Plant Responses to the Environment Stationary Life Animal

Plant Responses to the Environment

Stationary Life • Animal response to stimuli – Move toward or away • Plant response to stimuli – Adjust patterns of growth – Plasticity varied forms – Chemicals

Signal Transduction Pathways • Reception Transduction Response – Ex. Potato greening – Ex. Seed germination

• Reception – Receptor proteins undergo conformational changes in response to stimuli • Transduction – Second messengers amplify signal – Turn on kinases phosphorylate enzymes • Response – Stimulates RNA production • Make new enzymes – Activates existing enzymes • phosphorylation

Response

Hormones • Coordinate growth, response • Specific receptor, specific response • Minute quantities cause large reactions

Plant movement • Tropism- growth toward or away from stimuli – Light- phototropism – Gravity-gravitropism – Pressure-thigmotropism • Affect division, elongation and differentiation of cells

phototropism • Auxin (hormone) is distributed asymmetrically • One side grows more quickly • Plant grows toward light

Response to Mechanical stress • Triple response due to – Slowing of stem elongation – Thickening of stem – Horizontal growth • “feels” for obstacle • Seedlings respond the same way when ethylene is applied without an obstacle

Apoptosis-programmed cell death • Vessel element formation • Leaf abscission – Nutrients are stored in stem parenchyma – Abscission layer has weak cell walls, sensitive to ethylene

Fruit ripening • Ethylene triggers cell wall breakdown • Starch converted to sugar • Chain reaction: ethylene triggers ripening triggers more ethylene • Fruit ripens at the same time • Commercial use • GMO tomatoes lack ethylene

Delayed germination • Abscisic Acid prevents germination • Removal/inactivation of ABA allows germination • Cold • Light • Water

Gravity • • • Gravitropism Controlled by Auxin Statoliths=starch grains in cytoplasm High concentration of starch attracts Auxin High concentration of Auxin in roots slows down cell growth root bends down • High concentration of Auxin in stem speeds up stem growth

Touch • Thigmotropism-move toward solid object • React to touch –open ion transport chanels • Cells deflate, leaves collapse

Defense mechanisms • Secondary compounds – Tannins – Jasmonic acid= messenger • Symbiosis – Damaged leaves release volatile molecules – Attract parasitic wasps – Wasps kill caterpillars

• In a diseased state known as witches broom branches grow and proliferate excessively. Suggest a hypothesis to explain how a pathogen might induce this growth pattern?

Responses to light • Photosynthesis • Development – photomorphogenesis • Timing – germination – Flowering – Fruit

Light receptors • Blue light photoreceptors – Phototropism – Opening stoma – Slowing of cotyledon growth • Phytochromes (red and far red light) – Seed germination (break dormancy) – Shade avoidance (primary vs. apical growth)

Red-Far Red phytochrome switch • • Protein has two shapes: Pr and Pfr Phytochromes “see” red and far red light Pr absorbs red light turns into Pfr absorbs far red turns in to Pr

Germination and shade avoidance • Germination – Sunlight contains red light, Pr turns into Pfr – Pfr (exposure to sunlight )promotes germination • Shade avoidance – Canopy filters out more red light, leaves far red light – Pfr more resources to growing taller – Pr branching, more leaves

Circadian rhythms • Growth chamber experiments – Photosynthetic enzymes – Stomata – Leaf position Pfr is made during the day, reverts at night Dawn resets biological clock by putting more Pfr into the system when the sun comes out

Photoperiodism • Germination, budding, flowering, etc. correspond to the season • Seasons have different relative day/night • Day/Night length determine timing of events (temperature is irrelevant) • Fall leaves

Flowering • Short day (long night)- need longer period of continuous darkness • Long day (short night)- requires shorter period of continuous darkness • Leaves detect period of darkness, transmit signal to flower buds,

• Red light can interrupt night • Far red light cancels red light interruption • Manipulate plants to flower – Chrysanthymums long night plant, interrupt each night w/light, delay flowering until mother’s day