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The differing responses of two Arabidopsis ecotypes to ammonium are modulated by the photoperiod regime

Li, Baohai, Shi, Weiming, Su, Yanhua
Acta physiologiae plantarum 2011 v.33 no.2 pp. 325-334
Arabidopsis, amino acids, ammonia, ecotypes, glutamate dehydrogenase, glutamate-ammonia ligase, growth retardation, photoperiod, physiological response, plant response, shoots, soil nutrients
Responses to excessive ammonium (NH₄ ⁺) were compared between two Arabidopsis ecotypes (Col-0, JA22) with respect to different photoperiods in hydroponics. In this study, we showed that external extra NH₄ ⁺ led to severe growth suppression, accumulations of free NH₄ ⁺ and amino acids and increased the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in shoots of the two Arabidopsis ecotypes. However, the levels of free NH₄ ⁺ and total amino acids increased, whereas the activities of GS, NADH-dependent glutamate synthase and GDH decreased under the continuous light when compared with the light (16 h)-dark (8 h) cycle photoperiod. Statistical analyses suggested that strong correlations exist among the growth reduction, accumulations of free NH₄ ⁺, total amino acids and levels of GS activity in shoots under the high NH₄ ⁺ stress regardless of the photoperiod regimes. Interestingly, under the continuous light, Col-0 showed more resistant to such growth reduction and maintained about onefold higher capability of converting excess free NH₄ ⁺ into amino acids, with onefold higher GS activity induced by the external NH₄ ⁺ when compared with JA22. In contrast, these differences were abolished between Col-0 and JA22 under the light-dark cycle condition. Taken together, our results conclude that the sensitivity to NH₄ ⁺ of Col-0 and JA22 is changed between the continuous light and the light-dark cycle photoperiod, which is correlative to the alteration of the GS activity in shoots.