Powerpoint Templates Plant Responses to Internal External Signals

Powerpoint Templates Plant Responses to Internal & External Signals CHAPTER 39 Page 1

Tropism Powerpoint Templates • A plant growth response from hormones that results in the plant growing either toward or away from a stimulus • Hormones – chemical messengers that coordinate the different parts of a multicellular organism Page 2

Powerpoint Templates • Types of tropisms: • Phototropism – growth toward or away from light • Gravitropism – growth toward or away from a gravitational source • Thigmotropism – growth toward or away from a touch – Vines grow toward a support and then grow toward (around) that support Page 3

Positive vs. Negative Tropisms Powerpoint Templates • Positive is growth toward a stimulus • Positive Phototropism – growth toward light • Positive Gravitropism – growth toward a gravitational source • Positive Thigmotropism – growth toward a tactile stimulus • Negative is growth away from a stimulus Page 4

Hormones Powerpoint Templates • Auxins • Stimulate cell elongation » Cause proton pumps to activate Lower p. H weakening of cell wall turgor pressure expands & elongates cell wall • High concentrations of synthetic auxins KILL certain plants, usually weeds (eudicots) • Synthetically produced auxins in high Page 5 concentration = Herbicides

How do. Powerpoint you. Templates make a …? • Cytokinins • Stimulate cell division or cytokinesis • Proper ratio of auxins & cytokinins cell division & differentiation • Gibberellins • Work with auxins to stimulate stem elongation • Loosen cell walls allowing cellular expansion stem expansion • Signal the seed to cease dormancy and germinate • Many dwarf plant varieties have non-functional gibberellins Page 6

Hormones (Page 3) Powerpoint Templates • Abscisic acid • SLOWS Growth • Antagonistic to previously mentioned hormones » Promotes seed dormancy, but gibberellins cease it • Causes stomata to close to conserve water Page 7

Powerpoint Templates • Ethylene • Gas • Plays crucial role in programmed cell death (apoptosis) • Promotes ripening of fruit • Ripening in one fruit ripening in other fruits » Positive feedback mechanism = rapid ripening of fruit » One bad apple does spoil the lot. Page 8

Plants. Powerpoint respond to Light Templates • Plants can detect presence, direction, intensity, and wavelength of light • Red & Blue wavelengths are most important • Blue light is most important for phototropisms and light-induced opening of stomata • Sensed by photoreceptors Page 9

Phytochromes Powerpoint Templates • Photoreceptors for red light (mainly) • Exist in 2 isomer forms which can switch forms depending on wavelength available • Responsible for Circadian Rhythms • 24 hour cycles Page 10

Photoperiodism Powerpoint Templates • Physiological response to a photoperiod (relative lengths of day and night) • Night is always the more important of the 2!! • But we (humans) focus on the daylight. • Controls Flowering • Short-day plants • Require a period of continuous darkness exceeding a critical measure in order to flower • Early Spring or Fall flowering • Sometimes called “Long-Night” plants Page 11

Besides. Powerpoint Short-Day plants, Templates • Long-Day Plants • Flower only if a period of continuous darkness is less than a critical value • Flower in Late Spring or early Summer • Considered “short-night” plants • Day-Neutral Plants • No length of continual darkness is needed for flowering Page 12

Plants respond to things other than Powerpoint Templates light • Gravitropism – growth toward the earth (gravity) • Auxin plays key role • If root is plased horizontally, then gravity causes an accumulation of auxins in root’s lower side • Remember HIGH auxin = inhibition of growth at high concentration, so » lower side = no growth » Upper side = growth » Allows the root to grow down into the ground Page 13

Auxin Accumulation Powerpoint Templates Page 14

Plants respond to other things… Powerpoint Templates • Drought • • Stomata close Leaves will cease growth Leaves roll into shape that reduces transpiration Deep roots (where H 2 O is) will speed their growth, but shallow roots will stop growing • Predators • Thorns, chemicals, distasteful compounds • Some plants even attract parasites • First layer of defense - Epidermis Page 15

Coordinated Plant-Parasite Powerpoint Templates Defense Page 16