Gravity responsible protein and mRNA related to the survival of rice (Oryza sativa L.) from gravity stress

Rice (Oryza sativa L. var. Nipponbare) seeds, seedlings and suspension callus were subjected to powerful gravity stress ranging from 150,000 g to 450,000 g. Suspension callus and dehulled seeds showed 32% and 15% survival rates, respectively, after gravity treatment at 450,000 g for 6 hours, whereas all the seedlings died. Seedlings became increasingly sensitive to gravity stress as the growth stage advanced. The suspension callus, which gradually recovered viability during subculture under normal conditions, were used to analyze the protein patterns and in vitro translation products of poly(A)+RNA. Some 3 to 4 newly synthesized proteins and in vitro translation products were identified using two-dimensional electrophoresis, while 5 to 24 proteins disappeared during the treatment, demonstrating that rice suspension callus respond to gravity stress by producing new mRNA and their proteins. In addition, some newly synthesized proteins which resulted from gravity effects were maintained in the surviving cells during continuous growth on solid medium. There was an increase in the survival rate of suspension callus from the strong gravity stress as a result of treatment with 200 g/l sucrose, 10-5 M ABA or 5 g/l NaCl. This suggests that in addition to changes in protein patterns, another protection mechanism associated with some physiological changes is involved in the survival of rice suspension callus after gravity stress.