Survival mechanism of dried calli and regeneration of plants in rice

A system for long-term dry preservation of calli of rice (Oryza sativa L.) and a protection mechanism regulating the survival of dried calli were investigated. The highest survival of dried calli and the highest regeneration rate of plantlets were observed in calli which had been pretreated with 10-5 M abscisic acid (ABA) in the presence of 90 g/l of sucrose and were regrown on an R-2 medium. We detected a corresponding accumulation of the transcript RNA of the rab 16A gene (a rice gene induced by ABA and water stress) in dried calli, mature seeds, and calli pretreated with 10-5 M ABA. The levels of this mRNA increased with the increase of the sucrose concentation, indicating that the accumulation of rab 16A mRNA is regulated by ABA at higher concentrations of sucrose and related to the survival of dried calli. Analysis of proteins by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) demonstrated similar protein patterns in fresh and dried calli. However, in the dried calli pretreated with 10-5 M ABA and 90 g/l of sucrose, different protein patterns were found compared to those in a callus dried without the pretreatment, indicating that some specific polypeptides might be synthesized in the pretreated dried callus.