Effect of Boron on the Incorporation of Glucose from UDP-Glucose into Cotton Fibers Grown in Vitro

Boron is required for fiber growth and development in cotton ovules cultured in vitro. Incorporation of [¹⁴C]glucose by such fiber from supplied UDP-[¹⁴C]glucose into the hot alkali-insoluble fraction is rapid and linear for about 30 minutes. Incorporation of [¹⁴C]glucose from such substrate by fibers grown in boron-deficient ovule cultures is much less than in the case with fibers from ovules cultured with boron in the medium. Total products (alkali-soluble plus alkali-insoluble fractions) were also greater in fibers from ovules cultured with boron. The fraction insoluble in acetic-nitric reagent was a small part of the total glucans; however, in the boron-sufficient fibers, there was significantly more of this fraction than in fibers from boron-deficient ovule cultures. The hot water-soluble glucose polymers from the labeled fibers had a significant fraction of the total [¹⁴C]glucose incorporated from UDP-[¹⁴C]glucose. Both β-1,4- and β-1,3- water-soluble polymers were formed in the boron-sufficient fibers, whereas the same water-soluble fraction from the boron-deficient fibers was predominantly β-1,3-polymers. The incorporation of [¹⁴C]glucose from GDP-[¹⁴C]glucose by the fibers attached to the ovules was insignificant.