A defective pollen-pistil interaction contributes to hamper seed set in the parthenocarpic fruit tomato mutant

Abstract

In the parthenocarpic fruit (pat) tomato mutant, parthenocarpy is associated with partial aberrations of stamens (shortness and carpelloidy) and ovules (defective integument growth) that contribute to impair seed set. However, these do not seem to be the only reasons for seed infertility because hand-pollination fails to restore seed set in ovaries where a fraction of the ovules are still morphologically normal. Therefore, it is conceivable that other unreported defects occur during the reproductive process in the mutant. In this research, we show that the mutation does not affect pollen or embryo sac development and viability, but generates sporophytic effects that reduce seed production and seed size. While pollen germination and stylar growth were normal in mutant pistils, fertilization does not take place because of abnormalities in the pollen tube-ovary interaction in this genotype. Inside the ovary of pat plants, pollen tubes appeared to be disorientated; they wandered about in the ovarian cavity and often lost their adherence to the placental surface. Interestingly, in pat ovaries fertilization was strongly impaired even in those ovules that appeared normal. It may be that apparently 'normal' ovules cannot guide pollen tubes to their micropyle in the altered pat ovary because adhesion molecules are not properly arrayed on a placenta that is already preparing for cell division or, alternatively, chemotropic signals in the pat ovary may be altered by the presence of aberrant ovules, which are not simply devoid of attractivity, but disrupt pollen tube guidance overall.

Factors affecting seed set in the crosses between Dendranthema grandiflorum (Ramat.) Kitamura and its wild species

“…Failures in pollination are thought to be widespread in plants and a common cause of low seed set (Wilcock and Neiland 2002;Marta et al 2004;Pellegrino et al 2005;Hodnett et al 2005;Ram et al 2006;Lee et al 2008;Spielman and Scott 2008). For instance, Mazzucato et al (2003) indicated that a defective pollen-pistil interaction was a main factor leading to low seed set in the parthenocarpic fruit tomato mutant. The experiments described here demonstrated that in the cross between D. grandiflorum 'Yuhuaxingchen' and D. nankingense very few pollen grains germinated on stigmas and most pollen tubes failed to penetrate Fig.…”

RNA Interference Silencing of Chalcone Synthase, the First Step in the Flavonoid Biosynthesis Pathway, Leads to Parthenocarpic Tomato Fruits

“…Several tomato mutant genotypes resulting in parthenocarpic fruit growth have been described, of which pat (Mazzucato et al, 2003), pat2 (Philouze and Maisonneuve, 1978), pat3, and pat4 (Nuez et al, 1986) are the best characterized. In contrast to the Chs RNAi tomato, parthenocarpic fruit development of all these pat mutants is independent of pollination.…”

Parthenocarpy in the Tomato (<i>Solanum lycopersicum</i> L.) Cultivar ‘MPK-1’ is Controlled by a Novel Parthenocarpic Gene

“…In pat tomato mutants, there are partial aberrations of the stamens and ovules, and fertilization is strongly inhibited even where the ovules appear normal due to abnormalities in the pollen tube-ovary interaction (Mazzucato et al, 1998(Mazzucato et al, , 2003, indicating that pat may result from the mutation of a putative gene with homeotic functions. SEPATALA (SEP) is a MADS box gene that interacts with other MADS box genes to control the development of each floral whorl in Arabidopsis.…”