Plant Hormones Auxin Promotes plant growth Causes elongation of developing cells Increases the concentration of H+ in primary cell walls, in turns, loosens cellulose fibers which increase cell wall plasticity. In response, turgor pressure causes the cell wall to expand, thus generating growth. Produced at the tips of shoots and roots Active in phototropism and geotropism Active in leaves, friuts, and germinating seeds

Plant Hormones Gibberellins (gibberelic acid- GA) Promotes cell growth Synthesized in young leaves, roots, and seeds Involved in the promotion of fruit development and seed germination High concentrations of GA causes rapid elongation of stems called bolting

Plant Hormones Cytokinins Group of hormones that stimulate cytokinesis (cell division) Produce mainly in the roots and transported throughout the plant Stimulates the growth of lateral buds, thus weakening apical dominance

Plant Hormones Ethylene Gas- C2H4 Promotes the ripening of fruit Involved in stimulating the production of flowers In combination with auxin, ethylene inhibits the elongation of roots, stems, and leaves, and influences leaf abscission, the aging and dropping of leaves.

Plant Hormones Abscisic acid (ABA) Growth inhibiter Maintains dormancy in seeds, in many species of plants.