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Papers by Maya Velitchkova

Research paper thumbnail of β-Amylase Squirting Cucumber Between Immobilization, Kinetic Modeling and Application for Maltose Syrup Production

Chemistry Africa, Dec 7, 2023

Research paper thumbnail of Different impact of high light on the response and recovery of wild type and lut2 mutant of Arabidopsis thaliana at low temperature

Theoretical and Experimental Plant Physiology

Carotenoid composition is important for plant protection against unfavorable environment. In the ... more Carotenoid composition is important for plant protection against unfavorable environment. In the present study the effect of several days treatment with high light illumination at low temperature (500 µmol photons m −2 s −1 and (12/10 °C) on Arabidopsis thaliana plants—wt and mutant lut2 , was investigated. In addition, a comparative study of the ability of wt and lut2 plants to recover after one week return to control conditions was performed. The response of wt and lut2 to both stress factors was evaluated by changes in net photosynthesis, photochemistry and energy distribution and interaction between both photosystems. The alterations in oxygen evolving capacity were evaluated by registration of flash-induced oxygen yields and kinetics of initial oxygen burst. For the first time the effect of exposure at low temperature/high light on the fluidity of thylakoid membranes isolated from wt and lut2 mutant was followed. The analysis of low temperature (77 K) fluorescence emission and excitation spectra revealed that during exposition to both stress factors the antenna size of photosystem I and photosystem II were affected. Lut2 mutant showed higher sensitivity to the inhibitory action of high light at low temperature, with the grana-situated photosystem II centers being more affected. However, lut2 mutant exhibited a higher ability to restore the photosynthetic activity after recovery period under control conditions. Data presented showed that at low temperature, complete replacement of lutein in lut2 mutant by xanthophyll cycle-associated carotenoids did not result in higher protection against high light, but facilitated better recovery during the recovery period.

Research paper thumbnail of Exponential Equation Describing Kinetic Process of Immobilized β-Amylase Extracted from Glycine max Seeds

Research paper thumbnail of 光化学系IIの品質管理:ホウレンソウ・チラコイドの中の熱損害を受けたD1タンパク質の運命は、チラコイドでFtsHプロテアーゼとホスファターゼの分布と作用に依存

Plant and Cell Physiology, 2007

Research paper thumbnail of Photosynthetic Responses of a Wheat Mutant (Rht-B1c) with Altered DELLA Proteins to Salt Stress

Journal of Plant Growth Regulation, 2017

Research paper thumbnail of The Role of Alternative Electron Pathways for Effectiveness of Photosynthetic Performance of Arabidopsis thaliana, Wt and Lut2, under Low Temperature and High Light Intensity

Plants

A recent investigation has suggested that the enhanced capacity for PSI-dependent cyclic electron... more A recent investigation has suggested that the enhanced capacity for PSI-dependent cyclic electron flow (CEF) and PSI-dependent energy quenching that is related to chloroplast structural changes may explain the lower susceptibility of lut2 to combined stresses—a low temperature and a high light intensity. The possible involvement of alternative electron transport pathways, proton gradient regulator 5 (PGR5)-dependent CEF and plastid terminal oxidase (PTOX)-mediated electron transfer to oxygen in the response of Arabidopsis plants—wild type (wt) and lut2—to treatment with these two stressors was assessed by using specific electron transport inhibitors. Re-reduction kinetics of P700+ indicated that the capacity for CEF was higher in lut2 when this was compared to wt. Exposure of wt plants to the stress conditions caused increased CEF and was accompanied by a substantial raise in PGR5 and PTOX quantities. In contrast, both PGR5 and PTOX levels decreased under the same stress conditions ...

