Search

Abstract: Salt tolerance of Arabidopsis knockout mutant with T-DNA insertion in ASN2 gene encoding asparagine synthetase (AS, EC 6.3.5.4) (asn2-1) was investigated. Wild-type Arabidopsis Col0 and asn2-1 mutant were grown for one month by hydroponic culture and subjected to 100 mM NaCl stress for a short time from 6 to 24 h. The salt treatment decreased chlorophyll and soluble protein contents, and increased ammonium level in the asn2-1 leaves. The salinity induced ASN1 mRNA level in the wild-type and asn2-1 leaves. By contrast, the salt treatment inhibited the transcript and protein levels of chloroplastic glutamine synthetase 2 (GS2, EC 6.3.1.2) in the wild-type and asn2-1 leaves. Increase in asparagine and proline contents in response to the salt treatment provides evidence for the role of asparagine as a prevailing stress responding amino acid. Glutamate dehydrogenase (NADH-GDH, EC 1.4.1.2) exhibited a slight increase in the α-subunit and β-subunit in the wild-type line and the asn2-1 line, respectively under the salinity, whereas its in vitro aminating activity in the wild-type leaves was not affected. The results indicate that the asn2-1 mutant was impaired in nitrogen assimilation and translocation under salt treatment. [Copyright &y& Elsevier]

The GLU1 promoter for Fd-glutamate synthase (Fd-GOGAT, EC 1.4.1.7) of Arabidopsis thaliana (ecotype Columbia) confers the expression of the β-glucuronidase (GUS) reporter gene on transgenic tobacco (Nicotiana tabacum L. cv. Xanthi) transformed with the GLU1 promoter-GUS construct. Histochemical analysis reveals that GUS expression is associated with mesophyll and vascular tissue of 14-d-old tobacco seedlings. Red light substitutes for white light and induces a 2-fold increase in the GUS expression associated with mesophyll, veins and vascular tissue. Sucrose also serves as a signal to induce GUS expression in mesophyll and veins of cotyledons. Mature leaves, adapted to the dark for 3 d, conserves the red light- and white light-dependent inductions of GUS activity, while GUS expression is repressed by white light in roots. The mesophyll-located expression of the GLU1 promoter suggests that Fd-glutamate synthase has a function in the photorespiratory ammonium cycling and primary ammonium assimilation. The distinct location of GLU1 promoter expression in the vascular tissue supports the view that Fd-glutamate synthase synthesises glutamate for intracellular transport of glutamine and glutamate. [Copyright &y& Elsevier]