RESUMO
A pot experiment was conducted under natural conditions of screen house to evaluate the effect of saline irrigation given at flowering stage (30-35 DAS) on nodule functioning and their tolerance in two mungbean genotypes viz. Asha and Muskan based on various physiological traits. The pots containing sandy soil (Typic Torrispamments) were saturated with Cl-dominated saline irrigation to maintain ECe of 2.5, 5.0, 7.5 dS m(-1) as compared to control. In both the genotypes osmotic potential (Ψs) and relative water content (RWC %) of nodules decreased significantly, while a sharp rise in proline and total soluble sugars contents were observed with the increasing level of saline irrigation after 10 and 20 days of treatment. A marked increase in hydrogen peroxide (H2O2), lipid peroxidation (MDA content) and relative stress injury (RSI %) was noticed in nodules which were much higher in Muskan. The decrease in Ψs of nodules was more pronounced in Asha than in Muskan, while reverse was true for RWC and proline accumulation. A sharp decline in acetylene reduction assay (ARA) for N2-fixation, leghemoglobin content and dry matter of the nodules was observed, but was more in Muskan than in Asha. Nitrogen (N) content declined while Na(+)/K(+) ratio and Cl(-) content increased significantly. The genotype Asha maintained better N2-fixing efficiency but lower Na(+)/K(+) ratio and Cl(-) content in nodules than Muskan. Though the nodule functioning was further deteriorated at 20 DAT in both the genotypes yet the tolerance capacity of nodules in Asha was better than in Muskan under saline conditions which is correlated with the compensatory mechanism i.e. osmoregulation in nodules.
RESUMO
Salinity induced changes in ethylene evolution, antioxidant defense system, N(2)-fixing efficiency and membrane integrity in relation to water and mineral status in chickpea (Cicer arietinum L.) nodules were studied under screen house conditions. At vegetative stage (55-65 DAS) plants were exposed to single saline irrigation (Cl(-) dominated) of levels 0, 2.5, 5.0 and 10.0dSm(-1) and sampled after 3d. The other set of treated plants was desalinized by flooding and the plants were sampled after further 3d. Water potential (Psiw) of leaf and osmotic potential (Psis) of leaf and nodules significantly decreased from -0.44 to -0.56MPa and from -0.65 to -1.15MPa and from -0.75 to -1.77MPa, respectively upon salinization. RWC of leaf and nodules also reduced from 86.05% to 73.30% and 94.70% to 89.98%, respectively. The decline in Psis of nodules was due to accumulation of proline and total soluble sugar. In comparison to control, the increase in ethylene (C(2)H(4)) production was 35-108% higher and correspondingly increase in 1-aminocycloprane-1-carboxylic acid (ACC) content (37-126%) and ACC oxidase activity (31-118%) was also noticed. Similarly, marked increase in H(2)O(2) (25-139%) and thiobarbituric acid substances (TBRAS, 11-133%) contents was seen. N(2)-fixing efficiency i.e. N(2)-ase activity, leghemoglobin and N contents of nodules declined significantly after saline irrigation. The induction in specific activity of antioxidant enzymes was confirmed by the increase in activity of superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione reductase and glutathione transferase, whereas reverse was true for catalase. These activated enzymes could not overcome the accumulation of H(2)O(2) in nodules. Ascorbic acid content also declined from 20 to 38%, whereas Na(+)/K(+) ratio and Cl(-) content were significantly enhanced. Upon desalinization, a partial recovery in all above metabolic processes and water relations parameters was noticed. It is suggested that ethylene in relation to water status and lipid peroxidation and along with other metabolic processes has an important role in induced nodules senescence under salinity.