Botany 4 Lectures 25 and 26 Plant Sense

Botany 4 Lectures #25 and #26 Plant Sense and Response to the Environment 1

Plants can’t run away from, or run toward a stimulus. Plants can alter their growth responses… • So, the control of the timing of growth and the direction of growth is very important…. 2

The Outside Tells the Inside What to do…. . • In response to many Environmental Stimuli, plants respond by adjusting their growth and development. • External signals control internal physiology by light, temperature, gravity, touch, and water signals. 3

External Signals 4

Plants Respond to Environment by: • Sensing and responding to environmental signals using Membrane Receptors • Sending signals between different parts of plants using Hormones • Activating Specific Genes Proteins made allow plants to regulate their growth pattern and development. 5

How Do Plants Communicate With Their Environment? All cells have the ability to sense and respond to their environment. 6

Signals Hormones Environmental signals (Light) Internal responses Often gene activation and protein formation 7

Internal Control • Hormone – compound made in one part of the plant that is transported to another part where it triggers a response in target tissues and cells. • Hormones control plant growth and development by cell division, elongation and differentiation. • Coordinate the environmental stimuli with appropriate growth response 8

• There approximately 10 different plant hormones. • They often interact in development. 9

Auxin • The most common hormone in plants. • Root formation, cell expansion, ++++ • Concentration and site affect action. • Can inhibit or stimulate other hormones. 10

What is Happening Here? Why? 11

Example of Auxin Action… Apical Dominance. • How does this occur? • Auxin Represses action of another hormone: Cytokinin 12

Gibberellins • Stimulate Cell Division/Enlargement, • Regulate Stem Growth. • Seed Germination; Fruit size. 13

Ethylene, A Gaseous Hormone • Promotes senescence and fruit ripening. • Works with auxin to regulate leaf abscission. 14

Plants Measure Light Quantity and Quality in their Environment Using a variety of Light Receptors. We will focus on Phytochrome. 15

Phytochrome – Red Light Membrane Receptor Can Measure: Photoperiod Degree of Shading Using this info plants control timing of seed germination, root and shoot growth and flowering. 16

Phytochrome Acts as a switch to control… 17

Flowering • Time of flowering is controlled by photoperiod. (Amount of day/amount of night. ) • Photoperiod changes during the year. Sensed by Phytochrome! 18

Two Main Types of Plant Responses: • Tropisms • Turgor Responses Growth responses that move or turn plant organs toward or away from stimuli. ~ Hormones involved! 19

Tropisms (Long-termed) • Growth responses that result in curvature of organs away from or towards a stimuli. • Stimuli can be – Light – Gravity – Touch Why do roots grow down and stems grow up? Why do vines twine around objects? 20

Why Do Plants Grow Towards Light? 21

Phototropism • Auxin moves down the stem on the shaded side causing differential cell elongation. 22

Phototropin • Phototropism 23

Auxin Signaling in Phototropism: Activation of What’s the processes or cellular gene response? to transcription elongate cell Auxin 24

Turgor Movements (Short-term) • Swelling and collapsing of cells due to osmosis cause rapid and reversible movement of organs. (Sound familiar? ) • Think Stomatal opening and closing. 25

Opening and Closing of Flowers Sleep Movement of Leaves. 26

Venus Fly Trap Mimosa 27

Plants Cope w/ Stresses: Heat, Cold, Flood, Drought • One Example: • Drought in roots results in stomatal closure, using a hormone. 28

Plants constantly under attack • Pathogens – Bacteria – Fungi – Viruses How do plants respond and defend? Once invasion sensed, plants have multiple strategies for defense against pathogens 29

Defense Against Pathogens and Herbivores Two Types of Defenses: Mechanical Chemical 30

Mechanical Defenses • Physical barriers – Keep them out! 31

Active mechanical defenses • Attack stimulates reinforcement of cell wall with polysaccharides • Strengthens to prevent infection • Prevents spread – Can block plasmodesmata 32

Hypersensitive Response Containment …Sacrifice one or a few to save the whole 33

Hypersensitive Response • Pathogen invades • Cells around infection site: – Initiate Programmed Cell Death – Collapse and die (necrotic lesion) • Contains invader • Prevents spread Nicolle Rager Fuller, National Science Foundation 34

Longterm immunity? • We develop antibodies – future resistance to pathogens • What about plants? Systemic Acquired Resistance General increase in the whole plant’s ability to defend against many different future pathogens 35

During Hypersensitive Response, dying cells produce: Salicylic acid Functions as defense hormone 36

Salicylic acid (SA) produced during Hypersensitive response (HR) Exported to other parts of plant SA PR protein production Initiates PR protein production = Enhanced defenses in other parts of plant Infection of one cell by one pathogen yields long-lasting resistance to many future pathogens in the rest of the plant 37