Developmental Morphology and Anatomy of Direct Shoot Organogenesis from Melon Cotyledon

The morphology and anatomy of direct shoot organogenesis from quiescence cotyledon explants of melon (Cucumis melo L.) cv.ximoluotuo cultured in vitro was studied.Buds regene- rated when the explants were cultured with the abaxial side towards the inducing media.By 4 d on MSmedia with BA 0.5 mg/L,the explants turned green but there were no cell divisions observed.By 6 d,cells in the epidermal and subepidermal laryer on the adaxial side of the explant,near the cut edge where is morphological down divided and became some meristemoids.By 7～9 d,the meristemoids became small visible protuberances.By 10～14 d,more protuberances appeared and clustered near the cut edge of the explant.Some of them became long and thin and some developed into distinguished young leaves.But there were no typical bud structures by this time.By 15～20 d,a cluster of young leaves and leaf-like organs formed and several axillary meristems initiated at the base of the adaxial side of these young leaves.When transferring these explants onto the MSmedia with BA 0.05 mg/L,the young leaves extended fully and the whole explant presented"bush-like"3～5 d later.Buds elongated and shoots can be obtained with another 2～7 d.Cutting the elongated buds could promote other buds to develop on one explant.