GROWTH RETARDANTS IN RELATION TO THE GERMINATION OF SEEDS: I. A PARADOXICAL CONCENTRATION EFFECT OF N,N-DIMETHYLAMINO-SUCCINAMIC ACID ON THE GERMINATION OF KALE SEEDS AFFECTED WITH COUMARIN

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Abstract
As the concentration of N,N-dimethylaminosuccinamic acid (DMASA) increases, the germination of kale seeds (Brassica oleracea L. var. acephala) treated with 100 mg of coumarin per liter is initially reduced and then increased. A curve of germination versus concentration of DMASA is parabola-like with a minimum at 10−3 − 5 × 10−3 M. Kinetin at 10−4 M and gibberellic acid at 10−4 M reduce and reverse the inhibition of germination caused by coumarin and the growth retardant. On the other hand, DMASA at 5 × 10−3 M, in spite of its slight inhibitory activity, reduces the toxic effect of kinetin applied in the supra-optimal concentration of 5 × 10−4 M. Indole-3-acetic acid increases the inhibitory effects of coumarin and DMASA.In the germinating seed of kale, DMASA possibly acts as the antagonist of gibberellin biosynthesis; coumarin possibly blocks an unknown metabolic pathway, controlled by kinetin.The paradoxical concentration effect of DMASA remains unexplained.