Plant Growth & Photosynthesis Lecture Notes (BIOE 20B)

REMINDERS ANNOUNCEMENTS 1. Discussion sections this week are at Thimann Greenhouse! Thursday, 11/14/24 2. Due Sunday: HW 7, Quiz 7 3. Midterm 1 scores have been released Week 7, Day 2 4. Midterm 2 is on November 21st (Development to Photosynthesis) Plant Growth/...

REMINDERS ANNOUNCEMENTS 1. Discussion sections this week are at Thimann Greenhouse! Thursday, 11/14/24 2. Due Sunday: HW 7, Quiz 7 3. Midterm 1 scores have been released Week 7, Day 2 4. Midterm 2 is on November 21st (Development to Photosynthesis) Plant Growth/ 5. Extra credit for being caught up with videos by Nov. 19th Photosynthesis TODAY’S AGENDA (8-9:35AM) What is the role of auxin & how does it work? Kahoot: Plant Growth 5 min-break Photosynthesis overview The Calvin Cycle The Photo part of Photosynthesis: The light reactions C3, C4, and CAM plants Kahoot: Photosynthesis  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  Study Questions 1. What is the difference between auxin polar transport and acid growth hypothesis? Auxin Polar Transport = auxin moves in one direction; Acid Growth Hypothesis = cell gets bigger 2. What is the mechanism for trapping auxin in the cell? How does it get out? Difference in pH causes auxin to lose H+ in Auxin transporters on shady part of cell cytoplasm à can’t cross cell membrane (i.e. bottom of cell in omnidirectional light) 3. What part of auxin polar transport changes in response to directional light? Auxin transporters à move to shady side of cell 4. What are the two active mechanisms caused by auxin? 1) Movement of H+ pumps into cell membrane à brings down pH in cell membrane 2) Increase in transcription of H+ pump genes à makes more H+ pumps 5. What does auxin do in the cell? Decreases pH in cell wall à causes activation of expansins à loosens cell wall 6. What is the role of water potential in acid growth? Loosened cell wall à decreases pressure potential à makes water potential more negative à water enters cell DISCUSS: What would happen to a plant exposed to unidirectional light and Auxin was not allowed to move through the transporters? Plant would not get a phototrophic response; it would grow straight up! Auxin transport is unidirectional Auxin Polar Transport Auxin transport is unidirectional Acid Growth Review in your notes…. Coleoptile tip & Auxin is made in the _________________ unidirectionally downward. moves _________________ In plants exposed to directional light, shaded auxin moves to the ______________ side of the plant where it stimulates increased cell elongation. Kahoot Review: Plant Growth  5-min Break! Attendance Time Scan the QR code or go to https://tinyurl.com/W7D2photosynthesis to answer the following question: Q: What is the difference between C4 and CAM plants? (This will be used for taking attendance today.)  Plant (Question) of the Day! Would you ride a hot air balloon to admire sunflowers (Helianthus) from the air in Yolo county? YOLO! 70+ species in family Asteraceae (Daisy family) Native to North America National Flower of Ukraine Heliotropism = following the sun (same mechanism we discussed for phototropism)  Learning Goals for Today 1 Photosynthesis overview 2 The Calvin Cycle 3 The Photo part of Photosynthesis: The light reactions 4 C3, C4, and CAM plants  What is photosynthesis? Converting light energy into chemical energy What is the 6CO2 + 6H2O tradeoff with opening the stomata? C6H12O6 + 6O2 CO2 enters but water is lost  Photosynthesis Overview Process Location Reactants Products Light ATP Light Thylakoid H2O NADPH Reactions membrane NADP+ O2 ADP Glucose/ Light ATP fructose / Independent Stroma NADPH sucrose Reactions CO2 NADP+ ADP  What is the purpose of the light reactions? Make the energy (ATP, NADPH) that is used to make sugar (fix carbon) What is the purpose of the light-independent reactions? Make sugar (fix carbon). This is the Calvin Cycle  Label all the letters of the figure. A Light H 2O CO D 2 NADP+ ADP +Pi Stroma B Light- E Light independent Thylakoid reactions ATP reactions NADPH Chloroplast G (whole structure) C F O2 Sugar Photosynthesis Overview Fig 10.3 in your book PHOTO SYNTHESIS Photosynthesis takes place in the chloroplast.  Photosynthesis Overview chloroplast Endosymbiotic theory = chloroplast remnant of the absorption of the prokaryotic bacteria by the eukaryotic host cells 1mm2 of leaf = Two membranes ½ million chloroplasts Stacks of thylakoids = grana Stroma = fluid surrounding grana The oxygen that you breathe is coming from: A. H2O B. CO2  Learning Goals for Today 1 Photosynthesis overview 2 The Calvin Cycle 3 The Photo part of Photosynthesis: The light reactions 4 C3, C4, and CAM plants The Calvin Cycle - 1950 Melvin Calvin  The Calvin Cycle Remember à purpose of Calvin Cycle (aka the light independent reactions) is to make sugar (fix carbon) 3 Phases Fixation: CO2 is used to make 3PG (RuBP accepts carbon) Key Enzyme: Rubisco (fixes carbon from CO2) Reduction: 3PG is reduced to G3P Regeneration: RuMP gets regenerated to RuBP RuBP is the CO2 acceptor in Fixation step  The Calvin Cycle Takes place in the stroma of the chloroplast 3) Regeneration = CO2 1) Carbon fixation = G3P becomes RuMP and carbon binds with RuBP Rubisco uses energy for RuBP to 3PG with the help of Rubisco to be regenerated to start RuBP C-C-C make 2 molecules of 3PG C-C-C-C-C cycle again ATP ATP Calvin Cycle ADP ADP NADPH RuMP NADP+ 2) Reduction = G3P 3PG is reduced to G3P G3P in two step C-C-C C-C-C reaction that uses Glucose energy Don’t need to know all the numbers of molecules – just basic steps. C3 plants… Fixation - Reduction - Regeneration -