Fig. 11-1, p. 164

1
H2O vapor
product of photosynthesis (sucrose)
H2O vapor
H2O vapor
H2O
mineral ions
H2O
Fig. 11-1, p. 164
2
Symplastic and apoplastic flow through roots
root hair
plasmodesma
xylem
symplastic flow
apoplastic flow
cell wall
symplast of endodermis
Casparian strip of endodermis
cytoplasm
cortex
stele
epidermis
Fig. 11-7, p. 169
3
Control of Water Flow

• Environmental factors affecting rate of
  transpiration
• Temperature
• Relative humidity of bulk air
• Wind speed

4
Control of Water Flow

• Transpiration
• Slow at night
• Increases after sun comes up
• Peaks middle of day
• Decreases to night level over afternoon
• Rate of transpiration directly related to
  intensity of light on leaves

5
LIGHT
Events leading to the opening of a stoma The
production of malate and the influx of K and Cl-
powered by the electrical and pH gradients
produced by the proton pump increase the
concentration of osmotically active solutes in
the guard cells. As a result, water flows into
the cells by osmosis.
starch
malic acid
malate
plasma membrane
ATP
H
proton pump
ADP Pi
??
H
K

CI??
K
H
CI??
Fig. 11-8a, p. 170
6
cells connected
cellulose microfibrils (radial micellation)
reinforced inner wall
How radial micellation and reinforcement of guard
cell walls force an expanding cell to bow outward.
With increased pressure, cell gets longer.
Because the outer wall can expand more readily,
cell bows outward.
Fig. 11-9a, p. 170
7
Fig. 11-9b, p. 170
8
MINERAL UPTAKE AND TRANSPORT
9
H2O vapor
product of photosynthesis (sucrose)
H2O vapor
H2O vapor
H2O
mineral ions
H2O
Fig. 11-1, p. 164
10
- P
- K
Effects of suboptimal concentrations of mineral
elements on plant growth
- N
- Mg
- S
Fig. 11-10 (a-f), p. 173
11
Needed in large amounts
Needed in small amounts
Table 11-1, p. 171
12
Soil Formation
atmospheric gases CO2 SO2 N2O5
rock
rain
acids H2CO3 H2SO3 HNO3
wind and water erode rocks and soil
freeze-thaw produces cracks
roots crack rocks through pressure, secrete acid
Fig. 11-11, p. 175
13
Soil Formation

• Lichens and small plants start to grow on this
  soil solution
• Rhizoids and roots enlarge fissures in rocks
  through turgor pressure and emit respiratory CO2,
  which forms H2CO3, and thus more acid

• Accelerated soil formation leading to invasion of
  larger plants species
• Larger roots and more respiratory CO2 , and so
  on

14
?
Needed in large amounts
Needed in small amounts
Table 11-1, p. 171
15
Nitrogen Fixation and Symbiosis

• Clover root with root nodules that contain the
  nitrogen fixing bacterium Rhizobium.
• Leguminous plants (pea, bean,) benefit from the
  nitrogen-fixing association while supplying the
  bacterial symbiont with photosynthetic products
  (can be up to 20 of total photosynthesis
  performed by the plant).

16
Nitrogen

• Nitrogen predominantly exists as N2 gas in the
  atmosphere. Is not directly available to plants.
• Nitrogen becomes available after soil bacteria
  turn it into NH4 or NO3-. This is called
  nitrogen fixation.
• However, fixed nitrogen is not stably present in
  soil
• - NH4 (in equilibrium with NH3) is volatile.
• - NO3- is very water soluble and easily leached
  from the soil.
• Treatment with fertilizers that contain NH4 or
  NO3- is very effective in increasing crop yields,
  since it supplements the soil with an invariably
  scarce mineral element.

17
Fertilizer use and food production

• NH3 in water solution exists as NH4.
• NH3 is made industrially by the Haber-Bosch
  process
• N2(g) 3H2(g) --------gt 2NH3
• H2 is made from light petroleum fractions or
  natural gas
• CH4 H2O(g) --------gt CO(g) 3H2(g)
• Energy is needed to make H2 as well as to make
  NH3from H2 and N2.

Heat pressure
700 0C
18
Mineral uptake
H2O vapor
product of photosynthesis (sucrose)
H2O vapor
H2O vapor
H2O
mineral ions
H2O
Fig. 11-1, p. 164
19
Maintenance of Mineral Supply

• All plant cells require minerals
• Especially meristematic regions
• Four processes replenish mineral supply
• Bulk flow of water in response to transpiration
• Diffusion
• Active Uptake (requiring ATP)
• Growth
• As root grows, comes in contact with new soil
  region and new supply of ions

PASSIVE
ACTIVE
20
Minerals can passively follow water flow until
the endodermis. From there on, active uptake is
needed.
root hair
plasmodesma
xylem
symplastic flow
apoplastic flow
cell wall
symplast of endodermis
Casparian strip of endodermis
cytoplasm
cortex
stele
epidermis
Fig. 11-7, p. 169
21
Active Uptake of Minerals Into Root Cells
22
After passing the endodermal cell membrane(s),
nutrients move into the vascular system to be
transported throughout the plant.
root hair
plasmodesma
xylem
Symplastic flow
Apoplastic flow
cell wall
symplast of endodermis
Casparian strip of endodermis
cytoplasm
cortex
stele
epidermis
Fig. 11-7, p. 169
23
Root pressure is generated by an osmotic pump

• After passing the endodermis, mineral nutrients
  accumulate in the stele of the root. The
  endodermal cells provide the differentially
  permeable membrane needed for osmosis.
• Soil saturated with water
• Water tends to enter root and stele
• Builds up root pressure in xylem
• Forces xylem sap up into shoot

Fig. 11-13a, p. 178
24

• Guttation water forced out of hydathodes
• by root pressure

Guttation on a California poppy leaf
Fig. 11-13b, p. 178
25
PHLOEM TRANSPORT
26
Phloem transport
H2O vapor
product of photosynthesis (sucrose)
H2O vapor
H2O vapor
H2O
mineral ions
H2O
Fig. 11-1, p. 164
27
Mechanism of Phloem Transport
high pressure
low pressure
sieve tube
sucrose
sucrose
H2O
H2O
sucrose
sucrose
H2O
H2O
glucose
source
sink
H2O
glucose
CO2 H2O
sucrose
H2O
parenchyma
parenchyma
Fig. 11-14, p. 179
Sucrose is actively transported into the sieve
tubes at the food source region of the plant
(leaves or storage organs) and removed at the
sink regions (regions of growth or storage).
Water follows by osmosis, increasing the
hydrostatic pressure in the sieve tubes at the
source region and decreasing the pressure at the
sink region. The sieve-tube contents flow en
masse from high(source)- to low(sink)-pressure
regions.
28
Phloem Transport

• Concentration gradient maintained by
• Continual pumping of sucrose at source
• Removal of sucrose at the sink

• Sink or source behavior of cells is controlled by
  cell signaling mechanisms (developmental and
  hormonal controls, see lectures on hormone
  regulation).
• Change in signaling can abruptly switch a cell or
  tissue from source to sink behavior.