A novel pathway for rapid shoot regeneration from the proximal zone of the hypocotyl of melon (Cucumis melo L.)

Hypocotyl explants of melon (Cucumis melo L.) are capable of regenerating multiple shoots on Murashige and Skoog (1962) medium. augmented with 4.4 muM benzyladenine. Regeneration from the hypocotyl is much more rapid than the more commonly reported regeneration from cotyledonary explants, producing shoots within 2 wk compared to more than a month required for cotyledon explants. The rapid regeneration response depends on the presence of a fragment of the cotyledon remaining attached to the hypocotyl. Controls were performed to ensure that the regeneration was not due to the presence of the shoot apical bud of the melon seedling after explant production. Scanning electron microscopy revealed that microsurgery to remove the apical bud left no excess bud material. Regeneration from the proximal part of the hypocotyl was due to production of a new shoot apical meristem, observed by histology. The apical meristem can be produced before leaf primordia in regeneration from the hypocotyl, in contrast to the regeneration process from the melon cotyledon.