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 AgNO 3 . The presence of 20 μ M AgNO 3 or 5 μ M AVG in culture medium containing 5 μ M naphthaleneacetic acid and 10 μ M benzyladenine were equally effective in promoting shoot regeneration from leaf disc and petiole explants. However, AgNO 3 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 μ M 2‐chloroethylphosphonic acid (CEPA), but AgNO 3‐ 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, AgNO 3 stimulated all 3 parameters of ethylene synthesis. Both AgNO 3 and CEPA were inhibitory to plant growth, with more severe inhibition occuring in AgNO 3 . Leaf discs derived from plants grown with AVG or AgNO 3 were highly regenerative on shoot regeneration medium without ethylene inhibitor, but the presence of AgNO 3 in the medium was inhibitory to regeneration of those derived from plants grown with AgNO 3 .