Abstract
Boron deficiency and phytohormone interactions have been studied in unfertilized cotton (Gossypium hirsutum) ovules grown in vitro. Such ovules required exogenous indoleacetic acid and/or gibberellic acid for fiber elongation. Boron also was required for maintenance of fiber elongation and normal morphogenesis throughout 14 days of culture. The amount of exogenous boron necessary for maximum fiber elongation varied among experiments, presumably in relation to endogenous boron levels at anthesis. Some ovular epidermal cells distant from the liquid medium could be induced to elongate into fiber even after 6 days in boron-deficient medium in response to the later addition of boron.Boron deficiency, in the presence of exogenous indoleacetic acid, was characterized by lack of fiber development on the inundated ovular surface and reduced fiber growth on the ovular surface exposed to air. In the presence of gibberellic acid, boron deficiency was characterized by complete absence of fiber and callusing of the entire ovular surface. When both indoleacetic acid and gibberellic acid were added, the lack of boron resulted in proliferation of callus laterally and upward from the inundated epidermis, accumulation of brown pigments (presumably phenolic compounds) in the callus, and restriction of fiber to a small area of the upper ovular surface.