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Cell cultures initiated from Nicotiana sylvestris and Capsicum annuum were used in studies on mutation and the selection of variants. Both diploid and haploid derived cultures of N. sylvestris were used, but the genetic instability of these cultures invariably resulted in the application of selection pressures to cultures of mixed ploidy. No haploid material of C. annuum could be obtained, so diploid derived cultures alone were used for this species. A plating method was devised in which small aggregates from the cell suspensions were incorporated into a thin layer of agar medium in Petri dishes, and exposed to the selection pressures in this form. Using these methods, lines of both species were selected with improved chilling tolerance, high temperature tolerance and high salt resistance, in some cases chemical mutagens were shown to increase the yield of lines selected as tolerant. Many tolerant lines were maintained in culture for a number of passages and a proportion of them maintained their tolerance through extended periods in the absence of the selection pressures. For three chilling tolerant lines of N. sylvestris, fertile plants were regenerated and two of these exhibited the maintenance of an improved tolerant phenotype in the seedlings. Metabolic and anatomical aspects of the suspension cultures of variant lines were examined and certain characteristics were found which could relate to the improved tolerance. These included changes in the temperature dependance of respiration, associated with chilling tolerance and ultrastructural changes associated with high salt resistance. |