Research paper thumbnail of Effect of Low Light on Photosynthetic Performance of Tomato Plants—Ailsa Craig and Carotenoid Mutant Tangerine

Plants

The effects of a five-day treatment with low light intensity on tomato plants—Ailsa Craig and tan... more The effects of a five-day treatment with low light intensity on tomato plants—Ailsa Craig and tangerine mutant—at normal and low temperatures and after recovery for three days under control conditions were investigated. The tangerine tomato, which has orange fruits, yellowish young leaves, and pale blossoms, accumulates prolycopene rather than all-trans lycopene. We investigated the impact of low light at normal and low temperatures on the functioning and effectiveness of photosynthetic apparatuses of both plants. The photochemical activities of Photosystem I (PSI) and Photosystem II (PSII) were assessed, and the alterations in PSII antenna size were characterized by evaluating the abundance of PSII-associated proteins Lhcb1, Lhcb2, CP43, and CP47. Alterations in energy distribution and interaction of both photosystems were analyzed using 77K fluorescence. In Aisla Craig plants, an increase in thylakoid membrane fluidity was detected during treatment with low light at a low temperat...

Research paper thumbnail of Antioxidative Defense, Suppressed Nitric Oxide Accumulation, and Synthesis of Protective Proteins in Roots and Leaves Contribute to the Desiccation Tolerance of the Resurrection Plant Haberlea rhodopensis

Plants

The desiccation tolerance of plants relies on defense mechanisms that enable the protection of ma... more The desiccation tolerance of plants relies on defense mechanisms that enable the protection of macromolecules, biological structures, and metabolism. Although the defense of leaf tissues exposed to solar irradiation is challenging, mechanisms that protect the viability of the roots, yet largely unexplored, are equally important for survival. Although the photosynthetic apparatus in leaves contributes to the generation of oxidative stress under drought stress, we hypothesized that oxidative stress and thus antioxidative defense is also predominant in the roots. Thus, we aimed for a comparative analysis of the protective mechanisms in leaves and roots during the desiccation of Haberlea rhodopensis. Consequently, a high content of non-enzymatic antioxidants and high activity of antioxidant enzymes together with the activation of specific isoenzymes were found in both leaves and roots during the final stages of desiccation of H. rhodopensis. Among others, catalase and glutathione reduct...

Research paper thumbnail of Reactivation of the Photosynthetic Apparatus of Resurrection Plant Haberlea rhodopensis during the Early Phase of Recovery from Drought- and Freezing-Induced Desiccation

Plants

Haberlea rhodopensis is a unique desiccation-tolerant angiosperm that also survives winter frost.... more Haberlea rhodopensis is a unique desiccation-tolerant angiosperm that also survives winter frost. As, upon freezing temperatures, H. rhodopensis desiccates, the taxon is proposed to survive low temperature stress using its desiccation tolerance mechanisms. To reveal the validity of this hypothesis, we analyzed the structural alterations and organization of photosynthetic apparatus during the first hours of recovery after drought- and freezing-induced desiccation. The dynamics of the ultrastructure remodeling in the mesophyll cells and the restoration of the thylakoid membranes shared similarities independent of the reason for desiccation. Among the most obvious changes in thylakoid complexes, the proportion of the PSI-LHCII complex strongly increased around 70% relative water content (RWC), whereas the proportion of Lhc monomers decreased from the beginning of rehydration. We identified enhanced levels of cyt b6f complex proteins that contributed to the enhanced electron flow. The h...

Research paper thumbnail of Limiting steps and the contribution of alternative electron flow pathways in the recovery of the photosynthetic functions after freezing-induced desiccation of Haberlea rhodopensis

Research paper thumbnail of The role of antioxidant defense in freezing tolerance of resurrection plant Haberlea rhodopensis

