Lecture 5 Flashcards
Transpiration stream
flow of water through plant due to loss of water from leaves drawing water from soil into roots
ratio of water loss per CO2 fixed during photosynthesis
700-1300 mols of H2O per mole of CO2
what is the main driving force for transpiration stream
evaporative water loss from leaves; cohesion-tension
cohesion
attraction between water molecules
adhesion
attraction of water to xylem to form a strong column of water
how is water lost from plant
majority through stomata, some lost at night through epidermal cells and cuticle
what physiological processes require transpiration stream?
turgor pressure cytoplasmic solute concentrations transport of nutrients transport of phytohormones phloem loading evaporative cooling
apoplastic water movement in the root
transpiration rate is high
symplastic water movement in the root
transpiration rate is low
casparian strip
controls ion movement into the xylem; located in endodermis apoplastic pathway;
aquaporins
transmembrane protein water channels
purpose of the casparian strip
forces water moving in root apoplast to cross the plasma membrane which filters the water allowing plant to control what enters the inner root and what accesses the xylem
phloem
composed of sieve elements and companion cells; moves sugars and other molecules from source to sink
sieve elements
stacked into long vessels
sieve plates between elements
nucleus and vacuole lost
few and small ribosomes, chloroplast, er, golgi
companion cells
contain all sub cellular structures
provide sieve elements with physiological functions and products such as proteins
large plasmodesmata between sieve element and companion cells
pressure flow
process by which sugars move into sieve elements
source of sucrose loading from mesophyll cells into phloem
small veins in leaves
apoplastic phloem loading
sucrose moved to CC by energy consuming sucrose transporter in plasma membrane causing high SE sugar concentration resulting in water moving into SE from near xylem down water concentration gradient creating high phloem pressure
SWEETs
sugar efflux transporters transport sucrose from mesophyll to CC apoplastically
symplastic phloem loading
sucrose moves through plasmodesmata from mesophyll to CC where it is converted to larger raffinose which moves into SE via larger plasmodesmata
indicator of apoplastic phloem loading pathway:
invaginated plasma membrane to increase surface area form transporter proteins and lacking plasmodesmata between mesophyll and CC
evidence of symplastic vs apoplastic loaders
symplastic: transport larger sugars and have lots of mesophyll-CC plasmodesmata
apoplastic: transport sucrose - invaginated cell walls/plasma membrane in CCs to facilitate active transport of sugars
tobacco example:
transgenic tobacco with yeast gene encoding invertase enzyme in cell wall which breaks down sucrose.
if symplastic sucrose will be found in CC because it never enters cell wall
if apoplasitc no sucrose in CC because broken down by invertase while travelling through cell wall
Result: transgenic tobacco reduced growth therefore apoplastic loader
macronutrients
nitrogen, potassium, calcium, magnesium, phosphorus, sulfur
function of nitrogen
amino acid, nucleotides, other n containing compounds
function of potassium
osmotic and ionic balance, activator of enzymes in respiration and photosynthesis
function of calcium
intracellular signal transduction, forms a complex with pectin in cell walls
function of magnesium
component of chlorophyll, activator of enzymes
function of phosphorus
atp and phosphorylation reactions
function of sulphur
sulphur containing compounds such as methionine
Nitrogen assimilation
plants need reduced forms of N like NH3; plant uptakes nitrate which is reduced in root cells or transported to leaves to be reduced
bacterial symbiosis of legumes
symbiotic relationship with bacteria to fix nitrates into NH3; plant provides protected home and food sources, bacteria provides NH3
legumes
beans, chickpeas, peas, honey locust tree
legume nodule
home for bacteria on roots, looks like a bump
methods of obtaining phosphate
high affinity transporters in root plasma membrane
symbiotic relationship with mycorrhizal fungi
what do fertilizers provide?
N, P, K,
Ca, S, Mg,
B, Cl, Mn, Fe, Zn, Cu, Mo, Se,
p deficiency
stunted growth
k deficiency
dead edges of leaves
n deficiency
pale colour
mg deficiency
necrosis between veins in leaf
stele
core of root containing vascular tissue
fast root absorption method
symplastic
slow root absorption method
apoplastic
What are the three basic steps of water moving through a plant from soil to atmosphere?
- water uptake in roots
- transport in the xylem
- transport through the leaf and into the air
p-protein
when plant is wounded, p-proteins are produced to block sieve plates to prevent sugar loss—similar to blood clots
