STIMULATION OF SOMATIC EMBRYOGENESIS IN CARROT BY ETHYLENE - EFFECTS OF MODULATORS OF ETHYLENE BIOSYNTHESIS AND ACTION

Endogenous levels of ethylene appeared to be suboptimal for somatic em bryogenesis in a suspension culture of carrot. Low concentrations of 1 -aminocyclopropane-1-carboxylic acid (ACC), 2-chloroethylphosphonic ac id (ethephon) and ethylene stimulated embryogenesis whereas higher con centrations were inhibitory. The stimulation by ACC was through its co nversion to ethylene, whereas the inhibition by ACC was not. Low conce ntrations of AgNO3, an inhibitor of ethylene action, inhibited embryog enesis but stimulated ethylene production. Aminoethoxyvinylglycine (AV G) and aminooxyacetic acid (AOA), commonly used inhibitors of ACC synt hase, inhibited both embryogenesis and ethylene production. However, t he inhibition of embryogenesis was not related to the inhibition of et hylene production. Very low concentrations of AVG stimulated embryo pr oduction in a way unrelated to its effect on ethylene production. Sali cylic acid and CoCl2, inhibitors of ACC oxidase in other systems, inhi bited embryogenesis but, again, in way(s) unrelated to their inhibitio n of ethylene production. In fact, low concentrations of salicylic aci d stimulated rather than inhibited ethylene production. The results sh ow that in suspension-cultured cells, caution is warranted in the inte rpretation of results obtained with agents presumed to inhibit ethylen e biosynthesis. The stimulation of somatic embryogenesis by ethylene u nequivocally shows that the inhibition of embryo development by 2,4-di chlorophenoxyacetic acid (2,4-D) and other auxins cannot be through th eir stimulatory effect on ethylene production.