Bioe 20B Plant Growth - Week 7, Day 1 PDF

REMINDERS ANNOUNCEMENTS 1. Discussion sections this week are at Thimann Greenhouse! Tuesday, 11/12/24 2. Due Sunday: HW 7, Quiz 7 3. Midterm 1 scores have been released Week 7, Day 1 4. Midterm 2 is on November 21st (Development to Photosynthesis) Plant Growth...

REMINDERS ANNOUNCEMENTS 1. Discussion sections this week are at Thimann Greenhouse! Tuesday, 11/12/24 2. Due Sunday: HW 7, Quiz 7 3. Midterm 1 scores have been released Week 7, Day 1 4. Midterm 2 is on November 21st (Development to Photosynthesis) Plant Growth 5. Extra credit for being caught up with videos by Nov. 19th TODAY’S AGENDA (8-9:35AM) How do plants detect light? What are the major groups of plant hormones & how are they involved in plant growth? 5 min-break What is the role of auxin & how does it work? Kahoot!  Learning Goals for Today 1 How do plants detect light? 2 What are the major groups of plant hormones & how are they involved in plant growth? 3 What is the role of auxin & how does it work?  Why are plants green? A. Because they absorb green light. B. Because they reflect green light. C. Because they absorb red and blue light. D. Because they reflect red and blue light E. Both B and C F. Both A and D Plants have photoreceptors – respond to particular wavelengths of light What is this graph showing? The coleoptile is sensitive to blue light Where else do we see a blue light receptor? Opening the stomata  How do plants detect light? Blue Light receptors – phototropin Involved in plant movement, opening of stomata, seedling development Inactive form Red Light receptors – phytochromes Active form Involved in seed germination, flowering, stem elongation, many others  How do plants detect light? Inactive form Red Light receptors – phytochromes Active form Involved in seed germination, flowering, stem elongation, many others How do plants detect light? Red Light receptors – phytochromes ~668 nm Cis = Trans = inactive form active form ~730 nm How do plants detect light? Red Light receptors – phytochromes  How do plants detect light? Which plant is in the sun and in the active form? A B Pr = inactive When there is cis form more Pr than Pfr = Uh oh! I need Pfr = active trans form signal to the plant to grow taller to GROW! to get to the good light!! So….when does Pr dominate and when does Pfr dominate? Leaves at top of canopy getting a lot of red light… Plants in the shade = more far red light. What does far red light do to phytochrome? Pfr form is active = it stimulates Pr form is inactive = low the plant to make chlorophyll, chlorophyll synthesis, low leaf leaves to grow larger etc… growth BUT… These are all things you want to Other pathways stimulate stem do if you are in the sun! to grow = taller plant = get to the sun Thought question In a plant that starts off with all of its phytochrome molecules in the Pr form in the morning, what will happen to the phytochrome for this plant if it is in the sun for most of the day? If it is in the shade? Ratio of Pr to Pfr constantly switching all day due to working as a chemical switch; when past threshold will switch to either form on certain parts of the plant  Learning Goals for Today 1 How do plants detect light? 2 What are the major groups of plant hormones & how are they involved in plant growth? 3 What is the role of auxin & how does it work? Plants Sense Their Environment  Plants Sense Their Environment Tropisms – a directional response to a stimulus “tropism” is from the Greek word “tropos” meaning to turn Tropism Phototropism Gravitropism Thigmotropism Growth/ Gravity movement Light (positive = roots; Touch towards… negative = shoots) Picture WHERE do plants detect light? Why is light the most important resource for plants? Light influences: Movement Growth Seedling development Shoot elongation Flowering  WHERE do plants detect light? Coleoptile = “seedling” What was the result of Charles and Francis Light Darwin’s experiments? ~1880 Canary grass  WHERE do plants detect light? Result: The tip of the outer sheath of the seedling, the coleoptile, detects light seedling Light  How were plant hormones discovered? Let’s review the Went experiment. LIGHT 1 NO 4 LIGHT 3 2 Frits Went 2) Tip is cut off and placed on an agar block for hormone to travel into 4) Seedling 1) One seedling is 3) Agar block (with begins to grow exposed to light hormone) is placed on the side with on another seedling the agar block that was not exposed to light  How were plant hormones discovered? What does the orange color represent? Auxin (hormone) that has moved into the agar block Why is the block placed on only half the stem? To show that the side of the Frits Went new seedling with the block grows (aka shady side) Which way is light being simulated to come from? Right side Result: A chemical (aka a hormone) is moving from tip to cells on the shady side and stimulating growth….how does it do that? Yoga Plant demo Remember – Plants can grow in two ways: Cells expand: Ex: auxin (hormone) Cell elongation Plants make more Ex: meristems cells thru cell division (apical/root/cork cambium) 1) If the gelatin block were placed evenly on the cut tip of the coleoptile, how would the coleoptile grow? 2) Draw a model of the cells in the coleoptile after it has been exposed to directional light. Plant Hormones: Overview Auxin Stem elongation, fruit growth, apical dominance, abscission Seed germination, stem growth, Gibberellins fruit development Fruit ripening, inhibition of stem Ethylene elongation Inhibit leaf senescence, promote Cytokines cell division Stem & pollen tube elongation, Brassinosteroids Vascular tissue differentiation  5-min Break! Attendance Time Scan the QR code or go to https://tinyurl.com/W7D1plantgrowth to answer the following question: Q: Describe the difference between red light and far red light. (This will be used for taking attendance today.)  Learning Goals for Today 1 How do plants detect light? 2 What are the major groups of plant hormones & how are they involved in plant growth? 3 What is the role of auxin & how does it work? Q: How does Auxin Polar Transport A- + H+ HA Q: How does Auxin make Acid Growth Auxin get to LIGHT the cell get bigger? the shady side? A- = Auxin AH = neutral H2O enters H+ H+ AH = proton due to more negative ACID TRAP! pump A- H+ H+ water Difference in = Auxin potential A- pH causes Cytoplasm transporter Auxin to be pH = 7 H+ trapped in ↑H+ cytoplasm Cell A- Polar pumps wall transport pH = 5 because AH proceeds H+ in one Expansins = cleave cell wall direction! (cellulose + hemicellulose) 1) Auxin increases amount of of H+ in the cell wall in 2 ways: 1) Light triggers Auxin to be released in cell wall Auxin incorporates proton transporters into membrane 2) Auxin moves into cytoplasm and loses proton Auxin increases transcription of proton pumps 3) Proton pumps pump out H+ into cell wall 2) Decreases pH in cell wall 4) Auxin takes transporter down shady side of cell 3) Expansins cleave bonds between cellulose and hemicellulose 4) Loosens cell wall so water can enter What is the role of water potential in acid growth? Water potential = solute potential + pressure potential Ψ = Ψs + Ψp Ψ = -0.2 + 0.2 Normal; before light stimulus Ψ = -0.2 + 0.1 Light stimulus; loosened cell wall Ψ = -0.1 Negative water potential will allow water to rush into the cell à cell expands