of C 3 species, differing in the ability of starch accumulation, were determined. One group included starch-accumulating (SA) species with rates of starch synthesis on the average 38 % the rate of photosynthesis [Solanum tuberosum L., Arabidopsis thaliana (L.) Heynh, Helianthus annuus L., and Plantago lanceolata L.]. The second group represented starch-deficient (SD) species with rates of starch synthesis less than 8 % the rate of photosynthesis (Secale cereale L., Triticum aestivum L., Hordeum vulgare L., and Poa trivialis L.). In SA species the rate of respiration in the dark was significantly higher than in SD species. No differences were found in the rates of photosynthesis, photorespiration, and respiration under irradiation. Thus, the degree of inhibition of respiration by irradiation was in SA species higher than in SD species. It is concluded that starch does not provide substrates for respiratory and photorespiratory decarboxylations in irradiated photosynthesizing leaves.

Research paper thumbnail of Photorespiratory and respiratory decarboxylations in leaves of C<sub>3</sub>plants under different CO<sub>2</sub>concentrations and irradiances

Plant Cell and Environment, Dec 1, 2007

ABSTRACTWe used an advanced radiogasometric method to study the effects of short‐term changes in ... more ABSTRACTWe used an advanced radiogasometric method to study the effects of short‐term changes in CO2 concentration ([CO2]) on the rates and substrates of photorespiratory and respiratory decarboxylations under steady‐state photosynthesis and in the dark. Experiments were carried out on Plantago lanceolata, Poa trivialis, Secale cereale, Triticum aestivum, Helianthus annuus and Arabidopsis thaliana plants. Rates of photorespiration and respiration measured at a low [CO2] (40 µmol mol−1) were equal to those at normal [CO2] (360 µmol mol−1). Under low [CO2], the substrates of decarboxylation reactions were derived mainly from stored photosynthates, while under normal [CO2] primary photosynthates were preferentially consumed. An increase in [CO2] from 320 to 2300 µmol mol−1 brought about a fourfold decrease in the rate of photorespiration with a concomitant 50% increase in the rate of respiration in the light. Respiration in the dark did not depend on [CO2] up to 30 mmol mol−1. A positive correlation was found between the rate of respiration in the dark and the rate of photosynthesis during the preceding light period. The respiratory decarboxylation of stored photosynthates was suppressed by light. The extent of light inhibition decreased with increasing [CO2]; no inhibition was detected at 30 mmol mol−1 CO2.

Research paper thumbnail of Contribution of primary and stored photosynthates to photorespiration and respiration in the light and in the dark

Research paper thumbnail of Tree age-dependent changes in photosynthetic and respiratory CO2 exchange in leaves of micropropagated diploid, triploid and hybrid aspen

Tree Physiology, Jun 1, 2014

The growth rate of triploid European aspen (Populus tremula L.) and hybrid aspen (P. tremula × Po... more The growth rate of triploid European aspen (Populus tremula L.) and hybrid aspen (P. tremula × Populus tremuloides Michx.) significantly exceeds that of diploid aspen, but the underlying physiological controls of the superior growth rates of these genotypes are not known. We tested the hypothesis that the superior growth rate of triploid and hybrid aspen reflects their greater net photosynthesis rate. Micropropagated clonal plants varying in age from 2.5 to 19 months were used to investigate the ploidy and plant age interaction. The quantum yield of net CO 2 fixation (Φ) in leaves of young 2.5-month-old hybrid aspen was lower than that of diploid and triploid trees. However, Φ in 19-month-old hybrid aspen was equal to that in triploid aspen and higher than that in diploid aspen. Φ and the rate of light-saturated net photosynthesis (A NS) increased with plant age, largely due to higher leaf dry mass per unit area in older plants. A NS in leaves of 19-month-old trees was highest in hybrid, medium in triploid and lowest in diploid aspen. Light-saturated photosynthesis had a broad temperature optimum between 20 and 35 °C. Rate of respiration in the dark (R DS) did not vary among the genotypes in 2.5-month-old plants, and the shape of the temperature response was also similar. R DS increased with plant age, but R DS was still not significantly different among the leaves of 19-month-old diploid and triploid aspen, but it was significantly lower in leaves of 19-month-old hybrid plants. The initial differences in the growth of plants with different ploidy were minor up to the age of 19 months, but during the next 2 years, the growth rate of hybrid aspen exceeded that of triploid plants by 2.7 times and of diploid plants by five times, in line with differences in A NS of 19-month-old plants of these species. It is suggested that differences in photosynthesis and growth became more pronounced with tree aging, indicating that ontogeny plays a key role in the expression of superior traits determining the productivity of given genotypes.

Research paper thumbnail of Responses of respiratory and photorespiratory decarboxylations to internel and external factors in C3 plants

Publication of this thesis is supported by Estonian University of Life Sciences. This research wa... more Publication of this thesis is supported by Estonian University of Life Sciences. This research was supported by the EU through the European Regional Development Fund (Center of Excellence ENVIRON).

