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Inter and intraspecific variation was analyzed in two Catharanthus species with regard to isozyme polymorphism and indole alkaloid content in roots and leaves. No significant differences in alkaloid production were observed in three groups of C. roseus plants individualized for their flower color. Conversely, comparisons between C. trichophyllus and C. roseus, showed large differences of alkaloid profiles in both roots and leaves. Specific isozyme markers on four presumed loci were found allowing us to establish that natural hybridizations could occur between the two species when grown together. Experimental hybridizations confirmed that introgressions were feasible but suggested that a reproductive barrier was acting and involved interspecific incompatibility. The identification and assay of the main alkaloid compounds in natural interspecific hybrids displayed such a high hybrid vigor that interspecific hybridization may present a new and successful way of improving alkaloid production in Catharanthus species.

Regeneration of Aeschynomene sensitiva Sw. after caUogenesis was obtained from small (2-5 mm long) root explants of 30-day-old seedlings aseptically cultivated on Murashige and Skoog medium supplemented with various concentrations of growth regulators. After 4 weeks, the best results were observed with 0.54 ~ c~-naphthaleneacetic acid and 2.22 BM benzyladenine. On this medium, the rate of regeneration depended on seedling age and agar concentration. The highest number of shoots per explant was obtained with small cuttings from 30-day-old seedlings grown on a medium containing 8 g 1 -i of agar. Regeneration success was also dependent on explant size. When longer explants (7-20 mm) were cut from the main root, direct regeneration was obtained in two weeks. These cuttings also generated shoots through callogenesis in four weeks but always in lower quantities than with direct regeneration, whatever the seedling age. Here also, the best regeneration was obtained with cuttings from 30-day-old seedlings maintained on a medium with 8 g 1-1 of agar. Regenerants were rooted on growth-regulator-free Murashige and Skoog medium and then acclimatized in a greenhouse. A better survival to transplantation was observed when plantlets were inoculated with the photosynthetic Bradyrhizobium strain ORS 278. Stem and root nodules developed on the inoculated plantlets and were able to fix nitrogen.

No abstract

The treatment of a CATHARANTHUS ROSEUS cell suspension culture with a low concentration of PYTHIUM elicitor stimulated the alkaloid production. When these pretreated cells were resuspended in a medium that did not contain the fungal extract, the positive effects of the treatment on alkaloid synthesis and excretion were lost and, moreover, the standard level of production was not recovered. A second treatment of these cells with PYTHIUM elicitor at day 5 of the second culture cycle greatly impaired growth kinetics, but did not stimulate the alkaloid production observed with standard cultures. Repeated treatments with a low concentration of fungal elicitor seemed to have a negative long-term effect on both growth and alkaloid synthesis and did not appear to be a useful process for production purposes.