The leaves of soybeans (Glycine max L.) suddenly senesce (wither) over the field even in midsummer. Although this senescence is believed to be induced so as to deliver enough nutrients to the soybean seeds, what causes it remains unknown. The senescence inducing activity (SIA) of pod extracts reached its maximum(49%) on July 31 when soybean began to senesce. This suggests that the SIA of pod extracts triggers the process of monocarpic senescence. However, the amoung of abscisic acid, senescence inducing substance, did not aler signnificantly over this period. Moreover, the detected concentration could not explain the SIA on July 31. This difference suggests the presence of other substances in the crud extracgts besides abscisic acid. It was revealed that jasmonic acid and 12-hydroxyjasmonic acid isolated from soybean pods extracts accelerate the senescence induced by abscisic aced. Quantification analyses employing GCMS showed us that the amount of 12-hydroxyjasmonic acid in pods synchronizes with the commencement of senescence. The maximum amount reached 10.2μmol/kg, which would be sufficient to enhance the activity of abscisic acid. On the other hand, the amount of jasmonic acid was almost constant (around 0.8μmol per kg of pod) during this period. These results have led to the conclusion that 12-hydroxyjasmonic acid plays the role of a synergist for abscisic acid in soybean senescence.
