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Reason for Photosynthetic Declination in Rice from Water Stress Induced by Polyethylene Glycol(PEG)
SUN Jun-wei,YANG Yong,HUANG Zong-an,JIN Song-heng,JIANG De-an*
2004, 18(6):
539-543 .
After rice plants (japonica rice Azucena)were tre at ed with various concentrations of polyethylene glycol(PEG) for 16 days, characteristics of gas exchange,chlorophyll fluorescence, MDA content and activities of antioxidant enzymes (SOD, POD and CAT) in the leaves were measured.The reaso ns for photosynthetic declination caused by different PEG concentrations were re markably different, varying in three phases. In the first phase, under 10% PEG treatment, net photosynthetic rate (Pn) significantly decreased , but stomatal conductance (G s) and intercellular CO2 concentration (C i) increased slightly, while chlorophyll fluorescence parameters and photosynthetic pigment content showed little change, suggesting that the decrease in Pn was not due to the stomatal limitation. In the second phase, under 15% PEG treatment, the pigment content and fluorescence parameters began to change but Pn decreased with a significant decrease in Gs and Ci, ind icating Gs became a main factor limiting Pn. In the last phase, under 20% PEG treatment, Pn, Gs , fluorescence parameters and pigment content fell significantly further, whereas C i exhibited no further decrease, demonstrating that the decline in Pn was largely attributed to the damage of photosynthetic membrane. Although severe water stress caused the reduction of the abilities for harvesting and transferring light energy, the excess excitation energy still occurred and might lead to the production of reactive oxygen species triggering the antioxidant system. However, it could still damage photosynt hetic apparatus and result in the reduction of photochemical activity of PSⅡ.
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