Effects of different copper levels on photosynthetic parameters and active oxygen metabolism of Amaranthus tricolor seedlings

Chino. 明确铜毒影响苋菜（Amaranthus tricolor）幼苗光合作用和活性氧代谢的生理机制。采用土培试验测定了不同水平铜处理下苋菜幼苗生长、光合作用、矿质元素吸收和活性氧代谢的相关指标。2.0～4.0 mmol•kg-1铜处理下植株干重降至无铜处理（对照）的91%～73%，净光合速率和气孔导度均明显减小，但胞间CO2浓度并没发生显著变化，最大光化学效率的变化比实际量子效率小得多，这暗示着光合作用暗反应对ATP和NADH需求减少使光化学下调。此外，叶片光合色素、水分和矿质元素Fe、K和Mg含量均明显降低，Cu含量明显升高。2.0～4.0 mmol•kg-1铜处理显著增加叶片超氧化物歧化酶、过氧化物酶活性和脯氨酸含量，降低过氧化氢酶、抗坏血酸过氧化物酶活性及类胡萝卜素、还原型谷胱甘肽和抗坏血酸含量，并伴随丙二醛含量和细胞电解质渗漏率增加。2.0 mmol•kg-1以上铜处理引起苋菜活性氧代谢失衡，明显降低净光合速率和实际量子效率，加剧过氧化作用，导致植株生长严重受阻。

Inglés. The objective of this study was to gain better insight into the physiological mechanisms of copper (Cu) on photosynthesis and active oxygen metabolism in three-coloured amaranth plant (Amaranthus tricolor). Three-coloured amaranth seedlings were subjected to different Cu levels in soils during the whole experimental period. The parameters of growth, photosynthesis, mineral elements contents and active oxygen metabolism were investigated by using plant physiological methods. 2.0-4.0 mmol Cu•kg-1 treatment decreased the whole plant dry mass to 91%-73%. Net photosynthetic rate (Pn) and stomalal conductance (Gs) in the third leaves of three-coloured amaranth seedlings treated with 2.0-4.0 mmol Cu•kg-1 were similarly reduced. None of the investigated Cu levels decreased internal CO2 concentration (Ci). The effect of Cu on potential efficiency of photosystem Ⅱ (Fv/Fm) was negligible, while the effect of Cu on PSⅡ quantum efficiency (ΦPSⅡ) after plant adaptation in actinic irradiation was more noticeable. This could imply that the reduced demand of dark phase of photosynthesis for ATP and NADPH in leaves caused a down-regulation of PSⅡ photochemistry. On the other hand, decrease in water percentage, contents of photosynthetic pigments and mineral elements including Fe, K and Mg, significant increase in Cu content were observed in third leaves of Cu-treated plants. Superoxide dismutase (SOD) and guaiacol peroxidase (POD) activities as well as proline (Pro) content in third leaves of three-coloured amaranth seedlings treated with 2.0-4.0 mmol Cu•kg-1 significantly increased, while catalase (CAT) and ascorbate peroxidase (APX) activities as well as the contents of carotenoid (Car), glutathione (GSH) and ascorbic acid (AsA) decreased, and accompanied by the contents of hydrogen peroxide (H2O2), superoxide (O2－•) and malondialdehyde (MDA) and electrolyte leakage increased. As a result of unbalance of active oxygen metabolism, Pn and ΦPSⅡ decreased, and peroxidization was aggravated under levels of 2.0-4.0 mmol Cu•kg-1. Finally, the growth of three-coloured amaranth was significantly inhibited.