Textbook Flashcards
Stele:
core of vascular stem and root
contains vascular tissues/bundles
guttation:
secretion of xylem fluid from hydathodes of leaves (formation of dew drops)
source organs:
photosynthetic parts of the plant that synthesize sucrose (eg. leaves, some stems)
sink organs:
non photosynthetic parts of the plant that cannot synthesize sucrose and therefore have a demand for sucrose (eg. roots, meristems, flowers, seeds, fruits, tubers, rhizomes)
rhizosphere:
zone of influence in the soil surrounding a root
hydathodes:
specialized structures on the margin of leaves which are responsible for exudation of xylem fluids during periods of positive xylem pressure. (location of dew excretion)
symplast:
continuous network of interconnected plant protoplasts connected by plasmodesmata. (symplastic pathway)
sieve plates:
widened plasmodesmata between two sieve element cells which allow movement of solutes and proteins without resistance.
p-proteins:
sieve element specific proteins thought to be important in plugging the sieve plates to prevent loss of sugars if the phloem is damaged. synthesized in companion cells and transported to sieve elements for use.
two types of cell in the phloem:
sieve elements and their companion cells
companion cells:
provide a route of entry of sugars into the sieve elements and provide metabolic functions for the sieve elements (which do not have many sub cellular structures)
pressure flow:
process used for movement of sugars in the phloem using a pressure gradient caused by phloem loading in leaves and unloading in sink organs
phloem loading:
sugars are loaded into the phloem from the leaf mesophyll cells resulting in a large difference in sucrose concentration between cytosol of the mesophyll cells and the phloem causing osmotic transfer from xylem resulting in high phloem pressure.
apoplast:
region outside the plasma membrane consisting mainly of cell walls
symplast:
cellular volume bounded by the plasma membrane and connected by plasmodesmata
apoplastic phloem loading:
sucrose moves out of mesophyll cells into the apoplast then into companion cells or sieve elements against the concentration gradient using an active sucrose transporter protein.
symplastic phloem loading:
sucrose moves via plasmodesmata from mesophyll into companion cells where it is converted to higher molecular weight sugars which cannot reverse back to mesophyll and are therefore required to continue to sieve cells.
sucrose-proton co-transporters:
protein responsible for movement of sucrose from the apoplast to the phloem in apoplastic loaders which operate in conjunction with an ATP driven proton pump H+ ATPase
transpiration stream:
flow of water through the plant soil>root>xylem>leaves>atmosphere
replaces water lost through stomata and is responsible for maintaining physiological processes.
cohesion:
strong mutual attraction between water molecules
adhesion:
attraction of water molecules to solid surfaces
cohesion-tension theory:
hydraulic explanation for water movement involving water potential, adhesion, and cohesion.
apoplastic water movement pathway:
water moves from soil to xylem in apoplast; resistance is present due to the Casparian strip in the endodermis walls
Casparian strip:
a band of Suberin which is a hydrophobic material
symplastic water movement pathway:
water moves from soil via plasmodesmata into the stele where it moves out of cells into the xylem vessels
symplastic and aplastic water movement pathway:
water moves from cell to cell via aquaporins in the plasma membrane; aquaporin gene function is regulated by environmental stimuli
root conductivity:
permeability of the root to water; ease with which water can flow from soil to xylem; changes with conditions by using different pathways, (high resistance apoplastic pathway is only used under high shoot demand for water)
Nitrate (NO3-)
the main source of nitrogen in the soil for most plants
nitrogen fixing bacteria:
form symbiotic relationships with plants like legumes
location of nitrate assimilation:
herbaceous plants: primarily leaves
trees and shrubs: roots
location of assimilation in a single plant is often determined by nitrate availability; nitrate plentiful-leaves nitrate limited-roots
nitrate transporters:
facilitate transfer of nitrate from soil to epidermal and cortical root cells
elements required for growth (in addition to carbon, hydrogen, oxygen, nitrogen)
13 of them:
Macronutrients: potassium, calcium, magnesium, phosphorus, sulfur
Micronutrients: chlorine, iron, manganese, boron, zinc, copper, molybdenum, nickel
Macronutrients and their functions:
Nitrogen: amino acid, nucleotide, N-containing compound
Potassium: osmotic and ionic balance in cells; activator of enzymes in respiration and photosynthesis
Calcium: intracellular signal transduction; formation with pectin in cell wall
