Key Laboratory of Southern Vegetable Crop Genetic Improvement in Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing 210095, PR China.
J Plant Physiol. 2013 May 1;170(7):653-61. doi: 10.1016/j.jplph.2012.12.013. Epub 2013 Feb 9.
The plant growth, nitrogen absorption, and assimilation in watermelon (Citrullus lanatus [Thunb.] Mansf.) were investigated in self-grafted and grafted seedlings using the salt-tolerant bottle gourd rootstock Chaofeng Kangshengwang (Lagenaria siceraria Standl.) exposed to 100mM NaCl for 3d. The biomass and NO3(-) uptake rate were significantly increased by rootstock while these values were remarkably decreased by salt stress. However, compared with self-grafted plants, rootstock-grafted plants showed higher salt tolerance with higher biomass and NO3(-) uptake rate under salt stress. Salinity induced strong accumulation of nitrate, ammonium and protein contents and a significant decrease of nitrogen content and the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT) in leaves of self-grafted seedlings. In contrast, salt stress caused a remarkable decrease in nitrate content and the activities of GS and GOGAT, and a significant increase of ammonium, protein, and nitrogen contents and NR activity, in leaves of rootstock-grafted seedlings. Compared with that of self-grafted seedlings, the ammonium content in leaves of rootstock-grafted seedlings was much lower under salt stress. Glutamate dehydrogenase (GDH) activity was notably enhanced in leaves of rootstock-grafted seedlings, whereas it was significantly inhibited in leaves of self-grafted seedlings, under salinity stress. Three GDH isozymes were isolated by native gel electrophoresis and their expressions were greatly enhanced in leaves of rootstock-grafted seedlings than those of self-grafted seedlings under both normal and salt-stress conditions. These results indicated that the salt tolerance of rootstock-grafted seedlings might (be enhanced) owing to the higher nitrogen absorption and the higher activities of enzymes for nitrogen assimilation induced by the rootstock. Furthermore, the detoxification of ammonium by GDH when the GS/GOGAT pathway was inhibited under salt stress might play an important role in the release of salt stress in rootstock-grafted seedlings.
在盐胁迫下，利用耐盐冬瓜砧木 Chaofeng Kangshengwang（Lagenaria siceraria Standl.）对自根和嫁接的西瓜（Citrullus lanatus [Thunb.] Mansf.）幼苗进行了研究，观察了植物生长、氮吸收和同化。在 3d 内，用 100mM NaCl 处理。砧木显著增加了生物量和硝酸盐吸收速率，而盐胁迫则显著降低了这些值。然而，与自根植株相比，砧木嫁接植株在盐胁迫下具有更高的耐盐性，具有更高的生物量和硝酸盐吸收速率。盐度诱导硝酸盐、铵和蛋白质含量的强烈积累，以及氮含量和硝酸还原酶（NR）、亚硝酸还原酶（NiR）、谷氨酰胺合成酶（GS）和谷氨酸合酶（GOGAT）活性的显著降低在自根苗叶片中。相反，盐胁迫导致硝酸盐含量和 GS 和 GOGAT 活性显著降低，铵、蛋白质和氮含量以及 NR 活性显著增加，在砧木嫁接苗叶片中。与自根苗相比，在盐胁迫下，砧木嫁接苗叶片中的铵含量要低得多。谷氨酸脱氢酶（GDH）活性在砧木嫁接苗叶片中显著增强，而在自根苗叶片中则显著受到抑制，在盐胁迫下。通过天然凝胶电泳分离出三种 GDH 同工酶，它们在正常和盐胁迫条件下在砧木嫁接苗叶片中的表达均显著增强。这些结果表明，由于砧木诱导的氮吸收增加和氮同化酶活性提高，砧木嫁接苗的耐盐性增强。此外，在 GS/GOGAT 途径受到抑制时，GDH 对铵的解毒可能在砧木嫁接苗释放盐胁迫中发挥重要作用。
