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2. Effects of water stress and high-temperature stress on the structure and activity of photosynthetic apparatus of Zea mays and Helianthus annuus
- Creator:
- Dekov, I., Tsonev, T., and Yordanov, I.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- chloroplast, maize, photosynthesis, polyethylen glycol, relative water content, sunflower, thylakoids, and ultrastructure
- Language:
- Multiple languages
- Description:
- Effects of high-temperature stress (HTS) and PEG-induced water stress (WS), applied separately or in combination, on the functional activity and ultrastructure of the photosynthetic apparatus (PSA) of maize (Zea mays L.) and sunflower (Helianthus annuus L.) plants were investigated. In maize plant tissues WS provoked the decrease in RWC by 10.9 %, HTS by 7.0 %, and after simultaneous application of the both treatments the decrease was 32.7 % in comparison with control plants. Similar but more expressed changes were observed in sunflower plants. Sunflower was more sensitive to these stresses. Net photosynthetic rate decreased significantly after all treatments, more in sunflower. In mesophyll chloroplasts after separately applied WS and HTS the number of grana and thylakoids was reduced and electron-transparent spaces appeared. At combined stress (WS+HTS) granal and stromal thylakoids were considerably affected and chloroplast envelope in many of them was partially disrupted. and I. Dekov, T. Tsonev, I. Yordanov.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3. Evaluation of relative contribution of initial and variable chlorophyll fluorescence measured at different temperatures
- Creator:
- Goltsev, V., Yordanov, I., and Tsonev, T.
- Format:
- Type:
- model:internalpart and TEXT
- Language:
- Multiple languages
- Description:
- The temperature dependence of the induction kinetics parameters of chiorophyll (Chl) fluorescence in leaves and isolated chloroplasts of young plants of PhaseoliLt vulgaris L. was studied. Theoretical prerequisites for the influence of fluorescence measuring temperature as well as 3 min pretreatment of leaf discs cn both the photophysical and dark processes in the photosynthetic appaiatus were evaluated. The registration manner of fluorescence kinetics detennined the pattem of temperature dependence curve. The characteristic temperature of sharp changes of induction kinetics parameters, maximal and initial fluorescence and Fq, were in ranges of 45-47 and 55-60 °C, respectively. The fitting of experimental data from thermograms registered at weak exciting iiradiance in thermoinactivated leaf discs allowed to estimate the activation energy (FJ of the intemal energy conversion process in excited Chl molecule as 51.2±0.15 kJ moTT The theoretical analysis of /'q measured by a PAM fluorometer showed that Fq registered even at low inadiances markedly exceeded its ideál dark value. The Fq measured at 25 °C was increased by 125±5.3 % by the herbicide DCMU and diminished by -23.8±1.6 % by the elechon acceptor DCBQ. At the experimental conditions ušed there were about 25 % of 1\ from dosed Qg non-reducing reaction centres in the measured Fq value. Thus the thermoinduced increase in Fq observed within the temperature inteiwal of 45-50 °C might be doně by a transition of PS2 reaction centres from a statě capable of reducing Q3 to a Qg-non-reducing statě.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
4. Influence of drought, high temperature, and carbamide cytokinin 4-PU-30 on photosynthetic activity of bean plants. 1. Changes in chlorophyll fluorescence quenching
- Creator:
- Yordanov, I., Velikova, V., and Tsonev, T.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- acclimation, Phaseolus vulgaris, treatment duration, and water deficit
- Language:
- Multiple languages
- Description:
- Fifteen-day-old bean plants (Phaseolus vulgaris L.) grown in a climatic chamber were exposed to water deficit (WD) and high temperature (HT) stresses applied separately or in combination. Changes in chlorophyll fluorescence quenching were investigated. Bean plants that endured mild (42 °C, 5 h for 2 d) WD separately or in combination with HT did not change their qP and qN quenching (measured at 25 °C) compared with those of the control. After 5 min testing at 45 °C, qP in control and droughted plants strongly decreased, while qP of plants that experienced combined WD+HT stress was insignificantly influenced, suggesting the acclimation effect of HT treatments. At more severe stresses (after 3 d-treatment), qP measured at 25 °C was the lowest in WD+HT plants and qN values were the highest. But when measured at 45 °C, qP of WD+HT plants had practically the same values as at 25 °C. Under these conditions qP of WD plants also showed an adaptation to HT. Twenty-four hours after recovery, the unfavourable effects of the stresses were strongly reduced when measured at 25 °C, but they were still present when measured at 45 °C. Positive effect of the carbamide cytokinin 4-PU-30 was well expressed only in droughted plants. and I. Yordanov, V. Velikova, T. Tsonev.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
5. Influence of drought, high temperature, and carbamide cytokinin 4-PU-30 on photosynthetic activity of plants.. 2.. Chloroplast ultrastructure of primary bean leaves
- Creator:
- Stoyanova, D. and Yordanov, I.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- membrane system, Phaseolus vulgaris, starch, stress, and thylakoid
- Language:
- Multiple languages
- Description:
- Ultrastructural changes in chloroplasts of primary leaves of 15-d-old bean plants (Phaseolus vulgaris L. cv. Cheren Starozagorski) in response to a single stress (increasing water deficit, WD) as well as to combined stress (WD plus high temperature, WD+HT) were investigated under the possible protective or reparatory effects of the carbamide cytokinin 4-PU-30 [N-(2-chloro-4-pyridyl)-N-phenylurea] applied before or after the stress. Essential structural changes in chloroplast ultrastructure occurred mainly in plants that had experienced WD+HT: the thylakoids were swollen, the envelope was destroyed, and the spatial orientation of inner membrane system was not typical. Changed starch accumulation was also observed. 4-PU-30 protected chloroplast ultrastructure under WD+HT. and D. Stoyanova. I. Yordanov.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
6. Plant responses to drought, acclimation, and stress tolerance
- Creator:
- Yordanov, I., Velikova, V., and Tsonev, T.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- chlorophyll, fluorescence induction, high temperature, net photosynthetic rate, photosystem 2, and ribulose-1,5-bisphosphate carboxylase/oxygenase
- Language:
- Multiple languages
- Description:
- At the whole plant level, the effect of stress is usually perceived as a decrease in photosynthesis and growth. That is why this review is focused mainly on the effect of drought on photosynthesis, its injury, and mechanisms of adaptation. The analysed literature shows that plants have evolved a number of adaptive mechanisms that allow the photochemical and biochemical systems to cope with negative changes in environment, including increased water deficit. In addition, the acquisition of tolerance to drought includes both phenotypic and genotypic changes. The approaches were made to identify those metabolic steps that are most sensitive to drought. Some studies also examined the mechanisms controlling gene expression and putative regulatory pathways. and I. Yordanov, V. Velikova, T. Tsonev.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public