Salt stress induced changes in some organic metabolites and ionic relations in nodules and other plant parts of two crop legumes differing in salt tolerance

Abstract

A greenhouse experiment was conducted to assess the effect of salt stress on growth and metabolic changes in nodules and other plant parts of two leguminous species, Phaseolus vulgaris (salt sensitive) and Sesbania aculeata (salt tolerant) with the major objective if nodules play a vital role in salt tolerance. Plants of P. vulgaris subjected to 3.5 dS m−1 of NaCl and those of S. aculeata to 13.0 dS m−1 of NaCl showed a significant reduction in fresh and dry weights of shoots and roots, and shoot length and leaf area. The level of NaCl for each species was that at which 50% reduction in growth takes place. Salt stress caused a marked reduction in nodule fresh mass and nodule number in both leguminous species, but nodule dry weight did not decrease significantly in both species under salt stress. Percent reduction in nodule number due to salt stress was more in P. vulgaris than that in S. aculeata, but the reverse was true for nodule size. Free amino acids, proline, and glycine betaine increased, whereas soluble proteins decreased in all plant parts of both species under salt stress. Sesbania aculeata had significantly higher proline content in the leaves and glycine betaine in all plant parts than those in P. vulgaris under salt stress. Phaseolus vulgaris accumulated higher amounts of Na+ and Cl− in the nodules as compared to those in S. aculeata under saline conditions. The former species also showed a marked accumulation of Cl− in the leaves. In contrast, the transport of Cl− to the leaves of S. aculeata was low, but vice versa in roots. Salt stress also caused a marked reduction in net CO2 assimilation rate (Pn), transpiration rate (E) and stomatal conductance (gs) in both species. Percent reduction in Pn, E and gs under saline conditions was higher in P. vulgaris than in S. aculeata. Although nitrate reductase (NR) activity was reduced in all plant parts in both species, the species did not differ significantly. In conclusion, the nodules of S. aculeata seemed to have played an active role in the high salt tolerance of the species because the nodules had a lower accumulation of both Na+ and Cl− and a higher one of glycine betaine as compared to that in P. vulgaris. Other attributes related with a high salt tolerance of S. aculeata were a small reduction in number of root nodules, high proline content in leaves, high amount of glycine betaine in all plant parts, a high photosynthetic rate, and low uptake of Cl− in the leaves.