The induction of α‐amylase activity by sucrose starvation in suspension‐cultured rice cells is regulated by polyamines

When suspension‐cultured rice (Oryza sativa L. cv. Tainan 5) cells were deprived of sucrose, α‐amylase (EC 3.2.1.1) activity in the cells and the culture medium increased markedly. The increase in activity of α‐amylase caused by sucrose starvation in the cells and the medium was strongly reduced in the presence of exogenously added spermine. Putrescine and spermidine also inhibited, though only slightly, the increase in α‐amylase activity caused by sucrose starvation. Preincubation of the enzyme extract or enzyme in the medium with polyamines had no effect on α‐amylase activity. Sucrose starvation resulted in lower polyamine levels in rice suspension cells. D‐Arginine and α‐methylomithine, inhibitors of polyamine biosynthesis, caused reduced levels of polyamines and increased activity of α‐amylase in rice suspension cells cultured in the presence of sucrose. Our results indicate that the induction of α‐amylase activity by sucrose starvation in rice suspension cells is mediated, at least partly, through the internal level of polyamines.