Plant Physiology
I.
Plant Organization
a. CC levels of organization
II.
Tissue Systems
a. CC systems
b. SEQ, CC water, sugar transport
III.
Plant Growth
a. CC types of plant growth
IV.
Plant Hormones
a. CC plant hormones
--------------------------------------------------------------------------------------------------------------------I.
II.
Plant Organization
a. 2 systems
i. Root system- below ground
ii. Shoot system- above ground
iii. Stems, leaves, flower, fruit
b. Hierarchical Organization
i. Cells- basic functional unit
ii. Tissues: group of cells that work in a coordinated way
iii. Tissue systems- 3 in plants
iv. Organs- contain all 3 tissue system
1. Roots
a. Anchor plant to ground
b. Absorb minerals and water
c. Store carbohydrates (and other reserves) storage roots
d. Root hairs: thin, finger- like extensions of root epidermal
cells
i. Primarily near tip of elongated roots
ii. Function: Increase surface area
2. Stems:
a. Plant organs bearing leaves and buds
b. Elongate and orient shoot to maximize photosynthesis
c. Elevate reproductive structures- increase pollen and seed
dispersal
d. Green stems- limited photosynthesis
3. Leaves:
a. Main photosynthetic organ in vascular plants
b. Capture light, gas exchange
Tissue Systems: Each organ consists of all 3 systems. Continuous throughout plant
a. Dermal Tissue System
i. Outer protective covering
ii. 1st line of defense against physical damage, pathogens
iii. Nonwoody plants
1. Epidermis: Single layer of tightly packed cells
2. Cuticle: waxy coating- helps prevent water loss
iv. Wood plants- periderm (bark) replaces epidermis
v. Dermal tissue functions:
1. Absorption of water, minerals at root hairs
2. Reduce water loss, reflect sunlight, defend against insects
3. Guard cells- specialized cells in shoots- gas exchange
b. Ground tissue system
i. Most of plant
ii. Includes cells specialized for:
1. Storage
2. Photosynthesis
3. Support
4. Short distance transport
c. Vascular Tissue System
i. Transport materials throughout plant body
ii. Mechanical support
iii. 2 types of vascular systems
1. Xylem: conducts H2O dissolved minerals upward from roots
a. 1.) soil
b. 2.) root tissue
c. 3.) root xylem
d. 4.) stem xylem
e. 5.) leaf xylem
f. 6.) leaf mesophyll
g. 7.) stomata
h. 8.) atmosphere
2. Phloem: Transport sugars from where made (mostly leaves) to
where needed (usually roots and sites of growth)
3. Cohesion- tension hypothesis (xylem)
a. During photosynthesis, stomata open, H2O leaves leaves
i. Transpiration
b. Creates tension- like soda straw
i. H2O in root xylem pulled into stem
ii. H2O in root xylem pulled into stem
4. Phloem conducts dissolved sugar
a. Bidirectional movement- translocation
b. Source: area with excess sugar
c. Sink: area of storage or metabolism
d. Moves source  sink
e. Made in leaves  stored in roots
f. Stored in roots  throughout plant for growth,
maintenance
5. Pressure- Flow hypothesis (phloem)
6.
III.
IV.
a. Explanation for movements of sugars in phloem
b. Suggests translocation occurs via pressure gradient
c. At source- high pressure- sugar loaded in phloem
d. At sink- low pressure- sugar removed from phloem
Plasmodesmata
a. Cytoplasmis connections
b. Allows molecules, ions to pass between cells
c. Important in plants, we’ll see similar connections in
animals
Plant Growth
a. Indeterminate growth
i. Occurs throughout life of plant
ii. Continuous except for dormant periods
iii. Keep growing due to perpetually dividing, unspecialized tissue
iv. Growth at meristems
b. 1ogrowth: increase length by adding more cells
i. All plants have 1o growth
c. 2o growth: increase girth (circumference) of plant
i. Only woody plants have secondary growth
Plant Hormones
a. Introduction to plant hormones
i. Organic compounds- chemical messengers
ii. Control specific physiological responses in plants
iii. Also known as plant growth regulators
iv. General characteristics
1. Active at very low concentrations
2. Can have multiple effects
3. Interact- hard to tell cause of a specific effect
4. Natural or synthetic
v. Tropisms:
1. Directional growth response to environmental stimulus often due
to hormones
vi. Directional
1. Positive- grows towards stimulus
2. Negative- grows away from stimulus
3. Ex: phototropism – in response to light
b. Auxins
i. 1st plant hormone discovered- directional growth towards light
ii. Darwin’s experiments
1. Involved phototropism:
2. Coloeoptile: 1st part of grass seeding to emerge from soil
3. When exposed to light from one direction
a. Bends towards light
4. Phototropism experiments
a. Shielded or removed tip  no bending
b. Shield with transparent cap  bending
c. Shield below tip  bending
d. Conclusion: Coleoptile tip responsible for light sensing
e. Postulated: signal transmitted from tip to elongating region
iii. Boysen- Jensen experiment
1. Dutch botanist, 1913
2. Separated tip from rest of coleoptile with gelatin cube- bending
3. Separated with mica (impermeable) no bending
iv. Auxins
1. Group of natural artificial hormones (many synthetic)
2. Main site of production- shoot apical meristem
3. Transport is polar- unidirectional, shoot  root
4. Triggers cell elongation
5. Acid growth hypothesis
v. Phototropism explained
1. Light exposure  auxin produced moves laterally to shaded
side, down stem
a. Shade side elongates
2.  plant bends towards light
vi. Practical applications
1. Herbicides
a. Synethic auxins- 2,4 D, 2,4,5-T
b. Agent Orange- 50/50 mix
2. Fruit development
a. Can be sprayed to induce fruit development
b. Used in green houses
c. Cytokinins
i. Control of cell division and differentiation
ii. Produced in actively growing tissue
1. Roots, embryos, fruit
iii. Stimulate cytokinesis (where they got their name)
iv. Act with Auxin
1. Experiment- cultured ground tissue
2. Cytokinin does not produce cytokinin on its own
3. Cytokinin + auxin  cytokinin
d. Abscisic Acid (ABA)
i. Name is misnomer- not related to abscission (falling of leaves)
ii. Seed dormancy- cannot germinate until washed out
iii. Increases likelihood that seed only germinates under suitable conditionslots of water in spring- adaptation
e. Ethylene (C2H4)
i. Unique among plant hormones
ii. Triple response to mechanical stress
1. Behavior to avoid obstacles
2. Produced when growing shoot encounters obstacle
iii. 3 components of triple response
1. Slow elongation
2. thicken stem
3. Curve, grow horizontally