Effects of Pod Removal on the Transport and Accumulation of Abscisic Acid and Indole-3-Acetic Acid in Soybean Leaves

Abstract

Concentrations of abscisic acid (ABA) and indole-3-acetic acid (IAA) in the second most recently expanded trifoliolate leaf were determined during reproductive development of soybean (Glycine max [L.] Merr cv ;Chippewa 64'). The concentration of ABA in leaves was constant during most of the seed filling period until the seeds began to dry. The concentration of IAA in the leaves decreased throughout development. Removal of pods 36 hours prior to sampling resulted in increased concentrations of ABA in leaves during the period of rapid pod filling but had little effect on the concentration of IAA in leaves. ABA appears to accumulate in leaves after fruit removal only when fruits represent the major sink for photosynthate.ABA and IAA moving acropetally and basipetally in petioles of soybean were estimated using a phloem exudation technique. ABA was found to move mostly in the basipetal direction in petioles (away from laminae). IAA, primarily in the form of ester conjugate(s), was found to be moving acropetally (toward laminae) in petioles. The highest amount of IAA ester(s) was found in petiole exudate during the mid and late stages of seed filling. Removal of fruits 36 hours prior to exudation reduced the amount of IAA ester recovered in exudate, suggesting that fruits were a source of the IAA conjugate in petiole exudate.