Ammonium metabolism in Selaginella bryopteris in response to dehydration-rehydration and characterisation of desiccation tolerant, thermostable, cytosolic glutamine synthetase from plant

Abstract

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.

The mechanisms underlying melatonin improved soybean seedling growth at different nitrogen levels

“…GDH activity was determined by adding 0.1 mL enzyme solution to activate the reaction. The decreasing value in absorbance after 3 min was recorded at 340 nm (Lin and Kao 1996;Singh et al 2020).…”

Physiological and biochemical changes in desiccation and rehydration cycles of Selaginella convoluta (Selaginellaceae)

“…The decrease in total amino acids in S. convoluta, on the other hand, differs from other resurrection plants, including Selaginella species. In these plants, total amino acids typically accumulate during dehydration (Tymms & Gaff 1978;Gaff & McGregor 1979), and function as compatible solutes or as mobile nitrogen reserves for the rehydrating tissues (Martinelli et al 2007;Yobi et al 2012Yobi et al , 2013Dinakar & Bartels 2013;Singh et al 2021).…”

“…According to different authors, the magnitude of proline increase can vary even for the same species. For instance, Pandey et al (2010) reported an 11-fold increase in proline levels in Selaginella bryopteris branches following desiccation, while in Singh et al (2021), this compound increased twofold after 24 h of dehydration.…”