Effect of mercury ion on the stability of the lipid-protein complex of isolated chloroplasts.

Mercury is known to interact with different parts of living systems causing serious biochemical and physiological disorder. In order to know the effect of mercury (Hg2+) ion on chloroplasts, the cell free organelle are incubated in an isotonic buffer medium in presence of mercury ion. The metal ion is found to induce membrane lipid peroxidation, loss of photosynthetic pigments and degradation of proteins. Such degradation brings about a drastic modification of lipid-protein organization of chloroplasts as reflected from a blue shift of absorption peaks and lowering of chlorophyll-a fluorescence intensity. The detrimental effect of Hg2+ ion has been explained in terms of direct binding with lipid-protein complex of photosynthetic membrane. Such a binding of metal ion exposes the lipid-protein complex for an easier entry and attack of reactive oxygen species (ROS) generated during incubation of chloroplasts in light and dark, thereby resulting in higher disorganization, which is evident from cation- induced changes in absorption and emission characteristics of the organelle.

An Na+/H+ antiporter gene from wheat plays an important role in stress tolerance.

A vacuole Na+/H+ antiporter gene TaNHX2 was obtained by screening the wheat cDNA library and by the 5'-RACE method. The expression of TaNHX2 was induced in roots and leaves by treatment with NaCl, polyethylene glycol (PEG), cold and abscisic acid (ABA). When expressed in a yeast mutant (deltanhx1), TaNHX2 suppressed the salt sensitivity of the mutant,which was deficient in vacuolar Na+/H+ antiporter, and caused partial recovery of growth of delta nhx1 in NaCl and LiCl media. The survival rate of yeast cells was improved by overexpressing the TaNHX2 gene under NaCl, KCl, sorbitol and freezing stresses when compared with the control. The results imply that TaNHX2 might play an important role in salt and osmotic stress tolerance in plant cells.