Plants Flashcards
What is the problem with phytoliths?
The silicon makes plants less digestible and grinds down teeth
When are insectivorous plants found?
Where there is a lack of nitrogen
What factors determine plant distribution?
Water. Nutrients. Grazing. Seed spreading.
What is the main feature of moving from aquatic to land?
Coping with water loss
How do plants get what they need on land?
- Water, limiting, soil
- CO2, air, stomata
- Light, high UV, leaves
- Minerals, vary, soil
When did stomata and cuticles start to appear?
When mosses evolved
What are the features of the liverwort?
- Primitive, undifferentiated leaves
- Pores
- Thick, waxy cuticles
- No roots has rhizoids
- Lives in damp gloomy conditions
What are the features of Oleander?
- Thick cuticle
- Multi layer epidermis
- Gas exchange happens at the bottom
- Stomatal pits on the underside
What do we see in higher plants?
Leaf layer specialization. Upper surface, = light harvesting impermeable to water. Lower surface = gas exchange.
What are guard cells?
- Pair guards stomata
- Symplastically isolated
- Have chloroplasts
What are the stages of stomata opening?
- Response to light
- H+ ions out, K+ ions out
- Starch is metabolized
- Results in a fall of water potential
- Water moves in
- Guard cells swell and stomata open
What is Phytohormone and what does it do?
- It’s an Abscisic Acid
- Plant signalling molecule
- Control of guard cell turgor by light can be overridden when water is scarce
- ABA binds to receptor on plasma membrane
- Triggers signalling cascade
What do stomata have to balance?
Rate of CO2 entering and water vapor exiting
What is water potential?
Measure of pressure - water declines = more negative
What happens when roots wilt?
ABA is triggered.
What does stomatal density depend on?
Concentration of CO2 eg low CO2 = more stomata
How can plants survive with less water?
- Deep roots
- Store water eg succulents
- Lose less water eg spikes
- Cope with very little amounts of water
- Have dormant seeds
What do cells in the epidermis do?
Have no photosynthetic capacity - help refract light into the cells which do
What is meant by autotroph?
Synthesis everything they need
Where does the Calvin Cycle occur?
Chloroplast
What is RuBisCO?
Enzyme for carbohydrate synthesis
What happens when light hits PSII?
- Energy from photons excite electrons
- Move along the photosystem
- Electrons are replaced by splitting water
How is ATP generated?
Protons released by splitting water accumulate in the lumen. Protons are moved through ATP synthase to make ATP.
How is NADPH produced?
Through the PSI complex
What is the role of the Calvin Cycle?
To recycle compounds and use the energy to make compounds
What are the stages of the Calvin Cycle?
- Carboxylation - addition of CO2 to RuBP
- Reduction - NADPH transfers 2 electron and 1 proton, phosphate is release
- Regeneration - multi-step, 3 carbon compounds are reorganized and combined to produce RuBP, takes 3 turns to regenerate
What does RuBisCO catalyse?
The oxygenation of RuBP
Describe the problem of photorespiration.
Oxygenation and carboxylation of RuBP are both catalysed by RuBisCO. Meaning plants can lose 50% of fixed carbon. CO2 levels must be high to maintain carboxylation rates over oxygenation.
What is C3 photosynthesis?
Where plants only use the Calvin Cycle to fix carbon from the air
What is C4 photosynthesis?
Prevents photorespiration by providing RuBisCO with saturating levels of CO2
Describe the process of C4 photosynthesis
- Separates the CO2 uptake and the Calvin Cycle by space
- Enzyme PEP carboxylase catalyses the addition of CO2 to a 3C compound to produce a 4C compound
- Oxaloacetate is converted to a 4C compounds and shuttled into bundle sheath cells
- Malate converted to a 3C pyruvate and Co2 in the bundle cells
- 3C pyruvate diffuses back into mesophyll cells and is converted in POP
What do C4 plants use as their primary CO2 fixing enzyme?
PEPC
Why did C4 plants evolve from C3?
C3 plants were around when the concentration of CO2 was very high. C3 plants have been adversely impacted by lower CO2 concentration
Where is C4 photosynthesis found?
