Reduced activity of glycine decarboxylase: effects on photosynthesis and respiration in potato leaves (original) (raw)
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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 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.
Seibutsu kankyō chōsetsu, 2002
The CO2 dependent 02 evolution during the light period, at which the exogenous CO2 uptake was suspended, in 12 CAM plants (including pineapple (Ananas comosus)) was evaluated with a gas-phase oxygen electrode. At 5% CO2, the rate of photosynthetic 02 evolution in pineapple was saturated at 1 500 µmol m-2 s-1 PPFD and the maximum rate was 60 µmol m-2 s-1, which was 10 times those obtained at ambient CO2 conditions with the CO2 exchange system and significantly higher than the other CAM plants. At the saturated PPFD, the 02 evolution in pineapple substantially increased with increasing CO2 concentration up to 3% and decreased above 4%. However in the other CAM plants, such increment was small. By the use of a novel compensating CO2 gas exchange system, the rate of CO2 exchange in pineapple at very high CO2 was measured and found the enhancement of CO2 uptake in both light (Phases III and IV) and dark (Phase I) periods. Based on the results obtained, possibilities of the further increases in CO2 uptake in CAM plants, especially of pineapple, are discussed in terms of stomatal functions and malate storage capacities.
2002
The rates of CO 2 fixation and respiratory CO 2 fluxes in six C 3 species, namely Solanum tuberosum, Nicotiana tabacum, Arabidopsis thaliana, Hordeum vulgare, Triticum aestivum , and Secale cereale , were determined under steady-state photosynthesis. The plants may be divided into two groups: (a) cereals with a low rate of starch synthesis (7-5% of true photosynthesis); (b) plants with a high rate of starch synthesis (45-35% of true photosynthesis). In the light, primary and stored photosynthates are consumed as substrates for both respiratory and photorespiratory pathways. In leaves of cereals, the total rate of respiratory and photorespiratory decarboxylations of stored photosynthates was higher in the light than in the dark, while, in starch-synthesizing species, stored photosynthates were consumed at a higher rate in the dark. Under normal environmental conditions, respiratory decarboxylation of stored photosynthates was suppressed by light in all species studied. The total rate of respiration as the sum of decarboxylation of stored and primary photosynthates was not affected by light in cereals, but suppressed in starch-accumulating plants. This suppression was not compensated for by the additional supply of respiratory substrates from primary photosynthates in the light.
Photosynthesis Research, 2003
The photorespiration cycle plays an important role in avoiding carbon drainage from the Calvin cycle and in protecting plants from photoinhibition. The role of photorespiration is frequently underestimated in C 4 plants, since these are characterized by low photorespiration rates. The aim of this work was to study the relationship between CO 2 assimilation, PS II photochemistry and the xanthophyll cycle when the photorespiratory cycle is disrupted in Zea mays L. To this end, the photorespiration inhibitor phosphinothricin (PPT) was applied individually or together with the photorespiratory C 2 acids, glycolate and glyoxylate to maize leaves. Application of PPT alone led to the inhibition of CO 2 assimilation. Moreover, feeding with glycolate or glyoxylate enhanced the effect of PPT on CO 2 assimilation. Our results confirm that the avoidance of the accumulation of the photorespiratory metabolites glycolate, glyoxylate or phosphoglycolate, is of vital importance for coordinated functioning between the glycolate pathway and CO 2 assimilation. Relatively early changes in PS II photochemistry also took place when the photorespiratory cycle was interrupted. Thus, fluorescence photochemical quenching (qP) was slightly reduced (10%) due to the application of PPT together with glycolate or glyoxylate. A decrease in the efficiency of excitation-energy capture by open PS II reaction centres (F v/F m) and an increase in thermal energy dissipation (non-photochemical quenching, NPQ) were also measured. These observations are consistent with a limitation of activity of the Calvin cycle and a subsequent lower demand for reduction equivalents. The increase in NPQ is discussed on the basis of changes in the xanthophyll cycle in maize, which seem to provide a limited protective role to avoid photoinhibition when the glycolate pathway is blocked. We conclude that C 2 photorespiratory acids can act as physiological regulators between the photorespiratory pathway and the Calvin cycle in maize.
