BIOL 371: Themes 4 & 5 Plants

homeostasis

regulating the internal environment to maintain a relatively stable state, a dynamic process compensating/adjusting for changes in the internal and external environment

essential elements

17 for plants, components of nucleic acids (N,P), amino acids (N,S), function as enzyme cofactors (Ca2+), role in photosynthesis (Mg2+, Fe2+, Fe3+) or regulation of osmotic potential (K+)

macronutrients

essential in large quantities, C, H, O, from air and water (not considered minerals), N, P, K, S, Ca, Mg are mineral nutrients, available to plants through the soil as dissolved ions in water

micronutrients

essential in trace quantities - Cu2+, Cl-, Ni2+

nitrogen

abundant element in air, most limiting to plant, triple bond requires specific enzyme, nitrogen cycle provides soil nitrogen

nitrogen fixation

incorporates atmospheric N2 into plant-available compounds NH4+ with nitrogen-fixing bacteria

bacterial ammonification (N —> NH4+) and bacterial nitrification (NH4+ —> NO3-)

plants convert NO3- to NH4+ to assimilate N into organic compounds

bacterial ammonification

breaks decaying organic N compounds into NH4+, plants take up NH4+ but prefer NO3-

bacterial nitrification

oxidizes NH4+ to NO3-

legume root nodules

symbiotic association with nitrogen fixing bacteria

eutrophication

enrichment of an ecosystem with chemical nutrients such as compounds containing nitrogen and phosphorus, algal blooms - bacteria feed on them leading to the depletion of oxygen

chlorosis

yellowing of plant tissues due to lack of chlorophyll

soil

living skin of the earth, contains soil-mineral particles, compounds, ions, decomposing organics, water, air, organisms, particles vary in size (sand, silt, clay), relative amount of soil particles determine soil properties —> water and mineral availability

humus

decomposes organics, holds water and nutrients in soil

soil solution

available for plant uptake after gravity drainage, coats soil particles, partially fills pore spaces, sandy soil is looser, holds less water than clay soils (humus increases water availability)

a combination of water and dissolved substances that coats soil particles and partially fills pore spaces, water molecules are attracted by negatively charged clay and humus particles

mineral availability in soil

ions dissolved in water, passively enter plant roots along with the water, selectively absorbed by roots via ion-specific transport proteins, both cations and anions are present in soil solution but not equally available to plants

root systems

adaptations to limited mineral nutrients, make up 20-50% of total plant mass, roots grow as long as plant lives

cation exchange

mineral cations (Mg2+, Ca2+, K+) adsorbed to negative clay soil particles

replaces mineral with H+ produced by roots or excreted H+ or carbonic acid (respiration)

H+ displaces cations so they are available to the root hairs

anions availability

weakly bound to soil, move freely into root hairs, leach easily by excess water (N and P fertilizer replaces it)

alkaline soils

anions leach easily

acidic soils

cations leach out easily (displaced by H+)

passive transport

requires no metabolic energy, substance moves down a concentration or electrochemical gradient (membrane potential)

simple diffusion or use of transport proteins such as channels or carrier proteins (facilitated diffusion)

active transport

requires metabolic energy ATP, substance moves against gradient, transport proteins use energy

root hairs

increase uptake with large surface area, absorbs water and minerals

do not have cuticle/stomata

mycorrhizae

a fungus, symbiotic association with plant roots, both partners benefit by two way exchange of nutrients, plant provides fungus with carbon, fungus increases plant’s supply of soil nutrients (mostly PHOSPHORUS)

short distance transport

into and between cells, to and from vascular tissues

long distance transport

move substance between roots and shoot parts

osmosis

passive movement of water across a selectively permeable membrane

aquaporin

proteins that allow rapid movement of water through hydrophobic membrane core

water potential

the potential energy of water, driving force, moves from high potential to low potential

increase in solutes DECREASES water potential (water will not move out)

increase in pressure INCREASE water potential (water will move out)

central vacuole

maintains turgor pressure, has a tonoplast membrane

apoplastic pathway

water moves cortex to endodermis via cell walls and intercellular spaces (outside the plasma membrane)

occurs until casparian strip (in endodermis)

symplastic pathway

water flows from cytoplasm of one cell to the next via plasmodesmata (inside the plasma membrane)

casparian strip

in root endodermis, forces apoplastic water and nutrients into symplast (passive —> active), regulates the ions that pass into the vascular tissue, restricts back flow

transpiration

evaporation of water out of plants, greater than water used in growth and metabolism (90% evaporates)

affected by relative humidity, air temperature, and air movement (will increase/decrease as needed)

