Gibberellins are involved but not sufficient to trigger a shift between chasmogamous-cleistogamous flower types in Viola pubescens

At least 50 angiosperm families have plants that produce both chasmogamous flowers and cleistogamous flowers. Various environmental and physiological factors, including the plant growth regulators gibberellins (GAs), have been reported to influence the flower types. Here, the relationship between GAs and flower production was studied for the first time in Viola, a genus famous for the large number of species with the mixed breeding system. Orthologs of genes for GA20 oxidase (VGA20ox) and GA3 oxidase (VGA3ox) were identified by reverse transcription polymerase chain reaction (RT-PCR) from a widespread North American species, Viola pubescens. Semi-quantitative RT-PCR indicated that both genes had increased expression in chasmogamous flowers as compared to cleistogamous flowers, supporting a role for GA in the differential production of flower type. However, the application of exogenous GA3 (the most common commercially available GA) to V. pubescens failed to induce a conversion of production of cleistogamous flowers to chasmogamous ones. Thus, increased levels of GAs in the floral buds appeared be related to flower type in the chasmogamous-cleistogamous mixed breeding system in V. pubescens, but exogenous application was not sufficient to induce an alteration in the type of flower produced.