Australian Journal of Plant Physiology, 1998
A gas-exchange system with a rapid response time was used to study the interplay between rate-limiting processes of C3 photosynthesis in wild-type tobacco (Nicotiana tabacum L. cv. W38) and transgenic tobaccos with antisense DNAs directed against the Rubisco small subunit (anti-SSu plants) or the chloroplast glyceraldehyde-3-phosphate dehydrogenase (anti-GAPDH plants). High ribulosebisphosphate (RuBP) pools were generated in leaves by exposing them briefly to very low CO2, after which they were transferred to varying CO2 concentrations, and transient CO2 assimilation rates were measured within the first 23 s. Comparison of the transient (RuBP-saturated) and steady-state rates confirmed that the CO2 assimilation rate in anti-SSu plants was RuBP-saturated (i.e. Rubisco limited) at all intercellular CO2 partial pressures (Ci), and that, in anti-GAPDH plants, the transition from RuBP-saturation to RuBPlimitation occurred at lower assimilation rates and lower Ci as GAPDH activity was decreased. In addition, we investigated whether the integrated post-illumination CO2 uptake could be used as a non-destructive means of estimating RuBP pools in leaves. In wild-type plants there was generally a good agreement between RuBP pools extracted from leaves after rapid freeze-clamping and estimates made from post-illumination CO2 uptake. However, in the anti-SSu plants, the post-illumination CO2 uptake underestimated the actual RuBP content and the discrepancy became larger as the Rubisco content decreased. Possible explanations for this are discussed. *Abbreviations used: C i , intercellular CO 2 partial pressure; CPBP, unresolved mixture of 2Ј-carboxy-D-arabinitol-1,5-bisphosphate and 2'-carboxy-D-ribitol-1,5-bisphosphate; DTT, dithiothreitol; EPPS,; GAPDH, chloroplast glyceraldehyde-3-phosphate dehydrogenase; J, steady-state rate of electron transport; J max , the maximum, light-saturated rate of electron transport; K r , MichaelisMenten constant for RuBP; PFD, photon flux density; PMSF, phenylmethylsulfonyl fluoride; SSu, Rubisco's small subunit; Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase; RuBP, ribulose 1,5 bisphosphate; 3-PGA, 3-phosphoglycerate; V cmax , the maximal carboxylation rate of Rubisco.
PLANT PHYSIOLOGY, 1987
The sensitivity of photosynthesis to 02 and CO2 was measured in leaves from field grown plants of six species (Phaseolus vulgaris, Capsicum annuum, Lycopersicon escakntum, Scrophularia desertorum, Car-'Research supported by Department of Energy contract DE-FGO8-84ER1 3234. 2Abbreviations: RuBP, ribulose 1,5-bisphosphate; Ca, ambient partial pressure of C02; C,, intercellular partial pressure of C02; operational Ci, the Ci at a Ca of 320 ubar, Rubisco, ribulose-1,5-bisphosphate carboxyl
In Vivo Respiratory Metabolism of Illuminated Leaves
PLANT PHYSIOLOGY, 2005
Day respiration of illuminated C 3 leaves is not well understood and particularly, the metabolic origin of the day respiratory CO 2 production is poorly known. This issue was addressed in leaves of French bean (Phaseolus vulgaris) using 12 C/ 13 C stable isotope techniques on illuminated leaves fed with 13 C-enriched glucose or pyruvate. The 13 CO 2 production in light was measured using the deviation of the photosynthetic carbon isotope discrimination induced by the decarboxylation of the 13 C-enriched compounds. Using different positional 13 C-enrichments, it is shown that the Krebs cycle is reduced by 95% in the light and that the pyruvate dehydrogenase reaction is much less reduced, by 27% or less. Glucose molecules are scarcely metabolized to liberate CO 2 in the light, simply suggesting that they can rarely enter glycolysis. Nuclear magnetic resonance analysis confirmed this view; when leaves are fed with 13 C-glucose, leaf sucrose and glucose represent nearly 90% of the leaf 13 C content, demonstrating that glucose is mainly directed to sucrose synthesis. Taken together, these data indicate that several metabolic down-regulations (glycolysis, Krebs cycle) accompany the light/dark transition and emphasize the decrease of the Krebs cycle decarboxylations as a metabolic basis of the light-dependent inhibition of mitochondrial respiration. Human Potential Programme (grant no. fax 33-169153424.