Nodule metabolism in cold stress tolerant and susceptible chickpea cultivars

Early maturing short duration cold-tolerant chickpea cultivars are being introduced to avoid yield loss from spell faced by crops. However, the biochemical basis of the low temperature stress tolerance is not known. In the present study carbon and nitrogen metabolizing enzymes in nodules along with physiological indices were measured in early maturing short duration cold- tolerant chickpea cultivars (ICCV 93929 and ICCV 88503) and in normal cold - susceptible (PBG1 and GPF2) cultivars. The higher biomass in nodules of cold-tolerant cultivars might act as a greater sink for attracting photoassimilates to fuel N-2-fixation. The simultaneous increase of sucrose synthase and alkaline invertase in nodules of ICCV 93929 and ICCV 88503 at the stage corresponding to lower temperature, ensures hexose supply for meeting the energy and reducing power demands for active nitrogen fixation. The greater activity of glutamine synthetase observed in nodules of cold tolerant cultivars at stages exposed to lower temperature indicates an efficient assimilation of the symbiotically fixed nitrogen into amino acids. The total protein and amino acid contents were also higher in cold tolerant cultivars. There was a greater and more rapid dry matter accumulation in ICCV 88503 and ICCV 93929 as compared to PBG1 and GPF2 in which biomass accumulation extended up to 70 DAS. Sustainable photosynthetic efficiency and activities of carbon and nitrogen metabolizing enzymes for a longer period in ICCV 93929 and ICCV 88503 even after flowering and during the onset of pod setting indicates that period of active nitrogen fixation is extended in cold tolerant chickpea cultivars due to allocation of photosynthates for longer period. This will lead to more transfer of reduced N as amino compounds towards the shoots which will lead to more nitrogen availability to seeds and ultimately better seed filling. The molecular diversity characterized by using RAPD primers and clustering method revealed a greater similarity between cold tolerant cultivars than between the cold susceptible cultivars.