Aspects of embryogenesis and organogenesis in the in vitro culture of various explants of the eggplant (Solanum melongena L.)

Hussein, Hussein Salem (1991) Aspects of embryogenesis and organogenesis in the in vitro culture of various explants of the eggplant (Solanum melongena L.). University of Southampton, Doctoral Thesis.

Abstract

Explants from leaf, fruit, root, peduncle and epidermal thin cell layer were cultured with various auxin and cytokinin concentrations either alone or in combination. Callus formation and root and shoot organogenesis occurred but only leaf explants were able to produce somatic embryos. Tissues connected with leaf, such as petiole and vein, also failed to produce somatic embryos under conditions conducive for leaf explants. From the response of leaf explants from plants in flower, five cultivars were classified as either embryogenic or non-embryogenic. Leaf explants of cv. Oriental, non-embryogenic in flower, produced some embryos when juvenile, with the number varying with the leaf position, whereas, with cv. Dusky high frequency embryogenesis was obtained with explants from the 5th leaf of juvenile plants. Leaf age influenced the appearance or frequency of embryogenesis for cvs Oriental and Dusky respectively. Explants from 21 day old leaves of cv. Dusky gave the maximum number of embryos and the embryo number and culture weight was reduced with increasing leaf age. Attempts to increase embryogenesis in cv. Oriental using various carbohydrates either separately or in combination with sucrose failed. Some combinations (maltose + sucrose; glucose + sucrose and lactose + sucrose) produced more embryos with cv. Dusky than sucrose alone, but the appearance of embryos produced with sucrose alone was better. In connection with shoot organogenesis, some buds were formed on leaf explants taken from juvenile but not from flowering plants. Root explants produced shoots directly in basal medium and the frequency increased with addition of BAP. Thin cell layers formed shoots at low frequency and peduncle explants occasionally while none were formed with fruit explants. Hypocotyl explants on basal medium showed polarity for morphogenesis, shoots forming at the proximal and roots at the distal end. Transfer experiments between different media showed that leaf explants became determined for embryo production after 4 days on induction medium (NAA) and most of the explants were determined on the 5th day, with the number of embryos increasing with increasing exposure time. Root determination occurred after 1 day exposure and then root number increased with increasing exposure time, reaching a maximum after 5-6 days and then gradually decreasing as embryo production increased. Leaf explants became more competent to respond to NAA when cultured in basal medium for 4 days, although this competence was reduced gradually and finally lost after 10 days in basal medium. Using tissue transfer experiments it was shown that 2,4-D could induce embryogenesis in eggplant, but in comparison with NAA, it was much less effective. Using the scanning electron microscope the development of somatic embryos was followed and they were found to come from mesophyll cells and lower epidermal cells. Embryos were formed mainly from the explant edge while roots were formed from the explant edge and vein. A preliminary experiment was carried out to test the feasibility of characterising proteins specifically associated with embryogenesis using 2-D electrophoresis.

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