Physiology and Molecular Biology of Plants, 2021

Haberlea rhodopensis Friv. is unique with its ability to survive two extreme environmental stress... more Haberlea rhodopensis Friv. is unique with its ability to survive two extreme environmental stresses-desiccation to air-dry state and subzero temperatures. In contrast to desiccation tolerance, the mechanisms of freezing tolerance of resurrection plants are scarcely investigated. In the present study, the role of antioxidant defense in the acquisition of cold acclimation and freezing tolerance in this resurrection plant was investigated comparing the results of two sets of experiments-short term freezing stress after cold acclimation in controlled conditions and long term freezing stress as a part of seasonal temperature fluctuations in an outdoor ex situ experiment. Significant enhancement in flavonoids and anthocyanin content was observed only as a result of freezing-induced desiccation. The total amount of polyphenols increased upon cold acclimation and it was similar to the control in post freezing stress and freezing-induced desiccation. The main role of phenylethanoid glucoside, myconoside and hispidulin 8-C-(2-O-syringoyl-b-glucopyranoside) in cold acclimation and freezing tolerance was elucidated. The treatments under controlled conditions in a growth chamber showed enhancement in antioxidant enzymes activity upon cold acclimation but it declined after subsequent exposure to -10 °C. Although it varied under ex situ conditions, the activity of antioxidant enzymes was high, indicating their important role in overcoming oxidative stress under all treatments. In addition, the activity of specific isoenzymes was upregulated as compared to the control plants, which could be more useful for stress counteraction compared to changes in the total enzyme activity, due to the action of these isoforms in the specific cellular compartments. Supplementary information The online version contains supplementary material available at 10.1007/s12298-021-00998-0.

Research paper thumbnail of Recovery of photosynthetic activity of resurrection plant Haberlea rhodopensis from drought- and freezing-induced desiccation

Research paper thumbnail of Acquired tolerance of the photosynthetic apparatus to photoinhibition as a result of growing Solanum lycopersicum at moderately higher temperature and light intensity

Functional Plant Biology, 2019

The kinetics of photoinhibition in detached leaves from tomato plants (Solanium lycopersicum L. c... more The kinetics of photoinhibition in detached leaves from tomato plants (Solanium lycopersicum L. cv. M82) grown for 6 days under different combinations of optimal and moderately high temperature and optimal and high light intensity were studied. The inhibition of PSII was evaluated by changes in maximal quantum yield, the coefficient of photochemical quenching and the quantum yield of PSII. The changes of PSI activity was estimated by the redox state of P700. The involvement of different possible protective processes was checked by determination of nonphotochemical quenching and cyclic electron flow around PSI. To evaluate to what extent the photosynthetic apparatus and its response to high light treatment was affected by growth conditions, the kinetics of photoinhibition in isolated thylakoid membranes were also studied. The photochemical activities of both photosystems and changes in the energy distribution and interactions between them were evaluated by means of a Clark electrode ...

Research paper thumbnail of Effects of long-term action of high temperature and high light on the activity and energy interaction of both photosystems in tomato plants

Research paper thumbnail of Effect of membrane lipid order on the degree of freezing damage of thylakoid membranes

Cryo letters

The extent of freezing damage of the photosynthetic apparatus of isolated thylakoid membranes, co... more The extent of freezing damage of the photosynthetic apparatus of isolated thylakoid membranes, control and after modification of their membrane fatty acid acyl chain order by cholesterol and benzyl alcohol, was studied. The photochemical activity of photosystems I and II and the energy transfer between the main pigment protein complexes had been determined. Cholesterol-treated membranes are less susceptible to freezing damage, expressed by minor changes of the photochemical activity and retaining the 77K fluorescent characteristics. Benzyl alcohol incorporation enhanced the degree of freezing damage. The photochemical activity of both photosystems was severely decreased (by 80%) and considerable changes in the fluorescent properties were observed, mainly in the pigment pool associated with Photosystem I. The effects of different freezing media (artificial stroma medium, trehalose, glycine betaine and NaCl) were compared in respect to the maintaining of the activity of photosynthetic...

