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Biology 2601A/B
Tamsen Taylor

Plant Hormones – Lecture 14 12/4/2012 9:56:00 AM Gibberellins (GA)  Gibberellins make up a large family of STUCTURALLY RELATED COMPOUNDS, found in fungi and plants  Gibberellic acid (GA3) o Giberellin that appears to promote CELL ELONGATION, INCREASE RATES OF CELL DIVISION IN ROOTS Cytokinins (CK)  Cytokinins are a group of plant hormones that promote cell division  Cytokinins are synthesized in ROOT TIPS, YOUNG FRUITS, SEEDS, GROWING BUDS and other developing organs  Cytokinins regulate growth by activating genes that keep the cell cycle going  When lacking CKs, cells arrest at G1 o Cell cycle stops, stop growing  EX. Kinetin, Zeatin Brassinosteroids (BR)  Involved with elongation in the dark (ETOLIATION) Auxins (mainly IAA)  Produced in the apical meristems and young leaves (apical dom.)  The transport is polar o Produced in the ap. Meris. and travels top to bottom to the root were it will then move slightly upwards o Apical to Basal end in cells o Cotransporters at top of cells bring auxin in  Carrier proteins at bottom of cell send auxin out  Some auxin is destroyed in the process  Within the cells,  The pH between cytosol and cell wall is different  pH within cell is lowered by pumping protons out using ATP  the auxin itself has negative charge but is neutralized by protons, so that it may enter the cell easily Once auxin has entered the cell, it releases the proton and ATP pumps the proton out Auxins stimulate ELONGATION  Remember auxin brings in protons and those protons are pumped out of the cell by pumps  The protons that are pumped out activate EXPANSINS  The cellulose will loosen, cell elongates  ALLOWS FOR NATURAL ENLARGEMENT OF CELL BY MEANS OF WATER PRESSURE  Promotes cell divions and leaf expansion  Induces ethylene production Cytokinins and Auxins are used together to promote the growth and differentiation of cells in culture  CKs promote cell division in the prescence of auxin Ethylene  Involved in fruit ripening  Induces senescence in fruits, flowers and leaves  Produced when plants are under stress  Ethylene causes a decrease in growth and elongation o High Auxin  Cells in abscission zone are insensitive to ethylene o Low auxin:  Cells in abscission zone are more sensitive to ethylene, leaf senescence occurs  Leaf detaches from abscission zone Abiscisic acid (ABA)  Inhibits bud growth and seed germination  Induces closure of stomata in response to water stress o Water Control  ABA binds to receptors on guard cells  Stop the pumping out of H, opens outward directed Cl channels  Open outward directed K channels  H2O follows ions via osmosis  Stomata guard cells close Salicylic Acid (SA)  Occurs during HYPERSENSTIVE RESPONSE to pathogens  SA is produced at the infection site o Triggers a slower, more widespread set of events  SYSTEMIC ACQUIRED RESISTANCE (SAR)  Primes cells throughout the root and shoot systems for resistance to pathogen attack How Do Plants Sense and Respond to Herbivore Attack?  Many plant seeds and storage organs contain proteinase inhibitors o proteins that block the enzymes found in the mouths and stomachs of animals that digest proteins  If herbivore ingests a large amount of protinease inhibitor it will get sick, herbivores will then learn to detect and avoid plants that contain these proteins  Systemin o Hormone produced in response to wounds caused by herbivores o Initiates a protective response  Synthesis of Jasmonic Acid  Activates the production of proteinase inhibitors Hypersensitive Response (HR)  Causes the rapid and localized death of cells surrounding the site of infection, starving pathogen Pathogen  Disease causing agents Induced defenses  Responses to attacks that are induced by the presence of a threat Parasitoid  Organism that is free living as an adult but parasitic as a larva  Parasitoid attacks limit the amount of damage done to plants by herbivores, they kill their host Pheremones  Chemical messengers made by an individual that are released to elicit a response in a different individual Intro to Gas Physiology/Respiratory Structures – Lecture 15 + Lecture 16 12/4/2012 9:56:00 AM Introduction to Oxygen Physiology  Animals do not actively transport Oxygen across respiratory surfaces  Movement of O2 must depend on diffusion  All living cells must be bathed in fluid o Respiratory surfaces are moist  O2 must dissolve in fluid o Then must diffuse across liquid barrier  Respiratory surface supplies gas exchange for the entire body of the animal o Size dependent  Larger body will have larger resp. system o Water or land o Will vary dependent on metabolic demands ie. Endotherms vs ectotherms Terrestrial organisms have an invagination of the respiratory system  Allows for the retention of moisture John Dalton  Articulated the LAW OF PARTIAL PRESSURES o Pressure o Pressure differences determine direction when materials flow and affect the rate of flow, whether the flow is in blood circulation, breathing or filtration of water o Force per unit of area, standard unit of pressure is pascal  Each gas in a mix exerts pressure  Partial pressure is the amount of pressure that the gas exerts P xF Px tot o Px= partial pressure o Fx= fractional concentration of gas (moles or by volume) o Ptot Total pressure of the gas mixture As you increase in height, the pressure decreases Gases dissolve in liquids  Pliquid proportional to air  Amount of gas in solution depends on: o Temperature  Molecules will be moving at a greater rate at higher temps o Salinity o Gas *Gases that have reacted chemically do not contribute to partial pressure in solution Henry’s Law  The partial pressure and concentration of a gas in an aqueous solution are proportional to each other C xAP x o C x Concentration in solution o A = solubility of the gas in the liquid, (absorption coefficient) o P x Partial Pressure (in liquid) Diffusion of Gases (Derived from Fick equation) J=K∙(P1‐ P2) X  J = rate of net movement of the gas (per unit area)  K = Diffusion coefficient  (P1-P2) = Concentration gradient, movement of over time in relation to area  X = Distance to be diffused Diffusion Coefficient  Depends on gas, temperature and medium  Also depends on the permeability of any barriers, o eg. Cell membranes, cuticle, epidermis What can an organism do to improve gas exchange?  