THE PRODUCTION OF PYRETHRINS BY IN-VITRO SYSTEMS

Pyrethrins comprise a group of six structurally closed related esters. Economically, they are the most important natural plant insecticides. The principal source of pyrethrins is the plant Chrysanthemum cinerar iaefolium (Pyrethrum). The industrial production is based on the extra ction of pyrethrins from the dried flower heads of the field-grown pla nt. Harvesting of the flowers is labor intensive and the natural pyret hrins are not plentiful enough to provide for the global market demand s. Thus, attempts have been aimed at alternative in vitro production o f pyrethrins, by means of plant cell suspension cultures, callus cultu res, shoot/root cultures, and the bioconversions of precursors. Callus and cell suspension cultures of Pyrethrum seems not to be feasible fo r an industrial process, although technology for cell suspension cultu res exist. The dedifferentiation of plant tissue in vitro, necessary t o produce a callus and suspension culture, is accompanied by an appare nt loss of ability to produce and accumulate pyrethrins. Plantlets and morphologically differentiated shoot cultures (not roots), which prod uce significant amounts of pyrethrins, could be potential candidates f or an industrial process. However, pyrethrins production levels in the se cultures is still very low when compared with floral tissue, and la rge-scale organ culture technology is not yet feasible. Bioconversion of available precursors, by isolated plant enzymes or by genetically e ngineered microorganisms, appears to be a more attractive approach tod ay. The first small steps have been made, but technological and econom ical feasibility of this technology is still uncertain.