Plant Bio 2 Flashcards
What are the Vegetative organs?
Roots, Stems and Leaves
What are modules?
Internode, Leaf and Axillary buds
What are the Reproductive organs?
Flowers and Seeds
what are the Three Tissue systems?
Dermal, Ground and Vascular
Dermal tissue systems
Outer layer of the plant - Epidermal cells and cuticles
Ground tissue systems
Cells which carry out photosynthesis/hold photosynthetic products, supports the plant
Vascular tissue systems
Cells which conduct water and solutes through the plant
Key features of plant organisation
Organs made up from three tissue systems.
Modular construction.
Growth from meristems.
what is the Structure of dicot embryo?
L1 – epidermal cells (protoderm)
L2 – cortical cells (ground meristem)
L3 – vascular tissue (procambium)
what is the model plant used? why is it a good model plant?
Arabidopsis thaliana
Compact plants with a short life cycle, self fertile and has a small genome
what were the two factors that were found during experiments with Arabidopsis thaliana?
There are distinct regions in the embryo that develop independantly
Radial organisation is untouched
what are root apical meristems?
branch roots arise back from root cap
what are root caps?
mechanical protection for meristem – mucigel aids movement and gravity perception
what is the Quiescent zone?
slowly dividing cells – production of new tissues for elongation and regeneration of root cap
how is height added to the plant?
by adding new nodes and elongation of the internodes
which hormones regulate growth?
Auxins, cytokins and gibberellins
why are rosette plants different?
they’re radially symmetrical and growth is intermediate
what are lateral meristems used for?
Lateral meristems are cylindrical and are used for secondary growth, thickening roots and stems
what are the key features of cell enlargement?
Uptake of water into vacuole.
Expansins unlock linkages between cell wall components.
Cell wall can stretch and expand.
what is the equation for water uptake?
Rate of water uptake measured by increase in cell volume over time = LΔΨW = L(ΔΨS + P)
L = hydraulic conductance (property of membrane)
ΔΨW = water potential difference between cell and surroundings (must be negative for net movement).
ΔΨS = gradient in osmotic pressure between cell & surroundings (normally negative).
P = turgor pressure of cell (normally positive)
Higher conductance implies faster water uptake.
what is the equation for plant growth?
RGR = LAR x NAR RGR = Relative growth rate LAR = Leaf area ratio NAR = Net assimilation rate
how do you work out LAR?
LAR = SLA x LMR SLA = specific leaf area LMR = leaf mass ratio
what are the factors affecting growth?
Rate of photosynthesis
Water availability
Nutrition
Genetic factors
how is cell specialisation controlled?
Hormones and external signals (e.g light) changing genetic expression
what is the function of a pavement cell?
Structure and spacing, morphologically unspecialised
what is the function of stomata?
Regulation of water loss and gas exchange, distribution is affected by the environment
what is the function of root hair cells?
Nutrients uptake, increase root surface area, unicellular
what is the function of Trichomes?
Protection from predators via the production of specialised chemicals, physical barriers, reduces transpiration and UV light
what are the two processes of development?
- Unequal cell division
plant cells cannot move relative to one another
-Position effects
differences in exposure to chemical signals or physical influences associated with cell position, stomatal formation involves peptide signal molecules
How is flowering initiated?
- A development switch occurs, where vegetative development is switched to reproductive.
- Meristems stop producing leaves and produce flowers
What external factors effect flowering?
- Age
- Temperature (vernalisation)
- Day length (photoperiod)
- Combination
Give two examples of photoperiodism
-Mutant tobacco (Maryland Mammoth) – tall, large leaves but no flowering in field. In greenhouse, even small plants flowered in winter.
-Soybeans sown over a 3 month period all flower within a
3 week period in September.
What are the types of photoperiodism shown in plants?
- Short-day plants - Henbane - Spring/early summer
- Long-day plants - Maryland Mammoth - late summer/autumn
- Day neutral - Maize/ tomatoes - use age/temp
Where and how is the signal perceived?
- Signal called florigen and is produced by leaves, due to grafting experiments.
