Figure 8

Ethylene-auxin interactions in the control on sex determination and fruit set in zucchini squash. During female flower development (before anthesis), ethylene controls the arrest of stamens and the proper maturation of the flower. In the days immediately after anthesis, ethylene regulates negatively fruit set and early fruit development. In fact, a reduction of ethylene in the flower not only induces the conversion of female into bisexual flowers, but also promotes the parthenocarpic development of the fruit. After anthesis, therefore, ethylene production needs to be prevented for a proper development of the ovary and consequently for fruit set and early fruit development. The inhibition of ethylene biosynthesis and signalling in the ovary of zucchini is likely to be caused by auxin, since we have found that auxin regulate negatively ethylene production and signalling during this developmental period. The prevention of ethylene production after pollination is likely to be mediated by auxin, although this has not been proven in this paper (dashed lines).