IAA and 4-Cl-IAA Increases the Growth and Nitrogen Fixation in Mung Bean

A commonly occurring auxin indole-3-aceticacid (IAA) and a rarely occurring chlorosubstituted auxin (4-Cl-IAA) were compared for their impact on growth and nitrogen metabolism in mung bean for the first time. The plants were generated from healthy and Rhizobium coated seeds in earthen pots. The seedlings at 7 and/or 14 days were percolated with 0, 10(-10), 10(-8), or 10(-6) M of IAA or 4-Cl-IAA. The plants were sampled at 30 days after sowing (DAS) to assess the growth and various biochemical characteristics. The auxins significantly enhanced the growth (length and dry mass of shoot and root), nodule fresh mass, nitrogenase activity in fresh nodules, leaf carbonic anhydrase activity, chlorophyll content, and rate of photosynthesis. The effect of the auxins lasted up to the harvest where the seed yield, 100 seed mass, and number of pods per plant were significantly affected by the auxins. At a moderate concentration (10(-8) M), 4-Cl-IAA generated the best response. However, a comparable response was generated by the higher concentration (10(-6) M) of 4-Cl-IAA. The application of the hormone twice (at 7 and 14 DAS) was much more effective than single application (at 7 or 14 DAS). It was concluded that IAA and 4-Cl-IAA improved the growth and nitrogen fixation in mung bean. The 4-Cl-IAA proved more effective than IAA.