Characterization of physiochemical and anatomical features associated with enhanced phytostabilization of copper in Bruguiera cylindrica (L.) Blume.

Copper is an essential micronutrient for normal plant metabolism and it is involved in number of physiological processes in plants but at the same time, at concentrations above threshold level, it acts as a potential stress factor. In this study, the phytoremediation potential of Bruguiera cylindrica (L.) Blume with respect to Cu was evaluated for the first time. Various physiochemical and anatomical parameters were analyzed in three-month-old healthy plantlets of B. cylindrica on exposure to different concentrations of CuSO4 (0, 0.05, 0.15, and 0.25 mM)for 20 d. Higher uptake and accumulation of Cu in the roots indicates that the roots are the primary site of Cu accumulation and thus the plant perform as an excluder. Tolerance index values (TI > 60) reveals the phytoremediation potential of this plant. Metabolites are accumulated in plants to cope up with the oxidative damage due to Cu stress. Increased rate of proline and free amino acids content and soluble sugar content especially in leaves of B. cylindrica subjected to CuSO4 contributes toward higher osmolality so as to counter the reduced water transport from roots. Nonenzymatic antioxidants like ascorbic acid, glutathione, and phenolics are the ROS scavenging compounds in the Defense system of B. cylindrica toward higher concentrations of CuSO4, and of these, phenolics accumulation plays greater role in the antioxidative function in B. cylindrica in response to Cu stress. The histochemistry of B. cylindrica revealed the prominent occurrence of star-shaped calcium oxalate crystals when exposed to 0.25 mM CuSO4, and it seems to be a prominent defense mechanism under Cu stress. Also a remarkable finding was the accumulation of Cu in the xylem vessels of plants on exposure of 0.25 mM CuSO4 as compared to control. The infrared spectra were analyzed to compare the functional groups in the phenolics and carbohydrate constituents of control and CuSO4-treated B. cylindrica plantlets and it indicated that carboxyl and hydroxyl groups are involved in the Cu binding so as to achieve tolerance to Cu. Thus this study revealed the potential role of B. cylindrica as a promising candidate for phytostabilization of copper.