High-resolution two-dimensional electrophoresis separation of proteins from metal-stressed rice (Oryza sativa L.) leaves: drastic reductions/fragmentation of ribulose-1,5-bisphosphate carboxylase/oxygenase and induction of stress-related proteins.

Employing high-resolution two-dimensional electrophoresis (2-DE), we studied changes in the rice leaf protein patterns, in response to applied heavy and alkaline metals, important environmental pollutants in our surroundings. Drastic changes in 2-DE protein patterns after treatment with copper, cadmium, and mercury, over control were found, including changes in the morphology of the leaf segments. Changes in the major leaf photosynthetic protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO, both suppression and fragmentation), and induction of proteins are reported. A total of 33 proteins, which were highly reproducible in repeated experiments, were visually identified as changed over the control, and taken for N-terminal or internal amino acid sequencing. Among these, nine proteins were N-terminally blocked, and six proteins could not be sequenced. Most of the proteins showed homology to RuBisCO protein, and some to defense/stress-related proteins, like the pathogenesis related class 5 protein (OsPR5), the probenazole-inducible protein (referred to as the OsPR10), superoxide dismutase, and the oxygen evolving protein. Results presented here strongly indicate a highly specific action of some of these metals in disturbing the photosynthetic machinery, as evidenced by prominent reductions/fragmentation of the major photosynthetic protein, RuBisCO, and resulting in stress.