ROLE OF CARBOHYDRATES IN MICROPROPAGATION OF CORK OAK

The influences of carbon sources, fructose, glucose, sorbitol and sucr ose on shoot proliferation and in vitro rooting of cork oak (Quercus s uber L.) were compared at a wide range of concentrations (1-6%, w/v). The highest number of shoots occurred on glucose-containing medium. Ne vertheless, we have chosen 3% sucrose which induced a similar rate of proliferation but favoured shoot elongation, permitting an effectively higher number of shoots during transfers. Sorbitol and autoclaved fru ctose did not stimulate shoot proliferation. Adventitious root formati on was strongly dependent on carbohydrate supply. Sorbitol and autocla ved fructose were completely ineffectively on rooting induction. Gluco se was the most effective carbon source on rooting promotion followed by sucrose and filter-sterilized fructose. The rooting response induce d by fructose was dependent on the sterilizing procedure. The number o f adventitious roots produced per shoot increased with increasing gluc ose and sucrose concentration. The content of reducing sugars in leave s of proliferation cultures and in leaves and roots of rooted plantlet s was more dependent on carbon concentration than on glucose or sucros e supplement. The results presented here show that carbohydrate requir ements during cork oak micropropagation depend upon the phase of cultu re. Sucrose (3%) and glucose (4%) were the best carbon sources respect ively during proliferation and rooting phases.