The role of ethylene and brassinosteroids in the control of sex expression and flower development in Cucurbita pepo

Abstract

In this paper we compare the sensitivity of different squash genotypes to ethylene and brassinosteroids by studying the effects of different ethylene and brassinosteroid treatments on the sexual expression and flower development of different C. pepo genotypes: Bolognese (Bog) and Vegetable Spaghetti (Veg), two contrasting lines for ethylene production and sensitivity, as well as Cora, a standard commercial hybrid. Results have demonstrated that ethylene has a much greater effect on sexual expression and flower development in C. pepo than brassinosteroids. Ethephon increases the number of female flowers per plant and reduces the first male phase of development, while treatments with the ethylene inhibitors AVG and STS reduce the number of female flowers per plant and expand the first male phase of development. The differential response observed between genotypes appears to be related to ethylene production and sensitivity. Bog, which produces more ethylene and is more sensitive to this hormone, responded much better to AVG and STS, reducing the number of female flowers per plant, while Veg, which is characterised by lower production of and sensitivity to ethylene, responded better to ethephon by reducing the first male phase of development and increasing the number of female flowers per plant. The differential abortion of female and male flowers in ethephon, AVG and STS treatments, as well as the occurrence of bisexual flowers in the AVG and STS treated plants of the more ethylene sensitive genotypes, demonstrate that ethylene is also involved in the development of female flowers. Female flower buds require a minimal level of ethylene not only to complete their development and maturation without a premature abortion, but also to arrest the development of stamens in the third whorl and to promote the appropriate growth of the carpels. On the contrary, the role of brassinosteroids in the sexual expression of C. pepo was not so evident. The application of brassinazole, an inhibitor of brassinosteroid biosynthesis slightly changes the production of ethylene in the three analysed genotypes, but those changes have little effect on their sexual phenotypes, and they do not alter the development of the unisexual flowers.

Involvement of ethylene in sex expression and female flower development in watermelon (Citrullus lanatus)

“…Therefore, ethylene is responsible for the arrest of stamens in the floral bud whose fate is the formation of a female flower. Since the bisexual flowers with partial stamen development observed under high temperatures produced as little ethylene as male flowers, it is unlikely that they may be produced as a consequence of a partial reduction of ethylene in the floral bud, but rather due to a reduction of ethylene in already determined female floral buds, as was previously proposed in cucumber and zucchini (Yamasaki et al, 2003;Manzano et al, 2011). The genes responsible for monoecy in melon, cucumber and zucchini, CmACS7, CsACS2 and CpACS27A, are expressed very early in the development of female flowers, and their loss of function mutations or their inhibition at early developmental stages produces a complete conversion of female into bisexual flowers and of monoecy into andromonoecy (Boualem et al, 2008Li et al, 2009;Martínez et al, 2014).…”

“…While Bog develops the first female flowers between nodes 2e4, and produces a mean of 69e75% female flowers, the sex phenotype of Veg is strongly male, delaying the development of the first female flower to nodes 15e20, and producing less than 25% female flowers, with some of the plants producing less than 5% (Manzano et al, 2010). The extreme male phenotype of Veg is determined by a major gene that confers reduced ethylene production and sensitivity, while Bog produces much more ethylene and has a higher sensitivity to the hormone (Manzano et al, 2010(Manzano et al, , 2011. Grafting was carried out when the first true leaf developed in both the rootstock and scion seedlings, following standard methods in Almería nurseries.…”

“…Given that ethylene is required for the arrest of stamens in female flower development, it would be expected that this hormone promotes female flowering transition and the number of female flowers per plant. This is true for cucurbit species such as cucumber, melon and zucchini, in which ethylene treatments reduce the initial male phase of development and increase the female to male flower ratio, while treatments with inhibitors of ethylene biosynthesis or perception, such as aminoethoxyvinylglycine (AVG) or silver thiosulphate (STS), delay female flowering and reduce the female to male flower ratio (Byers et al, 1972;Manzano et al, 2011;Pay an et al, 2006;Perl-Treves, 1999;Rudich, 1990). In watermelon, however, previous reports had shown that ethylene regulates sexual expression in a completely opposite way.…”

“…The level of ethylene in flower buds seems to be essential for both sex determination and female flower development (Manzano et al, 2013). Thus, ethylene treatments promote the production of female flowers, while treatments with inhibitors of ethylene biosynthesis or perception, such as aminoethoxyvinylglycine (AVG) or silver thiosulphate (STS), increase the number of male flowers per plant (Byers et al, 1972;DenNijs and Visser, 1980;Manzano et al, 2011;Owens et al, 1980;Pay an et al, 2006;Rudich, 1990;Rudich et al, 1969). It has been demonstrated that the monoecious phenotype of melon and Abbreviations:…”

“…Treatment with ethylene-releasing agents resulted mostly in the suppression of ovary development (Rudich and Zamski, 1985), while inhibitors of its biosynthesis and perception, hastened the appearance of the first pistillate flower and increased the pistillate to male flower ratio (Rudich and Zamski, 1985;Sugiyama et al, 1998). The masculinizing effect of ethylene in watermelon is in stark contrast to the feminizing effect of this same hormone in other cucurbit species such as cucumber, melon and squash (Manzano et al, 2011).…”