Jasmonic acid inhibition of in vitro shoot organogenesis in Pinus radiata cotyledons

The effect of jasmonic acid (JA) on de novo shoot formation in excised coty ledons of radiata pine (Pinus radiata D. Don), was examined. JA had no effe ct on shoot-forming (SF) tissues at concentrations up to 10(-6) mol.L-1. At concentrations greater than that, JA caused a reduction in the number of s hoots formed. as well as the lengths of the shoots and fresh and dry masses of the tissues, Reciprocal transfer of excised radiata pine cotyledons fro m a SF medium with 10(-5) mol.L-1 JA to a SF medium without JA and vice ver sa showed that any exposure of the cotyledons to JA either during the shoot induction phase (days 0-21) or the shoot development phase (beyond day 21) led to a reduction in shoot formation. However, the JA effect was signific antly less if the cotyledons were not exposed to JA during the initial 10 d ays in culture; indicating that the JA effect was mainly during shoot primo rdia formation and the subsequent development into shoots.