- Detached leaves can be induced to flower and can ‘pass on’ the flowering signal when grafted.
Describe the function of phytochrome
- Photoreceptor for red light in plants
- Red light more present in daylight (stimulates flowering in short day plants)
What is phytochrome?
- Photoreceptor for red light in plants
- Soluble protein, ~120 KDa (~1100 AA)
- Has tetrapyrrole chromophore
Why is length of night important for flowering?
-Xanthium strumarium would only flower after a 9H continuous night, which is required for short day plants
What are the three classes of genes involved in flower initiation?
- Flowering time genes – determine when flowers are initiated. Example: FLOWERING LOCUS T (FT) gene codes for florigen protein.
- Floral identity genes – commit meristems to production of floral rather than vegetative structures. Examples: LEAFY (LFY), APETALA1 (AP1).
- Organ-identity genes – control development of floral parts (sepals, petals, stamens, carpels). Mutations cause abnormal flower development.
List the signalling pathway for florigen
- Photoperiodic stimulus at leaf companion cell stablises CO, which acts as a TF
- FT is made and enters sieve tube element through plasmodesmata
- FT is transported through the phloem up to apical bud
- FT combines with FD, and the complex acts as a TF for AP1
- AP1 is made and initiates flowering
List the 4 whorls of a plant
- Stamens
- Carpels
- Petals
- Sepals
Describe the ABC table?
Gene class A B C
Gene name APETALA1 APETALA3 Agamous
APETALA2 PISTILLATA
-Sepals + - -
-Petals + + -
-Stamens - + +
-Carpels - - +
- Loss of B - no stamens or petals
- Loss of C - no carpel or stamens
- A and C antagonistic - inhibit each other
Define endogenous clocks and give two examples of clocks
- Rhythmic leaf and flower movements are quite common in plants
- Linnaeus (1751) - Floral clock
- Jean-Jacques (1729) - Circadian rhythm (24 hr clock)
List 5 things the circadian rhythm controls
- Leaf movements
- Stomatal opening
- Stem growth
- Membrane potential
- Transcription
What three criteria are required for clock controlled rhythms?
- Rhythm persists in absence of external cues
- Rhythm can be reset by external signals (e.g. light)
- No lasting effect of temperature on timing of rhythm
What is a zeitgeber?
-A signal synchronising rhythms, E.g when bean plants are in continuous light, the period increases to 25.7 hrs
Describe the oscillator
- The oscillator is the clock and it contains a lot of negative feedback, mainly between the TOC1 (early evening gene) and the CCA (early morning gene)
- The oscillator produces overt rhythms that activate genes at different times of the day
Describe senescence
-When cells undergo cell death and are dismantled and redistributed
Define Carbon allocation
-The trade-off between growth and persistence
What is the Harvest index ratio?
–Ratio of useable biomass : total biomass
Describe what photo-assimilates are
- Primary compounds that conserve fixed carbons and energy: Sucrose in cytosol and vacuole, Starch in the chloroplast
- Species differ in proportions of starch:sucrose.
- Exported photo-assimilates are transported in phloem, most commonly as sucrose.
What are photo-assimilates used for?
Used for:
- Growth and maintenance of leaf.
- Local storage in leaf.
- Export to other tissues for growth or storage.
How is Sucrose synthesised in the cytosol?
-Triose-P translocator exchanges triose-P for phosphate, which then forms sucrose.
Describe photo-assimilate exportation
- From source to sinks
- Can be used for growth or stored
- Transportation occurs in the phloem, as phloem gridling blocks translocation
Describe the phloem anatomy
- Transportation occurs in the sieve tubes, supported by the companion cells
- Phloem also contains phloem parenchyma cells
- Sieve cells lack nucleus and most organelles
Explain the Pressure flow model
- Sugar loading into sieve element causes osmotic uptake of water from xylem.
- Water pressure forces sap flow through sieve tubes.
- Hydrostatic pressure lowered at sink end as sugar unloaded – pressure difference causes mass flow of solute from source to sink.
