Understanding of the Distribution, Translocation, Bioaccumulation, and Ultrastructural Changes of Monochoria hastata Plant Exposed to Cadmium

In the present research, the distribution and subcellular localization of cadmium in the roots, shoots, and leaves of Monochoria hastata were evaluated to understand structural and ultrastructural changes caused by the metal. Several visual toxic symptoms such as withering, chlorosis, and falling of leaves appeared in M. hastata, especially at 15 mg L-1 Cd concentration. Analysis of Cd concentration by ICP-OES showed that Cd concentrations in the root were significantly higher than those in the shoot and found to be in the following order: root > stem > leaf. Bioconcentration factor (BCF) and translocation factor (TF) were used to evaluate accumulation and transfer of metals from the root to aerial parts. TF of Cd in M. hastata was < 1 in all three Cd concentrations. But it has quite considerable extent of BCF value suggesting that M. hastata is a moderate accumulator. SEM has provided a strong evidence of closing of stomata due to Cd-induced stress. The results of TEM showed the deposition of electron-dense material in vacuoles, cell wall, chloroplasts, and mitochondria. Besides, significant ultrastructural changes such as changes of the shapes of the chloroplasts, reduction of the number of cristae, high vacuolization in the cytoplasm, decrease in the intercellular spaces, shrinkage of vascular bundle, and loss of cell shape were observed in the TEM micrograph study. FTIR analysis revealed the presence of different functional groups which are responsible for binding of Cd ions in the biomass. From the above study, it is clear that M. hastata can potentially be useful for the removal of Cd from Cd-containing wastewater.