亚低温条件下外源褪黑素对甜瓜幼苗氮代谢及渗透调节物质的影响

以甜瓜品种‘羊角酥瓜’幼苗为试材，利用人工气候室进行亚低温处理(昼/夜18 ℃/ 12 ℃)6 d，研究外源褪黑素（MT）对亚低温条件下甜瓜幼苗叶片氮代谢酶\硝酸还原酶(NR)、谷氨酰胺合成酶(GS)、谷氨酸合酶(GOGAT)和谷氨酸脱氢酶(GDH)\]活性、叶片总氮、铵态氮、硝态氮和渗透调节物质含量的影响.结果表明：与对照相比，亚低温处理降低了甜瓜总氮、硝态氮及硝酸还原酶活性，增加了铵态氮含量，抑制了甜瓜幼苗的生长.外源MT可显著提高亚低温下甜瓜幼苗氮代谢酶的活性，尤其可显著提高叶片GS和GOGAT活性，从而有效降低铵态氮含量；外源MT还可以提高叶片脯氨酸、可溶性蛋白质和可溶性糖的含量，进而降低了亚低温对细胞膜的伤害，表现为甜瓜叶片相对电导率和丙二醛(MDA)含量较低.总之，在亚低温条件下，外源MT在一定程度上可通过降低甜瓜叶片铵态氮含量和促进渗透调节物质的积累，降低膜质过氧化水平，从而增加其对亚低温的适应性.

Effects of exogenous melatonin on nitrogen metabolism and osmotic adjustment substances of melon seedlings under sub-low temperature.

The melon cultivar ‘Yangjiaosu’ was subjected to the treatment of 18 ℃/12 ℃ (day/night) in an artificial climate chamber for 6 days, and the activities of nitrogen metabolism related enzymes \nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH)\], the contents of total N, NO₃^--N and NH₄⁺-N as well as the osmotic adjustment substances of melon leaf were then determined. The results showed that, compared with the control, sub low temperature treatment reduced the contents of total N, NO₃^--N and the NR activity, but increased the content of NH₄⁺-N, thereby leading to the growth inhibition of melon. Exogenous MT treatment significantly improved the activities of nitrogen metabolism related enzymes, especially the activities of GS and GOGAT, effectively reducing the content of NH₄⁺-N. Moreover, MT treatment increased the contents of proline, soluble protein and soluble sugar, and alleviated the damage of sub low temperature on the cell membrane by reducing the relative electrical conductivity and MDA content of melon leaves. In short, this work suggested that exogenous MT would enhance the sub low temperature adaptability of melon by decreasing the leaf content of NH₄⁺-N, increasing the contents of osmotic adjustment substances and reducing the membrane lipid peroxidation levels.