Research paper thumbnail of Sensitivity of two Ecotypes of Arabidopsis thaliana (Cvi and Te) towards UV‑B Irradiation

Proceeding of the Bulgarian Academy of Sciences, 2013

Research paper thumbnail of Effects of 24-epibrassinolide Pre-treatment on UV-B-Induced Changes in the Pigment Content of Pea Leaves

Proceeding of the Bulgarian Academy of Sciences, 2013

Research paper thumbnail of Freezing tolerance of photosynthetic apparatus in the homoiochlorophyllous resurrection plant Haberlea rhodopensis

Environmental and Experimental Botany, 2020

Abstract Haberlea rhodopensis is unique among homoiochlorophyllous resurrection plants with its a... more Abstract Haberlea rhodopensis is unique among homoiochlorophyllous resurrection plants with its ability to tolerate also low temperatures at temperate climate. This study was carried out to elucidate the response and acclimation ability of photosynthetic apparatus to cold and the capacity to tolerate freezing temperatures. Cold acclimated plants experienced short-term freezing conditions under controlled-environment in climatic chamber and also long-term subzero winter temperatures in an ex-situ natural environment. Our results indicated strong freezing tolerance after cold acclimation. In fact, fresh leaves were exposed to and survived freezing stress under both controlled and ex-situ conditions, thus confirming their appropriate cold acclimation. Freezing temperatures induced desiccation of leaves and the corresponding ultrastructural changes in mesophyll cells under ex situ environmental conditions. However, while the complete rearrangement in the cells commenced at 20 % RWC under drought stress, this process started already at 60 % RWC under freezing conditions. The presence of epidermal channels on both leaf sides was observed and their role for the fast water loss is proposed. It was found that freezing-induced desiccation, reversible downregulation of photosynthesis, readjustments in the abundance/organization of the pigment protein complexes and the main photosynthetic proteins together with increased thermal energy dissipation during chilling and freezing temperatures enable plants to survive harsh winter conditions and their fast recovery with the onset of spring. Low temperature responses are discussed in comparison to desiccation-induced changes to point out both common and specific features.

Research paper thumbnail of Protective effect of histidine against pigment photobleaching in Photosystem I particles

Résumé/Abstract Photosystem I (PSI) is a supercomplex of a reaction centre and light-harvesting c... more Résumé/Abstract Photosystem I (PSI) is a supercomplex of a reaction centre and light-harvesting complexes. Photosystem I particles isolated from spinach leaves were studied by means of absorbance, 77 K fluorescence, and resonance Raman spectroscopy. During ...

Research paper thumbnail of Multiple effects of trypsin-and heat-treatments on the ultrastructure and surface charge density of pea chloroplast membranes. Influence on P700+ parameters

It has been shown that mild trypsyn-treatment and heat-treatment of isolated chloroplasts above 3... more It has been shown that mild trypsyn-treatment and heat-treatment of isolated chloroplasts above 35 C led to the disruption of grana structures resulting in the lack of thylakoid adhesion and formation of single nonappressed membranesO,2,13).These changes in chloroplast organization are very similar to those observed by resuspending of thylakoids in low salt media(3).It is generally believed that the light-harvesting Chl a/b protein complex of photosystem II (LHCII) is required for the formation of grana(4,5) and this process might be achieved via electrostatic screening of the repulsion forces between negatively charged thylakoid membranes(6).Allowing that trypsin-and heat-induced destacking processes are accompanied by the well established alterations in either,the composition(4,5) or the aggregation state of LHCII (2,7),it could be expected that electrostatic mechanisms are responsible for the observed structural changes in both cases.Trypsin- and heat-induced multiple effects on the chloroplast organization manifested in formation of destacked or concentric (mielin-like) structures are presented in this study.The formation of these structures strongly depend on the incubation conditions and are accompanied by reversible changes in surface charge density of thylakoid membranes.The influence of trypsin- and heat-induced dynamical rearrangements of the thylakoid protein components on the efficiency of P700 photooxidation is discussed in terms of redistribution of excitation energy between the photosystems in favour to PS I.

