Interaction of Boron with Components of Nucleic Acid Metabolism in Cotton Ovules Cultured in Vitro

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Abstract
Cotton (Gossypium hirsutum L.) ovules grown in a defined nutrient medium undergo normal morphogenesis, including fiber production. In identical medium lacking B, ovules callus and accumulate brown substances. B deficiency-like symptoms were induced by 6-azauracil and 6-azauridine in ovules growing in B-sufficient media. Other nucleoside base analogs either reduced or had no effect on over-all growth, but did not cause typical B-deficient callus growth of cotton ovules. Orotic acid and uracil countered the effects of 6-azauracil. Actinomycin D, fluorodeoxyuridine and ethidium bromide reduced not only fiber production on ovules growing in B-sufficient media but also callusing of ovules in B-deficient media. Similarities between symptoms of B deficiency and 6-azauracil injury, and the ability of uracil to suppress both, suggest that B deficiency symptoms are related to reduced activity in the pyrimidine biosynthetic pathway. Growth inhibition by most nucleoside base analogs tested, actinomycin D, fluorodeoxyuridine and ethidium bromide, as compared to callusing brought on by B deficiency and 6-azauracil, indicates that B deficiency symptoms are not related to a reduction in nucleic acid biosynthesis. Based on this information, a discussion of the possibility that B deficiency causes reduced synthesis of UDP-glucose is presented.