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 object-ive to test their tolerance on the basis of plant water status, N-2 fixation and mineral distribution. The water potential (psi(w)) of leaves and osmotic potential (psi(s)) 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 psi(w) of leaves and psi(s) 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 psi(w), psi(s), 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.