Research paper thumbnail of β-Amylase Squirting Cucumber Between Immobilization, Kinetic Modeling and Application for Maltose Syrup Production

Chemistry Africa, Dec 7, 2023

Research paper thumbnail of Different impact of high light on the response and recovery of wild type and lut2 mutant of Arabidopsis thaliana at low temperature

Theoretical and Experimental Plant Physiology

Carotenoid composition is important for plant protection against unfavorable environment. In the ... more Carotenoid composition is important for plant protection against unfavorable environment. In the present study the effect of several days treatment with high light illumination at low temperature (500 µmol photons m −2 s −1 and (12/10 °C) on Arabidopsis thaliana plants—wt and mutant lut2 , was investigated. In addition, a comparative study of the ability of wt and lut2 plants to recover after one week return to control conditions was performed. The response of wt and lut2 to both stress factors was evaluated by changes in net photosynthesis, photochemistry and energy distribution and interaction between both photosystems. The alterations in oxygen evolving capacity were evaluated by registration of flash-induced oxygen yields and kinetics of initial oxygen burst. For the first time the effect of exposure at low temperature/high light on the fluidity of thylakoid membranes isolated from wt and lut2 mutant was followed. The analysis of low temperature (77 K) fluorescence emission and excitation spectra revealed that during exposition to both stress factors the antenna size of photosystem I and photosystem II were affected. Lut2 mutant showed higher sensitivity to the inhibitory action of high light at low temperature, with the grana-situated photosystem II centers being more affected. However, lut2 mutant exhibited a higher ability to restore the photosynthetic activity after recovery period under control conditions. Data presented showed that at low temperature, complete replacement of lutein in lut2 mutant by xanthophyll cycle-associated carotenoids did not result in higher protection against high light, but facilitated better recovery during the recovery period.

Research paper thumbnail of Exponential Equation Describing Kinetic Process of Immobilized β-Amylase Extracted from Glycine max Seeds

Research paper thumbnail of 光化学系IIの品質管理:ホウレンソウ・チラコイドの中の熱損害を受けたD1タンパク質の運命は、チラコイドでFtsHプロテアーゼとホスファターゼの分布と作用に依存

Plant and Cell Physiology, 2007

Research paper thumbnail of Photosynthetic Responses of a Wheat Mutant (Rht-B1c) with Altered DELLA Proteins to Salt Stress

Journal of Plant Growth Regulation, 2017

Research paper thumbnail of The Role of Alternative Electron Pathways for Effectiveness of Photosynthetic Performance of Arabidopsis thaliana, Wt and Lut2, under Low Temperature and High Light Intensity

Plants

A recent investigation has suggested that the enhanced capacity for PSI-dependent cyclic electron... more A recent investigation has suggested that the enhanced capacity for PSI-dependent cyclic electron flow (CEF) and PSI-dependent energy quenching that is related to chloroplast structural changes may explain the lower susceptibility of lut2 to combined stresses—a low temperature and a high light intensity. The possible involvement of alternative electron transport pathways, proton gradient regulator 5 (PGR5)-dependent CEF and plastid terminal oxidase (PTOX)-mediated electron transfer to oxygen in the response of Arabidopsis plants—wild type (wt) and lut2—to treatment with these two stressors was assessed by using specific electron transport inhibitors. Re-reduction kinetics of P700+ indicated that the capacity for CEF was higher in lut2 when this was compared to wt. Exposure of wt plants to the stress conditions caused increased CEF and was accompanied by a substantial raise in PGR5 and PTOX quantities. In contrast, both PGR5 and PTOX levels decreased under the same stress conditions ...