Magnesium: component of chlorophyll; activator of enzymes
Phosphorus: ATP and phosphorylation reactions
Sulphur: sulphur containing compounds (methionine)
meristems:
responsible for development of all plant organs after germination
plant development stimuli:
temperature, day length, light, gravity, availability of water and nutrients
growth regulators or phytohormones:
small signalling molecules responsible for mediation of response to surroundings
dormancy:
an adaptive trait that ensures germination occurs at times and in environments likely to be favourable to plant growth; selected against in crop domestication
far-red light
sunlight that has passed through vegetation is rich in far-red light; an indicator of shading for plants
germination and dormancy controls:
light, temperature, hydration, niche characteristics (such as heat and smoke of wildfires), host plant signals for parasites,
photoreceptor:
convert physical energy of light to chemical energy; perceive light quality, quantity, duration, direction
skotomorphogenesis:
developmental pathway of plants grown in the dark
etiolation:
occurs when a plant is grown in the dark; embryonic stems become long and spindly, seedling is pale yellow or white due to lack of chloroplast formation, apical hook remains, cotyledons remain unexpanded, shoot apical meristem is inactive
photomorphogenesis:
developmental pathway of plants grown in sunlight; short embryonic stems, no apical hook, green expanded cotyledons, leaf and internode development at shoot apical meristem
de-etiolation:
process of switching from skotomorphogenesis to photomorphogenesis after emerging from soil and becoming exposed to light
phytochrome:
a family of photoreceptors which respond especially to red and far-red light; a developmental switch that is controlled by sensitivities to red and far red light. red induces growth responses and far red inhibits them. ex. lettuce seed germination
crypto chromes:
detect and mediate responses to light in the blue and ultraviolet regions
phototropins:
responsible for blue light activated phototropism and mediate the photoreceptor of blue light in guard cells controlling the blue light induced opening of stomata
chromophore:
attached to an apoprotein to make a phytochrome; captures a light signal and undergoes isomerization causing a conformational change in the protein and a different gene expression
apoprotein:
the polypeptide chain attached to the chromophore to constitute a phytochrome
PIF3
phytochrome that has been activated by absorption of light in the cytoplasm enters the nucleus and interacts with PIF3 to alter the regulation of gene transcription
shade avoidance response:
plants ability to detect shade cast by other plants and to alter growth accordingly by investing more resources into the elongation of stems and less into the expansion of leaves
phytochrome B
major phytochrome involved in mediating shade avoidance and end of day responses as inferred from lab tests
phototropism:
directional growth of plants toward a light source
PHOT1 gene:
encodes the blue light photoreceptor phototropin1 which contains a serine/threonine kinase domain called a LOV domain (Light, Oxygen, Voltage)
FMN
flavin mononucleotide; the chromophore attached to LOV to make a phot1 protein
chloroplast migration:
chloroplast migrate in response to changes in light intensity, at low light intensities chloroplast distribute to maximize exposure but at high light intensities they position to minimize exposure and thereby photodamage
triple response:
response to protect delicate structures such as shoot apical meristem when forcing through soil; hypocotyls become shorter and thicker, roots become shorter and thicker, apical hook becomes exaggerated; triggered by interaction between ABA and ethylene
ETR1:
ethylene receptor; etr1 mutants don’t exhibit a triple response
ethylene receptors:
Negatively regulate: ethylene receptors inhibit ethylene responses until ethylene binds to them at which point inhibition stops and the signalling cascade proceeds unimpeded
ETR1
Ethylene triple response 1 gene
CTR1
Constitutive triple response 1 gene; a kinase
Kinase
enzyme that catalyzes transfer of a phosphate group from ATP to another molecule
EIN2
integral membrane protein; downstream of CTR1 in the signal transduction pathway of ethylene
EIN3
regulator of ethylene response; transcription factor that binds to the promoter region of ethylene-inducible genes in the presence of ethylene
ABA
abscisic acid; represses germination
embryo dormancy:
independent from seed dormancy, controlled by growth regulators (phytohormones) GA and ABA which act antagonistically
GA
gibberellin; initiates germination
radicle
embryonic root
testa
seed coat
water deficit:
occurs as a result of drought, salinity, freezing temperatures
