The involvement of Ca2+-dependent protein kinase in the regeneration of rice cultured suspension cells.

Short-term cultured cells of rice (Oryza sativa) were found to be capable of regeneration, in contrast to those obtained from long-term cultures. For clarification of the mechanism of regeneration, it was first necessary to distinguish protein kinase activity in long-term and short-term cultured cells; this activity was found greater in the former than latter. The activity was dependent on calcium, not phospholipid, phorbol ester or calmodulin. The apparent Mr of both Ca2+-dependent protein kinases was 32 kDa according to gel phosphorylation. Phosphoserine was identified in serine residues in phosphorylated histone III-S by phosphoamino acid analysis. A Ca2+-dependent protein kinase having a relative Mr of 32 kDa is thus shown to be possibly essential to regeneration in rice cultured cells.