Morphological and Histological Evaluations of In Vitro Regeneration in Elliottia racemosa Leaf Explants Induced on Media with Thidiazuron

Abstract

Georgia plume (Elliottia racemosa Muhlenb. ex. Elliott) is a rare deciduous shrub or small tree. It has sustained severe loss of habitat and its range is now restricted to a limited number of sites in the state of Georgia. Tissue culture protocols have been developed as a means to propagate and conserve this threatened species using leaf explants induced on medium supplemented with 10 μm thidiazuron (TDZ) and 5 μm indole-3-acetic acid (IAA). Bud-like clusters, elongated embryo-like protrusions, and shoot-like structures were produced from the leaf explants. Morphological and histological evaluations of cultures during induction and development were conducted using light microscopy of sectioned material and scanning electron micrography. Histology of explant tissues indicates that plant regeneration of Georgia plume occurs through a shoot organogenesis pathway that involves the formation of actively dividing meristematic regions originating in subepidermal cell layers that proliferate to form protuberances on the explant surface. Numerous well-formed shoot apical meristems with leaf primordia are produced, as well as fused shoot-like structures. Elongated, embryo-like structures had various degrees of shoot apex development. Evaluations of serial sections found that they lacked a defined root apex, and that basal portions were composed of parenchymatous files of cells with a broad point of attachment to the parent tissue. The lack of bipolarity and a root pole signifies that true somatic embryogenesis does not occur.