What Is Plant Growth Regulator

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WHAT IS PLANT GROWTH REGULATORS (HORMONES)? Plant hormones are chemicals that regulate plant growth. Plant hormones are signal molecules produced at specific location in the plant and in extremely low concentrations. Different hormones affect different plant processes. Understanding how hormones work allows agriculturists to manipulate plants for specific purposes. * Auxins produced in the terminal buds suppress the growth of side buds and stimulate root growth. They also affect cell elongation (tropism), apical dominance, and fruit drop or retention. Figure 1. Auxins produced in the rapidly growing terminal buds suppress growth of side buds, giving a young tree a more upright form. As growth rates slow with age, reduction in apical dominance gives the maturing tree a more rounded crown. * Gibberellins affect: * The rate of cell division * Flowering * Increase in size of leaves and fruits * Seed and bud dormancy * Induction of growth at lower temperatures (used to green up lawns 2 to 3 weeks earlier) * Cytokinins promote cell division, and influence cell differentiation and aging of leaves. * Abscisic acid is considered the “stress” hormone. It inhibits the effects of other hormones to reduce growth during times of plant stress. Hormone Influence on Pruning Understanding hormones is key to proper pruning. Auxin produced in the terminal buds suppresses growth of side buds and stimulates root growth. Gibberellins produced in the root growing tips stimulate shoot growth. Pruning a newly planted tree removes the auxin, slowing root regeneration. Figure 2. A tree balances canopy growth with root growth with the levels of auxins and gibberellins. Heading cuts (removal of a branch tip) releases the apical dominance caused by auxins from the terminal bud. This allows side shoots to develop and the branch

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