Transcript Root Structure, Osmosis, Cation Exchange

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©1996 Norton Presentation Maker, W. W. Norton & Company
Radish seedlings have roots with long root hairs that
increase the surface area for water and mineral uptake
Dicot Mature Root Structure - Anatomy
Ranunculus acris - buttercup
Epidermis
Cortex
Storage of
starch
Vascular Cylinder
Selective
mineral
uptake and
conduction
Make root
hairs for
cation
exchange
Root Vascular Cylinder and Cortex
Storage of
Starch, etc.
Cortex
Sieve Tube
Cell
conducts
organic
molecules
Ranunculus acris - buttercup
Endodermis
Companion
Cell keeps
the sieve
tube cell
alive!
Selective
mineral
uptake via
these
“window
cells”
Phloem
Xylem
Conducts
minerals and
water up to
shoot
system
Divides to
make branch
roots
Pericycle
Xylem cells lack cytosol when mature and
functional, and thus are dead. Which human
parts are made of dead cells at maturity?
A. Hair shafts.
B. Finger nails.
C. Epidermal surface
cells.
D. All of these are dead
at maturity.
Osmosis: passive movement of water from pure to saltier area
cell membrane cell wall
Do solutes cross
the membrane?
Virtually not; the
bilayer is impermeable
to solutes, and
transport proteins keep
solutes concentrated
in the cell
water flow
cytoplasmic solutes
more concentrated
soil solutes
more dilute
Water potential low
Water potential high
This passive movement obeys the 2nd Law of Thermodynamics!
Root hairs are responsible for cation exchange
cortex cell
epidermal cell
root hair penetrates soil spaces
intercellular
gas space
Ca2+Ca
H 2+
soil particles
covered with
capillary water
and minerals
+
to
endodermis
and
vascular
cylinder
then up the
xylem to the
shoot
Ca2+
H+
voids with air
space
water
Fig. 39.7-8 pp. 781-2
Root Vascular Cylinder and Cortex
Storage of
Starch, etc.
Cortex
Sieve Tube
Cell
conducts
organic
molecules
Ranunculus acris - buttercup
Endodermis
Companion
Cell keeps
the sieve
tube cell
alive!
Selective
mineral
uptake via
these
“window
cells”
Phloem
Xylem
Conducts
minerals and
water up to
shoot
system
Divides to
make branch
roots
Pericycle
endodermis
xylem inside
The endodermis is
thus responsible for
selective mineral
uptake.
suberinwaxy barrier
to apoplastic
movement
cortex outside
minerals cannot
go between cells
minerals must
go through cells
cell membrane
proteins (active
transporters)
determine which
minerals may be
taken up
Important?: All human minerals in food come via this path!
Mineral uptake: Active transport against concentration gradient
cell membrane cell wall
Calcium
transport
protein
ADP + Pi
Ca2+
too expensive?
Ca2+
Ca2+
ATP
Possible solute diffusion gradient
water flow
cytoplasmic solutes
more concentrated
Water potential low
soil solutes
more dilute
Water potential high
Osmosis: passive movement of water from pure to salty area
Which tissue conducts water and
soil minerals up the plant?
A.
B.
C.
D.
E.
F.
Epidermis.
Cortex.
Endodermis.
Pericycle.
Phloem.
Xylem.
This is a cross-section of a “typical” leaf: Syringa vulgaris (lilac)
soil mineral entry
evaporative cooling means
the solute concentration
increases!
Element Concentration
Solute availability is pH dependent
iron
4 acidic
nitrogen
7 neutral
pH of soil water
The optimal pH?
molybdenum
alkaline 10
Which pH would be optimal
(ideal) for mineral availability?
A.
B.
C.
D.
E.
4.
A little below 7.
7.
A little above 7.
10.
Element Concentration
Solute availability is pH dependent
iron
4 acidic
nitrogen
optimum
7 neutral
pH of soil water
molybdenum
alkaline 10
©1996 Norton Presentation Maker, W. W. Norton & Company
Soil pH is less than 4
Dionaea (Venus’ fly trap) leaves have evolved three trip hairs
on each half-blade, an electrical potential is produced, osmosis
causes the trap to snap shut, This fly is about to touch the
second trip hair…
©1996 Norton Presentation Maker, W. W. Norton & Company
The trap halves have folded together, and the marginal
spines have turned inward…the compound action makes an
effective trap…have you ever tried to catch a fly?
©1996 Norton Presentation Maker, W. W. Norton & Company
Saracennia (pitcher plant) leaves hold water to drown insects
and mine their minerals
Soil pH is less than 4
Remember that
carnivorous plants are
not eating insects for
energy or carbon…
they are mining the
insects for minerals
unavailable from the
acidic bog soil.
©1996 Norton Presentation Maker, W. W. Norton & Company
Drosera (sundew) uses sticky pads that look like nectaries
but are actually glandular hairs secreting botanical “super
glue” with digestive enzymes:
Mycorrhizal fungi assist with nutrient uptake
fungal mycelium
©1996 Norton Presentation Maker, W. W. Norton & Company
root
Can you distinguish
heterocysts and vegetative
cells?
©1996 Norton Presentation Maker, W. W. Norton & Company
Anabaena heterocysts fix nitrogen and support bacterial
growth as amino acids (organic nitrogen) leaks out into the
surrounding water…vegetative cells provide carbohydrate
too.
http://www.interet-general.info/IMG/rhizobium-nodule-1.jpg
Rhizobium needs anaerobic conditions to convert N2 into NH4+.
Legumes produce heme based molecules and have rapid
respiration to eliminate oxygen from root nodules that house the
bacterial
“symbiosis.”
©1996 Norton Presentation Maker, W. W. Norton & Company
Here are legumes with Rhizobium
and without Rhizobium
But shrubs also generally have
some compromise for
uprooting forces…feeder roots
extending laterally.
In shrubs like this tea plant
(Camellia sinensis), the root
system will be more tap root
than fibrous root.
Notice the diameter of this tap
root compared to this man’s
waist!
Tropical soils are
nutrient-poor.
Roots must traverse the surface
for minerals, so roots grow on
the surface (no tap root).
So, to keep this tree standing
upright, the roots grow in
diameter but only in the vertical
dimensions to form ridge
roots…called buttress roots.
These roots inspired gothic
cathedral architects to design
buttress walls.
How do buttress roots work?
Buttress roots inspired
supports for long city walls
and cathedral walls to
prevent collapse.
http://www.oxc.com.hk/raoul_nathalie/gallery/images/04%20Buttress.jpg
http://www.dublincity.ie/dublin/citywalls/buttress.jpg
The foundation is critical!
Prop roots such as these inspired flying buttresses.
Pandanus utilis - screw pine
http://williamcalvin.com/BHM/img/FlyingButtressND.jpg
http://www.contrib.andrew.cmu.edu/~ajm/Pages/Graphics/flyingbuttress.JPG