Make the diffusion distance as small as possible (decrease the distance of a membrane) o Ex. capillary walls are responsible for diffusion of oxygen across particular membranes  It is made up of a single, eplithelial cell layer, very thin  Maximize the area o Increase the surface area by for example, many folds.  Maximize the concentration gradient to maximize the rate of diffusion Convection can minimize the dependence of diffusion  Convection can move gases such as oxygen much farther than just diffusion alone  Utilize convection through o Active pumping of water  Eg. Choanocytes o Passive Pumping of water  Created by current  Created by propulsion mechanisms (jellyfish)  Ex. The Sponge Pump o Sponge pumps a volume of water equal to its body volume once every 5 seconds o 1 litre sponge pumps about 720 of water in an hour o The engine of the pump is the CHOANOCYTES which is its active pumping mechanism, it brings in water through currents in the ocean which is its passive pumping mechanism o Convection can be used to get rid of CO2 and bring in O2 to replace it  This example was used for the tunnel system used by groundhogs  The same system applies for jellyfish using propulsion to move fluid and remove oxygen depleted water for oxygen rich water Breathing water  Getting rid of CO2 isnt a problem o CO2 has a high diffusivity and absorption in water  Getting O2 is o It has a low solubility in water o It has a low partial pressure How to breath water?  Fast ventilation o More water across respiratory surface means more oxygen will come in contact to absorb  Efficient Absorption o Via countercurrent exchange  Highly vascularised system with a large surface area  Ventilatory structures o Gas exchange surfaces o Usually highly vascularised o Open to the ‘outside world’ o Actively ventilated using a convective flow of medium  These structures would be o Skin o Gills (evaginations) o Lungs (invaginations) o Or combination of the three Gas Exchange in Plants – Lecture 17 12/4/2012 9:56:00 AM Gas exchange in PhotoSynthesis  Plants get CO2 out of air and into the leaf through FICKIAN diffusion through stomata o Relies on a concentration gradient that allows for the diffusion to occur, resistance affects this diffusion  The diffusion of CO2 also allows for the diffusion of water vapour as well When oxygen diffuses in and carbon dioxide moves out, photorespiration takes place When carbon dioxide is taken in and oxygen is released, photosynthesis takes place How do gases get in and out of a plant?  This occurs through the stomata o These are pores in the leafs surface that allow for access from the outside air to air spaces within the leaf  Here >90% of all gas exchange takes place  Vast majority of water loss occur through these pores  These pores open and close  When they are open it is good for CO2 uptake but bad for WATER loss Structure of Stomata  Stomata are located: o On top – floating aquatic plants o Underside - most angiosperms o Rows on needles – conifer o Top and Bottom – Grasses Two Types of Stomata o Ellipsoid Graminceous  dumbell shape, the cytosolic and vasculature are at the ends, the pore is very small How do plants open and close their stomata? When water enters the guard cells, these cells will swell, the swelling will be limited by cellulose microfibrils that act as ‘bands’  Think of strength bands or tightened rope These guard cells swell by water uptake? But How?  The water uptake is driven by POTASSIUM INFLUX  Lower cell water potential within the cell caused by osmotic (solute) potential, causes water to flow into the cell which will increase turgor pressure  When guard cells are open, the potassium levels are higher than when they are closed  A guard cell with its vacuole. When you have a trigger such as light, an ATPase proton pump will use ATP energy to pump out protons into the apoplast, this will generate an electron proton gradient. Voltage gated potassium channels will bring in K in and chloride will follow.  Water will then follow as the water potential in guard cell declines How is stomatal opening and closing regulated?  If you shut the stomata completely the pressure inside the cell will build up and when it opens up finally, more water will leave as a result  The stomata will respond to internal PCO2  Close in response to water stress  Respond to light  Have endogenous, diel rhythms Photorespiration  Dominates when there is high levels of Oxygen o Oxygen competes for Rubisco which also acts as an oxygenase o If you want to use photosynthesis, you would need to increase the amount of CO2 coming into contact with rubisco  In stomata o There is a trade off  You wlll obtain CO2 but lose water in the process  Atmospheric CO2 conc. have been lower in the past  Soil moisture can very low, and atmospheric demand for water can be very high  Plants may use 2 different ways to sequester CO2 while retaining water for use -> -> -> -> C4 photosynthesis o SPATIAL separation of CO2 influx and Calvin Cycle o (Light Rxns)  Mesophyll cells contain low conc. of CO2  Carboxylation of PEP to C4 acid occurs and acid is transported to bundle sheath cells o (Dark Rxns)  Bundle Sheath Cells have high conc. of CO2  Decarboxylation of C4 acid  Allow
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