Histological Observation of the Processes during Somatic Embryogenesis in the Two Most Commonly Used PGR Regimes in Cotton

The two most commonly used plant growth regulator regimes(PGR) are the IK and DK treatments for somatic embryogenesis.Segments from hypocotyls of Gossypium hirsutum cv.YZ-1 were cultured on callus induction medium for 4 weeks,and sub-cultured on differentiation medium for somatic embryogenesis.The results demonstrated that somatic embryogenesis occurred in the two treatments.In the IK treatment,somatic embryos appeared on day 33 after inoculation,the ratio of differentiation was 97.6%,and somatic embryos commonly appeared prior to an obvious embryogenic callus.One the other hand,somatic embryogenesis was represented at a late stage in the DK treatment,somatic embryos developed from obvious embryogenic calli,and the ratio of callus differentiation was distinctly lower than that with IK treatment,being only 28.6%.Furthermore,adventitious roots almost appeared on the surface of all explants in the IK treatment,but none were found in the DK treatment.Therefore,two distinct patterns of somatic embryogenesis occurred in the two treatments,with histological observation suggesting that the majority of somatic embryos originated from primary meristem and cortex in the DK and the IK treatments,respectively.