plant hormone (redirected from Plant growth substance)
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plant hormone any of several chemical substances produced in very low concentrations in plants, that control growth and development. They are now usually called growth substances. Plant HORMONES are produced in active MERISTEMS (e.g. root and shoot apices) from where they diffuse to other parts of the plant. A distinct contrast with animal hormonal systems is the fact that plants do not possess specific tissues for hormone production, nor a well-defined distribution system equivalent to the blood system.
Plant hormones are classified generally into several groups, discussed under separate headings: ABSCISSIC ACID, AUXINS, CYTOKININS and GIBBERELLINS.