Role of sodium ion transporters and osmotic adjustments in stress alleviation of Cynodon dactylon under NaCl treatment: a parallel investigation with rice

Abstract

Comparative analyses of the responses to NaCl in Cynodon dactylon and a sensitive crop species like rice could effectively unravel the salt tolerance mechanism in the former. C. dactylon, a wild perennial chloridoid grass having a wide range of ecological distribution is generally adaptable to varying degrees of salinity stress. The role of salt exclusion mechanism present exclusively in the wild grass was one of the major factors contributing to its tolerance. Salt exclusion was found to be induced at 4 days when the plants were treated with a minimum conc. of 200 mM NaCl. The structural peculiarities of the salt exuding glands were elucidated by the SEM and TEM studies, which clearly revealed the presence of a bicellular salt gland actively functioning under NaCl stress to remove the excess amount of Na ion from the mesophyll tissues. Moreover, the intracellular effect of NaCl on the photosynthetic apparatus was found to be lower in C. dactylon in comparison to rice; at the same time, the vacuolization process increased in the former. Accumulation of osmolytes like proline and glycine betaine also increased significantly in C. dactylon with a concurrent check on the HO levels, electrolyte leakage and membrane lipid peroxidation. This accounted for the proper functioning of the Na ion transporters in the salt glands and also in the vacuoles for the exudation and loading of excess salts, respectively, to maintain the osmotic balance of the protoplasm. In real-time PCR analyses, CdSOS1 expression was found to increase by 2.5- and 5-fold, respectively, and CdNHX expression increased by 1.5- and 2-fold, respectively, in plants subjected to 100 and 200 mM NaCl treatment for 72 h. Thus, the comparative analyses of the expression pattern of the plasma membrane and tonoplast Na ion transporters, SOS1 and NHX in both the plants revealed the significant role of these two ion transporters in conferring salinity tolerance in Cynodon.

Mechanisms of Environmental Stress Tolerance in Turfgrass

“…This result suggested that the salt tolerance strategy of seashore paspalum was via maintaining high K + concentration in the shoots and repressing Na + transference from roots to shoots when exposed to salt stress. In bermudagrass, in addition to higher K + concentration in shoots, Na + exclusion from the surface of leaves was also observed under salt stress [30]. The results implied that unlike seashore paspalum, bermudagrass preferred the strategy of Na + exclusion to withstand salt stress.…”

Adaptation of Plants to Salt Stress: Characterization of Na+ and K+ Transporters and Role of CBL Gene Family in Regulating Salt Stress Response

“…Variations in its amino acid sequences result in a change in Na + affinity and a subsequent change in salt tolerance in two species of Triticum. Comparative analysis of antioxidant mechanisms in Cynodon dactylon (salt-tolerant grass) and Oryza sativa (salt-sensitive plant) was corroborated by the high expression levels of SOS 1 and NHX1 transporters in Cynodon [159]. Salt tolerance in barley has been attributed to the regulation of Na + loading in root xylem elements [160].…”

Mechanisms of Sodium Transport in Plants—Progresses and Challenges

“…On the other hand, salt-sensitive varieties are unable to sequester salt in vacuoles and the salt accumulates rapidly in the cytoplasm followed by a reduction of photosynthesis and assimilation [ 2 , 11 ]. Salt stress causes various physiological changes such as: (1) decrease in the rate of photosynthesis [ 2 , 12 , 13 , 14 , 15 ]; (2) smaller stomatal aperture and lower stomatal conductance due to disturbed water relations and sensitivity to abscisic acid (ABA) [ 2 , 12 , 13 , 15 , 16 , 17 ]; (3) decrease in transpiration rate [ 12 , 18 , 19 ]; (4) decrease in chlorophyll a and b, total chlorophyll, and carotenoids concentrations [ 14 , 17 , 20 , 21 , 22 , 23 ]; (5) decrease in chlorophyll fluorescence [ 15 , 24 , 25 , 26 ]; (6) changes in leaf anatomy, such as a decrease in the thickness of the epidermis and mesophyll and a decrease in intercellular spaces in the leaves [ 27 , 28 ], and a reduction in root length density [ 29 , 30 ]; (7) nutrient imbalance with a decrease in the content of phosphorus, nitrogen, Ca 2+ , Mg 2+ , and K + [ 21 , 31 ]; (8) decrease in leaf relative water content [ 8 , 32 , 33 , 34 , 35 ]; (9) membrane instability and increase in membrane permeability [ 35 , 36 , 37 , 38 ].…”