Leaf cell expansion auxin

In general, then, we may view the auxins and GA s as promoters of cell elongation and ABA and ethylene as inhibitors. The cytokinins act as promoters of leaf cell expansion and inhibitors of stem elongation. This is somewhat oversimplified in light of the aforementioned exceptions, and the evidence that effects of applied hormones are often modified by or mediated by other hormones. 

The mode of the germination-stimulatory action of coumarin on plant cells has been widely studied [106—110], and it is similar to the action of plant hormones which control different functions and processes of growth. The relationship between the effects of coumarins and auxins has been suggested [106, 107]. Coumarin in different concentrations stimulates stem and shoot elongation [108, 109] it also elicits a similar action [111] on substances which affect root initiation, cambial activity, and leaf expansion [108, 110]. The plant hormones and coumarin also stimulate the growth of roots. In low concentrations, coumarin exerts a synergistic action with plant growth substances, while with... 

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