JASMONIC ACID - EFFECTS ON GROWTH AND DEVELOPMENT OF ISOLATED TOMATO ROOTS CULTURED IN-VITRO

The effect of jasmonic acid (JA) on growth, morphology, and developmen t of roots and the possible interaction of JA with ethylene were inves tigated using isolated tomato roots (Lycopersicon esculentum Mill. cv. Bush Beefsteak) cultured in vitro. JA had a number a direct effects o n the growth and development of these isolated root tissues. Lower con centrations of JA (10(-9)-10(-8) M) in the culture medium promoted the frequency of lateral root initiation and lateral root elongation but had little effect on the elongation of the main axis. Higher (10(-7) M ) concentrations of JA caused a rapid irreversible inhibition of root growth, with lateral and main root axis elongation more severely affec ted than lateral root initiation. With 10(-5) M JA, the main root axis showed stunted growth, increased cellular vacuolation, and decreased cell elongation. Root apices were swollen and root hairs were aggregat ed closer to the root tip. In addition, phenolic compounds were presen t in the cytosol, and large cuboidal protein crystals were abundant in the epidermal and cortical cells of JA-treated roots. Treatment with ethylene mimicked some of the JA effects. Jasmonic acid-treated roots produced more ethylene than controls, but this was only evident after several days of culture. Inhibitors of ethylene action and synthesis d id not block the effects of JA. We conclude that JA was not acting dir ectly through ethylene.