Effects of 2,4-D on Seed Germination and Respiration

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Abstract
Seeds of barley and rice were treated for 24 hrs. with various dilutions of 2,4-D ranging from 0.0035 to 0.1%, washed, placed on moist filter paper in Petri dishes which were kept at 25 [degree]C, and the rate of germination was followed. 2,4-D accelerated germination at low concs. but delayed it above a threshold conc. This threshold was higher in rice (ca. 0.07%) than in barley (ca. 0.01%), and 0.07% 2,4-D inhibited barley germination completely, but it only delayed germination in rice. There was a striking resemblance between seeds treated with 2,4-D and seeds kept under anaerobic conditions. It appeared as if O2 were no longer available to the treated seeds so that an aerobic seed like barley was inhibited, whereas an anaerobic seed like rice was only duly delayed in germination. Expts. with various other types of seeds substantiated the facts regarding 2,4-D treatment. Gas exchange in treated seeds was analyzed with Warburg microrespirometers. The low ratios in respiratory intensity between treated and untreated seeds indicated that the treated seeds could not utilize O2 during germination. The reduction in aerobic respiration was partly compensated for by fermentative activity. The expts. showed that 2,4-D at low cones. (0.01%) promoted germination, while at higher cones. (0.1%) it inhibited aerobic respiration and germination.