Research paper thumbnail of Effect of Low Light on Photosynthetic Performance of Tomato Plants—Ailsa Craig and Carotenoid Mutant Tangerine

Plants

The effects of a five-day treatment with low light intensity on tomato plants—Ailsa Craig and tan... more The effects of a five-day treatment with low light intensity on tomato plants—Ailsa Craig and tangerine mutant—at normal and low temperatures and after recovery for three days under control conditions were investigated. The tangerine tomato, which has orange fruits, yellowish young leaves, and pale blossoms, accumulates prolycopene rather than all-trans lycopene. We investigated the impact of low light at normal and low temperatures on the functioning and effectiveness of photosynthetic apparatuses of both plants. The photochemical activities of Photosystem I (PSI) and Photosystem II (PSII) were assessed, and the alterations in PSII antenna size were characterized by evaluating the abundance of PSII-associated proteins Lhcb1, Lhcb2, CP43, and CP47. Alterations in energy distribution and interaction of both photosystems were analyzed using 77K fluorescence. In Aisla Craig plants, an increase in thylakoid membrane fluidity was detected during treatment with low light at a low temperat...

Research paper thumbnail of Antioxidative Defense, Suppressed Nitric Oxide Accumulation, and Synthesis of Protective Proteins in Roots and Leaves Contribute to the Desiccation Tolerance of the Resurrection Plant Haberlea rhodopensis

Plants

The desiccation tolerance of plants relies on defense mechanisms that enable the protection of ma... more The desiccation tolerance of plants relies on defense mechanisms that enable the protection of macromolecules, biological structures, and metabolism. Although the defense of leaf tissues exposed to solar irradiation is challenging, mechanisms that protect the viability of the roots, yet largely unexplored, are equally important for survival. Although the photosynthetic apparatus in leaves contributes to the generation of oxidative stress under drought stress, we hypothesized that oxidative stress and thus antioxidative defense is also predominant in the roots. Thus, we aimed for a comparative analysis of the protective mechanisms in leaves and roots during the desiccation of Haberlea rhodopensis. Consequently, a high content of non-enzymatic antioxidants and high activity of antioxidant enzymes together with the activation of specific isoenzymes were found in both leaves and roots during the final stages of desiccation of H. rhodopensis. Among others, catalase and glutathione reduct...

Research paper thumbnail of Reactivation of the Photosynthetic Apparatus of Resurrection Plant Haberlea rhodopensis during the Early Phase of Recovery from Drought- and Freezing-Induced Desiccation

Plants

Haberlea rhodopensis is a unique desiccation-tolerant angiosperm that also survives winter frost.... more Haberlea rhodopensis is a unique desiccation-tolerant angiosperm that also survives winter frost. As, upon freezing temperatures, H. rhodopensis desiccates, the taxon is proposed to survive low temperature stress using its desiccation tolerance mechanisms. To reveal the validity of this hypothesis, we analyzed the structural alterations and organization of photosynthetic apparatus during the first hours of recovery after drought- and freezing-induced desiccation. The dynamics of the ultrastructure remodeling in the mesophyll cells and the restoration of the thylakoid membranes shared similarities independent of the reason for desiccation. Among the most obvious changes in thylakoid complexes, the proportion of the PSI-LHCII complex strongly increased around 70% relative water content (RWC), whereas the proportion of Lhc monomers decreased from the beginning of rehydration. We identified enhanced levels of cyt b6f complex proteins that contributed to the enhanced electron flow. The h...

Research paper thumbnail of Limiting steps and the contribution of alternative electron flow pathways in the recovery of the photosynthetic functions after freezing-induced desiccation of Haberlea rhodopensis

Research paper thumbnail of The role of antioxidant defense in freezing tolerance of resurrection plant Haberlea rhodopensis

