Stress induced changes in osmoprotectants, ionic relations, antioxidants activities and protein profiling characterize Sporobolus marginatus Hochst. ex A. Rich. salt tolerance mechanism

Abstract

Soil salinization and alkalinization frequently co-occur in nature, but very few studies focus on the interactive effects of mixed salt and alkali stresses on plants. Sporobolus marginatus Hochst. ex A. Rich. (perennial halophytic grass) collected from extreme saline sodic Kachchh plains, Bhuj, Gujarat was analyzed to evaluate the stress specific responses in osmoprotectants, antioxidants, ionic relations and protein profiling under saline, sodic and mixed saline-sodic soils. Osmotic adjustments in terms of total soluble sugars (TSS), glycine betaine, proline content and protein concentration exhibited differential responses to variable stress conditions. Proline content increased 4.8 folds at pH2 10.0, 5.2 folds at ECe 35 dSm-1 and 5 folds at pH2 9.0 + ECe 20 dSm-1. The greater accumulation of proline in Sporobolus, may presumably be one of the factor for tolerance to higher salt. At the same time, superoxide dismutase (SOD) activity in leaves increased with increasing sodicity i.e. 30.73 and 33.55 units g-1 FW at pH 9.5 and pH 10.0, respectively. Gradual increase in peroxidase enzyme (POX) activity was observed under all the stresses. Under control condition, POX activity was 21.67 units g-1 FW in Sporobolus, which increased to 26.56 units g-1 FW at pH 10.0, 27.89 units g-1 FW at ECe 35 dSm-1 and 27.44 units g-1 FW at pH 9.0 + ECe 20 dSm-1. The basal activity of APX increased with increasing stress conditions and was maximum (43.91 units g-1 FW) at pH 10.0. On the other hand, 2 times higher glutathione reductase (GR) activity was obtained under sodic stress of pH 9.5 and pH 10.0. SDS-PAGE revealed that five new polypeptide bands of MW 58.5, 53.7, 39.7, 31.8 and 28.3 kDa were expressed at higher saline level while one polypeptide band of 39.7 kDa disappeared at higher salinity level of 35 dSm-1 which may be due to its degradation at higher salt concentration. Synthesis of common polypeptides of MW 98.1, 69.3, 35.45, 24.89 and 23.3 kDa under all the stress conditions need special mention. Furthermore, the enhanced expression of these proteins, which also existed in the control plants, were specifically increased under stress condition which revealed that these proteins were up-regulated in specific regions of Sporobolus adapted to salt stress. Therefore, further exploration is needed to test the contribution of salt stress related proteins/genes or regulatory factors from the salt tolerant grasses (STGs) for possible utilization in cereal crop improvement.