Anatomical and physiological adaptations of mangroves

This review focused on some specific histo-physiological features of the mangroves that help them to adjust and grow extensively in the saline rich coastal regions. Sundarban, the largest chunk of coastal ecosystems of the world located between India and Bangladesh has the widest range of mangrove species in its tidal influenced highly saline soil. Several anatomical characteristics to conserve water are mostly species specific and unique to these plants as such characteristics are not found in their genetically close relatives. The most conspicuous features are succulent leaves with increased mesophyll area, thick cuticle and wax deposition on epidermis. Chlorenchyma cells with large vacuoles are often found associated with different forms of salt secreting glands. A cavitation resistant xylem structure in the stem is one of the mechanisms of mangroves to safeguard their water transport. Non-annual growth ring in some mangroves could be a potential proxy for past environmental conditions. Most root systems show reduced cortex with aerenchyma but wider casparian strip. These anatomical characteristics are the basis for their physiological adaptation to high saline condition. Mangroves can regulate ion homeostasis under salt stress by salt secretion, ultrafiltration and ion sequestration. Salinity stress leads to accumulation of reactive oxygen species (ROS), peroxidation of membrane lipids and inactivation of proteins. Mangroves can activate diverse components of their antioxidative system to eliminate H2O2 and restrict the accumulation of ROS. All these characteristics help the mangroves to photosynthesize optimally and show a good vegetative growth under tidal influenced varied saline condition.