22 5 Plant Hormones and Responses KEY CONCEPT

22. 5 Plant Hormones and Responses KEY CONCEPT Plant hormones guide plant growth and development.

22. 5 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

22. 5 Plant Hormones and Responses • Gibberellins are plant hormones that produce dramatic increases in size. – ending seed dormancy – Stimulates stem elongation, germination, and flowering

22. 5 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

22. 5 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

22. 5 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. *

22. 5 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

22. 5 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

22. 5 Plant Hormones and Responses • Gravitropism is a plant’s growth or turning in response to gravity. – positive gravitropism is downward growth (roots) – negative gravitropism is upward growth (shoots)

22. 5 Plant Hormones and Responses • Some plants have rapid responses not involving growth. – Some responses protect plants from predators. – Some responses allow plants to capture food. When leaves of a Venus Fly Trap are touched, water rushes to the cells in the bases of the leaf making it bend inward- - closing the “mouth” of the plant!

22. 5 Plant Hormones and Responses • Photoperiodism is a response to seasonal changes in day length. – triggers some plants to flower – triggers fall colors/winter dormancy of deciduous trees

22. 5 Plant Hormones and Responses Asexual Plant Propagation Lab • For this lab, you will be conducting plant propagation using a philodendron plant. • The first step in plant propagation from existing plants is to take cuttings. • Before making a cut, look for nodes—these are the beginnings of new leaves and stem systems and resemble small roots or buds. • After you have cutting, place the cutting in a cup with water reaching right below the leaf, but above the nodes. • Record your observations for day 1 (drawing and written description). • You will make weekly observations and drawings. At the end, you will construct a line graph to show your results.