Effects of elevated temperature on photosynthesis in desert plant <Emphasis Type="Italic">Alhagi sparsifolia</Emphasis> S |
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Authors: | W?Xue Email author" target="_blank">X?Y?LiEmail author L?S?Lin Y?J?Wang L?Li |
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Institution: | (1) Department of Horticulture, Huajiachi Campus, Zhejiang University, Kaixuan Road 268, Hangzhou, 310029, P.R. China;(2) Key Laboratory of Horticultural Plant Growth, Development and Biotechnology, Agricultural Ministry of China, Kaixuan Road 268, Hangzhou, 310029, P.R. China;(3) Departament de Biologia Vegetal, Universitat de Barcelona, 645 Diagonal Av, E-08028 Barcelona, Spain; |
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Abstract: | Most plants growing in temperate desert zone exhibit brief temperature-induced inhibition of photosynthesis at midday in the
summer. Heat stress has been suggested to restrain the photosynthesis of desert plants like Alhagi sparsifolia S. It is therefore possible that high midday temperatures damage photosynthetic tissues, leading to the observed inhibition
of photosynthesis. In this study, we investigated the mechanisms underlying heat-induced inhibition of photosynthesis in A. sparsifolia, a dominant species found at the transition zone between oasis and sandy desert on the southern fringe of the Taklamakan
desert. The chlorophyll (Chl) a fluorescence induction kinetics and CO2 response curves were used to analyze the thermodynamic characters of both photosystem II (PSII) and Rubisco after leaves
were exposed to heat stress. When the leaves were heated to temperatures below 43°C, the initial fluorescence of the dark-adapted
state (Fo), and the maximum photochemical efficiency of PSII (Fv/Fm), the number of active reaction centers per cross section (RCs) and the leaf vitality index (PI) increased or declined moderately.
These responses were reversed, however, upon cooling. Moreover, the energy allocation in PSII remained stable. The gradual
appearance of a K point in the fluorescence curve at 48°C indicated that higher temperatures strongly impaired PSII and caused
irreversible damage. As the leaf temperature increased, the activity of Rubisco first increased to a maximum at 34°C and then
decreased as the temperature rose higher. Under high-temperature stress, cell began to accumulate oxidative species, including
ammoniacal nitrogen, hydrogen peroxide (H2O2), and superoxide (O2
·−), suggesting that disruption of photosynthesis may result from oxidative damage to photosynthetic proteins and thylakoid
membranes. Under heat stress, the biosynthesis of nonenzyme radical scavenging carotenoids (Cars) increased. We suggest that
although elevated temperature affects the heat-sensitive components comprising of PSII and Rubisco, under moderately high
temperature the decrease in photosynthesis is mostly due to inactivation of dark reactions. |
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