Indole‐3‐acetic acid production by bacteroids from soybean root nodules

Abstract

This study examined the question: do bacteroids within the nodule have the ability to produce indole‐3–acetic acid (IAA) and does their IAA‐producing ability correlate with the amount of IAA contained in the nodule? Soybean [Glycine max, (L.) Merr. cv. Tracy] plants were inoculated with a wild‐type clone of Bradyrhizobium japonicum, 1–110 known to form nodules that contain low amounts of IAA or with 5‐methyltryptophan‐resistant B. japonicum, clones known to form nodules that contain large amounts of IAA. The resulting bacteroids were isolated from the nodules and examined for their ability to synthesize IAA. IAA production by wild‐type bacteroids was 90 pmole IAA (mg protein)−1 h−1 and IAA production by mutant bacteroids was 620 to 690 pmole IAA (mg protein)−1 h−1. These data indicate that bacteroids from high IAA‐containing nodules have an enhanced ability to produce IAA, implying that bacteroid‐produced IAA accumulates in the nodule.