Research paper thumbnail of CO2 Exchange Of Potato Transformants With Reduced Activities Of Glycine Decarboxylase

Elsevier eBooks, 2000

Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in ph... more Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in photosynthesising leaves of potato ( Solanum tuberosum L., var. Desiree) control plants and of its transformants (P1 and P15) with limited expression of glycine decarboxylase have been determined under normal environmental conditions. The rate of true photosynthesis was highest in leaves of control plants (16.0 μmol CO 2 m - 2 .s - 1 ). In transformant P1 it was 2 times lower while P15 showed an intermediate value. The same relationship was found for the total rate of intracellular decarboxylation in the light: 2.6, 1.3 and 1.8 μmol CO 2 m - 2 .s - 1 in leaves of control plants, P1 and P15, respectively. No differences were detected in the relative rate of intracellular decarboxylation indicating that transformants did not have any advantage with respect to respiratory losses during photosynthesis in the light. In all varieties the main substrates of decarboxylation were primary photosynthates, the contribution of stored photosynthates varied in the range from 15 to 25% the total rate of decarboxylation. The rate of photorespiration exceeded the rate of respiration 7.5 times in control plants and 1.8-2.5 times in transformants. The rate of respiration in the dark was in leaves of control plants 30-40% higher than in leaves of transformants. Light severely, about 20 times, inhibited this component of respiration in control plants but only 1.5 times in P1 and 5.5 times in P15. The specificity of Rubisco, determined in intact leaves in vivo , had significantly higher values in transformants compared to control plants. It has been shown that in transformants a portion of glycine was not decarboxylated by glycine decarboxylase but transported out of the glycolate cycle which results in a change of the stoichiometry between RuBP oxygenation and photorespiration and in an apparent increase of Rubisco specificity. In leaves of transformants the content of non-protein glycine was 3-5 times higher and the content of non-protein serine 6-15 times lower than in leaves of control plants.

Research paper thumbnail of Regulation of the Photosynthetic and Respiratory CO 2 Exchange in Leaves by External Factors in the Light

The problems of interrelation of photosynthesis and respiration are actual up today. It has been ... more The problems of interrelation of photosynthesis and respiration are actual up today. It has been shown that respiratory processes are functioning in parallel with photosynthesis in the light (1, 2, 3, 4). Respiratory activity of mitochondria may be suppressed or enhanced by light depending on availability of substrates and the adenylate status of the cell (5). Both the primary and stored photosynthates may be the substrates of the Krebs cycle and the rate of mitochondrial decarboxylations to great extent is determined by their availability in different environmental conditions. The substrate level may be regulated by the mitochondrial pyruvate dehydrogenase complex (mPDC) which activity is reduced under photorespiratory conditions (2). Photorespiratory decarboxylation of glycine is the main CO2-producing reaction in mitochondria of C3 plants under normal conditions. Respiratory reactions made 3-15% the total rate of the decarboxylation of primary photosynthates. Photorespiratory dec...

Research paper thumbnail of Effects of O2 and irradiance on CO2 assimilation in phaseolus vulgaris

Research paper thumbnail of Reduced activity of glycine decarboxylase: effects on photosynthesis and respiration in potato leaves

Science Access, 2001

Photosynthesis, respiration and carbon metabolism in photosynthesizing leaves of potato (Solanum ... more Photosynthesis, respiration and carbon metabolism in photosynthesizing leaves of potato (Solanum tuberosum L., var. Desiree) control plants and of its transformants (P1 and P15) with limited expression of glycine decarboxylase (GDC, EC 2.1.2.10) have been

Research paper thumbnail of CO2 Exchange Of Potato Transformants With Reduced Activities Of Glycine Decarboxylase

Developments in Plant Genetics and Breeding, 2000

Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in ph... more Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in photosynthesising leaves of potato ( Solanum tuberosum L., var. Desiree) control plants and of its transformants (P1 and P15) with limited expression of glycine decarboxylase have been determined under normal environmental conditions. The rate of true photosynthesis was highest in leaves of control plants (16.0 μmol CO 2 m - 2 .s - 1 ). In transformant P1 it was 2 times lower while P15 showed an intermediate value. The same relationship was found for the total rate of intracellular decarboxylation in the light: 2.6, 1.3 and 1.8 μmol CO 2 m - 2 .s - 1 in leaves of control plants, P1 and P15, respectively. No differences were detected in the relative rate of intracellular decarboxylation indicating that transformants did not have any advantage with respect to respiratory losses during photosynthesis in the light. In all varieties the main substrates of decarboxylation were primary photosynthates, the contribution of stored photosynthates varied in the range from 15 to 25% the total rate of decarboxylation. The rate of photorespiration exceeded the rate of respiration 7.5 times in control plants and 1.8-2.5 times in transformants. The rate of respiration in the dark was in leaves of control plants 30-40% higher than in leaves of transformants. Light severely, about 20 times, inhibited this component of respiration in control plants but only 1.5 times in P1 and 5.5 times in P15. The specificity of Rubisco, determined in intact leaves in vivo , had significantly higher values in transformants compared to control plants. It has been shown that in transformants a portion of glycine was not decarboxylated by glycine decarboxylase but transported out of the glycolate cycle which results in a change of the stoichiometry between RuBP oxygenation and photorespiration and in an apparent increase of Rubisco specificity. In leaves of transformants the content of non-protein glycine was 3-5 times higher and the content of non-protein serine 6-15 times lower than in leaves of control plants.

Research paper thumbnail of The Effects of Cold Acclimation on the Photosynthetic Carbon Metabolism in Leaves of Winter Rye (Secale Cereale L.)

Photosynthesis: from Light to Biosphere, 1995