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.

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 • Auxinsare hormones involved in plant-cell elongation, shoot and bud growth, and rooting. • A well-known natural auxin isindoleacetic acid, or IAA.

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

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).

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

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

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

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

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

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

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

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

Section 2 Plant Movements Chapter 31 Objectives • Listthe environmental stimuli to which plants respond for each type of tropism. • Explainthe current hypotheses regarding auxins and their function in phototropism and gravitropism. • Describetwo 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. • Atropismis a response in which a plant grows either toward or away from an environmental stimulus.

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

Section 2 Plant Movements Chapter 31 Tropisms, continued Phototropism • Phototropismis 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 calledheliotropism, is the motion of leaves or flowers as they follow the sun’s movement across the sky.

Section 2 Plant Movements Chapter 31 Tropisms, continued Thigmotropism • Thigmotropismis 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.

Section 2 Plant Movements Chapter 31 Tropisms, continued Gravitropism • Gravitropismis a plant’s response to gravity. • Itis 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.

Section 2 Plant Movements Chapter 31 Gravitropism in Plants

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

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

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

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

Section 3 Seasonal Responses Chapter 31 Objectives • Definephotoperiodism. • Describethe role of critical night length in flowering. • Explainthe process of vernalization. • Explainchanging fall colors in leaves.

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

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 plantshave a specific requirement for darkness, called the critical night length. Day neutral plants are not affected by day length.

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.

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

Section 3 Seasonal Responses Chapter 31 Flowering and Photoperiodism

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

Section 3 Seasonal Responses Chapter 31 Vernalization • Vernalizationis 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.

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

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