Bulb development in onion plants (Allium cepa L.) is considered to be regulated by bulbing and anti-bulbing hormones. Since bulbing involves the disruption of microtubules, both jasmonic acid (JA) and methyl jasmonate (JAMe) are candidates for the bulbing hormone because of their microtubule-disrupting activities and wide distribution in higher plants. To survey JA and JAMe in onion plants, we developed a radioimmunoassay (RIA) for JAMe that is sensitive enough to detect femtomole amounts of JAMe. Using this RIA, we detected JA in leaf blades, leaf sheaths and roots of onion plants, but no JAMe was detected in any tissue. The endogenous levels of JA in leaf blades, leaf sheaths and roots of 4-week-old bulbing and non-bulbing onion plants were determined by gas chromatography/selected ion monitoring with [2H2]JA as an internal standard. The amount of JA per plant in leaf sheaths of bulbing onion plants was about three times higher than that of non-bulbing onion plants, although the difference in levels of JA in leaf blades between bulbing and non-bulbing onion plants was quite small, and the level of JA in roots of bulbing onion plants was lower than that of non-bulbing onion plants. However, the relationship between endogenous JA and the development of onion bulbs remains to be clarified.
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Nojiri et al. (1992) studied this question.