Shabnam Nisha, Pardha-Saradhi P
Department of Environmental Studies, University of Delhi, Delhi - 110007, India.
Funct Plant Biol. 2016 Apr;43(4):346-355. doi: 10.1071/FP15293.
During evaluations of the ecophysiological adaptations of floating and submerged leaves of Potamogeton nodosus Poir, investigations were carried to assess their antioxidant status. Floating leaves possessed a significantly higher level of C skeletons per unit of area compared with submerged leaves as they possessed greater PSI and PSII activity (hence had superior potential to harness absorbed light energy and generate assimilatory power) and carboxylase activity of Rubisco (hence superior potential to fix CO2) compared with the latter. Interestingly, submerged leaves possessed ~2 times higher H2O2 levels compared with floating leaves. In contrast, the activity of all antioxidant enzymes tested (catalase, guaiacol peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase) were significantly higher in floating leaves than in submerged leaves. Amazingly, catalase activity (a H2O2 detoxifying enzyme) was over fourfold higher in floating leaves than in submerged leaves. Among the nonenzymatic antioxidants, although levels of phenolics, ascorbate and thiols did not vary significantly between floating and submerged leaves, the level of total carotenoids was significantly higher in the former than the latter. In summary, floating leaves possess superior and efficient photosynthetic machinery for light and dark reactions, and also possess strong and superior enzymatic antioxidant machinery for scavenging reactive oxygen species and maintenance of the NAD(P)H to NAD(P)+ ratio compared with submerged leaves. Accordingly, floating leaves possessed superior potential to withstand photodamage compared with submerged leaves. We believe that excess H2O2 provides an ideal defence tool for submerged leaves to counter predators, pests and pathogens.
在对波叶眼子菜漂浮叶和沉水叶的生态生理适应性评估过程中，开展了相关研究以评估它们的抗氧化状态。与沉水叶相比，漂浮叶每单位面积的碳骨架水平显著更高，因为它们具有更高的光系统I（PSI）和光系统II（PSII）活性（因此具有更强的利用吸收光能并产生同化力的潜力），并且与沉水叶相比，其核酮糖-1,5-二磷酸羧化酶（Rubisco）的羧化酶活性更高（因此具有更强的固定二氧化碳的潜力）。有趣的是，沉水叶的过氧化氢（H₂O₂）水平比漂浮叶高约2倍。相比之下，所有测试的抗氧化酶（过氧化氢酶、愈创木酚过氧化物酶、抗坏血酸过氧化物酶、单脱氢抗坏血酸还原酶、脱氢抗坏血酸还原酶和谷胱甘肽还原酶）的活性在漂浮叶中显著高于沉水叶。令人惊讶的是，过氧化氢酶活性（一种H₂O₂解毒酶）在漂浮叶中比在沉水叶中高出四倍多。在非酶抗氧化剂中，虽然酚类、抗坏血酸和硫醇的水平在漂浮叶和沉水叶之间没有显著差异，但总类胡萝卜素水平在前者中显著高于后者。总之，与沉水叶相比，漂浮叶拥有用于光反应和暗反应的更优越且高效的光合机制，并且还拥有强大且优越的酶促抗氧化机制，用于清除活性氧并维持烟酰胺腺嘌呤二核苷酸磷酸（NAD(P)H）与烟酰胺腺嘌呤二核苷酸磷酸（NAD(P)⁺）的比率。因此，与沉水叶相比，漂浮叶具有更强的抵御光损伤的潜力。我们认为，过量的H₂O₂为沉水叶提供了一种对抗捕食者、害虫和病原体的理想防御工具。
