EFFECTS OF GELLING AGENTS ON GROWTH, MINERAL-COMPOSITION AND NAPHTHOQUINONE CONTENT OF IN-VITRO EXPLANTS OF HYBRID WALNUT TREE (JUGLANS-REGIA X JUGLANS-NIGRA)

Gelling agents affect growth of walnut in vitro cultured shoots. Gelri te promoted shoot elongation and bud production, whereas agar inhibite d growth, induced mature leaf formation and necroses. The 2 gelling ag ents differed significantly in mineral content. They altered the chemi cal composition of the medium as well as that of the explants. A prono unced accumulation of Na and several microelements was observed in lea ves after 16 d of culture on agar, probably due to a disturbance in th e K selectivity mechanism and membrane permeability. Moreover, on agar , the level of hydrojuglone glucoside, a marker of juvenility in walnu t, decreased drastically in the callus. Mineral element accumulation a nd decrease of hydrojuglone glucoside were evident after growth inhibi tion, indicating that they are a result rather than a cause of this in hibition. Lack of growth, mature foliar morphology, Na and microelemen t accumulation and hydrojuglone glucoside decline support the hypothes is that agar accelerates the ageing of in vitro propagated walnut tree s.