A. S. Nandwal

Salinity induced changes in plant water status, nodule functioning and ionic distribution in phenotypically differing genotypes of Vigna radiata L.

Summary 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.

Ethylene evolution, H2O2 scavenging enzymes and membrane integrity of Cicer arietinum L. nodules as affected by nitrate and aminoethoxyvinylglycine

Summary Nitrate induced changes on ethylene evolution, H 2 O 2 scavenging enzymes and membrane integrity in chickpea ( Cicer arietinum L.) cv. HC-1 nodules were studied under green house conditions. Plants were exposed to 10, 20 and 40 mmol/L NO − 3 at vegetative stage (40-45 DAS). Aminoethoxyvinyl-glycine (5 μmol/L, AVG) was added to nodules 24 h after NO − 3 treatment. An increase in ethylene evolution (388 % to 832 %) was noticed 3 d later in NO − 3 treated nodules. However, this declined 58-69 % with addition of AVG. The H 2 O 2 scavenging enzyme i.e. catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.11.1.9) increased by 9-27 %, 155-227 %, 33-117 % and 53-109 %, respectively. Despite the increase in the activity of these enzymes H 2 O 2 content increased by 116 to 168 %. Superoxide dismutase (EC 1.15.1.1) decreased from 32 % to 63 % with NO − 3 . Application of AVG to NO − 3 treated nodules also showed a decline in activity of catalase (16-23 %), peroxidase (21-30 %), ascorbate peroxidase (25-49 %) and glutathione reductase (46-53 %) with simultaneous depletion of H 2 O 2 content (29-34 %). Lipid peroxidation and electrolyte leakage increased 5-9 fold and 2-4 fold, respectively. However, these effects were also overcome to some extent by added AVG, showing a reversible loss in membrane integrity. It is concluded that ethylene production is increased in nodules on NO − 3 application. H 2 O 2 content increased significantly even on the activation of H 2 O 2 scavenging enzymes. The membrane integrity was adversely affected. AVG treatment showed partial recovery in above parameters showing the involvement of ethylene directly or indirectly in the functioning of nodules on NO − 3 application.

DROUGHT TOLERANCE IN CHICKPEA AS EVALUATED BY ROOT CHARACTERISTICS, PLANT WATER STATUS, MEMBRANE INTEGRITY AND CHLOROPHYLL FLUORESCENCE TECHNIQUES

Root traits, such as depth and root biomass, have been identified as the most promising plant traits in chickpea for terminal drought tolerance. With this objective, five contrasting genotypes of chickpea, viz. ICCV-4958, H-208, HC-5, RSG-931 and CSJ-379, having wide adaptability to drought prone areas at national level were assessed for various root characteristics under two environments, i.e. irrigated and rain-fed. The sampling was done at full bloom stage and there were significant differences in the rooting depth among the genotypes both under irrigated and rain-fed conditions. The chickpea roots penetrated to a minimum depth of 92 cm in CSJ-379 and maximum of 122 cm in ICCV-4958 under rain-fed conditions. The rooting depth remained higher under rain-fed than irrigated environment. Under irrigated conditions, the chickpea roots were able to grow to a maximum depth of 99 and 97 cm in HC-5 and ICCV-4958, respectively. Among the genotypes, biomass per plant of the root was higher in ICCV-4958 (6.7 g) and HC-5 (5.6 g) under rain-fed conditions. Similar observations were recorded for root/shoot ratio, dry weights of stem, leaf, nodules and total dry weight per plant. The moisture stress increased the biomass partitioning towards the roots. The water potential (ψ w ), osmotic potential (ψ s ) and relative water content (RWC %) of leaf were –0.98 MPa, –1.82 MPa and 60%, respectively, in the genotype HC-5, and –1.02 MPa, –1.72 MPa and 64%, respectively, in ICCV-4958 under rain-fed conditions. The rates of photosynthesis, and transpiration, values of the stomatal conductance and photochemical efficiency/quantum yield as indicated by F v /F m ratio were in the range of 6.7 to 10.6 (μmol m −2 s −1 ), 1.27 to 2.38 (mmol m −2 s −1 ), 0.23 to 0.48 (mol m −2 s −1 ) and 0.457 to 0.584, respectively, under rain-fed conditions. Genotypes HC-5 and ICCV-4958 also maintained higher photosynthetic and transpiration rates and F v /F m ratio than others. The maximum F v /F m values in these genotypes were correlated with the higher photosynthetic rate and dry matter yield per plant. Relative stress injury (RSI %) values in HC-5 and ICCV-4958 noticed were 25.3% and 23.7%, respectively. The results of this study indicate that under rain-fed conditions, genotypes ICCV-4958 and HC-5 had higher dry weight of stem, leaves, roots, nodules and total dry weight per plant, rooting depth, root/shoot ratio, photosynthetic and transpiration rates, photochemical efficiency and better plant water status but lower stomatal conductance than other genotypes. These traits are directly associated with maximum seed yield per plant, i.e. 15.6 g and 14.7 g per plant, respectively, in these genotypes. Therefore, both the genotypes in future can be used in crop improvement programme of chickpea breeding for drought tolerance.

Genotypic differences in water status, membrane integrity, ionic content, N2-fixing efficiency and dry matter of mungbean nodules under saline irrigation

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.