ABSTRACT

The presence of the toxic terpene gossypol limits the value of cottonseed as animal food, including humans. FDA regulations in effect since 1980 set a limit of 450 ppm of free gossypol in products for human consumption, although limits for animals can be much higher. Because gossypol and related sesterterpenoids (heliocides) are critical for insect resistance, a project was initiated to eliminate gossypol from seed but not from other tissues. Plants transformed to express an antisense version of δ-cadinene synthase, the first enzyme unique to biosynthesis of gossypol, were regenerated and self-pollinated in order to recover plants homozygous for the insert. Plants with the antisense construct produced seed with significantly reduced levels of gossypol but surprisingly, the progeny that produced seed with the lowest level of gossypol did not include an antisense insert. Second and third generation seed from this apparent somaclonal variant maintained a 50% reduction in seed gossypol, but total heliocides in leaf tissues were reduced only 30% from the parental cultivar. The decrease in terpenoid products was not associated with a decrease in number or size of glands. Crosses have been made between the variant and commercial varieties to determine if the low seed gossypol trait is simply inherited.