聚乙二醇诱导水分胁迫引起水稻光合下降的原因探讨

在水稻品种Azucena(粳稻)6叶期用不同浓度的聚乙二醇(PEG 6000)模拟干旱处理，结果表明，随着PEG处理浓度提高，净光合速率（Pn）呈下降趋势， 但各阶段起主导作用的因素不同。第一阶段, 在10%PEG处理下Pn显著下降，色素和叶绿素荧光保持不变，气孔导度(Gs)和胞间CO2浓度(Ci)反而上升，表明为非气孔因子限制光合速率；第二阶段，在15%PEG处理下色素和叶绿素荧光虽开始变化，Pn继续降低, 并伴随Gs和Ci的下降而下降，因此气孔导度成为光合速率的主要限制因子；第三阶段，在20%PEG处理下Pn继续降低，Gs虽下降，但Ci并没有进一步下降，而色素和荧光参数均进一步下降，此时光合膜的损伤成为限制光合的主导因子。上述结果表明，严重水分胁迫虽使光合机构吸收和传递光能效率下降，但过剩的激发能仍可能导致活性氧积累；尽管水稻叶内启动了超氧化物防御系统，但仍能导致光合器官受损及PSⅡ光化学活性降低。

Reason for Photosynthetic Declination in Rice from Water Stress Induced by Polyethylene Glycol(PEG)

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 (P_n) 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 P_n 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 P_n decreased with a significant decrease in G_s and C_i, ind icating G_s became a main factor limiting P_n. In the last phase, under 20% PEG treatment, P_n, G_s , fluorescence parameters and pigment content fell significantly further, whereas C _i exhibited no further decrease, demonstrating that the decline in P_n 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.