DEFENSIVE EFFORTS OF SALIX MYRSINIFOLIA PLANTLETS IN PHOTOMIXOTROPHICCULTURE CONDITIONS - THE EFFECT OF SUCROSE, NITROGEN AND PH ON THE PHYTOMASS AND SECONDARY PHENOLIC ACCUMULATION

Explants excised from in vitro willow (Salix myrsinifolia L.) plantlet s were cultured in vitro for seven weeks on Murashige & Skoog (MS) bas al solid media with four levels of sucrose, six levels of NH4NO3 and t hree levels of pH. The effect of sucrose, nitrogen and pH of the mediu m on phytomass distribution and phenolic glucoside contents were studi ed. Increasing the level of sucrose in the medium to 3% caused a signi ficant increase in the phytomass and phenolic glucoside accretion. At the sucrose level of 6% the phytomass accretion exceeded the expected phenolic glucoside accretion. Changing the NH4NO3-level in the medium to half that of the MS or lower resulted in a drop in phytomass produc tion while at the level of 1/8 and 1/32 of the MS-medium level, the am ounts of phenolic glucosides rose considerably. The phytomass and phen olic glucoside production was at its highest at pH 5.7. The results em phasize the fine balance between the allocation of carbon for primary metabolite production (growth, maintenance, storage functions) and for secondary metabolite production in small in vitro plantlets, which de pend almost entirely on external energy. They also show that carbon pa rtition into secondary phenolics is determined by nitrogen availabilit y found also in in vivo conditions.