Defensive efforts ofSalix myrsinifoliaplantlets in photomixotrophic culture conditions: The effect of sucrose, nitrogen and pH on the phytomass and secondary phenolic accumulation

:Explants excised from in vitro willow (Salix myrsinifolia L.) plantlets were cultured in vitro for seven weeks on Murashige & Skoog (MS) basal solid media with four levels of sucrose, six levels of NH4NO3 and three levels of pH. The effect of sucrose, nitrogen and pH of the medium on phytomass distribution and phenolic glucoside contents were studied.Increasing the level of sucrose in the medium to 3% caused a significant 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 production while at the level of 1/8 and 1/32 of the MS-medium level, the amounts of phenolic glucosides rose considerably. The phytomass and phenolic glucoside production was at its highest at pH 5.7. The results emphasize 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 depend almost entirely on external energy. They also show that carbon partition into secondary phenolics is determined by nitrogen availability found also in in vivo conditions.