Department of Biotechnology, University of North Bengal, Raja Rammohunpur, Siliguri-734013, India.
Department of Microbiology, University of North Bengal, Raja Rammohunpur, Siliguri-734013, India.
Funct Plant Biol. 2021 Feb;48(3):257-267. doi: 10.1071/FP20144.
Water deficit (WD) has adverse effects on plant growth, and acclimation requires responses allowing primary metabolism to continue. Resurrection plants can serve as model system to gain insight into metabolic regulation during WD. We herein report the response of a resurrection lycophyte, Selaginella bryopteris, to dehydration-rehydration cycle with emphasis on ammonium metabolism. Dehydration of S. bryopteris fronds resulted in decrease of total protein and increase of free ammonium levels and the effect was reversed on rehydration. The proline content increased twice after 24 h of dehydration, which again recovered to background levels comparable to that at full turgor state. The specific activity of glutamine synthetase (GS) didn't change significantly till 6 h and then declined by 21% after 24 h of dehydration, whereas specific activities of glutamate synthase (GOGAT) and aminating glutamate dehydrogenase (GDH) were enhanced significantly during dehydration. The deaminating activity of GDH also increased during dehydration albeit at a slower rate. Immunoblot analysis indicated overexpression of GS and GDH polypeptides during dehydration and their levels declined on rehydration. The results suggested significant role of GDH along with GS/GOGAT in production of nitrogen-rich amino acids for desiccation tolerance. Unlike higher plants S. bryopteris expressed GS only in cytosol. The enzyme had pH and temperature optima of 5.5 and 60°C, respectively, and it retained 96% activity on preincubation at 60°C for 30 min indicating thermostability. Hence, like higher plants the cytosolic GS from S. bryopteris has a conserved role in stress tolerance.
水分亏缺（WD）对植物生长有不利影响，适应需要允许初级代谢继续的反应。复苏植物可以作为模型系统，深入了解 WD 过程中的代谢调控。我们在此报告了复苏石松 Selaginella bryopteris 对脱水-复水循环的响应，重点是铵代谢。S. bryopteris 叶片的脱水导致总蛋白减少，游离铵水平增加，复水后效果逆转。脯氨酸含量在脱水 24 小时后增加了两倍，然后恢复到与完全膨胀状态相当的背景水平。谷氨酰胺合成酶（GS）的比活在 6 小时内没有明显变化，然后在脱水 24 小时后下降 21%，而谷氨酸合酶（GOGAT）和氨化谷氨酸脱氢酶（GDH）的比活在脱水过程中显著增强。GDH 的脱氨酶活性也在脱水过程中增加，尽管速度较慢。免疫印迹分析表明，GS 和 GDH 多肽在脱水过程中表达上调，复水后其水平下降。结果表明，GDH 与 GS/GOGAT 一起在产生富含氮的氨基酸以耐受干燥方面发挥重要作用。与高等植物不同，S. bryopteris 仅在细胞质中表达 GS。该酶的 pH 和温度最适值分别为 5.5 和 60°C，在 60°C 预孵育 30 分钟后保留 96%的活性，表明其热稳定性。因此，与高等植物一样，S. bryopteris 的细胞质 GS 在应激耐受中具有保守作用。
