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Chapter 19: Plants Respond to Their Environments Regulating and defending while rooted in the ground Lecture by Danielle DuCharme, Waubonsee Community.

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Presentation on theme: "Chapter 19: Plants Respond to Their Environments Regulating and defending while rooted in the ground Lecture by Danielle DuCharme, Waubonsee Community."— Presentation transcript:

1 Chapter 19: Plants Respond to Their Environments Regulating and defending while rooted in the ground Lecture by Danielle DuCharme, Waubonsee Community College


3 19.1. Hormones help plants respond to their environments  Environmental variables influence plant growth.  Chemicals called hormones respond to environmental variables and influence the growth and development of the plants.

4 Environment affects the growth pattern of the arrowleaf plant.

5 Plant Hormones Are Chemical Signals  Hormones are produced in various places within the plant.  They may have their effect in the place where they are produced, or they may be transported to another part of the plant before they take effect.

6 Hormones  Hormones convey information about the physiological state of the plant’s tissues, or the environment in which the plant finds itself.  Hormones then regulate metabolism.

7 Hormone Action  Hormones may stimulate a certain response in the target cell.  Hormones can suppress an action in the target cell.

8 There Are Five Major Types of Plant Hormones The five categories are:  Gibberellins  Auxins  Ethylene  Abscisic acid  Cytokinins

9 Plant Hormones Are Different from Animal Hormones  Animal hormones are produced in glands and tissues and are transported for use.  Plant hormones are produced in many types of cells throughout the plant, and can be used on site.

10 Take-home message 19.1  Plant hormones are chemical signals produced by plant cells that enable the plant’s responses to environmental variables (such as amount of moisture, amount and direction of sunlight, and temperature) and influence its growth and development.

11 19.2. Seed germination and stem elongation are stimulated by gibberellins  Gibberellins are a group of about 125 hormones that regulate a plant’s growth processes.  They stimulate cell division and cell elongation.

12 Gibberellins Have Four Main Types of Effects 1.Speeding seed germination 2.Stem elongation 3.Inducting early blooming of flowers 4.Enlargement of fruits

13 The Effects of Gibberellins

14 Gibberellins Have Powerful Growth-Stimulating Effects Gibberellins can create radishes the size of beach balls, and cabbages 10 feet tall!

15 Take-home message 19.2  Gibberellins are a group of about 125 hormones, produced primarily in meristems and seeds, that regulate a plants growth processes, mainly by stimulating cell division and cell elongation.

16 19.3 Seedlings grow and properly orient themselves under the direction of auxins. Auxins are a small group of synthetic and naturally occurring hormones that stimulate and regulate a plant’s growth and development.

17 Auxins  Auxins are found in apical meristems and immature plant tissue.  Auxins stimulate the expression of genes that promote cell division, stem elongation, and formation of roots.

18 The chief effects of auxins are of four types: 1.Stimulating shoot elongation 2.Controlling seedling orientation 3.Stimulating root branching 4.Promoting fruit development

19 Auxins’ Influence on Plant Orientation  Auxins influence plant orientation.  Auxins cause plants to grow toward light.

20 Synthetic Auxins  Synthetic auxins can use hormone properties to kill unwanted weeds.  These chemicals work by causing extreme growth of the plant, leading to plant death.

21 Take-home message 19.3  Auxins are a small group of naturally occuring horomones (and a larger group of synthetic variants) found primarily in meristems and immature plant tissue.

22 Take-home message 19.3  These hormones play several important roles in stimulating and regulating a plant’s growth and development, often by increasing the usually rigid cell wall’s flexibility and permeability.

23 19.4. Other plant hormones also regulate flowering, fruit ripening, and responses to stress.  Ethylene, abscisic acid, and cytokinins also play critical roles in directing germination, sprouting, and fruiting.  They also initiate appropriate molecular and cellular activities when environmental conditions are favorable.

24 Ethylene  Ethylene is a gas produced in every part of the plant.  This gas speeds the rate at which fruit ripens.

25 The Effect of Ethylene on Flowers Ethylene also hastens the aging and dropping of leaves from trees and the death of flowers at specific times.

26 Abscisic Acid  This hormone is synthesized primarily in leaves, fruits, and root tips.  This hormone has the general effect of inhibiting growth and reproductive activities under adverse environmental conditions.

27 Cytokinins  These hormones are stimulators of cell division throughout the plant body.  They are produced primarily in the roots and the fruits.

28 Cytokinins Work with Auxins to Produce Four Main Types of Effects 1.Causing rapid cell division 2.Inducing seed germination 3.Initiating new branches from lateral buds 4.Retarding leaf death

29 Take-home message 19.4  In addition to auxins and gibberlellins, three types of hormones also play critical roles in plant regulation.