cohesion-tension mechanism

water transport, replaces evaporated water by cohesion (H-bonded) water in xylem, adhesion of water to xylem walls adds tension (resists gravity)

root pressure

positive pressure in roots that forces xylem sap upward, occurs in high humidity or low light, moves water up short distances (need cohesion to go all the way up)

guttation

when root pressure is strong enough to force water out of leaf openings, water is pushed up and out of veins

translocation

long-distance transport of substances via phloem (multidirectional), driven by differences in pressure between source and sink regions

phloem sap

water and organic compounds (amino acids, nitrogen compounds, hormones)

source

any region of plant where organic substances are loaded into phloem, eg. mature leaves

sink

any region of plant where organic substances are unloaded from phloem, eg. growing tissues and storage regions

seasons

changes which parts are sources and sinks, eg. spring —> sources are roots, sinks are new buds

sieve tubes

alive at maturity, undergo partial programmed cell death, connected to companion cells

features of mature sieve elements

• present: plasma membrane, plastids, mitochondria, endoplasmic reticulum

• absent: nucleus, tonoplast, ribosomes, cytoskeleton, golgi bodies

sugar loading

both apoplastic and symplastic

sugar moved into cell walls of phloem cells and from there transporter proteins actively transport sucrose into phloem (need for plasma membrane) - ACTIVE

sucrose comes through smaller plasmodesmata into companion cells, processed into larger sugars and through larger plasmodesmata transferred to phloem, trapped in companion cells and can’t return

unloading is mostly symplastic

pressure flow mechanism

moves substances by bulk flow under pressure from sources to sinks, based on water potential gradients, load from source —> transport in sieve tube —> unload into sinks

bulk flow from source to sink

more sucrose in the sieve tubes (low water potential)

influx of water increases pressure in the sieve tubes

sap flows in bulk toward the sink (lower pressure)

sucrose in unloaded into sink cells

water flow back to xylem through osmosis

gas exchange

need a supply of CO2 for photosynthesis and need to dispose O2 as waste

via simple diffusion, uses large leaf surface area, gas filled space within leaves

stomata

aperture on epidermis of a leaf (lower epidermis), consists of two specialized guard cells that surround a stoma (a tiny pore)

open —> CO2 is absorbed, water is lost (transpiration-photosynthesis compromise)

opening/closing controlled by active K+ transport into and out of guard cells

cuticle

covers epidermis, reduces water loss from leaves and stems, limits CO2 diffusion for photosynthesis

abscisic acid (ABA)

hormonal signal for the closure of stomata, synthesized by roots

mesophyll cells take up ABA from xylem and release it

transpiration-photosynthesis compromise

plants balance transpiration and gas exchange by opening and closing stomata as environmental conditions change

open stomata

turgid guard cells (K+ mostly in guard cells)

closed stomata

guard cells are flaccid (K+ mostly in epidermal cells, H+ pumped out actively during stomatal opening)

plant hormones

auxins, gibberellins, cytokinins, ethylene, brassinosteroids, abscisic acid, jasmonates

auxins

a plant hormone, promotes growth and elongation of cells, mainly indoleacetic acid (IAA), synthesized primarily in shoot apical meristem and young stems and leaves, govern growth responses to light and gravity

acid growth hypothesis

auxin kickstarts ATPase —> activates expansin —> expands cell wall

phototropisms

growth responses to directional light source, blue light receptors trigger auxin transport —> auxin triggers differential cell elongation

accumulates on one side so plant can bend

gibberellin

bolting - development of a flowering stem, allows for fruit enlargement

plant defense

defend against viruses, bacteria, fungi, worms and parasitic plants, physical and chemical deterrents, produce chemicals to defend, around 30% of all medicinal chemistries comes from these chemicals

potato blight

responsible for Irish potato famine (1845-1852)

one million died due to starvation

due to monoculture - no variation, 1 disease wiped out everything

hypersensitive response

uninfected cells around site of infection undergo cell death which contains the spread of the pathogen

strength cell walls, close stomata, selective plugging of xylem to prevent spread, produce antimicrobial compounds, hypersensitive response

systemic acquired resistance

development of an immune response at a distal site, sends signals throughout plant to defend themselves

eg. infected on one leaf, won’t affect another distal leaf

mate recognition

critical to successful reproductive development, many surrounding plants leads to exposure to pollen of many species

pollination

requires compatible pollen and female tissues

self-incompatibility

ability of a stigma to reject its own pollen to promote outcrossing

will only grow a pollen tube if the pollen has a completely different genotype