Developmental regulation of polyamine metabolism in growth and differentiation of carrot culture.

Polyamine levels and the activities of two polyamine biosynthetic enzymes, arginine decarboxylase (EC 4.1.1.19) and S-adenosylmethionine decarboxylase (EC 4.1.1.50), were determined during somatic embryogenesis of carrot (Daucus carota L.) cell cultures. Embryogenic cultures showed severalfold increases in polyamine levels over nondifferentiating controls. A mutant cell line that failed to form embryos but grew at the same rate as the wild-type line also failed to show increases in polyamine levels, thus providing evidence that this increased polyamine content was in fact associated with the development of embryos. Furthermore, inhibition of these increases in polyamines caused by drugs inhibited embryogenesis and the effect was reversible with spermidine. The activities of arginine decarboxylase and Sadenosylmethionine decarboxylase were found to be suppressed by auxin; however, the specific effects differed between exogenous 2,4-dichlorophenoxyacetic acid and endogenous indole-3-acetic acid. The results indicate that increased polyamine levels are required for cellular differentiation and development occurring during somatic embryogenesis in carrot cell cultures.