水淹对水芹叶片结构和光系统II光抑制的影响

通过探讨在水淹条件下水芹(Oenanthe javanica)叶片结构的变化以及出水对其光系统II功能和光抑制的影响, 阐明水芹光合机构在水淹条件下及出水后死亡的可能原因。结果表明: 水淹条件下新生沉水功能叶光系统II(PSII)最大光化学效率(Fv/Fm) 、电子传递活性与对照叶片差异很小, 但水淹使气生功能叶的Fv/Fm显著降低; 植株总生物量呈负增长趋势; 活体弱光条件下, 沉水叶出水后2小时叶片相对含水量(RWC)和Fv/Fm无显著变化; 中等光强和强光条件下其RWC和Fv/Fm迅速降低; 离体条件下, 5小时的中等光强对沉水叶的Fv/Fm影响不显著, 在随后的弱光下能恢复到出水时的初始状态; 强光能使沉水叶的Fv/Fm大幅降低, 且弱光下不能恢复到出水时的初始水平; 在解剖结构上, 水芹沉水叶的叶片总厚度、上下表皮厚度和气孔大小都显著低于气生叶, 而且沉水叶没有明显的栅栏组织分化, 但是沉水叶上表皮的气孔密度显著高于气生叶。研究结果表明, 水淹使水芹原气生叶PSII功能迅速衰退, 但对新生沉水叶片影响很小。水芹植株出水后, 沉水叶片结构变化使其在光下保水能力下降, 而强光导致了光合机构的光抑制和反应中心失活。田间条件下两者共同作用则加剧了对叶片光合机构的破坏, 进而致使其死亡。

Effects of Submergence on Leaf Anatomy and Photoinhibition of Photosystem II in Oenanthe javanica Plants

The aim of this study was to reveal the causes of death in aquatic leaves by analyzing leaf anatomy and photoinhibition of photosystem II (PSII) in Oenanthe javanica seedlings. Total biomass, leaf relative water content (RWC), chlorophyll a fluorescence transience and leaf anatomy were measured during total submergence. Submergence resulted in a significant reduction in total biomass and Fv/Fm ratio in terrestrial leaves. However, the maximal quantum yield of PSII photochemistry (Fv/Fm) and electron transport did not differ between normal terrestrial leaves and aquatic leaves. In vivo, the RWC and Fv/Fm ratio did not decrease significantly after plants were exposed to weak light; Never the less, under moderate and high light conditions, the RWC and Fv/Fm ratio significantly decreased after 2 h treatment. In in vitro experiments, Fv/Fm ratio in aquatic leaves were not significantly affected by moderate light, and it was restored to its initial value under weak light; however, the Fv/Fm ratio decreased significantly under high light and failed to recover completely under weak light. Structurally, as compared with terrestrial leaves, aquatic leaves had lower total thickness, upper epidermis layer, lower epidermis layer and stomatal size; however, the palisade parenchyma and spongy parenchyma of aquatic leaves did not differ. The stomatal density of the upper epidermis was higher than that of terrestrial leaves. The performance of PSII in terrestrial leaves declined quickly with total submergence, but submergence had no obvious effects on newly developed leaves. When the plant was re-exposed to a terrestrial environment, the changes in the structure of aquatic leaves caused a large decrease in its water-retention capacity under light, whereas high light led to pronounced photoinhibition and inactivation of PSII. The combination of weak water-retention capacity and strong photoinhibition accelerated the damage of the photosynthetic apparatus in the field, which resulted in the death of the aquatic leaves.