Abstract
BackgroundSeveral 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.ResultsSalinity 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.ConclusionThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-9) contains supplementary material, which is available to authorized users.
Highlights
Several studies have shown that brassinosteroids attenuate the effects of salt stress
We investigated whether 24-epibrassinolide can revert the adverse effects of salt on growth of C. cajan through changes in nitrate uptake and metabolism
If only plants cultivated under salinity are compared, it may be seen that applications of 24-epibrassinolide resulted in increases in all parameters of nitrogen metabolism measured while the inhibitor of these hormones lead to a reduction in nitrate and nitrate reductase activity, but not free amino acids or soluble proteins (Figures 1 and 2)
Summary
Several studies have shown that brassinosteroids attenuate the effects of salt stress. Since the recognition of brassinosteroids as growth regulators, many studies have been carried out concerning their capacity of attenuating the effects of diverse types of stress, including salt stress (Zullo and Adam 2002; Ozdemir et al 2004; Kagale et al 2007). Despite such reports and the well documented adverse effects of salt on N metabolism, information is scarce (Anuradha and Rao 2001) regarding the influence of these hormones on nitrate uptake and metabolism under saline conditions
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