Hot, tropical and arid regions. Only 5% of plants are C4. Includes maise, sugarcane and tropical weeds. Used to drought.
Describe CAM photosynthesis?
- Separated by time rather than space
- Use PEP
- Stomata open to take up CO2 at night
- Carbon is fixed and stored in the vacuole
- During the day stomata shut to conserve water
- Material retrieved and transferred to chloroplasts
What are macronutrients?
Bulk. Need large quantities. Essentials.
What are some examples of macronutrients?
N (proteins, nucleic acids), K (osmoregulation), P (nucleic acids, ATP), Ca (membrane integrity), Mg (chlorophull, cofactor), S (amino acids)
What are micronutrients?
Small quantites
What are some examples of micronutrients?
Fe (redox systems), Mn (PSII), Zn (cofactor), B (cell walls)
How do the concentration gradients across the plasma membrane work?
- pH and electrochemical gradient
- Generated by proton-pumping ATPase
- Can also create gradients by suffling things out the cytoplasm into the vacuole
- Can’t rely on diffusion
What is the Symport Channel?
Mostly anions, high affinity for K+ because ion moves with H+
What is the Uniport Channel?
Cations like phosphate. Takes energy to make but they don’t need energy to move as its a membrane pore.
What is the Antiport Channel?
Secretes cations
What is the Apoplast pathway?
Between cells. Gradient drive. Cannot extend beyond Casparian strip
What is the Symplast pathway?
Within cells, controlled by transporters, controls entry to vascular tissues.
What are the main nutrients?
Phosphate and Nitrogen
What is the problem with getting phosphate?
- Not very soluble in soil
- Immobile
- Low bio-availability
- Forms complexes with cations in soil
- Rock phosphate = finite source
Describe Liverwort getting phosphate?
- Not true roots, rhizoids are mainly for anchorage
- Very low surface area for P absorption
- Zone of depletion quickly develops
How does Fungi-root symbioses work?
- Mycorrhizas
- Mutalistic symbiosis
- Fungus penetrates the cell wall but not the cytoplasm
- Fungi are obligate biotrophs
What is Arbuscular mycorrhizas structure?
Highly branched, maximizes SA for exchange of materials
Why is the relationship between fungi and mycorrhiza beneficial?
- Fungus provides increased phosphorus uptake for the plant as well as other nutrients
- Plants provide the fungus with a carbon source
What is the Hyphal network?
- Fungus soil interface
- External mycelium in soil
- Massively extends roots system
- Hyphae are fine
- Connects plants trhough a common mycelial network
What do Myc factors do?
- Trigger host responses via Ca2+ signalling
- Change in cytoplasmic CA concentration initiates cell processes
What is root hair development dependent on?
Nutrients
How does Rhizosphere increase phosphate capture?
- Volume of soil influenced by the presence of the plant root
- Some plants secrete organic acids inthe the rhizosphere
- Citrate exchanged for phosphate
How do Cluster Roots increase phosphate capture?
- Some plants produce cluster roots under low P conditions
- Citrate released in a burst
- Cluster roots secrete enzymes to release P from organic sources
How do Root Exudates increase phosphate availability?
- In alkaline soils phosphate forms insoluble salts
- Roots secrete organic acids, reduces local pH and release phosphate
- Secrete mucilage habitat for bacteria that mineralise P
Why is Nitrogen sometimes hard to get?
- Freely mobile but hard to get from
- Acid bogs and sandy soils
- There is heavy interplant competition
What is Ectomycorrhizal symbiosis?
Important in N capture, soils with complex organic N, occurs in fewer plant families (often forest trees). More recent.
What is nodulation?
- In leguminous plants
- Bacterial nitrogen fixation
- Only prokaryotes carry out this reaction
- Catalysed by nitrogenase complex
What is root nodule symbiosis?
- Highly specialist association between rhizobia and leguminous plants
- Rhizobia fix N2 making it available to plants
- Plants provide rhizobia with carbon
What does Leghaemoglobin do?
