STUDIES ON THE IN VIVO AND IN VITRO SYNTHESES OF CHIMERAS BETWEEN NICOTIANA TABACUM L. AND SOLANUM LACINIATUM AIT

Rana  L. KADDOURA

Intergeneric chimera synthesis between Nicotiana tabacum L. and Solanum laciniatum Ait. was attempted using grafting and tissue mixing approaches in vivo and in vitro. Investigations were carried out to assess factors that might affect  chimeral shoot recovery.

In vivo, the results of an experiment in which decapitated graft unions were treated with either auxin (p‑CPA) or cytokinin (BAP) showed that BAP was inhibitory to shoot formation at the graft union, while p‑CPA increased the total number of adventitious shoots produced by raising the frequencies of shoot‑forming plants. About 9% (14/151) of the total shoots produced in such situations were intergeneric chimeras. The auxin treatment clearly increased the level of chimeral shoot recovery by enhancing the formation of chimera per shoot‑forming plant, indicating a direct auxin effect on chimeral shoot production.

In vitro, treatments which would have been expected to have a beneficial effect on the recovery of chimeras were tested under a wide range of tissue or cell mixing approaches which included: callus grafts, mixed plated cell suspensions, cocultured protoplasts and differentiated tissues grafts of the two species. A total of 7,813 shoots were regenerated from the mixed cultures when both species were successfully cocultured. None of these shoots was an intergeneric chimeral one.

Results of experiments in which either the culture of chimeral leaf discs on media containing different types and combinations of growth regulators of the culture of explants on one optimal media after exposure to different doses of x‑irradiation showed that; (a) shoots obtained in vitro could be of multicellular origin since some intergeneric chimeral shoots were recovered, (b) the auxin/ cytokinin type and balance, as well as, increased doses of x‑irradiation can affect the frequency of chimeral shoot regeneration. The effects of these factors in determining the origin of derived shoots, (e.g., original cell number, genotype involved in meristem formation) may be greater than had been anticipated previously.

The morphological characteristics of the intergeneric Nicotiana‑Solanum chimeras produced were compared with those of the parental species. The LII layer (LI, LII and LIII denote the outermost, middle and innermost histogenic layers, respectively) appeared to designate the general characteristics of the vegetative and floral components. However, the LI layer could modify the qualitative traits of both components. The LIII layer could alter the quantitative traits of the vegetative organs and actual flower, but, most strikingly, it could determine growth type, branching behavior and inflorescence type. These latter functions of the LIII layer have not been reported previously in the literature.

The outcomes of this study have generated information which will be useful for devising future strategies for studies on cell‑to‑cell interactions in relation to chimeral meristem formation under both, in vitro and in vivo situations.