Salinity Induced Changes in Plant Water Status, Nodule Functioning and Ionic Distribution in Phenotypically Differing Genotypes of Vigna radiata L.

Two phenotypically differing mungbean genotypes, i.e. K-851 (trifoliate) and a mutant (pentafoliate), were raised in earthen pots containing dune sand under natural conditions of a screen-house. At vegetative stage (30–35 DAS), plants were exposed to salinity levels of 0, 2.5, 5.0 and 10 dSm−1 for the duration of 3, 6, and 9 days with the objective to test their tolerance on the basis of plant water status, N2 fixation and mineral distribution. The water potential (ψw) of leaves and osmotic potential (ψs) of leaves, roots and nodules became more ‹−ve› with increasing salt stress. Relative water content (RWC %) of leaves, roots and nodules decreased significantly, while a sharp rise in proline content was observed. In a mutant (Code No. 97003), the values of ψw of leaves and ψs of leaves, roots and nodules were more negative than with K-851, while the reverse was true for RWC(%), showing better osmoregulation in the mutant than in K-851. A conspicuous increase in ethylene evolution was noticed from nodulated roots under salt stress, and genotype K-851 showed higher ethylene production than the mutant. A sharp decline in ARA and leghemoglobin content of nodules was recorded and K-851 was more sensitive than the mutant. The mutant maintained a better N-status in different plant parts than K-851, though N content of leaves, roots and nodules declined under stress. The Na+/K+ ratio in leaves, roots and nodules was enhanced significantly, being highest in roots. The mutant exhibited a low value of Na+/K+ ratio in plant parts. Cl− concentration was significantly higher in roots of the mutant than K-851, whereas the reverse was true for leaves and nodules. Dry weight of nodules plant−1 decreased more in genotype K-851. The better plant water status in the mutant, based upon ψw, ψs, RWC, proline and Na+/K+ ratio, resulted in a relatively better nodule dry weight, ARA and leghemoglobin content of nodules, and moreover less ethylene production. Hence, the mechanism of salt tolerance was better in the mutant than in K-851, as found from the physiological traits studied.