PHYSIOLOGICAL, BIOCHEMICAL AND MOLECULAR STUDIES ON EFFECT OF SALT STRESS IN CLUSTERBEAN

Abstract

Clusterbean or guar is an industrially important crop because of galactomannan gum present in its seed endosperm. The productivity of clusterbean is reduced under saline conditions which often occur in areas under clusterbean cultivation. Despite the commercial importance of this crop, there is no report on the response of clusterbean plants to salt stress at molecular level, lo understand the molecular mechanism of salt tolerance in clusterbean, a salt tolerant landrace PLG- 15 and a salt sensitive landrace IC- 116824 were selected by testing the germination of seeds of' Ii commercial varieties and 59 landraces of clusterbean at various concentrations of NaCl. ICPMS analysis revealed that the Na accumulation in the roots and leaves of salt tolerant landrace PLG-15 seedlings was less than that in the salt sensitive landrace IC-i 16824. The K loss from the roots and leaves of PLG-15 seedlings was also less than that from the roots and leaves of IC- 116824 seedlings. The changes in activities of antioxidant enzymes, total carbohydrate and protein contents, and accumulation of proline and glycine betaine under salt stress were also determined in the two selected landraces. The specific activities of three antioxidant enzymes, namely, catalase, superoxide dismutase and peroxidase, were found increased in the salt tolerant landrace PLG-15 under salt stress. An increase in total carbohydrate and protein contents, and proline and glycine hetaine accumulation was also found in both salt sensitive and salt tolerant landraces under salt stress. By designing primers from 12 ion-transporter genes of soybean, ion-transporter genes of clusterbean were searched by polymerase chain reaction (PCR) technique. The PCR results confirmed the presence of six ion-transporter genes in clusterbean. Out of these six genes, four genes, namely, V-ATFASE, NHXI, KUP and KEA3, were found to express in the roots and leaves of clusterbean seedlings. The quantitative real time (qRT) PCR results revealed that these four expressed genes were upregulated in the roots and leaves of the salt tolerant PLG-15 seedlings under salt stress. Fluorescence microscopy using Na-specific cell permeant fluorescent CoroNa Red dye confirmed the results obtained by the ICP-MS analysis that at 50 mM NaCl stress Na accumulation in the roots and leaves of the salt sensitive landrace IC- l 16824 was more than that in the salt tolerant landrace PLG-15. On the basis of above findings, a molecular mechanism of salt tolerance in clusterbean has been proposed.