Effects of abscisic Acid treatment on the thermostability of the photosynthetic apparatus in barley chloroplasts |
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Authors: | Ivanov A G Kitcheva M I Christov A M Popova L P |
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Institution: | Central Laboratory of Biophysics, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Building 21, 1113 Sofia, Bulgaria. |
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Abstract: | Thermostability of the photosynthetic apparatus of abscisic acid (ABA)-treated seedlings of barley (Hordeum vulgare) was studied by light-scattering and by fluorescence measurements of isolated chloroplasts. ABA treatment markedly decreased heat damage of the chloroplast ultrastructure; an exogenous ABA concentration of 10−5 molar was most effective. Heat-induced increase of the 77 kilodalton fluorescence ratio F740/F685 was also smaller at this ABA concentration. The heat-induced increase of the initial chlorophyll fluorescence level (Fo) was virtually eliminated in ABA-treated (10−5 molar) chloroplasts up to 45°C and slightly increased at 50°C, relative to control chloroplasts where Fo increased even at 35°C and reached its maximal value at 45°C. In control chloroplasts, Fo increased with a 5-minute pretreatment temperature, an effect observed as low as 35°C. Fo was maximal at 45°C. In contrast, chloroplasts treated with 10−5 molar ABA did not exhibit a heat-induced increase in Fo until 50°C. |
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