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Center of meristem Figure 37.12 Figure 40.11 Gravity Sensing Occurs in the Root Cap. 2

Cell in root tip (or shoot) Gravity Figure 37.13 Cell in root tip (or shoot) Gravity Amyloplasts are pulled to bottom of cells by gravity Figure 40.12 The Statolith Hypothesis States that Amyloplasts Stimulate Sensory Cells. Activated pressure receptors 3

1. Normal distribution of auxin. Gravity Figure 37.14 Auxin distribution 1. Normal distribution of auxin. Gravity 2. Root tip rotated. Auxin 3. Auxin is redistributed, move to bottom. Figure 40.13 The Auxin Redistribution Hypothesis for Gravitropism. 4. Root bends. 4

(a) Shoots bend toward full-spectrum light. Figure 37.3a (a) Shoots bend toward full-spectrum light. Figure 40.3a Experimental Evidence that Plants Sense Specific Wavelengths of Light. 5

(b) Shoots bend specifically toward blue light. Figure 37.3b (b) Shoots bend specifically toward blue light. Figure 40.3b Experimental Evidence that Plants Sense Specific Wavelengths of Light. 6

Figure 37.5 Light is not sensed at the tip of the coleoptile. Light is sensed at the tip of a coleoptile. Where is light sensed to initiate phototropism in grass seedlings? Light Light responsible for triggering phototropism is sensed at the coleoptile tip. Control: Bends toward light Tip removed: No bending Tip covered: No bending Lower portion of coleoptile covered: Bends toward light 1. Cells at coleoptile tip sense light. 2. Hormone travels from tip down the coleoptile. 3. Cells lower in coleoptile respond to hormone. Bending results. Light (stimulus) Sensing tissue Hormonal signal Responding tissue This interpretation explains the hormone concept, but does not explain differential growth on the lighted and shaded sides of the coleoptile… Based on what you know about gravitropism, give a parsimonious (i.e. parallel) interpretation. Figure 40.5 The Sensory and Response Cells Involved in Phototropism Are Not the Same. 7

Biology: What is Life? life study of Properties of Life Cellular Structure: the unit of life, one or many Metabolism: photosynthesis, respiration, fermentation, digestion, gas exchange, secretion, excretion, circulation--processing materials and energy Growth: cell enlargement, cell number Movement: intracellular, movement, locomotion Reproduction: avoid extinction at death Behavior: short term response to stimuli Evolution: long term adaptation

Obtaining Food Autotrophs use ambient energy and carbon dioxide to make their own organic molecules. So the only matter they need to take up is minerals! Sadly they are sometimes called “plant food.”

Johann Baptista van Helmont 1577-1644 Physician Scientist In 1648 experiment with Salix (willow) he tested whether the bulk of a plant comes from the soil or from some other source. His experiment was carefully documented but, because he was so far ahead of his time, his conclusion was wrong. Interestingly, however, his results suggest that plants do use soil minerals for growth. In the light of knowledge of carbon dioxide gas, the project shows that the plant grows mostly from air. http://upload.wikimedia.org/wikipedia/commons/1/1d/Jan_Baptist_van_Helmont.jpg

sunlight H2O 200 lbs soil 200 lbs - 2 oz soil 169 lbs + 3 oz sapling Adapted from: Figure 36.1 Because the role of air was not understood yet, van Helmont concluded that the weight increase was due only to water…WRONG. Even if the plant is 90% water, the 10% dry weight (16.9 lbs) would have to come from somewhere. sunlight 169 lbs + 3 oz sapling Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley H2O 5 lbs branch 200 lbs soil 200 lbs - 2 oz soil

sunlight CO2 O2 H2O CH2O 200 lbs soil 200 lbs - 2 oz soil Adapted from: Figure 36.1 Because the role of air was not understood yet, van Helmont concluded that the weight increase was due only to water…WRONG. Even if the plant is 90% water, the 10% dry weight (16.9 lbs) would have to come from somewhere. Could it be minerals from the soil? sunlight 169 lbs + 3 oz sapling CO2 O2 Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley H2O 5 lbs branch CH2O 200 lbs soil 200 lbs - 2 oz soil This decrease could be sample error, or minerals taken from the soil by the growing plant.

