Plant regeneration in cotton: A short-term inositol starvation promotes developmental synchrony in somatic embryogenesis

Despite high commercial interest, the success of biotechnological applications in cotton (Gossypium hirsutum) has been limited due to difficulties in genetic transformation. Major problems have been genotype dependence and low frequency of somatic embryogenesis, making it difficult to regenerate plants from transgenic, tissue. This study reports an increase in somatic embryogenesis efficiency and the induction of developmental synchrony in embryogenic callus cultures of cotton by a single cycle of myo-inositol depletion in liquid culture. Calluses were initiated on hypocotyl or cotyledon explants of cultivar Coker 312 by culturing these explants on callus-inducing solid medium [Murashige and Skoog salts plus vitamins of Gamborg's B-5 medium, 30 g l(-1) glucose, 100 mg l(-1) myo-inositol, 2.2 muM 2,4-dichlorophenoxyacetic acid, and 0.88 muM 6-benzyladenine]. The calluses were transferred to an identical liquid basal medium devoid of plant growth regulators. This induced the development of embryogenic cells. Friable chimps of cells formed after 20d in the medium were selectively collected over filter mesh 40 and subjected to one cycle of myo-inositol starvation. This induced a highly synchronized embryogenesis in the culture. The optimized protocol gave 100% embryos at the globular stage, out of which more than 80% developed into bipolar torpedo-stage embryos. About 68% of these Were converted to plantlets by subculturing onto a simplified solid medium, and finally grown into healthy, fertile plants.