外源水杨酸对镉胁迫下玉米幼苗的叶氮素代谢和根系抗氧化酶的影响

Role of Exogenous Salicylic Acid in Alleviating Nitrogen Metabolism in Leaves and Antioxidase in Root by Cadmium Stress in Maize Seedling

采用溶液培养方法，研究不同浓度外源水杨酸（sA）对镉（Cd）胁迫下玉米幼苗的生长、光合色素的变化、叶片氮代谢及根系抗氧化系统酶活性的影响。结果表明，cd胁迫抑制了玉米的生长发育和叶绿素合成，使硝态氮在叶中累积，同时影响了根系的抗氧化系统。应用50～250Ixmol·L-1浓度范围外源SA，叶绿素含量与胁迫情况下相比可提高81．3％、115．2％和45．9％，硝酸还原酶活性提高了1．32和1．29倍，降低了叶中硝态氮的含量30％，提高了谷氨酰胺合成酶（Gs）和谷氨酸合成酶（GOGAT）活性60％以上，维持了氮素代谢过程的良好进行。外源50～250Ixmol·L-1SA可将玉米根系过氧化物酶（POD）活性减小至0．026min·mg-1，POD和超氧化歧化酶（SOD）的活性与无cd胁迫下的酶活性无显著差异，降低了cd胁迫对质膜氧化系统的伤害。但外源sA对cd胁迫的修复缓解作用受浓度的影响较大，低浓度的SA具有良好的修复效果，高浓度的SA反而影响了光合色素的合成以及酶的活性，抑制了玉米的生长。综合考虑各项指标，具有良好修复作用的外源SA浓度为50～100Ixmol·L-1。

The nutrient solution culture experiment was carried out to examine the effects of exogenous salicylic acid（ SA ） on growth, chloro- phyll, nitrogen metabolism and antioxidase activities in maize seedling exposed to cadmium（Cd） stress. The Cd stress dramatically reduced the seedling growth and leaf chlorophyll content, and increased the nitrate accumulation in leaves due to interfering with the nitrogen metabolism. At the same time, Cd stress disturbed the antioxidase activities in seedling root. Applying exogenous SA in the concentration range of 50-250 μ mol L-1, the leaf chlorophyll contents increased 81.3%, 115.2% and 45.9%. The exogenous SA improved the nitrate re- ductase activities of leaf 1.32 and 1.29 times, the nitrate content was reduced with 30%, and the enzymatic activities of glutamine synthetase （GS） and glutamate synthase （GOGAT） all increased more than 60%, comparing with that under Cd stress. It shows that the exogenous SA maintained the nitrogen metabolism to work well in maize leave. The application of exogenous SA could reduce the peroxidase （POD） activi- ty to 0.026 rain＂ mg-~, and the activity of POD and superoxide dismutase （SOD） in maize root had no markedly difference with that under Cd stress condition. The lower POD and SOD reduced the damage of Cd stress on the plasma membrane oxidation system. But the role degree of exogenous SA alleviating Cd stress was affected by SA application concentration. Application with lower concentration SA had markedly re- pairing effects, and the higher SA concentration could inhibit chlorophyll synthesis and enzyme activities. The SA concentration with good renairing results was in the range of 50-100 μmol L-1 through compressively consideration factors.