Protective mechanism of desiccation tolerance in <Emphasis Type="Italic">Reaumuria soongorica</Emphasis>: Leaf abscission and sucrose accumulation in the stem |
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Authors: | Liu YuBing Zhang TengGuo Li XingRong Wang Gang |
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Institution: | 1. School of Life Sciences, Lanzhou University, Lanzhou 730000, China;Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China 2. School of Life Sciences, Lanzhou University, Lanzhou 730000, China 3. Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China |
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Abstract: | Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub, is widely found in semi-arid areas in northwestern China and can survive severe desiccation
of its vegetative organs. In order to study the protective mechanism of desiccation tolerance in R. soongorica, diurnal patterns of net photosynthetic rate (Pn), water use efficiency (WUE) and chlorophyll fluorescence parameters of
Photosystem II (PSII), and sugar content in the source leaf and stem were investigated in 6-year-old plants during progressive
soil drought imposed by the cessation of watering. The results showed that R. soongorica was characterized by very low leaf water potential, high WUE, photosynthesis and high accumulation of sucrose in the stem
and leaf abscission under desiccation. The maximum Pn increased at first and then declined during drought, but intrinsic WUE
increased remarkably in the morning with increasing drought stress. The maximal photochemical efficiency of PSII (Fv/Fm) and
the quantum efficiency of noncyclic electric transport of PSII(ΦPSII) decreased significantly under water stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed
plants maintained a higher capacity of dissipation of the excitation energy (measured as NPQ) with the increasing intensity
of stress. Conditions of progressive drought promoted sucrose and starch accumulation in the stems but not in the leaves.
However, when leaf water potential was less than −21.3 MPa, the plant leaves died and then abscised. But the stem photosynthesis
remained and, afterward the plants entered the dormant state. Upon rewatering, the shoots reactivated and the plants developed
new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation. |
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Keywords: | Reaumuria soongorica desiccation photosynthesis sucrose water use efficiency leaf abscission |
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