Polyamines and somatic embryogenesis in carrot. I. The effects of difluoromethylornithine and difluoromethylarginine

Abstract

2,4-Dichlorophenoxyacetic acid (2,4-D) is the most commonly used and a very effective inhibitor of somatic embryogenesis in carrot. This growth regulator not only suppresses differentiation of cultured cells but it can also cause a reversion of the developing embryos to undifferentiated callus. Data presented here show that the addition of 1–10 mM DFMO (difluoromethylornithine) to the medium allowed the normal development of somatic embryos to continue even in the presence of inhibitory concentrations of 2,4-D. DFMO caused a significant increase in ADC activity, an increased accumulation of polyamines in the cells, and inhibited the accumulation of ethylene in cell cultures both in the presence or the absence of 2,4-D. Difluoromethylarginine (DFMA) at 0.1–1.0 mM concentration completely inhibited embryogenesis even in the absence of 2,4-D. DFMA also inhibited ADC activity and caused a reduction in the cellular polyamine levels. ODC activity was detected only when fully mature somatic embryos appeared in the cultures. It is suggested that auxin-induced ethylene biosynthesis plays an important role in the development of somatic embryos in carrot. The promotion of polyamine biosynthesis (by DFMO in the present case) may cause a reduction in the cellular pools of S-adenosylmethionine, which in turn may cause a reduction in ethylene biosynthesis, thus allowing embryogenesis to occur in the presence of an auxin