Fig. 11-1, p. 164 H2OH2O product of photosynthesis (sucrose) H 2 O vapor H2OH2O mineral ions

Fig. 11-7, p. 169 plasmodesma symplastic flow apoplastic flow cell wall cytoplasm xylem epidermis cortex stele Casparian strip of endodermis symplast of endodermis root hair 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 plasma membrane proton pump starch malic acid malate– ATP ADP + Pi K+K+ K+K+ H+H+ H+H+ 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+H+

Fig. 11-9a, p. 170 cells connected With increased pressure, cell gets longer. Because the outer wall can expand more readily, cell bows outward. 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 H2OH2O product of photosynthesis (sucrose) H 2 O vapor H2OH2O mineral ions

Fig (a-f), p 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 , p. 175 roots: crack rocks through pressure, secrete acid atmospheric gases: CO 2 SO 2 N 2 O 5 acids: H 2 CO 3 H 2 SO 3 HNO 3 rock rain freeze-thaw produces cracks wind and water erode rocks and soil 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 CO 2, which forms H 2 CO 3, and thus more acid…… Accelerated soil formation leading to invasion of larger plants species: –Larger roots and more respiratory CO 2, 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 N 2 gas in the atmosphere. Is not directly available to plants. Nitrogen becomes available after soil bacteria turn it into NH 4 + or NO 3 -. This is called nitrogen fixation. However, fixed nitrogen is not stably present in soil: - NH 4 + (in equilibrium with NH 3 ) is volatile. - NO 3 - is very water soluble and easily leached from the soil. Treatment with fertilizers that contain NH 4 + or NO 3 - is very effective in increasing crop yields, since it supplements the soil with an invariably scarce mineral element.

Fertilizer use and food production NH 3 in water solution exists as NH 4 +. NH 3 is made industrially by the Haber-Bosch process: N 2 (g) + 3H 2 (g) > 2NH 3 H 2 is made from light petroleum fractions or natural gas: CH 4 + H 2 O(g) > CO(g) + 3H 2 (g) Energy is needed to make H 2 as well as to make NH 3 from H 2 and N 2. Heat pressure C

Fig. 11-1, p. 164 H2OH2O product of photosynthesis (sucrose) H 2 O vapor H2OH2O 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 strip of endodermis symplast of endodermis root hair Minerals can passively follow water flow until the endodermis. From there on, active uptake is needed.

Fig , 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 strip of endodermis symplast of endodermis root hair After passing the endodermal cell membrane(s), nutrients move into the vascular system to be transported throughout the plant.

Fig a, 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 b, p. 178 Guttation: water forced out of hydathodes by root pressure

PHLOEM TRANSPORT

Fig. 11-1, p. 164 H2OH2O product of photosynthesis (sucrose) H 2 O vapor H2OH2O mineral ions Phloem transport

Fig , p. 179 high pressure low pressure sieve tube sucrose H2OH2O H2OH2O H2OH2O CO 2 + H 2 O glucose parenchyma source sink parenchyma H2OH2O H2OH2O H2OH2O 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.