The exposure of 25-day-old Avena nuda plants to Cd concentration of 100 μM for 14 d caused a decrease in plant dry weight relative to control, while application of I mM SA or 5 mM H2O2 one day before Cd exposure effectively reduced the Cd-induced inhibition. The Cd-caused phytotoxicity may be related to the impairment of photosynthesis and oxidative damage as revealed by decreased chlorophyll content, CO2 assimilation, maximum photochemical efficiency (Fv/Fm), operating quantum efficiency of PS Ⅱ ( φPS Ⅱ), and antioxidant capability, and by enhanced membrane lipid peroxidation. The negative effect of Cd on photosynthesis was counteracted partially by SA but not H2O2 treatment, while the oxidative damages were ameliorated by both SA and H2O2, which may be associated with the maintenance of antioxidant levels. The Cd exposure increased proline levels, whereas the values were much lower in SA- or H2O2-treated plants. In addition, the activities of SOD, POD and CAT isoenzymes detected by polyacrylamide gel electrophoresis were correlated well to their parallel activities as assayed in solution. Together, these data suggested that exogenous SA or H2O2 might partially protect plants against Cd-induced growth inhibition, and the role of SA appeared to alleviate Cd-induced photosynthesis impairment and oxidative damage, while H2 O2 only mitigated the oxidative damage.%对25d龄的裸燕麦(Avena nuda)植株进行14d镉(000μM)胁迫处理,与对照相比,植株的干重显著降低.然而,在镉暴露前1d对植株进行水杨酸(1mM)或H2O2(5mM)预处理可有效地缓解镉引发的植株生长抑制.镉抑制生长与植物光合作用的降低和氧化胁迫伤害有关,具体表现为叶绿素含量、二氧化碳同化率、最大光化学量子产量、光系统Ⅱ实际量子产量、抗氧化力等参数显著低于对照植株,而膜脂过氧化水平则明显高于对照.镉对光合作用的抑制可被外施水杨酸部分地逆转,但不受H2O2影响:而水杨酸和H2O2均可减轻镉引发的氧化伤害,且与细胞中抗氧化能力的维持有关.镉胁迫明显提高了细胞的脯氨酸含量,而水杨酸或H2O2处理则有效地阻止其升高.通过聚丙烯酰胺凝胶电泳所显示的超氧化物歧化酶、过氧化物酶和过氧化氢酶同工酶活性与各自的分光光度计测得的酶活性基本一致.研究表明,外施水杨酸或H2O2可保护植物抵御适当浓度的镉引发的生长抑制,其中水杨酸的作用是减缓镉诱导的光合作用抑制与提高抗氧化胁迫能力,而H2O2只是减轻镉诱导的氧化胁迫伤害.
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