Changes in Soybean Raceme and Petiole Anatomy Induced by 6-Benzylaminopurine

An enlargement of the peduncle and rachis of the terminal raceme and the petiole of the uppermost mainstem leaf was observed in soybean plants [Glycine max (L.) Merr.] treated with the cytokinin, 6-benzylaminopurine (BAP). Histological studies were performed to determine the timing and extent of anatomical changes accompanying BAP treatment. Swelling of treated ‘Tracy-M’ peduncles, rachises, and petioles was observed within 4–6 d after treatment initiation. A significant increase in total cross-sectional tissue area was observed at lower and intermediate internodes of treated rachises after 11 d. Rachis enlargement was due to increases in both cell size and cell number, particularly of the vascular tissue. In treated petioles of IX93-100, procambial cells of vascular bundles were the first to respond to the BAP treatment. These cells differentiated into a vascular cambium which formed secondary xylem and phloem.