Photosynthetic electron transport and carbon-reduction-cycle enzyme activities under long-term drought stress in Casuarina equisetifolia Forst. & Forst. |
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Authors: | Sánchez-Rodriguez J Martínez-Carrasco R Pérez P |
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Institution: | (1) Instituto de Recursos Naturales y Agrobiología de Salamanca, CSIC. Apartado 257, E-37071 Salamanca, Spain |
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Abstract: | The inhibition of photosynthetic electron transport and the activity of photosynthetic carbon reduction cycle (PCR) enzymes under long-term water stress after slow dehydration was studied in non-nodulated Casuarina equisetifolia Forst. & Forst. plants. Initially, drought increased the fraction of closed Photosystem II (PS II) reaction centres (lowered qP) and decreased the quantum yield of PS II electron transport (PSII) with no enhancement of non-radiative dissipation of light energy (qN) because it increased the efficiency of electron capture by open PS II centres (Fv/Fm). As drought progressed, Fv/Fm fell and the decrease in PSII was associated with an increased qN. The kinetics of dark relaxation of fluorescence quenching pointed to an increase in a slowly-relaxing component under drought, in association with increased contents of zeaxanthin and antheraxanthin. Total NADP-dependent malate dehydrogenase activity increased and total stromal fructose-1,6-bisphosphatase activity decreased under drought, while the activation state of these enzymes remained unchanged. Water stress did not alter the activity and the activation state of ribulose bisphosphate carboxylase oxygenase. |
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Keywords: | chlorophyll fluorescence fructose bisphosphatase NADP-malate dehydrogenase Photosystem II ribulose bisphosphate carboxylase water stress |
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