Anatomy of shoots and tumors of in vitro habituated rhododendron ‘montego’ (Ericaceae) cultures with tissue proliferation

Abstract

Tissue proliferation (TP) is characterized primarily by the formation of galls or tumors at the crown of container-grown rhododendrons that were initially propagated in vitro. In the cultivar 'Montego', TP-like symptoms are first observed in vitro as shoot clusters with small leaves and nodal tumors. In addition, unlike the normal in vitro non-TP (TP-) shoots, in vitro TP (TP+) shoots proliferate rapidly without the presence of the plant growth regulator cytokinin in the tissue culture medium. Comparisons of the anatomy of TP+ and TP- shoot tips showed that TP+ shoots had a less developed vascular system, longer cells in the pith and cortex, and altered internodal elongation at the shoot apex. In addition, TP+ axillary buds were abnormal in that they were displaced onto the stem above the leaf axil, and a small group of proliferating cells replaced the shell zone at the base of the bud. Initiation of tumor formation began with the expansion of this region of cell proliferation (RCP) and shoot growth from the abnormal axillary bud (tumor bud). Organization of the tumor bud and extension of the RCP characterized the further development of two types of tumors. In polar shoot tumors, shoot growth continued from the persistent tumor bud and the tumor at the base of the shoot remained small in size. The RCP extends downward to the vascular junction of the subtending leaf and the stem of the TP+ shoot. In nonpolar tumors, continuous de novo meristem formation led to the development of large tumors with or without shoots. The RCP is present throughout the tumor and is associated with de novo meristem formation. Comparisons to the anatomy of other tumor-like structures showed that TP tumors of Rhododendron 'Montego' are most similar to tobacco genetic tumors.

Anatomy of normal and hyperhydric leaves and shoots of in vitro grown Simmondsia chinesis (link) schn

“…During the past decade, numerous anatomical and ultrastructural studies of diverse species cultivated in vitro have been reported (Johansson et al, 1992;Sallanon et al, 1993;Gribble et al, 1996;Noe  and Bonini, 1996;Mercure et al, 1998;Olmos and Hellõ Ân, 1998). However, there is sparse information on jojoba anatomy in either ex vitro or in vitro conditions (Birnbaum et al, 1984).…”

Response of Rhododendron `Montego' with “Tissue Proliferation” to Cytokinin and Auxin In Vitro

“…1). Most of the shoots were highly branched, had short internodes, small leaves (2-3 mm long) and nodal tumors (Mercure et al, 1998). These shoots are referred to as TP(+) dwarf shoots.…”

Redevelopment of Tissue Proliferation Symptoms in Rooted Rhododendron Cuttings

“…The morphology of TP also appears to be similar to that of lignotubers, which are woody outgrowths at the stem base that contain numerous dormant buds (Del Tredici, 1992). However, TP tumors do not generally exhibit normal lignotuber characteristics (Brand and Kiyomoto, 1994;Del Tredici, 1992;Mercure et al, 1998). The most widely accepted theory is that TP results from epigenetic changes that are induced by the tissue culture process (Brand and Kiyomoto, 1997;Linderman, 1993).…”