- Accumulates in the cytosol of rhibozium
- Contains a haem group, is red
- Regulates O2 to the bacteria
- Too much inactives nitrogenase complex
- Too little prevents O2 respiration
How is a nodule made?
- Signal recognition
- Contact with root hair leads to root hair deformation
- Infection thread within the root hair cell develops
- Bacteria enters
What is insectivory?
Solution to low nitrogen. Evolved more than ones. Hairs and movement. Secretes digestive enzymes.
What are some examples of plants that are insectivory?
Sundews. Venus fly trap. Bladderworts.
What does plant parasitism achieve?
A solution to low N
What was Darwins ‘abominable mystery’?
- Angiosperms more successful than other plant groups
- Expanded dramatically in a short space of time
What are the features of a buttercup?
Simple saucers. No pollinator guides for non-specialised pollinators. Many anthers, stigmas. Allow for multiple different pollination events
What are the features of a Dandelion?
Unprotected pollen and plenty of nectar. Attracts lots of pollinators
What is key to pollination?
Insects
Why did insects aid flowering plant success?
Diversification of insects coincides with flowering plants. They coevolved? Floral designs recognisable. Problem: insects could have been increasing anyway
Why did Angiosperm radiation lead to flowering plant success?
Early angiosperms limited to aquatic or very dry sites. Higher growth rates and increased nutrient supplies. Leaf litter easily decomposed. Nutrient feedback. Became dominant.
Why did angiosperm diversification lead to flowering plant success?
Ancestral angiosperm was polypoid. Whole genome duplication predated angiosperm diversification. Provided a large number of genes.
What are the floral colours on plants?
Combinations of pigment
How many phenolic rings are there?
3
What is the major class of flavonoids?
Anthocyanins
What happens if you increase the number of hydroxyl groups?
Absorption to a longer wavelength
What happens if you increase the number of methoxyl groups?
Absorption to a shorter wavelength
What does the colour depend on?
Chemical sub groups attached to the B ring
What can the petal shape determine?
The intensity of petal colour
Explain the colour in a petal.
- Cells in a petal contain the same amount of pigment
- Darker patches = different shaped epidermal
- Can be conical or have a mutation that results in flattened cells
What do flower petals have to attract bees?
Blue halos
What are blue halos on petals?
Repeated arrays of nanostructures. Scatters blue lights
What are floral electric fields?
A charge that attracts bees
Describe bee orchids.
- Sexual attraction of bees to orchids
- Co-evolution of bee and orchid chemistry
- Have the right pheromones (14/15 of the sexual attractants)
Why are seeds important?
- Storable food supply
- Can cause famines
- Allow plants to survive mass extinction events
- Plants can germinate more quickly
- Seed vaults
What is an examples of a Seed vault?
The Arctic ‘Doomsday Vault’ - has been to supply seeds to Syria. Important resource for the world
What problem does pollination provide?
Conflict between certainty of fertilisation and outbreed - evolved new strategies to avoid inbreeding
What are some examples of how plants pollinate?
Vector animals or wind/water
Describe pollination strategy of exploitation of echolocation.
- Cuban bat = messy eater
- Drinks nectar from rainforest vine Marcgravia evenia and gets covered in pollen
- Takes pollen to another plant for pollination
- Dish shaped leaf halves foraging time for visitng bats
Describe pollination strategy of multiple rewards?
- Thermogenic flower (produces heat)
- Attracts scarab beetles who are facultative endotherms
- Would have to move to keep warms
- Beetle gets heat
- Beetle leaves to pollinate another flower and reproduce
Describe pollination strategy of deceit by resource mimicry.
- Dead horse arum volatiles are like a rotting carcass and flies respond the same way
- Flies go in on the floor, get trapped and covered in pollen
- They are released in the morning to pollinate another flower
Describe pollination strategy of Wind Pollination: Trees
- Flowers in catkins pollination early in year
- No attraction required
Describe pollination strategy of Wind Pollination: Grasses
- Hanging anthers
- Feathery stigmas
Describe how plants avoid inbreeding by Dicogamy.