Physiology and Molecular Biology of Plants, 2021

Haberlea rhodopensis Friv. is unique with its ability to survive two extreme environmental stress... more Haberlea rhodopensis Friv. is unique with its ability to survive two extreme environmental stresses-desiccation to air-dry state and subzero temperatures. In contrast to desiccation tolerance, the mechanisms of freezing tolerance of resurrection plants are scarcely investigated. In the present study, the role of antioxidant defense in the acquisition of cold acclimation and freezing tolerance in this resurrection plant was investigated comparing the results of two sets of experiments-short term freezing stress after cold acclimation in controlled conditions and long term freezing stress as a part of seasonal temperature fluctuations in an outdoor ex situ experiment. Significant enhancement in flavonoids and anthocyanin content was observed only as a result of freezing-induced desiccation. The total amount of polyphenols increased upon cold acclimation and it was similar to the control in post freezing stress and freezing-induced desiccation. The main role of phenylethanoid glucoside, myconoside and hispidulin 8-C-(2-O-syringoyl-b-glucopyranoside) in cold acclimation and freezing tolerance was elucidated. The treatments under controlled conditions in a growth chamber showed enhancement in antioxidant enzymes activity upon cold acclimation but it declined after subsequent exposure to -10 °C. Although it varied under ex situ conditions, the activity of antioxidant enzymes was high, indicating their important role in overcoming oxidative stress under all treatments. In addition, the activity of specific isoenzymes was upregulated as compared to the control plants, which could be more useful for stress counteraction compared to changes in the total enzyme activity, due to the action of these isoforms in the specific cellular compartments. Supplementary information The online version contains supplementary material available at 10.1007/s12298-021-00998-0.

Research paper thumbnail of Recovery of photosynthetic activity of resurrection plant Haberlea rhodopensis from drought- and freezing-induced desiccation

Research paper thumbnail of Acquired tolerance of the photosynthetic apparatus to photoinhibition as a result of growing Solanum lycopersicum at moderately higher temperature and light intensity

Functional Plant Biology, 2019

The kinetics of photoinhibition in detached leaves from tomato plants (Solanium lycopersicum L. c... more The kinetics of photoinhibition in detached leaves from tomato plants (Solanium lycopersicum L. cv. M82) grown for 6 days under different combinations of optimal and moderately high temperature and optimal and high light intensity were studied. The inhibition of PSII was evaluated by changes in maximal quantum yield, the coefficient of photochemical quenching and the quantum yield of PSII. The changes of PSI activity was estimated by the redox state of P700. The involvement of different possible protective processes was checked by determination of nonphotochemical quenching and cyclic electron flow around PSI. To evaluate to what extent the photosynthetic apparatus and its response to high light treatment was affected by growth conditions, the kinetics of photoinhibition in isolated thylakoid membranes were also studied. The photochemical activities of both photosystems and changes in the energy distribution and interactions between them were evaluated by means of a Clark electrode ...

Research paper thumbnail of Effects of long-term action of high temperature and high light on the activity and energy interaction of both photosystems in tomato plants

Research paper thumbnail of Effect of membrane lipid order on the degree of freezing damage of thylakoid membranes

Cryo letters

The extent of freezing damage of the photosynthetic apparatus of isolated thylakoid membranes, co... more The extent of freezing damage of the photosynthetic apparatus of isolated thylakoid membranes, control and after modification of their membrane fatty acid acyl chain order by cholesterol and benzyl alcohol, was studied. The photochemical activity of photosystems I and II and the energy transfer between the main pigment protein complexes had been determined. Cholesterol-treated membranes are less susceptible to freezing damage, expressed by minor changes of the photochemical activity and retaining the 77K fluorescent characteristics. Benzyl alcohol incorporation enhanced the degree of freezing damage. The photochemical activity of both photosystems was severely decreased (by 80%) and considerable changes in the fluorescent properties were observed, mainly in the pigment pool associated with Photosystem I. The effects of different freezing media (artificial stroma medium, trehalose, glycine betaine and NaCl) were compared in respect to the maintaining of the activity of photosynthetic...

