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Understanding Plant Growth Regulators

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What is a Plant Growth Regulator? Chemicals which affect the plant in many complex ways Cell division and differentiation, root and shoot growth, flowering and ripening

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2 Types of Plant Growth Regulators Natural Made inside the plant Low concentrations Five groups Auxins, cytokinins, ethylene, gibberellins and abscisic acid Man-made/Synthetic Applied to plants to obtain a wide variety of changes Makes the plant better or more saleable!

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Which grapes would you rather eat? The ones on the right were treated with gibberellic acid to make them larger.

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Naturally Made Plant Hormones

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Auxins Produced by the tip, or apical meristem Stem cells elongate and divide They also flow down from the tip of the stem, preventing lateral buds blooming early

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3 Effects of Auxin on Plants 1. Auxin causes the tip of the middle stem to grow at a faster rate This trunk should be a single stem; however, the terminal bud was removed forcing it to branch.

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2. Auxins are responsible for allowing a plant stem to grow toward the sun The left side of the plant was exposed to the sun. The right side had shade and grew faster.

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3. Auxins allow a plant to respond to the touch of a person or other object

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Cytokinins Responsible for cell division and differentiation Produced in the root tips They tend to travel up the stem Effect is Apical Dominance

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Ethylene This is a gas that affects the plant like a hormone It is produced in ripening fruit and dying plant material It stimulates flowering in some plants and causes other fruits and flowers to ripen more quickly and evenly

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Effects of Ethylene Ripen fruits faster in a paper bag, than on the counter On cut flowers & foliage will die In this experiment, two holly twigs were placed under separate jars for a week. At the same time, an apple was placed in the second jar. The ethylene given off by the apple caused the holly to lose its leaves and die.

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Gibberellins Helps promotes growth and stem elongation for trees Produced in the stems, roots and young leaves Effects are flowering of plants early and breaking seed dormancy too soon

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Abscisic Acid (ABS Acid) Found in dormant seeds and in dying leaves Effects are inhibiting growth and induced bud dormancy Helps a plant prepare its buds for winter The dormant bud on the left has a high concentration of abscisic acid. As spring nears, the acid level drops and the bud begins to develop a new shoot.

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Synthetic Plant Growth Regulators Useful for commercial plant crops They can save money, time, and can lead to a better crop Help reduce size and make plant look shorter Root more completely Help ripen faster

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Assignment You and a partner will make up a poem/ song/riddle/ect about natural and synthetic plant growth regulators. You must have the following: Auxins, cytokinins, ethylene, ABS acid, and Gibberlines What they do to the plant Be creative and appropriate You will present to the class your poem/song/riddle