Pyrimidine Pathway in Boron-deficient Cotton Fiber

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Abstract
Cotton ovules cultured in an insufficiency of B (10 .mu.M), showed inhibition of fiber growth by the 9th day in culture. Averaging data from 8-11 days of culture under these conditions, total incorporation of [6-14C]orotic acid into fiber was inhibited by 59%. Inhibition was evident in all radioactively labeled pools, indicating that the effect may be at the membrane transport level or at an early stage of orotic acid metabolism. On a percent basis, incorporation into RNA under B deficiency was higher than under sufficiency. The effect is greater on the 8th day of culture, with a decreasing difference from controls up to the 11th day. Conversely, the percent incorporation into UDP-glucose was lower under B deficiency than in controls, having a more or less constant value from 8-11 days of culture. Thus, a primary event of B deficiency in cotton fiber culture is an alteration in the flow of metabolites through the pyrimidine synthesis pathway.