Fig. 11-1, p. 164
H2O
product ofphotosynthesis
(sucrose)
H2O vapor
H2O vapor
H2O vapor
H2O
mineral ions
Fig. 11-7, p. 169
plasmodesma
symplastic flow
apoplastic flow
cell wall
cytoplasm
xylem
epidermis cortex stele
Casparian stripof endodermis
symplastof endodermis
roothair
Symplastic and apoplastic flow through roots
Control of Water Flow
• Environmental factors affecting rate of transpiration– Temperature– Relative humidity of bulk air– Wind speed
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
Fig. 11-8a, p. 170
plasmamembrane
protonpump
starch
malic acid
malate–
ATP
ADP+ Pi
K+
K+
H+
H+
CI
CI
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.
LIGHT
H+
Fig. 11-9a, p. 170
cells connected
With increased pressure, cell getslonger. Because the outer wall canexpand more readily, cell bowsoutward.
reinforced inner wall
cellulose microfibrils(radial micellation)
How radial micellation and reinforcement of guard cell walls force an expanding cell to bow outward.
Fig. 11-1, p. 164
H2O
product ofphotosynthesis
(sucrose)
H2O vapor
H2O vapor
H2O vapor
H2O
mineral ions
Fig. 11-10 (a-f), p. 173
- P - K
- N - S - Mg
Effects of suboptimal concentrations of mineral elements on plant growth
Fig. 11-11, p. 175
roots: crack rocks throughpressure, secrete acid
atmospheric gases: CO2
SO2
N2O5
acids:H2CO3
H2SO3
HNO3
rock
rain
freeze-thawproduces cracks
wind and watererode rocks
and soil
Soil Formation
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……
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).
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.
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) --------> 2NH3
• H2 is made from light petroleum fractions or natural gas:
CH4 + H2O(g) --------> CO(g) + 3H2(g)
• Energy is needed to make H2 as well as to make NH3from H2 and N2.
Heat
pressure
700 0C
Fig. 11-1, p. 164
H2O
product ofphotosynthesis
(sucrose)
H2O vapor
H2O vapor
H2O vapor
H2O
mineral ions
Mineral uptake
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
Fig. 11-7, p. 169
plasmodesma
symplastic flow
apoplastic flow
cell wall
cytoplasm
xylem
epidermis cortex stele
Casparian stripof endodermis
symplastof endodermis
roothair
Minerals can passively follow water flow until the endodermis. From there on, active uptake is needed.
Fig. 11-7, p. 169
plasmodesma
Symplastic flow
Apoplastic flow
cell wall
cytoplasm
xylem
epidermis cortex stele
Casparian stripof endodermis
symplastof endodermis
roothair
After passing the endodermal cell membrane(s), nutrients move into the vascular system to be transported throughout
the plant.
Fig. 11-13a, p. 178
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
Guttation on a California poppy leaf Fig. 11-13b, p. 178
Guttation: water forced out of hydathodes
by root pressure
Fig. 11-1, p. 164
H2O
product ofphotosynthesis
(sucrose)
H2O vapor
H2O vapor
H2O vapor
H2O
mineral ions
Phloem transport
Fig. 11-14, p. 179
highpressure
lowpressuresieve tube
sucroseH2O
sucrose
H2O
H2O
CO2 + H2O
glucose
glucose
parenchyma
source sink
parenchyma
H2O
H2O
H2O
sucrose
sucrose
sucrose
Mechanism of Phloem Transport
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.
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.