- Anthers and stigma matures sequentially
- Female stigma matures first (protogyny)
- Stigmas open (cross pollination favoured)
- First 5 anthers (cross and selfing possible)
- Stigmas wither (next 5 anthers, mature can act as male parent to another flower)
Describe how plants avoid inbreeding by Fail Safe Mechanisms.
- Ensures pollination by selfing in protandrous flowers (male/pollen first)
- Secondary pollen presentation: stigma lobes initially receptive to cross pollen then curl round and collect pollen
- Male produces pollen, female ensures fertilisation
Describe how plants avoid inbreeding by Dioecy and Monoecy.
- Male and female flowers on separate male and female plants
- In some plants dioecy is due to sex chromosomes
- Monoecious, male and female plants on a single plant
Describe how plants avoid inbreeding by Self Incompatibility
- Inability of pollen to fertilise ovules of the same flower
- Self incompatible same SI alleles, no fertilisation
Describe how plants avoid inbreeding by Sporophytic and Gametophytic Incompatibility
- Sporophytic, SI alleles are produced by diploid sporophyte and deposited on the developing polen grains
- Gametophytic, SI proteins produced by haploid pollen cells
Why was the evolution of fertilisation and dispersal important?
- Problems when plants moved to land
- First evolved sperm which still used water
- Pollen and seeds were much more effective
What fertilisation does a Cycad use?
Uses sperm. They’re dioecious. Need raid to propel sperm from male cone to female cone.
What is meant by Sporophyte?
Diploid state. Produces a flower
What happens when a flowering plant goes through meiosis during reproduction?
Produces Megaspores and Microspores. Known as the haploid state. Gamete generation.
What happens to the megaspores in flowering plant reproduction?
3 megaspores degenrate and one divides 3 times. Cell division.
What is the alteration of generation?
Life cycle in plants that have distinct haploid and diploid stages.
How does alteration of generation work?
- Diploid goes through meiosis and grows in a hploid organism
- Haploid produces gametes
- Gametes fertilised
- Grows into a diploid organism
What is fertilisation like in ferns?
- Gamete is hermaphrodite
- More likely to generate a sporophyte
- Cross fertilisation is not guaranteed
What is fertilisation like in Gymnosperms?
- Haploid state is suppressed and internalised
- Heterospory, clear distinction between male and female parts
- Megaspore is shed and is a free living sporophyte
- Wind dispersal
- Can avoid self fertilisation events
Where is the Gametophyte in flowering plants?
Enclosed in the sporophyte
What does the microspore produce in flowering plants?
Pollen grain
What does the megaspore produce in flowering plants?
Embryo sac
What does the double fertilisation in flowering plants produce?
Zygote. Endosperm
Describe the gametophytic generation in flowering plants.
- Male gametophyte grow through the sporophytic tissue
- Ovule enclosed undergoes meiosis
- Sometimes just the nucleus divides
- Get a multicelled gametophyte
- Polar nuclei cell that contains two haploid nuclei
- 7 celled, 8 nucleate embryo sac
- Female will be fertilised by the two male gametes travelling down the pollen tube
Describe persistence as a strategy for reproduction.
Many plants can occupy the same habitat over time. Develop a suitable ecosystem
Describe multiplication as a strategy for reproduction.
Many plants are good at increasing their number so they can conquer new territories
Describe dispersal as a strategy for reproduction.
Many plants have evolved to colonise new territories by developing sophisticated dispersal mechanisms
What are some examples of plants that use persistence?
- Vegetative preoduction in grasses
- Marram grass (sand dunes & salt marshes)
- Trees
What are some examples of plants that use multiplication?
Pando the trembling giant - single root system with genetically identical shoots or trees
What are some examples of plants that use multiplication and dispersal?
Viola secual - produces a capsule that disperses seeds
What are some examples of plants that use dispersal?
Mistletoes - parasatic plant - hooks into xylem and phloem. Marsupial eats the seeds and disperses them
How many times have parasitic plants evolved?
12/13 times
How does a Dodder plant use volatiles?
