EFFECTS OF CYTOKININ ON ADVENTITIOUS ROOT-FORMATION IN CALLUS-CULTURES OF VIGNA-UNGUICULATA (L.) WALP

Yellowish compact callus, induced from cowpea hypocotyls on Murashige and Skoog (MS) medium (1962 ) containing 0.2 mg/l(0.93 mu M) kinetin a nd 0.4 mg/l (1.81 mu M) 2,4-dichlorophenoxyacetic acid (2,4-D), was su bcultured on RIS medium containing cytokinin alone, auxin alone, or au xins plus cytokinins in order to determine the effect of cytokinins on root organogenesis in callus cultures. The callus actively proliferat ed on the same medium but did not show any organogenic activity macros copically as well as microscopically, On medium with N-6-benzyladenine (BA) and 1-naphthaleneacetic acid (NAA), the yellowish compact callus first changed to pale green compact callus and then many green spots appeared on its surface under light culture. But the yellowish compact callus remained yellowish and white spots appeared on its surface in dark culture. These spots gradually became white nodular structures. A dventitious root formation from the nodular structures occurred not on ly on the same medium, but also on medium with either auxin or cytokin in but not both. Yellowish compact callus on medium with auxin alone w as transformed to yellowish friable callus, which did not develop adve ntitious roots. The yellowish friable callus could gain rhizogenic act ivity only after morphological modification to pale green compact call us on medium with auxin plus cytokinin. The modified callus did not fo rm adventitious roots on medium with auxins but only with cytokinins. Therefore, it is suggested that cytokinins have stimulating effects on root formation from callus that previously did not show rhizogenic ac tivity on medium with auxins alone. In addition, the rhizogenic potent ial of cowpea callus was discriminated from that of leaf explants, whi ch formed adventitious roots directly on medium with auxin alone.