Stimulation of somatic embryogenesis in carrot by ethylene: Effects of modulators of ethylene biosynthesis and action

Abstract

Endogenous levels of ethylene appeared to he suhoptimal for somatic embryogenesis in a suspension culture of carrot. Low concentrations of 1‐aminocyclopropane‐1‐carboxylic acid (ACC). 2‐chloroethylphosphonic acid (ethephon) and elhylene stimulated embryogenesis whereas higher concentrations were inhibitory. The stimulation by ACC was through its conversion to ethylene. whereas the inhibition by ACC was not. Low concentrations of AgNO3. an inhibitor of ethylene action, inhibited embryo‐genesis but stimulated ethylene production. Aminoethoxyvinylglycine (AVG) and aminooxyacetic acid (AOA). commonly used inhibitors of ACC synthase. inhibited both embryogenesis and ethylene production. However, the inhibition of embryogenesis was not related to the inhibition ote ethylene production. Very low concentrations of AVG stimulated embryo production in a way unrelated to its effect on ethylene production. Salicylic acid and CoCl2. inhibitors of ACC oxidase in other systems, inhibited embryogenesis but. again, in way(s) unrelated to their inhibition of ethylene production. In fact, low concentrations of salicylic acid stimulated rather than inhibited ethylene production. The results show that in suspension‐cultured cells, caution is warranted in the interpretation of results obtained with agents presumed to inhibit ethylene biosynthesis. The stimulation of somatic embryogenesis by ethylene unequivocally shows that the inhibition of embryo development by 2.4‐dichlorophenoxyacetic acid (2.4‐D) and other auxins cannot be through their stimulatory effect on ethylene production.