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Unformatted text preview: Types of Plant Hormones There are five general classes of hormones: auxins, cytokinins, gibberellins, ethylene, and abscisic acid. Auxins An auxin, indole-3-acetic acid (IAA) , was the first plant hormone identified. It is manufactured primarily in the shoot tips (in leaf primordia and young leaves), in embryos, and in parts of developing flowers and seeds. Its transport from cell to cell through the parenchyma surrounding the vascular tissues requires the expenditure of ATP energy. IAA moves in one direction onlythat is, the movement is polar and, in this case, downward. Such downward movement in shoots is said to be basipetal movement, and in roots it is acropetal . Auxins alone or in combination with other hormones are responsible for many aspects of plant growth. IAA in particular: Activates the differentiation of vascular tissue in the shoot apex and in calluses;...
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- Fall '08