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TA: Zara Tabi (ztabi@ucsd.edu)AIM: ztabi06 OH: By email Appt.

BICD 120: Dr. CrawfordWeek 7

Plant Nutrition

-Nutrients essential for life Found dissolved in the soil solution and taken up bythe roots

The Macronutrients: S(SO42-), P(PO43-),N(NO3-, NH4+),

K, Mg, Ca, Fe SPaNKMyCaFe!

The Micronutrients: B, Cu, Mo, Mn, etc.

Root Structure

Matching:(1) Root Meristem- Site of cell division(2) Root Cap- Protects root meristemfrom damage(3) Epidermis- Outermost layer of a root

- Reponsible for H2O absorbtion(4) Root Hairs- Projections fromepidermal cells

- Increased surface area for H2O

(5) Cortex- Middle layer of root- Can consist of one or many layers

depending onthe plant

(6) Endodermis- Surrounds vasculartissue(7) Casparian Strip- Layer of endodermisimpermeable by Ions and H2O

(8) Stele- Region of vascular tissue(xylem, phloem)

Nutrient Uptake- Ions can travel 2 ways through a root:

1) Symplasm- System of cytoplasm connected viaplasmodesmata

2) Apoplasm- System of cell walls- Cannot reach the stele of a root through apoplasmictransport

Casparian strip of the endodermis acts as a block- Ions eventually need to cross a plasma membrane toenter the symplasm

Active transport Needs ATP!- Uses ATPase & Co-transporter

Can bypass the Casparian strip by plasmodesmata

mailto:ztabi@ucsd.edumailto:ztabi@ucsd.edu

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Transpiration: How H2O & Salts travel from roots to shoots

- H2O evaporation from the stomata pulls water up shoot Pulling/Tension Force- H-Bonding between water molecules allows H2O column to stay in

tact Cohesion

-Controlled by the opening & closing of stomates!

When open, allows CO2 in (for Photosynthesis) and H2O out

Photosynthate Transport: Occurs through the phloem and can bemultidirectional; Primarily SuccroseSource: Where photosynthate isproduced or stored

Sink: Where photosynthate is needed

Mature Leaves

Storage Organs Cotyldons

Leaves (in

Summer) Roots (in Spring)

Young Leaves

Fruits Flowers

Seeds

Roots (in

Summer)Leaves (in Spring)

- Osmotic Pressure Flow Theory- Use of osmotic pressure, based on sucrose [ ], totransport

Nitrogen Fixation: The conversion of N2 into a usable form (NH4) SymbioticRelationship

- Key Enzyme: Nitrogenase Provided by the Bacteria (Rhizobium)

Energy Intensive process Needs ATP

Needs Fe & Mo Sensitive toO2

} Energy and Proper environmentsupplied by plant!

The Steps:1) Plants release compounds to attractbacteria

- Nod genes in bacteria are activatedto synthesize

nitrogenase

2) Bacteria attach to roots, causing roothair to curl.

-Open: Light,Low O2

-Close: Dark, High Temp, High CO2,Low H2O (ABA)

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3) Bacteria enter the plant via an infectionthread

- Bacteria is protected from plantdefense systems

4) New plant meristem formation- Site of future nodule

5) Bacteria terminally differentiate tobacteroids

- Can NO LONGER DIVIDE

6) Nodule formation is complete

Plant Pathology and Defense- Plant EpidemicsResult in a large amount of crop lost

Ex. Great Potato Blight (Phytoptera), SD Citrus Quarantine (Psylid)

Chance of epidemic is greater with monoculturing use of one variety overa large area

- Plant Stresses: Can be Abiotic or Biotic understand the difference between thetwo and know examples!

- Methods of biotic attack:

Herbivoryeating of plant tissue Performed by insects and animals

Cell Infectiongain acess to cytoplasm Microbes (bacteria, fungi, etc.)

-Plants vs. PredatorsPlant DefenseHow do they protectthemselves?

Microbe AttackHow do they get pastthese defenses?

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1) Physical Defense- Protect entry intocytoplasm

Ex. Bark, Wax cuticle, cell wall

2) Chemical Defense

Proteins: Lectins (fungi, bacteria) orprotease

inhibitors (insects, animals)

Organics: Secondary metabolites- Phenolics, Tanins, Alkaloids- Phytoalexins- similar to

antibiotics

Most toxins are PATHOGEN SPECIFIC- If a general toxin, can be stored

safely invacuole, cell wall, or specialized

structures until

needed

1) Oppurtunistic- Infect at wound sitesalready present (due to herbivory,pruning, etc.)

2) Brute Force- The breaking down ofprotective layers with enzymes or toxins

Enzymes are HOST SPECIFIC:

Hydrolases- Break down cell wall

Toxins: Small organics,phytohormones (auxin, cytokinin,gibberellin)

3) Specialized mechanisms: can differbetween different microbes

Ex. Entrance through naturalopenings (stomates)

- Specific Case: Herbivory Defense in Potato

When attacked, protease inhibitors (PIs) are released,disrupting

digestion in the herbivores stomach- Simple wounding induces this effect

Leaf-to-leaf communication is possible

Signal molecule systemin (protein)- Transported through the phloem

Plant-to-Plant communication also possible Signal molecule methyl jasmonate (volatile)

- Only wounded plants can produce signal