Research paper thumbnail of Sensitivity of two Ecotypes of Arabidopsis thaliana (Cvi and Te) towards UV‑B Irradiation

Proceeding of the Bulgarian Academy of Sciences, 2013

Research paper thumbnail of Effects of 24-epibrassinolide Pre-treatment on UV-B-Induced Changes in the Pigment Content of Pea Leaves

Proceeding of the Bulgarian Academy of Sciences, 2013

Research paper thumbnail of Freezing tolerance of photosynthetic apparatus in the homoiochlorophyllous resurrection plant Haberlea rhodopensis

Environmental and Experimental Botany, 2020

Abstract Haberlea rhodopensis is unique among homoiochlorophyllous resurrection plants with its a... more Abstract Haberlea rhodopensis is unique among homoiochlorophyllous resurrection plants with its ability to tolerate also low temperatures at temperate climate. This study was carried out to elucidate the response and acclimation ability of photosynthetic apparatus to cold and the capacity to tolerate freezing temperatures. Cold acclimated plants experienced short-term freezing conditions under controlled-environment in climatic chamber and also long-term subzero winter temperatures in an ex-situ natural environment. Our results indicated strong freezing tolerance after cold acclimation. In fact, fresh leaves were exposed to and survived freezing stress under both controlled and ex-situ conditions, thus confirming their appropriate cold acclimation. Freezing temperatures induced desiccation of leaves and the corresponding ultrastructural changes in mesophyll cells under ex situ environmental conditions. However, while the complete rearrangement in the cells commenced at 20 % RWC under drought stress, this process started already at 60 % RWC under freezing conditions. The presence of epidermal channels on both leaf sides was observed and their role for the fast water loss is proposed. It was found that freezing-induced desiccation, reversible downregulation of photosynthesis, readjustments in the abundance/organization of the pigment protein complexes and the main photosynthetic proteins together with increased thermal energy dissipation during chilling and freezing temperatures enable plants to survive harsh winter conditions and their fast recovery with the onset of spring. Low temperature responses are discussed in comparison to desiccation-induced changes to point out both common and specific features.

Research paper thumbnail of Protective effect of histidine against pigment photobleaching in Photosystem I particles

Résumé/Abstract Photosystem I (PSI) is a supercomplex of a reaction centre and light-harvesting c... more Résumé/Abstract Photosystem I (PSI) is a supercomplex of a reaction centre and light-harvesting complexes. Photosystem I particles isolated from spinach leaves were studied by means of absorbance, 77 K fluorescence, and resonance Raman spectroscopy. During ...

Research paper thumbnail of Multiple effects of trypsin-and heat-treatments on the ultrastructure and surface charge density of pea chloroplast membranes. Influence on P700+ parameters

It has been shown that mild trypsyn-treatment and heat-treatment of isolated chloroplasts above 3... more It has been shown that mild trypsyn-treatment and heat-treatment of isolated chloroplasts above 35 C led to the disruption of grana structures resulting in the lack of thylakoid adhesion and formation of single nonappressed membranesO,2,13).These changes in chloroplast organization are very similar to those observed by resuspending of thylakoids in low salt media(3).It is generally believed that the light-harvesting Chl a/b protein complex of photosystem II (LHCII) is required for the formation of grana(4,5) and this process might be achieved via electrostatic screening of the repulsion forces between negatively charged thylakoid membranes(6).Allowing that trypsin-and heat-induced destacking processes are accompanied by the well established alterations in either,the composition(4,5) or the aggregation state of LHCII (2,7),it could be expected that electrostatic mechanisms are responsible for the observed structural changes in both cases.Trypsin- and heat-induced multiple effects on the chloroplast organization manifested in formation of destacked or concentric (mielin-like) structures are presented in this study.The formation of these structures strongly depend on the incubation conditions and are accompanied by reversible changes in surface charge density of thylakoid membranes.The influence of trypsin- and heat-induced dynamical rearrangements of the thylakoid protein components on the efficiency of P700 photooxidation is discussed in terms of redistribution of excitation energy between the photosystems in favour to PS I.