ABSTRACT

Wild-type (WT) Arabidopsis thaliana (L.) Heynh. Col0, (ASN2)-deficient mutant (asn2 mutant) and knockout T-DNA mutant inserted in the ASN2 gene (asn2-1 mutant) were grown for one month by hydroponic culture at high nitrate level (HN=12mM). Then, plants were divided into HN and low nitrate (LN=0.2 mM) medium. Effects of short term (6h) salt stress (100mM NaCl) were assessed in each kind of medium. On HN-WT leaves, NaCl stress decreased chlorophyll, soluble protein (SP) contents and glutamine synthetase (GS, EC 6.3.1.2) activity. Despite the lack of ammonium accumulation, salt treatment induced aminatrice activity of glutamate dehydrogenase (NADH-GDH, EC 1.4.1.2). In (Asn2)-deficient mutant grown on HN medium, salt treatment reduced chlorophyll content and induced the SP and ammonium contents. In asn2-1 leaves, salt treatment induced NADH-GDH activity. GS activity and SP content were reduced under salinity. The transfer of plant to low nitrate (LN) medium for 6h had a stimulator effect on chlorophyll, SP contents, GS and NADH-GDH activities in WT leaves. This stimulator effect was lesser important in leaves of (Asn2)-deficient mutant. In asn2-1 mutant, the transfer to LN medium had no significant effect on different studied parameters. In WT and (ASN2)-deficient mutant grown on LN medium, changes were related to low nitrate supply rather than salt stress effects. In asn2-1 mutant, NaCl effects were accentuated by LN treatment in term of ammonium accumulation, NADH-GDH activity stimulation and GS activity inhibition. Salinity reduced GS1 protein level under LN medium, however it was more stable on HN one. The asn2-1 mutant appeared to be more sensitive to salt treatment under LN medium compared to WT and (Asn2)-deficient mutant. The asn2-1 mutant was the most resistant to nitrate level reduction in the culture medium relative to WT and (ASN2)-deficient mutant. Keywords: Salt, ASN, nitrate, Arabidopsis thaliana, ammonium assimilation

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https://doi.org/10.31032/IJBPAS/2019/8.4.4683