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. 11-9b, p. 170

MINERAL UPTAKE AND TRANSPORT

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

Table 11-1, p. 171

Needed in large amounts

Needed in small amounts

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……

Table 11-1, p. 171

Needed in large amounts

Needed in small amounts

?

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. 11-12, p. 177

Active Uptake of Minerals Into Root Cells

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

PHLOEM TRANSPORT

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.