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