Autotrophic Organisms Typically autotrophs carry out photosynthesis: CO2 + H2O O2 + CH2O As you can see, the plant needs NO food. But the enzymes and ion transporters for photosynthesis require metal cofactors: The essential macroelements are: CHOPKNS CaFe Mg The essential microelements are: CuMn CoZn Si Mo B Al Cl light chlorophyll “C. Hopkins Café Mmm, good!” “CoMe on, Cousin, See Mike over By Al and Cleo”

Essential “macroelements” for plants Requirement Functions N (nitrogen) 21 g/m3 Amino acids, nitrogenous bases, vitamins P (phosphorus) 5 Nucleic acids, phospholipids, ATP, enzyme cofactor K (potassium) 16 Ion balance, enzyme cofactor S (sulfur) 10 Cysteine and methionine, vitamins Mg (magnesium) 7 Chlorophyll cofactor, enzyme cofactor Ca (calcium) Membrane permeability, pectin glue, enzyme cofactor Fe (iron) 0.3 Cytochrome cofactor, enzyme cofactor “Plant Food” has N-P-K analysis = %N-%P-%K

Essential “microelements” for plants Requirement Functions Mn (manganese) 0.04 g/m3 Enzyme cofactor B (boron) 0.008 Enzyme cofactor, pollen tube attraction Cl (chlorine) Ion balance, cofactor Zn (zinc) trace Enzyme cofactor, hormone synthesis, DNA binding protein cofactor Cu (copper) Enzyme cofactor (polyphenol oxidase), plastocyanin cofactor Mo (molybdenum) Cofactor for nitrate reductase, nitrogen reductase (N2 fixation) Ni (nickel) Cofactor for urease (for uptake of organic N source)

Macroelements Microelements http://www.elementsdatabase.com/Images/periodic_table.gif

Compare: Figure 36.9 Radish seedlings have roots with long root hairs that increase the surface area for water and mineral uptake ©1996 Norton Presentation Maker, W. W. Norton & Company

Selective mineral uptake and conduction Compare: Figure 35.6 Dicot Mature Root Structure - Anatomy Ranunculus acris - buttercup Epidermis Make root hairs for cation exchange Cortex Storage of starch Vascular Cylinder Selective mineral uptake and conduction

Root Vascular Cylinder and Cortex Compare: Figure 35.6 Ranunculus acris - buttercup Endodermis Selective mineral uptake via these “window cells” Storage of Starch, etc. Sieve Tube Cell conducts organic molecules Cortex Companion Cell keeps the sieve tube cell alive! Phloem Xylem Conducts minerals and water up to shoot system Divides to make branch roots Pericycle

This passive movement obeys the 2nd Law of Thermodynamics! Osmosis: passive movement of water from pure to saltier area Read: Chapter 35.1 cell membrane cell wall Virtually not; the bilayer is impermeable to solutes, and transport proteins keep solutes concentrated in the cell Do solutes cross the membrane? 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!

to endodermis and vascular cylinder then up the xylem to the shoot Root hairs are responsible for cation exchange cortex cell root hair penetrates soil spaces epidermal cell soil particles covered with capillary water and minerals intercellular gas space Ca2+ Ca2+ H+ Ca2+ H+ to endodermis and vascular cylinder then up the xylem to the shoot voids with air space water Compare: Fig. 36.8

Root Vascular Cylinder and Cortex Ranunculus acris - buttercup Endodermis Selective mineral uptake via these “window cells” Storage of Starch, etc. Sieve Tube Cell conducts organic molecules Cortex Companion Cell keeps the sieve tube cell alive! Phloem Xylem Conducts minerals and water up to shoot system Divides to make branch roots Pericycle

The endodermis is thus responsible for selective mineral uptake. Compare: Figure 35.7 endodermis xylem inside cortex outside minerals cannot go between cells The endodermis is thus responsible for selective mineral uptake. minerals must go through cells cell membrane proteins (active transporters) determine which minerals may be taken up suberin- waxy barrier to apoplastic movement Important?: All human minerals in food come via this path!

Mineral uptake: Active transport against concentration gradient cell membrane cell wall too expensive? Calcium transport protein ADP + Pi Ca2+ Ca2+ Ca2+ ATP Possible solute diffusion gradient water flow cytoplasmic solutes more concentrated soil solutes more dilute Water potential low Water potential high Osmosis: passive movement of water from pure to salty area

This is a cross-section of a “typical” leaf: Syringa vulgaris (lilac) soil mineral entry evaporative cooling means the solute concentration increases!

Solute availability is pH dependent iron nitrogen molybdenum Element Concentration 4 acidic 7 neutral alkaline 10 pH of soil water The optimal pH?

©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…

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 ©1996 Norton Presentation Maker, W. W. Norton & Company Soil pH is less than 4

Drosera (sundew) uses sticky pads that look like nectaries but are actually glandular hairs secreting botanical “super glue” with digestive enzymes: 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