The embryogenic response of immature embryo cultures of durum wheat (Triticum durum Desf.): histology and improvement by AgNO3

Immature zygotic embryos of durum wheat cv Ardente were cultured vitro on 2,4-D to induce somatic embryogenesis. Five days after culture initiation, somatic proembryos were directly initiated from the scutellum of immature embryos. After 28 days, somatic embryos were fully developed with a scutellum-like structure. Histological observations between the first and the eighty day in culture showed a clear unicelllar origin for a few of these somatic embryos, whilst most of them originated from a meristematic multilayer. Furthermore, estimation of the mitotic index of outer epithelium, subepithelium and inner epithelium of the scutellum during the first week of culture, showed a strict epidermal origin of these early developed structures. The addition of 1 mg·L^–1 of AgNO₃ enhanced the induction of direct somatic embryogenesis (a more than 22 fold increase), affecting both the percentage of embryogenic explants and the number of somatic embryos per explant, suggesting the possible involvement of ethylene.