The expression of the salt-responsive gene sal T from rice is regulated by hormonal and developmental cues

. The expression pattern of the sal T gene was analyzed in different cell types and organs of rice ( Oryza sativa L.) in response to saline and hormonal treatments to obtain detailed information on the physiological cues controlling gene expression. Gel blot analysis of RNA and in-situ hybridization performed on seedlings grown for 10 ds in the presence of 1% NaCl revealed that sal T was expressed mainly in the younger tissues of the plant. In contrast, 6-week-old plants exhibited maximal sal T mRNA accumulation in sheaths of older leaves. In addition, sal T was normally expressed in rapidly dividing suspension-cultured cells, but not in quiescent ones. Altogether, these results may indicate that sal T expression in each region of the plant is dependent on the metabolic activity of the cells as well as on whether or not they are stressed. The effects of two growth regulators, abscisic acid (ABA) and gibberellic acid, were investigated in combination with the effects of NaCl. Gibberellic acid had a synergistic effect on the induction of the sal T gene when combined with 0.5% NaCl, but did not induce sal T on its own. At 10 μM, ABA induced sal T both in the absence of NaCl and in its presence. Whereas 1 μM ABA acted additively with NaCl to induce gene expression, 5 μM ABA with NaCl was only as effective as NaCl alone. This may indicate that the two stimuli act independently and possibly through antagonistic signal transduction pathways.