- Xylem recycles water from sink to source leaf.
What are the effects of translocation from source to sink?
- Minimal energy is required for translocation
- Direction is from source to sink
- Loading and unloading regulate translocation and partitioning
List the 3 routes of loading
- Symplastic - Passive movements between cells through plasmodesmata requires high conc of sucrose in mesophyll than phloem
- Apoplastic - Active movement of sucrose from mesophyll to companion cells, requires energy
- Polymer-trapping model
List the 3 methods of phloem unloading
- Sucrose moving down a conc gradient in symplast
- Sucrose released into apoplast, then hydrolysed by acid invertase and take up via active transport
- Energy-dependent export into apoplast
Give the equation form sink strength
-Sink strength = Sink size X Sink Activity
List feature of a stomata
- Two guard cells
- Subsidiary cells
- Stomatal cavity
How do stomata vary?
- Shape
- Distrubution - Aligned, Random and clustered
What is the stomatal index?
-Number of stomata in relation to total number of epidermal cells.
What is the function of the stomata?
-Guard cells function as hydraulic values that open and close to limit water loss
How does a stomata open?
- K+ enters guard cells driven by a electrochemical gradient caused by H+ ATPase
- Cl- also enter the cell and both ions are transported into the vacuole
- Malate ppt are used as a counter ion to increase water potenial, therefor water moves into the cell (can also be sucrose)
How do stomata close?
-Movement of Ca2+ into the guard cell leading to k+ efflux and reduction of osmotic pressure
What is a patch clamp?
-A piece of equipment that allows measurement of ions movement in a channel protein
How can pharmacology interfere with the putative processes in guard cells?
- Fusicoccin - stimulates H+ ATPase
- Vanadate and cccp - inhibit H+ ATPase
How can genetics interfere with the putative processes in guard cells?
-ABi, mutant that can never close it’s stomata therefore wilting occurs. Due to ABA being non-functional
List and describe the factors effecting the regulation of stomata
- Internal CO2 conc - high conc will cause stomatal closure, even under high light
- Light - blue light opens stomata, light effects mediated by phytochrome, CAM plants respond differently to blue light
- Water vapour - Hydropassive closure: as a result of direct water loss by evapotranspiration by guard cells. Hydroactive closure: as a result of induced Ca2+ ion influx into guard cells
- Abscisic acid (ABA) - Mediator of stomata water stress, produced in guard cells or surrounding cells
- Circadian control - C3/C4 have stomata open during day, CAM have stomata open during night
Describe the Transpiration ratio and reasons for it
-Water loss and carbon gain - CO2 is a heavier molecule and has to cross more membranes.
Why does stress affect plants so much?
- Plants are immobile and sessile, therefore cannot escape stress and must adjust their physiology.
- Stress is either continuous or chronic
What are the three ways plants can respond to stress?
-Specific or generalistic
-Localised or systemic
-Short-term, Mid-term and long-term
(some environmental signals are intergrated)
Define ‘Resistance’ and ‘Avoidance’
- The plant changes it’s physiology and adapts it’s metabolism to alleviate stress effects
- The plant perceives the stress signal but ignores it and accepts the costs in terms of growth
Describe Water deficit stress effects
- Osmotic imbalances in cell
- Cellular membranes become porous to solutes upon rehydration
- Reduced photosynthesis caused by limited CO2 uptake due to stomatal closure
- Changed root and shoot growth
- Accelerates ‘ageing’
Describe Water deficit stress biochemical responses
- Production of compatible solutes: AA - Proline and betaine, sugar alcohols - sorbitol, pinitol, ononitol and myoinositol
- Increase osmotic force to drive water into the cell
- Production of hydrophilic proteins
Describe Water deficit stress morphological responses
- Rapid stomatal closure to limit evapotranspiration
- Lower stomatal density on new leaves
- Leaf expansion is reduced
- Leaves produce more wax on surface
- Plants show enhanced root extension into soil
- Old leaves are rapidly lost
Describe Water deficit stress adaptations
- Reduced metabolism - only metabolise when water present
- Evasion - short life cycles
- Opportune leaf production - only reproduce leaves when there is sufficient H2O for photosynthesis
- Extended roots - some roots can go as deep as 50M
Describe Water excess stress effects
-Hypoxia and anoxia can occur, cutting a plants respiration and nutrient uptake
Describe Water excess stress metabolic responses
- Reduced metabolism
- Production of alcohol fermenting enzymes to produce ATP from sugar degradation
Describe Water excess stress morphological responses
-Pneumatophores - root extensions in the air used to take up O2. -Aerenchyma - large parenchymatic cells around the vascular system used to transport O2 from the shoots to the roots.
