STEM SWELLING OF STEM MUSTARD, AS AFFECTED BY TEMPERATURE AND GROWTH-REGULATORS

Changes in the levels of zeatin + zeatin ribosides (ZRs) and indole ac etic acid (IAA) were determined in plants grown either in the greenhou se (25 degrees C constant temperature) or in a tunnel (ambient tempera ture, 4-15 degrees C) from the beginning of stem swelling until harves t. The plant fresh weight (FW) was lower at 25 degrees C than at ambie nt temperature, stem swelling was almost completely suppressed and lev els of ZRs and IAA were lower. Under ambient temperature, stem swellin g occurred and ZRs and IAA levels were higher in both leaves and stem. At the end of the experiment, plants at high temperature had a long s tem, tended to bolting, and the ratio of stem length to diameter was 4 .1. Plants at ambient temperature formed a swollen stem, with a stem l ength/diameter ratio of 0.8. Microcuttings were cultured in Murashige and Skoog (MS) media containing various concentrations (1-5 mg l(-1)) of B-benzylaminopurine (BA) and alpha-naphthaleneacetic acid (NAA). Th e stem diameter of microcuttings was significantly promoted by BA in t he absence of NAA, Addition of NAA counteracted the stimulatory effect of BA on stem diameter. NAA increased the stem length of microcutting s more than BA. The promotive effect of NAA on the stem length was cou nteracted by BA supplement to the medium.