Plant Hormones and Responses KEY CONCEPT Plant hormones

Plant Hormones and Responses KEY CONCEPT Plant hormones guide plant growth and development.

Plant Hormones and Responses Plant hormones regulate plant functions. • Hormones are chemical messengers. – produced in one part of an organism – stimulates or suppresses activity in another part – Often have adaptive advantages

Plant Hormones and Responses Five major groups of plant hormones • • • Gibberellins Ethylene Cytokinins Auxins Abscisic acid

Plant Hormones and Responses • Gibberellins are plant hormones that produce dramatic increases in size. – ending seed dormancy – rapid growth of young seedlings – rapid growth of some flower stalks

Plant Hormones and Responses • Ethylene causes the ripening of fruits. – some fruits picked before they are ripe – sprayed with ethylene to ripen when reach destination – Promotes abscission - The detachment of leaves, flowers, or fruits

Plant Hormones and Responses • Cytokinins stimulate cytokinesis. – final stage in cell division – produced in growing roots, seeds, and fruits – involved in growth of side branches

Plant Hormones and Responses • Auxins lengthen plant cells in the growing tip. – stimulates growth of primary stem – controls some forms of tropism • A tropism is the movement of plant in response to an environmental stimulus.

Plant Hormones and Responses • Abscisic acid – Promotes dormancy in plant buds, maintains dormancy in seeds, and causes stomata to close

Plant Hormones and Responses Tropisms • A tropism is a response in which a plant grows either toward or away from an environmental stimulus

Plant Hormones and Responses Plants can respond to light, touch, gravity, and seasonal changes. • Phototropism is the tendency of a plant to grow toward light. – auxins build up on shaded side of stem – cells on shaded side lengthen – causes stem to bend toward light

Plant Hormones and Responses • Solar tracking, also called heliotropism, is the motion of leaves or flowers as they follow the sun’s movement across the sky.

Plant Hormones and Responses • Thigmotropism is a plant’s response to touch-like stimuli. – climbing plants and vines – plants that grow in direction of constant wind

Plant Hormones and Responses • Gravitropism is a plant’s response to Earth’s gravitational pull. – positive gravitropism is downward growth (roots) – negative gravitropism is upward growth (shoots)

Plant Hormones and Responses • Chemotropism – Plant growth that occurs in response t oa chemical is called chemotropism – An example of chemotropism is the growth of a pollen tube after a flower is pollinated.

Plant Hormones and Responses Nastic Movements • Thigmonastic movements – Occur in response to touch, such as the closing of the leaf trap of a Venus’ flytrap around an insect. • 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.

Plant Hormones and Responses • Photoperiodism is a response to the changing lengths of day and night. – triggers some plants to flower – triggers fall colors/winter dormancy of deciduous trees • 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