Histological study of shoot organogenesis in melon (Cucumis melo L.) after genetic transformation

Leave and cotyledon explants from two melon genotypes 'Vedrantais' and 'Paul' were cultured on different media and their regeneration was followed during 60 days. High frequency of plant regeneration was observed with 'Vedrantais' cotyledons cultured on MS medium added with BAP and 2-iP. Using this protocol, Agrobacterium mediated transformation was developed and a significant reduction of the plant regeneration rate was observed. Explants histological analysis revealed the presence of transformed meristematic areas but a rapid and premature cell vacuolization was observed. During plant regeneration, meristematic cells were affected by important cytological damages: cell dislocation accompanied by cell death and final collapsus. This disruption of meristematic areas may be related to an effect of A. tumefaciens transformation on melon cells and would explain the difficulties encountered to regenerate plants.