外源钙离子对小麦幼苗氮素代谢的影响

以普通小麦豫麦34为材料,研究了不同浓度的外源Ca2 对小麦幼苗氮素代谢的影响.在小麦第一片叶完全展开后,开始外源Ca2 处理,设0 (对照)、2、4 mmol · L-1 和8 mmol · L-1 4个Ca2 浓度梯度.处理5d后,测定氮同化酶活性、氮同化量及其它相关代谢物含量.结果表明,小麦幼苗叶片中硝酸还原酶(NR)和谷氨酰胺合成酶(GS)在2 mmol · L-1 Ca2 处理下活性比对照有显著增加,4 mmol · L-1 Ca2 处理的NR活性增加明显,但GS活性增加不显著;8 mmol · L-1 Ca2 处理下NR和GS活性比对照均明显降低.谷氨酸脱氢酶(NADH-GDH)活性在2 mmol · L-1 Ca2 处理下活性增加不明显,而在4、8 mmol · L-1 Ca2 处理下活性显著增加.小麦幼苗氮同化量以4 mmol · L-1处理最大,2 mmol · L-1处理与4 mmol · L-1之间差异不显著;Ca2 浓度为8 mmol · L-1时,氮素同化量明显降低.结果揭示了小麦幼苗不同氮同化途径对Ca2 的响应不同,GS途径比GDH途径对小麦氮素同化量的增加作用更大;4 mmol · L-1对小麦幼苗的氮素利用可能是最有效的Ca2 浓度.

Effects of exogenous Ca2+ on nitrogen metabolism in wheat seedlings

The exogenous calcium-induced effects on nitrogen assimilation enzymes and nitrogen use efficiency in wheat seedlings were investigated hydroponically using an ordinary wheat cultivar (Triticum aestivum L. cv. Yumai 34) as the material. Ca2+ treatments with solutions containing 0, 2, 4, and 8 mmol?L-1 Ca2+ were initiated immediately after the complete expansion of the first leaf. Wheat seedlings were sampled five days later to determine the activities of nitrate reductase(NR), glutamine synthetase(GS) and NADH-dependent glutamate dehydrogenase (NADH-GDH) in leaves, as well as the amount of nitrogen assimilation. The results showed that Ca2+ had obvious effects on the ability of nitrogen assimilation in wheat seedlings, and ammonium assimilation enzymes responded variously to different Ca2+ concentrations. Significant increases in NR activity were found in plant leaves exposed to 2 and 4 mmol?L-1 Ca2+ concentrations, among which the former induced the highest activity, whereas 8 mmol?L-1 Ca2+ concentration significantly reduced NR activity. GS activity was markedly increased by 2 mmol?L-1 Ca2+ application, but further increase in the concentration reversed the above effect, even 8 mmol?L-1 Ca2+ induced striking decrease in GS activity. Unlike NR and GS, NADH-GDH activity in leaves manifested pronounced increases with all Ca2+ concentrations in nutrient solution. High nitrogen content in leaves was found always together with Ca2+ concentration of 4 mmol?L-1. All the above results suggested that GS activity was important for nitrogen assimilation, and 4 mmol?L-1 Ca2+ was the most effective concentration to make wheat plants own high ability to assimilate nitrogen.