Groups Of Hormones

Plant hormones are chemical messengers that affect a plant's ability to respond to its environment. Hormones are organic compounds that are effective at very low concentrations; they may be made in one part of the plant and transported to another part. They interact with specific target tissues to cause physiological responses, such as growth or fruit ripening. Each response may be the result of two or more hormones acting together.

Because hormones stimulate or inhibit plant growth, many botanists also refer to them as plant growth regulators. Many hormones can be synthesized in the laboratory, which increases the quantity of hormones available for commercial applications. Botanists recognize at least five major groups of hormones: auxins, gibberellins, ethylene, cytokinins, and abscisic acid. These groups of hormones are examined in Table 31-1 on the next page.

objectives

• List the actions of the five major types of plant hormones.

• Describe agricultural or gardening applications for each of the five major types of plant hormones.

• Discuss how growth retardants are used commercially.

vocabulary plant hormone growth regulator auxin indoleacetic acid naphthalene acetic acid apical dominance 2,4-D

Agent Orange gibberellin ethylene ethephon abscission cytokinin abscisic acid growth retardant

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