Post on 30-May-2018
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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
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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