Salt Stress: A Biochemical and Physiological Adaptation of Some Indian Halophytes of Sundarbans

Abstract

Experiment was conducted with five typical mangroves (Bruguiera gymnorrhiza, Excoecaria agallocha, Heritiera fomes, Phoenix paludosa, and Xylocarpus granatum) both from Sundarbans (in-situ) and grown in mesophytic condition (ex-situ, in the Indian Statistical Institute’s premises) since 15–17 years. A comparative account on PAR utilization for maximum photosynthesis, stomatal conductance, total leaf proteins, and polymorphic expression of two antioxidative enzymes (peroxidase and superoxide dismutase) and two hydrolyzing enzymes (esterase and acid phosphatase) were estimated both qualitatively and quantitatively. The present work revealed that the net photosynthesis was higher in mangroves from mesophytic habitats than those of the native plants, but the PAR acquisitions for maximum photosynthesis were greater in most of the Sundarbans species, except H. fomes and X. granatum. At the same time, the stomatal conductance was remarkably depleted under salinity stressed habitats than those of the nonsaline counterparts and ranged between nearly 25 and 52%. Total leaf protein content form the above said taxa revealed that the increment of total protein occurred in mesophytic habitat and it was ranged between 156% (in P. paludosa) and 5.7% (in X. granatum). PAGE analysis revealed that in most of the cases there were extra numbers of protein bands expressed with relatively low molecular weight in saline habitat plants. In all salinity imposed plants, there were sharp increase in band intensity and number of isoforms of each enzyme. Peroxidase increment in saline plants was ranged between 257% (in Bruguiera) and 139% (in Excoecaria). Similarly, superoxide dismutase (SOD) was estimated as 247% (in Heritiera) to 147% (in Excoecaria) in saline habitats. Increments of esterase and acid phosphatase were varied from 287% (in Phoenix) to 154% (in Excoecaria) and 293% (in Bruguiera) to 139% (in Excoecaria), respectively. Salinity imposed increment of antioxidant enzymes proved their efficient scavenging ability to evolved reactive oxygen species (ROS), but these increments were relatively lower in Heritiera and Xylocarpus even though the net photosynthesis was higher. This might be related to their less adaptability in elevated salinity stress than those of the other three species investigated from the same regime. Among the plants grown in in situ condition, some taxa have the better ability of enzyme production, which might be correlated with the efficient stress management practice. A statistical relationship was observed between the total protein content and the investigated enzyme concentration, dependent on the habitat and discussed accordingly.