Plant Physiology: Resource Acquisition & Transport PDF

Plant Physiology: Resource Acquisition & Transport  Overview of Plant Evolution & Structures Plants arose from algal ancestors Water-based, non-vascular lacking de leaves and roots; minimal stomata man and waxy cuticles reduced water lo...

Plant Physiology: Resource Acquisition & Transport  Overview of Plant Evolution & Structures Plants arose from algal ancestors Water-based, non-vascular lacking de leaves and roots; minimal stomata man and waxy cuticles reduced water loss; materials primarily collected from water via diffusion Land plants grew taller (requiring more structure & anchoring roots for support & collecting water, minerals), often with broader leaves and extensive branching to collect light more efficiently · dominant haploid => gameotype · vascular tissue arose = roots/shorts develop , more specialization 3 flowers seeds main adaptation pollen General Vascular Plant Parts Roots: anchor, collect water, minerals Taproot: main, vertical root Lateral roots: branching roots Root hairs: ‘fuzzy’ extensions increasing surface area (mycorrhizae help too) I fungal symbiant ↳ help in exchange for sugar collect General Vascular Plant Parts Con’t Shoots: support (stem) and photosynthesis (leaves) Stem: supports increased height (may be woody); in some cases can photosynthesize Leaves: light capture, gas exchange via stomata Blade: ‘body’ of leaf Petiole: ‘stem’ of leaf Leaf Adaptations · diff pigments to broaden range of light Size, shape, orientation of leaves varies based on environment If water loss is minimal or light is weak, broad leaves If water loss is high or light intensity harsh, reduce leaves > - exposure less to sun Modify into spines, orient vertically rather than horizontally Concentrate stomata on underside (shaded) Orient leaves to minimize overlap; if lower leaves too shaded self-prune lots of light/H2 broad leaves intense sun + min. H2o => small leaves  Vascular Tissue - transport system As plants increased in height they needed more efficient transport systems: a vascular system of hollow tubes acting Q as a circulatory system Xylem: carry water, minerals ~ shorts roots to from roots to shoots; dead - , hollow ② composed of dead tissue Phloem: carry food (mainly -nutrients hormones , sugars) in both directions; alive , directly - can composed of living tissue regulate  Transport want to avoid fransmem. bc. requires specialized proteins General transport pathways to move short distances: ↑ around the Apoplastic: materials move via Cells extracellular spaces & cell walls rapid , quick- Symplastic: materials move in between - cytoplasm between cells via through cells plasmodesmata gap junc con : Cell pathogens -. in can easily run crossing cells wo mem. + hm Transmembrane: materials move cell to cell through membranes & cell walls for regulation purposes - Crossing membranes accomplished via passive or active transport active => [low] to [high] passive => [High] to [low] Transport Con’t Diffusion & membrane transporters similar to animal cells, BUT H+ rather than Na+ used in ions pumps and Ca2+ used for electrical signals passive trems (similar to action potentials). ↑ Osmosis occurs via aquaporins and driven by concentration gradient, BUT ↓ due to having plant cells a cell wall Osmosis harnessed as water potential: potential energy of water based on where it will move Water flows from regions of higher water potential to regions of lower water potential Influenced by solute concentration and physical pressure osmosis moves towards soln. hypertonic  Water Potential gradient concentration Calculated as: Ψ = ΨS + ΨP Ψ = water potential (measured in megapascals, MPa) only negative, Ψ S = solute potential (measure of pulls H20 s ! solute concentration) lowers Pure water value would be zero, so , H20 potential any solute should give a negative F value; more solute = lower water ↓ potential - ↑↓ D ΨP = pressure potential (physical D - N pressure on the solution) W + Can be positive (‘pushing’) or Higher > - lower lower > - high negative (‘pulling’)  nigh - I In I physical pressure Heo wants to into cell go prevents osmosis structure plants like this gives , & stability Water Potential Con’t Movement of water causes cells to become: Flaccid (wilted) if water is lost, reducing pressure (ΨP) can lead to plasmolysis (shriveling of cell within cell wall) Turgid (firm) if water is gained, adding pressure (ΨP) Unlike animal cells this doesn’t lead to cells bursting as the cell wall prevents over-expansion  Long-Distance Transport this is what bryophies do ~ Diffusion only works efficiently over very short distances; bulk flow carries materials over longer distances Movement of liquid in response to a pressure gradient (higher -> lower pressure) Independent of solute concentration -main is focus physical Operates in xylem and phloem pressure diffusion cannot help w/taller plants  Xylem Transports water and minerals from roots to leaves Diffuse into apoplast (everything external to cytoplasm: cell walls, extracellular spaces, interior of dead cells) mostly at root hairs Some minerals actively transported across plasma membrane H20 follows a solute into the symplast (entire mass of cytosol and plasmodesmata) Apoplast materials move into xylem by crossing endodermis; symplastic enter via plasmodesmata Direct entrance to xylem from apoplast prevented by Casparian strip (waxy barrier) to force all materials to cross the semi-permeable membrane  * explain process ~ cross min.. Of I mem. no cuticle : dissolve in cell wall ( active transport Transpiration more 20 potential #yo · > at roots - less at the top · using20 potential One water/minerals are in xylem, how to transport long distances against gravity? > pulling ofco - Bulk transit accomplished via transpiration: loss of water from shoots Evaporation of water ‘pulls’ a string of water molecules (and dissolved materials) up the thin xylem tubing system Addition of solutes in roots draws water in (osmosis), increasing pressure (root pressure) to ‘push’ solution up Can lead to guttation: pushing excess water out of ‘escape valves’ in leaves (NOT stomata) if insufficient transpiration occurs short plants few erap , - , Note that root pressure is not a major transport force; most movement is due to transpiration evaporation occurs => at the top 0 advesion - - H-bonds -It both - - cohesion o I H low H20 pot Transpiration Con’t Transpiration relies on cohesion and adhesion of water molecules (H- bonding due to the polar nature of water) Xylem must be strong enough not to collapse under the powerful negative pressure (sucking force); in large plants that may be 100+ feet tall reinforced with lignin (not just cellulose), aka wood Rate of transpiration largely controlled by stomata: · where gas Heo escapes exchange · Located on underside of leaves to minimize water loss site trade off ~ In arid environments reduced leaf size also reduces stomata (but this reduces surface area for light-capture/photosynthesis too) Stomata density varies (lower in desert-adapted plants; also varies within plants due to environmental conditions such as CO2 levels) open too long in not conditions > - water loss for plants  Stomata Stomata open/close due to turgidity of guard cells, controlled by ion channels that influence osmosis controlled by Stomata open/close in response to: - solute concent. Light: exposure to light opens stomata CO2 03 - - needs remove O for too much o - > photorespiration photosynthesis CO2 levels: lowered CO2 opens stomata to collect more Circadian cycles: even without light, stomata open during “daylight” hours and close at “night” [not in CAM plants] Signals: stress conditions such as drought will lead to more stomata closing to conserve water Note: water isn’t primarily for photosynthesis reaction, but rather to transport minerals Also thermoregulates the leaf (evaporative cooling) > Eurose ( /water flows in water ↳Close flows out  [low] Phloem tissue living moves nutrients [High] ↑ E Bidirectional flow of nutrients = Hop (translocation) through living tissues; phloem into it to dilute controlled/powered by pressure Transports from source to sink; not always shoots to roots Clow] since Early growth may transfer nutrients from solutes are sucked storage in roots to growing buds into companion cell Leaves may transport nutrients to other shoots - regions undergoing growth (ex: fruits) Phloem also transports communication molecules, non-sugar biomolecules, and even electrical signals