30 Take-home message 19.4  Among these multiple functions, ethylene induces and speeds fruit ripening, abscisic acid inhibits growth and reproduction under stressful conditions, and cytokinins stimulate cell division throughout the plant body.

31 19.5. Tropisms influence plants’ direction of growth.  Plants use a variety of growth patterns called tropisms to grow toward or away from various environmental stimuli.  Plants can bend, curve and twist in response to light, gravity, and physical impediments.

32 There Are Three Main Types of Tropisms  Phototropism Growth in response to a light source.  Gravitropism Growth in response to gravity.  Thigomotropism Growth in response to touch or physical contact with an object.

33 Phototropism  Cells in a plant’s stem grow unevenly, so the stem bends toward the light.  This allows the plant to photosynthesize more efficiently.

34 Heliotropism  Heliotropism is a special type of phototropism.  This is growth in response to the position of the sun.

35 Gravitropism  This is the reason that stems grow upward, and roots grow downward.  This allows the leaves to access light, and the roots to access water in the soil.

36 Gravitropism  Starch-containing bodies, pulled by gravity, settle toward the bottom of the cells.  Auxin molecules migrate toward the starch causing uneven growth and causing stems and roots to grow in the right direction.

37 Thigmotropism Climbing plants will wrap around structures, using tendrils— specialized thread- like leaves or stems.

38 Take-home message 19.5  Plants have a variety of growth patterns, known as tropisms, by which they grow toward or away from various environmental stimuli.

39 Take-home message 19.5  Phototropism is growth in response to light, gravitropism is growth in response to gravity, and thigmotropism is growth in response to touch or contact with physical objects.

40 19.6. Plants have internal biological clocks.  Plants have a “biological clock,” an internal method of keeping time.  The internal clock of plants is continuously adjusted by environmental cues.

41 The Purpose of a “Biological Clock”  The clock tells the plant when to turn on or turn off the expression of certain genes, which can orient leaves for efficient photosynthesis or make flowers accessible when pollinators are available.

42 Environmental Cues  The most important environmental cues that set and reset a plant’s biological clock are light-dark cycles and temperature cycles.

43 The Biological Clock in Plants

44 Take-home message 19.6  Plants have internal methods of keeping time that enable them to initiate various biochemical and physiological actions at the appropriate time.

45 Take-home message 19.6  Plants constantly adjust their biological clocks to environmental cues, such as light-dark cycles and temperature cycles.

46 19.7. With photoperiodism and dormancy, plants detect and prepare for winter.

47 Photoperiodism  Plants use the length of the dark period in a day, in a process known as photoperiodism, to regulate their flowering time and numerous other responses to seasonal changes.

48 1)Long-day plants 2)Short-day plants 3)Day-neutral plants The amount of daylight determines when they produce flowers.

49 Timing  The critical amounts of daylight occur at different times of the year, when conditions are best suited for reproduction for a particular species.

50 How do plants regulate photoperiodism? This appears to be related to the ratio of different light-sensitive pigments in the leaves of a plant at different points during the day and night.

51 Take home message 19.7  Plants exhibit photoperiodism, responding to seasonal changes over the course of a year, timing their production of flowers or initiation of winter dormancy, for example, according to environmental factors such as the length of the period of darkness each night.


53 19.8. Plants actively resist being eaten by herbivores. Plants have evolved numerous defenses—these fall into four major categories: 1)Mechanical defenses 2)Chemical defenses 3)Mimicry and camouflage 4)Enlisting other organisms for “security”


55 Chemical Defenses Chemical compounds deter herbivory by making the plant toxic or by reducing the digestibility of the plant.

56 Beneficial Effects of Secondary Compounds  Spices  Medicines

57 Mimicry and Camouflage To avoid being eaten by insects, plants can mimic being already infested by insect eggs.

58 Enlisting Other Organisms for “Security”  Plants seem to outsource some of their defenses to other species.  An example is ants on acacia plants in Central America.

59 Take-home message 19.8  Rooted in the ground, plants are targets for predators and pathogens. They actively resist infection and herbivory by producing toxic chemicals that make them distasteful, poisonous, or difficult to consume.


61 19.9 Special adaptations help some plants thrive in extreme habitats.  There are adaptations plants utilize in a variety of ecosystems, including: super-dry habitats salty environments cold and windy habitats

62 Super-Dry Habitats In these habitats, plants have adapted features:  succulent leaves and stems  deep taproots  long-dormant seeds

63 Salty Environments To survive in these habitats, plants can:  transport much of the absorbed salts to vacuoles within cells, or  transport much of the salt through the plant and excrete it from the leaves.

64 Cold and Windy Habitats  Plants here grow close to the ground, and have smaller- than-average leaves.  Also, plants tend to have shallow root systems.

65 Take-home message 19.9  Plant evolution has produced adaptations to some of the most extreme habitats in the world, with plants managing to thrive where few animals can survive.

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