Chapter 27, Problem 41A

Summary Introduction

To write:

About the three plant hormones that affects the plants.

Introduction:

Hormones are organic compounds that are made in one part of an organism, and then are transported to another part where they affect. It takes only a tiny amount of a hormone to cause a change in an organism. Plant hormones can affect cell division, growth, or differentiation. Plant hormones act by chemically binding to the plasma membrane at specific sites called receptor proteins. These receptors can affect the expression of a gene, the activity of enzymes, or the permeability of the plasma membrane.

Explanation of Solution

Auxin was the first plant hormones to be identified. Auxin stimulates the lengthening, or elongation of cells. Auxin promotes a flow of hydrogen ions through proton pumps from the cytoplasm into the cell wall. It also activates certain enzymes that help to break down the cell wall. Depending on the concentration of auxin, it can either promotes stem growth and inhibit root growth. Low concentrations usually stimulate elongation of a cell and higher concentration can have reverse effect. Auxins affect fruit formation and inhibit the dropping of fruit.

Gibberellins are the plant hormone which causes cell elongation, stimulates cell division and affects seed growth. It transported in vascular tissue. Dwarf plants often lack either the genes for gibberellins production or the genes for gibberellins protein receptors. When treated with gibberellins, plants that lack the genes for gibberellins but have gibberellins receptors grow taller. Applying gibberellins to a plant can cause an increase in height.

Ethylene is a hormone that found in plant tissues such as ripening fruits, dying leaves, and flowers. Ethylene is a gas; it can diffuse through the spaces between cells. It primarily affects the ripening of fruits

Conclusion

Plant hormones are chemical compounds which arise in plants at very low concentration. Plant hormones regulate all aspects of plant growth and development, including embryogenesis, organ size regulation, pathogen protection, stress tolerance, and reproductive development.