Evidence for the involvement of jasmonic acid in the control of the stem-growth habit of soybean plants

Soybean plants show diversity in stem-growth habit which ranges from the determinate type to the indeterminate type. Stem growth of determinate plants abruptly terminate near the beginning of flowering. The possible involvement of jasmonic acid (JA) in the control of the stem growth-habit was examined in indeterminate and determinate isolines of soybean Glycine max (L.) Merril cv. Harosoy]. JA-like activities in leaves of both isolines were very low 20 days before the commencement of flowering. The activity increased rapidly thereafter and reached a maximum near the time of flowering. Although the activities in leaves of both isolines fluctuated in a similar manner, the activity in the determinate isoline was much higher than that in the indeterminate isoline after flowering. The presence of JA in the leaves of the determinate isoline was confirmed by purification by high-performance liquid chromatography and by mass spectrometry. Exogenous application of JA to cultured shoot apices of the indeterminate isoline strongly inhibited growth. These results suggest that jasmonic acid is a major endogenous factor that controls the growth habit of soybean plants.