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

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.