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Elevated substrate salinity and anthropogenic impulse are the major threat to the mangrove ecosystem. In the Indian subcontinent, Sundarbans have the richest mangrove species diversity. Due to geomorphic characteristics and unplanned management, the elevated salinity prevails in the western part and that has direct impact on vegetation. Seven mangrove taxa were examined, of which four (Aegialitis rotundifolia, Heritiera fomes, Xylocarpus granatum, and X. mekongensis) were considered as degrading and three (Bruguiera gymnorrhiza, Excoecaria agallocha, and Phoenix paludosa) were considered as natural control. The targeted taxa were collected from five different islands and were selected on the basis of increasing salinity gradient. As salinity increased from site I to V (11.76-15.2 ppt), the amount of total leaf proteins decreased in all the targeted species and ranged between 5.67 and 25.23%. The percentage of protein depletion was less in Aegialitis, Heritiera, and Xylocarpus than the other three taxa in higher salinity that pointed out their less adaptability, as degradation of protein may be essential for efficient stress management. Two antioxidative (peroxidase and superoxide dismutase) and two hydrolyzing (acid phosphatase and esterase) enzymes showed a positive correlation with salinity. In four degrading taxa, the percentage of enzyme increment was less than those of their natural control taxa. Salinity imposed increment of antioxidant enzymes facilitate ROS scavenging, which is an inevitable elevated byproduct during photo-inhibition. Lower amount and number of isoforms in higher salinity indicated towards less suitability of Aegialitis rotundifolia, Heritiera fomes, Xylocarpus granatum, and X. mekongensis in increased salinity level of western Sundarbans.

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A comparative account of the polymorphic expression of two antioxidative enzymes (Peroxidase and Superoxide dismutase), two hydrolyzing enzymes (Esterase and Acid phosphatase) and total proteins was estimated both qualitatively and quantitatively from the leaves of five mangroves (Bruguiera gymnorrhiza, Excoecaria agallocha, Heritiera fomes, Phoenix paludosa and Xylocarpus granatum) from two different habitats (in situ habitat of Sundarbans and their replicas from ex situ habitat in fresh water condition) and discussed. The higher amount of total protein occurred in fresh water plants compared to their Sundarbans counterparts. The increment of total protein ranged among 156% to 5.7%. Gel electrophoresis experiments revealed that in most of the cases there were extra numbers of protein bands expressed with relatively low molecular weight in saline habitat. In all salinity imposed plants, there were sharp increases in band intensity and the number of isoforms of investigated enzyme. Peroxidase increment in saline plants ranged from 257Á139%. Similarly, SOD was estimated at 247Á147% in saline habitats. Increments of Esterase and Acid phosphatase varied from 287Á154% and 293Á139%, respectively.

Increased salinity distresses some key species severely in Indian Sundarbans. Geomorphic characteristics coupled with demographic obligations have proven to be pivotal factor towards the prevalence of elevated salinity in this zone. Better adaptation to rapid changes in microclimate demands wide range of genetic polymorphism as well. RAPD and ISSR molecular markers were used for this genetic diversity study. Degree of polymorphism was found relatively higher in Bruguiera gymnorrhiza (26.43 % in RAPD and 24.36 % in ISSR) than the other taxa, Heritiera fomes (14.43 and 12.76 % respectively) in case of RAPD and ISSR. Dendrogram constructed based on the similarity matrix showed that for H. fomes, least saline and highest saline zones are positioned in the same clade; whereas in B. gymnorrhiza the higher saline areas were clustered together. Nei's gene diversity (h) as revealed from RAPD and ISSR analysis were found to be 0.0821, 0.0785 and 0.0647, 0.0592 in B. gymnorrhiza and H. fomes respectively. The higher degree of polymorphism as revealed from UPGMA Dendrogram and Nei's genetic diversity might be attributed towards the comfortable growth of B. gymnorrhiza all along the Indian Sundarbans. On the other hand the relatively lesser degree of genetic polymorphism of H. fomes might be attributed towards their precarious status in present days elevated salinity in Indian Sundarbans.

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