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Effects of short time heat stress on photosystem II, Rubisco activities and oxidative radicals in Alhagi sparsifolia

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Author(s): XUE Wei | LI Xiang-Yi | LIN Li-Sha | WANG Ying-Ju | LI Lei

Journal: Chinese Journal of Plant Ecology
ISSN 1005-264X

Volume: 35;
Issue: 04;
Start page: 441;
Date: 2011;

Keywords: activation of Rubisco | Alhagi sparsifolia | heat stress | photosystem II | oxidative radical

ABSTRACT
Aims Our general objective was to determine the effects of short time heat stress on photosystem II (PSII) activity and Rubisco activity in Alhagi sparsifolia. Specifically, we wanted to determine that temperature range within which the plant can photosynthesize, the critical temperature that damaged leaves and characters of reactive oxidative accumulation under high temperature.Methods Samples of A. sparsifolia were collected on a sunny morning with low winds in early August 2010. We selected healthy growing shoots randomly, washed them lightly to remove leaf dust, cut and quickly inserted them into damp soil and covered them with a plastic cover. Samples were immediately put into black plastic bags, which contained damp filter papers. The bags were placed into a heat-resistant case for transport to the laboratory and then immersed in water baths for 15 min at temperatures of 30, 38, 43, 48, 53, 58 and 63 ℃. Twenty intact and mature leaves were used to measure leaf fluorescence and CO2 response curves at each temperature.Important findings At leaf temperatures up to 43 ℃, the maximum photochemical efficiency of PSII, number of active reaction centers and leaf vitality index all decreased markedly. At moderately high temperatures, the electron donors of PSII were more heat-vulnerable than the electron acceptors of PSII, and the appearance of fluorescence K point (300 μs) in the fluorescence curve at 58 ℃ indicated that the structure of oxygen-evolving complexes was damaged, resulting in loss of oxygen-evolving function. At higher leaf temperatures, the activity of Rubisco first increased and then decreased, with a maximum at 34 ℃. Under high temperature stress, considerable oxidative radicals, e.g., ammoniacal nitrogen, H2O2 and O2–· were produced and continually accumulated in cells. We conclude that heat stress has strong impacts on both light reaction and dark reaction phases of photosynthesis, especially their two heat sensitive components comprised of PSII and Rubisco.

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