Stomatal Closure and Photosynthetic Inhibition in Soybean Leaves Induced by Petiole Girdling and Pod Removal

Abstract

The presence of strong sinks of photoassimilates is thought to stimulate photosynthesis by minimizing photosynthetic end product accumulation in leaves. This hypothesis was examined in soybeans (Glycine max [L] Merr.) with treatments designed to alter the phloem translocation of photoassimilates out of source leaves. Pod removal and petiole girdling resulted in 70 and 90% reductions, respectively, in leaf CO₂ exchange rate. Reductions of similar magnitude also were observed in stomatal diffusive conductivity.