Abstract
The effects of water stress, abscisic acid (ABA), and gibberellic acid (GA3) on flower production and differentiation by Collomia grandiflora were investigated. An untreated plant typically produced both small, closed cleistogamous (CL) and large, open chasmogamous (CH) flowers. The larger corolla of CH flowers was due to a greater cell number and size. When plants were water-stressed or sprayed with ABA, both the percentage of CH flowers and the total number of flowers were reduced significantly. The corolla dimensions and epidermal cell numbers and sizes of CL flowers produced by water-stressed and ABA-sprayed plants did not differ from those of CL flowers produced by control plants. Application of GA3 to both well-watered and water-stressed plants significantly increased the percentage of CH flowers formed compared to well-watered controls. In the absence of GA3, water-stressed plants produced almost entirely CL flowers. GA3-sprayed plants produced CH flowers whose corolla dimensions were intermediate between those of CL and CH flowers formed by control plants. Epidermal cells of these intermediate corollas were reduced only in number and not in size when compared to control CH flowers. Endogenous levels of ABA and gibberellins may control the type of flower produced by C. grandiflora and may mediate some of the observable effects of water stress on flowering.
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