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Biology 4608G
Norman Huner

Lecture 1 Photoautotroph - use light to reduce carbon source January-09-12 10:01 AM - Distinct from any other living organism, physiologically - Metabolic pathways used to convert light are unique - Metabolic regulation is unique compared to heterotrophs Equilibrium constant (Ke) tells us about the driving force of the reaction, doesn’t describe the mechanism of the reaction - Delta G - free energy of the reaction (energy available to do useful work) - Delta G represents the driving force of the reaction At equilibrium - delta G = 0 - Living organisms have to remain far from equilibrium - Homeostasis - steady state - NOT equilibrium Steady State (13.1) - A requires energy in because it is living - need energy to maintain homeostatic state - Need constant input on energy just to maintain homeostasis - Eout - byproducts, carbon dioxide, heat - Constant flux of energy through the system - Homeostasis - steady state flux of energy through the system STRESS - Any environmental condition that would tend to push an organism out of homestatic state - Abiotic - temperature, light, water - Biotic - pathogen infection, herbivory - 13.2 - any physiological process - respiration, photosynthesis ○ Plot as a function of time ○ Rate of photosynthesis of a mature, healthy plant - constant rate (homeostatic) ○ Impose a change in the environment (change temperature, remove nutrient) ○ With time, rate of photosynthesis decreases - plant response to stress ○ If unable to counteract the stress, can succumb to stress - photosynthesis/respiration comes to 0 - 13.3 ○ Resistant - can acclimate (adjust to the stress)  Continue to grow and survive ○ Susceptibility  Senescence - the programmed death of plants  Death ○ Avoidance  Deciduous trees dropping leaves in the fall  Induced to go to seed before the stress occurs - seeds survive, germinate post-stress - Acclimation - the ability of a plant to re-establish a homeostatic state after exposure to a stress/ establish a new homeostatic state - 14.1 ○ Under a stress, what would you expect to happen to the growth rate?  Slow down ○ Growth rate can be measured by change in biomass over time  Increase in number of cells and size of cells ○ State B and state C are new homeostatic states - allow plant to survive, life cycle continues ○ Reversible if remove stress ○ Change in gene expression can cause new homeostatic state  Transcriptional regulation  Translational regulation  Post-translational modification (phosphorylation, methylation) □ Quicker, more energetically favourable - 14.2 ○ Short-term process, normally don’t see a change in phenotype ○ Long-term processes --> phenotypic change ○ Time-nesting  Acclimation is a time-nested reponse  Plant is integrating a whole series of processes over time  Rapid processes kick in right away upon introduction to stress □ Don’t tend to last very long (knee jerk response) □ Until long-term processes kick in ○ Plant is integrating processes a-g in order to maintain new homeostatic state ADAPTATION - acclimation of a plant over evolutionary time - Stress response genes are passed on form generation to generation - Change in genome has occurred Acclimation is one plant, single lifecycle, single lifetime - Gene expression not necessarily transferred to next generation SENSORS - establish homeostatic state - In order to acclimate, plants have to be able to sense the stress Lecture 1 Page 1 SENSORS - establish homeostatic state - In order to acclimate, plants have to be able to sense the stress - Three major categories of sensors 1) Sensing of light quality (wavelength, not irradiance) - Plants have sensors that are sensitive to changes in the wavelength of light - Light quality important in regulating photomorphogenesis --> light-dependent development - Two photoreceptors - critical in regulating plant development  Molecule that is activated by a specific wavelength of light  Photochemistry - must be absorbing light, exhibit an absorption spectrum - will tell us what wavelengths that photoreceptor absorbs  Phytochrome - protein present in cytoplasm of a plant cell □ Chromophore is necessar
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