Describe Salt stress effects
- Changes in the soils properties to have less aeration and hydraulic conductance
- Low water potential causing reduced water and nutrient uptake
- Inhibits cellular enzymes inducing cellular toxicity
- Causes ionic imbalances in cellular compartments
List 4 areas where salt stress present
- Costal salinity marshes
- Lakes where evaporation exceeds precipitation
- Excessively irrigated soils
- Groundwater under reduced rainfall
Describe Salt stress physiological responses
- Glycophytes - Plants which are sensitive to salt stress, usually die around 100mM NaCl
- Salt-tolerant non halophytes - Plants that tolerate relatively high salt conc >200mM NaCl
- Halophytes - Plants adapted to salinity and that can resit conc <500mM NaCl
Describe mechanisms used to escape/alleviate Salt stress
- Production of compatible solutes to increase the osmotic force driving water into the cell.
- High ion selectivity, toxic ions are not taken up by the roots.
- These roots have high capacities of ion extrusion that allow the removal of any toxic ions taken up.
- The cell have ion transporters that allow the sequestration of ions in the vacuole.
Describe Salt stress adaptations
- Osmoregulation - produces high levels of proline
- Bladder cells - Mesembryanthemum crystallium has specialised epidermal cells with massive vacuoles called bladder cells, store a lot of salt
- Glands - used to excrete salt onto the surface of the leaf
Describe High temperature effects
- Increased evaporation and induced wilting of the plant
- Increased respiration and photorespiration
- Reduced photosynthesis: enzyme inhibition and excessive membrane fluidity
Describe Low temperature effects
- Reduced metabolism - reduced enzyme activities
- Reduced membrane fluidity and even crystallisation
- Reduced water availability in free form in the cell
- Reduced photosynthesis and growth
Describe High temperature physiological responses (>35)
- Closure of stomata to reduce water loss
- Synthesis of protective proteins like heat shock proteins
- Production of saturated fatty acids to stabilise membranes
Describe Low temperature physiological responses (<15)
- Synthesis of compatible solutes to prevent freezing
- Uptake of ions from soils to decrease the freezing point
- Synthesis of unsaturated fatty acids to stabilise membranes
Describe High temperature adaptations
- Formation of radiation reflective and waxes on the leaves
- Leaf rolling and vertical leaf orientation
- Formation of small thin dissected leaves to maximise heat dissipation
Describe Low temperature adaptations
- Induction of dormancy by change in the photoperiod
- Production of organic phosphates, conversation of starch into soluble sugars
- Accumulation of glycoproteins and LEA proteins
List the toxins which cause Air pollution
- SO2
- NO/NO2
- Peroxyacetyl
- CO
- O3
- Heavy metals
Describe Air pollution effects
- Inhibition of stomatal movement
- Reduced photosynthesis and growth
- Lesion caused by the high oxidative potential of these pollutants
- Induction of necrosis and eventually plant death
Describe Air pollution physiological responses
- Stomatal closure
- Production of detoxication enzymes like catalases, peroxidases, superoxide dismutases
- Production of ROS-scavanging compounds like glutathione and ascorbic acid (Vitamin C),
Describe Air pollution adaptations
- Selective uptake of nutrients
- Uptake of heavy metals by combining them with organic compounds
- Phytoremediation - removal of toxic elements using metal-hyperaccumlating plants
Define ‘Transducer’
-Any device by which variations in one physical quanity are quantitatively converted into variations in another
