Plant Responses and Adaptations

1. Plant Responses and Adaptations Ms. Moore 9/19/12

2. How do plants “talk”? • Hormones: substance produced in one part of an organism that affects another part of the same individual • In plants, hormones are chemical substances that control a plant’s growth patterns, development, and response to environmental conditions. • Target cell/tissue: contains a receptor that hormone binds to • This is the part that is affected by the hormone.

3. Plant Movement • Phototropism: tendency of a plant to grow towards light • Auxin: stimulates elongation; located in apical meristem • Gravitropism: response of plant to force of gravity

4. Auxin and Branching • Auxins also regulate cell division in meristems. • Lateral bud: meristematic area on the side of a stem that gives rise to “branches” • Apical dominance: the closer a bud is to the stem’s tip, the more its growth is inhibited; this is due to auxin moving out from the apical meristem • Snipping the tip will also remove the inhibiting auxin affect, giving you a rounder, fuller plant. • Herbicides: auxin-like compounds that are toxic to plants

5. Hormones con’t • Cytokinins: plant hormones that are produced in growing roots and developing fruits and seeds • Cytokinins stimulate cell division and the growth of lateral buds, and cause dormant seeds to sprout. • Gibberellins: growth-promoting substance • Gibberellins produce dramatic increases in size, particularly in stems and fruit. • Ethylene: stimulates fruits to ripen • Supermarkets use this to keep fruits on the shelves longer.

6. Plant Responses • Tropisms: responses of plants to external stimuli • Gravitropism • Phototropism • Thigmotropism: touch

7. Seasons • Photoperiodism: plant responses to periods of light and dark • Responsible for the timing of seasonal activities such as flowering and growth. • Short-day plants • Chrysanthemums and poinsettias • Long-day plants • Spinach and irises • Phytochrome: plant pigment that is responsible for photoperiodism; absorbs red light

8. Winter’s Coming • Dormancy: growth and activity stop • As cold weather approaches, deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves off from the rest of the plant. • Abcission layer: seals leaf off from vascular system • Before long, the leaf falls towards the ground, a sign that the tree is ready for winter. “Winterized”

9. Adaptations • Aquatic plants have tissues with large air-filled spaces through which oxygen can diffuse. • Xerophytes: plants that live in the desert biome • Adaptations include extensive roots, reduced leaves, and thick stems that can store water. Why? • Plants that have specialized features for obtaining nutrients include carnivorous plants and parasites. • Epiphytes: plants not rooted in soil, but grow directly on the bodies of other plants • Many plants defend themselves against insect attack by manufacturing compounds that have powerful effects on animals.

10. Questions?