Understanding Plant Growth Regulators

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

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

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

Naturally Made Plant Hormones

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

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

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.

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

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

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

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.

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

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.

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

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