Role of 1-aminocyclopropane-1-carboxylic acid in the control of female flowering in Cucurbita pepo

Cucurbita pepo L. cv. Trailing Marrow is monoecious, bearing separate male and female flowers and the first functional flowers are usually male. Treatment with 300 ppm ethephon delayed and greatly reduced male flower production and also increased female flower numbers. When plants were sprayed with aminoethoxyvinylglycine (AVG) no female flowers were produced but male flower production was unaffected. Even when ethephon was applied to AVG-treated plants there was still complete inhibition of female flower production. Similarly, AVG-treated plants subsequently exposed to 4000 ppm ethylene for two days never produced female flowers. AVG inhibits the penultimate stage in ethylene biosynthesis i.e. immediately before 1-aminocyclopropane-1-carboxylic acid (ACC). Although spraying AVG-treated plants with ACC did not reverse the inhibition, application of ACC via a cut petiole for a 72 h period following AVG application did cause female flowers to form. The evidence indicates that ACC and not ethylene is the factor controlling female flower production in C. pepo .