STIMULATION OF IN-VITRO ROOT AND SHOOT GROWTH OF POTATO BY INCREASINGSUCROSE CONCENTRATION IN THE PRESENCE OF FLURIDONE, AN INHIBITOR OF ABSCISIC-ACID SYNTHESIS

Fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, strongly stimulated rooting of nodal stem segments of potato (Solanum tuberosum L.) cultivar Arran Banner cultured in darkness on tuberisation medium . Inclusion of 10(-6) M ABA in the culture medium prevented this rooti ng response, indicating that root proliferation in the presence of flu ridone could be due to inhibition of ABA synthesis. The rooting respon se to fluridone (increased total root number and root fresh weight) wa s obtained only at high sucrose concentrations (0.175 and 0.234 M) and was demonstrated with two potato cultivars and two culture media; one which favoured tuberisation and one which did not. Shoot numbers were also increased, but to a lesser extent than root numbers,and total fr esh weight of plant material per culture was greatly increased by incl usion of both fluridone (10(-6) or 10(-5) M) and 0.234 M sucrose in th e culture medium. The role of sucrose was not simply osmotic because w hen the osmolarity of fluridone medium was increased using mixtures of mannitol and sucrose, no root proliferation occurred unless sucrose p redominated in the mixture.