Ultradian Movements of Shoots of two Species of SoybeansGlycine soja(Sieb. and Zucc.) andGlycine max(L.) Merr

Circumnutation movements of shoot tips of two species of soybean were studied. Shoot tips of Glycine soja (Sieb. and Zucc.) moved in a counterclockwise direction with a mean period (+/- SD) of 108 +/- 9 minutes when the shoots were not handled prior to monitoring (n = 17). Effects of mechanical stress or stimulation (thigmomorphogenesis) resulted in the lengthening of the mean period by 15% when shoot lengths were measured (handled) prior to monitoring movements (124 +/- 18 minutes, n = 49) or handled and restaked prior to monitoring movements (124 +/- 14 minutes, n = 11). Shoot tips of G. max cultivars moved counterclockwise, and, depending on the cultivar, periods ranged from 112 minutes to 133 minutes, with an overall average period of 124 +/- 21 minutes (n = 21). This period was identical to the mean period of comparably handled G. soja shoot tips. Amplitudes for the four G. max cultivars were much smaller (0.12 cm to 1.43 cm) than for G. soja (2.9-8.7 cm). Factors that may have contributed to differences in rhythm characteristics between species and among cultivars included the presence of a distinguishable bending zone in G. soja, but not in G. max, and morphological features associated with shoot development.