Chapter 31 Table of Contents Section 1 Plant Hormones Plant Responses Chapter 31 Table of Contents Section 1 Plant Hormones Section 2 Plant Movements Section 3 Seasonal Responses

Section 1 Plant Hormones Chapter 31 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.

Chapter 31 Groups of Hormones Section 1 Plant Hormones Chapter 31 Groups of Hormones Plant hormones are formed in many plant parts and regulate many aspects of growth and development. Hormonal responses often have adaptive advantages. There are five major groups of plant hormones: auxins, gibberellins, ethylene, cytokinins, and abscisic acid.

Types of Plant Hormones Section 1 Plant Hormones Chapter 31 Types of Plant Hormones Click below to watch the Visual Concept. Visual Concept

Section 1 Plant Hormones Chapter 31 Auxins Auxins are hormones involved in plant-cell elongation, shoot and bud growth, and rooting. A well-known natural auxin is indoleacetic acid, or IAA.

Chapter 31 Auxins Section 1 Plant Hormones Click below to watch the Visual Concept. Visual Concept

Chapter 31 Auxins, continued Synthetic Auxins Section 1 Plant Hormones Chapter 31 Auxins, continued Synthetic Auxins Synthetic auxins are used for killing weeds, stimulating root formation, and stimulating or preventing fruit drop. Naphthalene acetic acid, or NAA, is used to promote root formation on stem and leaf cuttings. NAA can also be applied to a cut shoot tip of the stem to mimic apical dominance (inhibition of lateral bud growth due to presence of a shoot tip).

Chapter 31 Apical Dominance Section 1 Plant Hormones Click below to watch the Visual Concept. Visual Concept

Section 1 Plant Hormones Chapter 31 Gibberellins Gibberellins are used to increase the size of fruit, to stimulate seed germination, and to brew beer.

Section 1 Plant Hormones Chapter 31 Ethylene Ethylene is used to ripen fruit and promote abscission, the detachment of leaves, flowers, or fruits.

Chapter 31 Ethylene Section 1 Plant Hormones Click below to watch the Visual Concept. Visual Concept

Section 1 Plant Hormones Chapter 31 Cytokinins Cytokinins are used to culture plant tissues in the lab and to promote lateral bud growth of flower crops.

Chapter 31 Cytokinins Section 1 Plant Hormones Click below to watch the Visual Concept. Visual Concept

Section 1 Plant Hormones Chapter 31 Abscisic Acid Abscisic acid promotes dormancy in plant buds, maintains dormancy in seeds, and causes stomata to close.

Other Growth Regulators Section 1 Plant Hormones Chapter 31 Other Growth Regulators Growth retardants are widely used to reduce plant height.

Section 2 Plant Movements Chapter 31 Objectives List the environmental stimuli to which plants respond for each type of tropism. Explain the current hypotheses regarding auxins and their function in phototropism and gravitropism. Describe two types of nastic movements, and explain how they help a plant survive.

Section 2 Plant Movements Chapter 31 Tropisms Tropisms and nastic movements are plant responses to environmental stimuli. Tropisms occur slowly; nastic movements happen more quickly. A tropism is a response in which a plant grows either toward or away from an environmental stimulus.

Chapter 31 Tropism Section 2 Plant Movements Click below to watch the Visual Concept. Visual Concept

Chapter 31 Tropisms, continued Phototropism Section 2 Plant Movements Chapter 31 Tropisms, continued Phototropism Phototropism is thought to occur in some plants when auxin moves to the shaded side of a plant and causes cells there to elongate more than the cells on the lighted side. Solar tracking, also called heliotropism, is the motion of leaves or flowers as they follow the sun’s movement across the sky.

Chapter 31 Tropisms, continued Thigmotropism Section 2 Plant Movements Chapter 31 Tropisms, continued Thigmotropism Thigmotropism is a plant’s growth response to touching a solid object. For example, tendrils and stems of vines, such as morning glories, coil when they touch an object.

Chapter 31 Tropisms, continued Gravitropism Section 2 Plant Movements Chapter 31 Tropisms, continued Gravitropism Gravitropism is a plant’s response to gravity. It is thought to occur when auxin accumulates on the lower sides of a horizontal root and stem. This accumulation causes cell elongation on the lower side of the stem and inhibits cell elongation on the lower side of the root.

Gravitropism in Plants Section 2 Plant Movements Chapter 31 Gravitropism in Plants

Chapter 31 Tropisms, continued Chemotropism Section 2 Plant Movements Chapter 31 Tropisms, continued Chemotropism Plant growth that occurs in response to a chemical is called chemotropism. An example of chemotropism is the growth of a pollen tube after a flower is pollinated.

Chapter 31 Nastic Movements Section 2 Plant Movements Chapter 31 Nastic Movements Nastic movements are responses to environmental stimuli but are independent of the direction of the stimuli.

Nastic Movements, continued Section 2 Plant Movements Chapter 31 Nastic Movements, continued Thigmonastic movements Thigmonastic movements occur in response to touch, such as the closing of the leaf trap of a Venus’ flytrap around an insect.

Nastic Movements, continued Section 2 Plant Movements Chapter 31 Nastic Movements, continued Nyctinastic movements Nyctinastic movements occur in response to the daily cycle of light and dark, such as the cyclical vertical and horizontal positioning of leaves in prayer plants.

Section 2 Plant Movements Chapter 31 Types of Plants

Chapter 31 Objectives Define photoperiodism. Section 3 Seasonal Responses Chapter 31 Objectives Define photoperiodism. Describe the role of critical night length in flowering. Explain the process of vernalization. Explain changing fall colors in leaves.

Chapter 31 Photoperiodism Section 3 Seasonal Responses Chapter 31 Photoperiodism Photoperiodism is a plant’s response to changes in the length of days and nights.

Photoperiodism, continued Section 3 Seasonal Responses Chapter 31 Photoperiodism, continued Day Length and Night Length Plants fit in one of three photoperiodic classes for flowering: day-neutral plants (DNPs), short-day plants (SDPs), and long-day plants (LDPs). Short-day and long-day plants have a specific requirement for darkness, called the critical night length. Day neutral plants are not affected by day length.

Photoperiodism, continued Section 3 Seasonal Responses Chapter 31 Photoperiodism, continued Adjusting the Flowering Cycles of Plants Flower growers who want to obtain winter flowering of LDPs simply expose them to a low level of incandescent light in the middle of the night. Summer flowering of SDPs is obtained by covering the plants in the late afternoon with an opaque cloth so that the SDPs receive enough darkness.

Photoperiodism, continued Section 3 Seasonal Responses Chapter 31 Photoperiodism, continued Regulation by Phytochrome Plants monitor changes in day length with a bluish, light-sensitive pigment called phytochrome.

Flowering and Photoperiodism Section 3 Seasonal Responses Chapter 31 Flowering and Photoperiodism

Chapter 31 Photoperiodism Section 3 Seasonal Responses Click below to watch the Visual Concept. Visual Concept

Chapter 31 Vernalization Section 3 Seasonal Responses Chapter 31 Vernalization Vernalization is the promotion of flowering by cold temperatures. Farmers often plant wheat seeds in the fall so that the seedlings can be exposed to winter temperatures and will flower before summer droughts begin.

Section 3 Seasonal Responses Chapter 31 Fall Colors Changing fall colors in tree leaves are due to chlorophyll degradation, which reveals other pigments already present.

Chapter 31 Dormancy Section 3 Seasonal Responses Click below to watch the Visual Concept. Visual Concept