Growth, photosynthesis, nodule nitrogen and carbon fixation in the chickpea cultivars under salt stress

Abstract

Four cultivars of chickpea, two of them of Mediterranean origin (kabuli), CSG 9651, BG 267 and two Indian (desi) types, CSG 8962, DCP 92-3, differing in their salt sensitivities were identified after screening ten genotypes in saline soils. The cultivars CSG 9651 and CSG 8962 were salt tolerant while BG 267 and DCP 92-3 were salt sensitive, respectively. The seeds of different cultivars were inoculated with Mesorhizobium ciceri, strain F: 75 and the plants were grown in the greenhouse. After the establishment of symbiosis, 15-day-old seedlings were administered doses of saline at varying concentrations (0, 4, 6, 8 dSm-1 NaCl, Na2SO4, CaCl2). Plants were harvested at 40, 70 and 100 days after sowing, for analyses. The main aim was to compare the relative salt tolerance of both desi and kabuli cultivars in terms of nitrogen fixation and carbon metabolism, as well as to ascertain whether the negative effects of saline stress on nitrogen fixation were due to a limitation of photosynthate supply to the nodule or to a limitation on the nodular metabolism that sustains nitrogenase activity. Plant growth, nodulation and nitrogenase activity was more severely affected in BG 267 and DCP 92-3 under salinity treatments (6 and 8 dSm-1) compared with CSG 9651 and CSG 8962. Nodule number as well as nodule mass increased under salt stress in CSG 9651 and CSG 8962 which might be responsible for their higher nitrogen fixation. Salinity reduced leaf chlorophyll and Rubisco activities in all cultivars. However, tolerant cultivars CSG 9651 and CSG 8962 showed smaller declines than the sensitive ones. Phosphoenolpyruvate carboxylase (PEPCase) activity increased significantly in the nodules of tolerant cultivars under salt stress at all harvests, and this was clearly related to salt concentrations. Our results suggest that in salt-affected soils tolerant cultivars have more efficient nodulation and support higher rates of symbiotic nitrogen fixation than the sensitive cultivars.

Photosynthesis and antioxidant activity in Jatropha curcas L. under salt stress

“…The data presented in Table 1 are consistent by the results obtained by Garg and Singla (2004) or Netondo et al(2004) with chickpea or sorghum plants. These authors report that stomatal closure is a prime constraint to photosynthesis by limiting CO 2 flux into the leaves of salt-stressed plants.…”

“…The decrease in Chl may be attributed to increased chlorophyllase activity (Sudhakar et al, 1997). Several investigators have shown that Rubisco activity in leaves is inhibited by salinity, similar to the degradation of leaf Chl (Garg and Singla, 2004). The decrease in Rubisco activity caused by salt exposure may be attributed to the sensitivity of this enzyme to chloride ions (Seeman and Chritchley, 1985).…”

“…When it is unregulated, transpiration can result in toxic levels of ion accumulation in shoots. An immediate response to salinity, which mitigates ion flux to the shoot, is a stomatal closure (Zhu, 2002;Garg and Singla, 2004;Praxedes et al, 2010), which can negatively affect photosynthesis (Praxedes et al, 2010). The water stress induced by salt accumulation promotes the lowering of the osmotic potential of the xylem and, consequently, the water potential that limits water absorption by plants.…”

“…Plants respond to salt through changes in several morphological, physiological, biochemical, and metabolic processes (Lee et al, 2001;Zhu, 2002). Salt stress can also trigger various interacting events, including inhibition of enzymatic activities in metabolic pathways, and decreased carbon-use efficiency and decomposition of proteinaceous and membrane structures (Hasegawa et al, 2000;Flagella et al, 2004;Garg and Singla, 2004).…”

“…Moreover, there is no unified concept of the nonstomatal events that constrain photosynthesis. It is well-known that salt may result in impairments in photosystem II activity (Garg and Singla, 2004), chlorophyll (Chl) content (Sudhakar et al, 1997;Silva et al, 2010), and in the activities of key enzymes involved in the photosynthetic carbon reduction cycle (Guerrier, 1988).…”