DE-NOVO SHOOT MORPHOGENESIS AND PLANT-GROWTH OF MUSTARD (BRASSICA-JUNCEA) IN-VITRO IN RELATION TO ETHYLENE

Role of ethylene in de novo shoot morphogenesis from explants and plant growth of mustard (Brassica juncea cv. India Mustard) in vitro was investigated, by culturing explants or plants in the presence of the ethylene inhibitors aminoethoxyvinylglycine (AVG) and AgNO3. The presence of 20 muM AgNO3 or 5 muM AVG in culture medium containing 5 muM naphthaleneacetic acid and 10 muM benzyladenine were equally effective in promoting shoot regeneration from leaf disc and petiole explants. However, AgNO3 greatly enhanced ethylene production which reached a maximum after 14 days, whereas ethylene levels in the presence of AVG remained low during 3 weeks of culture. The promotive effect of AVG on shoot regeneration was overcome by exogenous application of 25 muM 2-chloroethylphosphonic acid (CEPA), but AgNO3-induced regeneration was less affected by CEPA. For whole plant culture, AVG did not affect plant growth, although it decreased ethylene production by 80% and both endogenous levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC by 70-80%. In contrast, AgNO3 stimulated all 3 parameters of ethylene synthesis. Both AgNO3 and CEPA were inhibitory to plant growth, with more severe inhibition occurring in AgNO3. Leaf discs derived from plants grown with AVG or AgNO3 were highly regenerative on shoot regeneration medium without ethylene inhibitor, but the presence of AgNO3 in the medium was inhibitory to regeneration of those derived from plants grown with AgNO3.