Collective term for chemical messengers (signal molecules) from higher plants. These plant hormones control important biochemical processes for differentiation and growth. They can be described as the nervous system of plants. These substances, which are only present in very small quantities, are physiologically highly effective. The content depends on the state of development of the plant. Often it is not the absolute concentration that is decisive, but the quantitative ratio of the individual phytohormones to each other. These often function in interaction. The most important are abscisic acid
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