24-epibrassinolide restores nitrogen metabolism of pigeon pea under saline stress.

BACKGROUND: Several studies have shown that brassinosteroids attenuate the effects of salt stress. However, nothing is known about their effects on amino acid transport, nor the effects of these hormones on nitrate uptake under saline conditions. This study set out to determine the effects of 24-epibrassinolide, at concentrations of 10-7 M and 0.5 × 10-9 M, and clotrimazole (inhibitor of brassinosteroid synthesis), at 10-4 M, on nitrate uptake and metabolism in plants of C. cajan (L.) Millsp, cultivar C11, growing under salinity. The following aspects were analyzed: levels of proteins, amino acids, nitrate, nitrate reductase of roots and the composition of xylem sap amino acids. RESULTS: Salinity reduced the proportion of N-transport amino acids ASN (the major component), GLU, ASP and GLN. The effect of the hormone in reducing the adverse effects of salt was related to the reestablishment (totally or partially) of the proportions of GLU, ASN and GLN, transported in the xylem and to the small but significant increase in uptake of nitrate. Increased nitrate uptake, induced by 24- epibrassinolide, was associated with a higher activity of nitrate reductase together with greater levels of free amino acids and soluble proteins in roots of plants cultivated under saline conditions. CONCLUSION: The decline in several components of nitrogen metabolism, induced by salt, was attenuated by 24-epibrassinolide application and accentuated by clotrimazole, indicating the importance of brassinosteroid synthesis for plants growing under salinity.

Effect of salt on the growth and metabolism of Glycine max

Soybean plants cultivated with 50, 100 and 200 mM of NaCl, revealed that root growth was less affected by salinity than shoots. Salinity led to a reduction in leaf area and an increase in water content of the roots. These factors could contribute to the adaptation of the plant, improving its hydration. Although nitrate and free amino acid levels were reduced by salt treatment in roots, protein content of leaves was not altered. Salinity led to alterations in xylem amino acid composition, with increases in Ser, Ala, Gaba and Pro and a decrease in Asn. Similar changes were seen for Asn and Ser in roots together with a much stronger increase in Gaba. It is suggested that the decline in Asn reflects its conversion to Ala and Gaba (via Glu) in the roots while the increase in Pro and Gaba could be related to the adaptation of the plant to salinity.