Reduced yield of crop plants and is good at selecting a host. Seeds germinate and vines find it. Detects by chemicals produce. Uses volatile cues for host location and to direct grwoth
Describe the parasitic plant Rafflesia
Largest flower in the world. Lives inside the host plant and cannot see it until it flowers
Describe the parasitic plant Mistletoe
Parasitism evolved 5 times and independently
Describe the Potato Blight.
Causes famines. Millions died of starvation. Microorganism - oomycetes. Phytophthora infestans
How are potatos infected from potato blight?
Forces stomata open. Releases chemicals which fools the plant. Provides a root to grow into the plant.
What is innate immunity in plants?
The epidermis, thich walls and waxy cuticle
How do pathogens avoid this defense system?
Enter through wounds. Through stomata - secrete chemicals that keep stomata open. Enzymes to soften and digest walls. Viruses (ssRNA) can move through plasmodesmata.
What are biotrophic pathogens?
Obtain resources from living cells and weaken the plants
What are necrotrophic pathogens?
Kills cells before colonising - kills the plant
What does the cell wall mean when there is an infection in the plant?
Each plant cell is trapped so each individual cell has to fight then communicate to other cells
What is an oomycete?
Causes the potato blight. Genome has been sequenced to find resistance
What are virulent pathogens?
Overcome host defenses and lead to disease
What are avirulent pathogens?
Damage only a small part of the plant because the host can contain the infection. More common
What are the 2 parts of the plant immune system?
Basal resistance and specific resistance.
Describe Basal Resistance
- Pathogen attacks
- Molecules produced by pathogens are recognized by the plant
- Become ligands
- Triggers defense response
- Binds, conformational change
What is Pattern Triggered Immunity?
Type of basal immunity. Recognition of conserved microorganism associated molecular patterns by specific transmembrane receptors. Protect host against non-specialised pathogens
What are Microbe Associated Molecular Patterns (MAMPs)?
Molecule signature typical of whole classes of microbes. Recognition of microbes in innate immunity.
What are Damage Associated Molecular Patterns (DAMPs)?
Recognize damaged fragments of the cell wall that are breaking off. Elicits a response
What are Pattern Recognition Receptors (PRRs)?
Pathogens could cause a change in the shape of receptor which is the recognized
What is Flg22?
Flagellin is a protein present in the flagella of bacteria, recognizes highly conserved molecules from a broad class of pathogens
What is specific resistance?
Responds to specific pathogens
How is specific resistance different from basal resistance?
Specific resistance consists of receptors located inside the cell as opposed to on the cell membrane
What are the receptors used in specific resistance?
R proteins - each black a specific AVR protein
What are the stages of specific resistance?
- Pathogens secrete AVR proteins - enter the cell
- R proteins recognise a specific AVR
- R protein will bind with an AVR protein and prevents it from blocking plants basal resistance
- Directly activates defensive genes
Describe the gene-for-gene model of plant immunity.
- Depends on interactions between specific plant and pathogen genes
- Resistance varieties and sensitive varieties offlax
- Can look at old genes, single gene is responsible
Describe how a Pseudomonas Syringe works.
- Produces AVR protein
- Plant has evolved produces a protein which sense the interaction of the AVR
- Gene for gene resistance
- Triggers another defence
- Known as the guard hypothesis, no contact between Prf and AVR, mutations have much less effect
What are Pseudomonas?
Protein that raises the freezing point of water so it kills the plant as water freezes
What do Pseudomonas produce?
Syringomycin - destabilises the cell membrane
What is a hypersensitive response?
- Pathogen detected
- Sacrifices infected cells and the ones surrounding
- Uninfected cells raplidly produce reactive oxygen species and die
- Produces a plug to stop it spreading
- Forms a barrier of dead tissue
Describe the immunity experiment by Frank Ross
Infected a tobacco plant with tobacco mosaic virus. Infected one leaf, after 7 days infected a second leaf. Second leaf showed no signs of infection
How many plant pathogen viruses are there?
450
Describe targeted response.
- Virus infects plant cell (inject ssRNA genome)
- During replication dsRNA are formed
- Plants recognize dsRNA as foreign
- Enzymes cleave the dsRNA into fragments of 21 nucleotides - interfering RNA
- Fragments enable the plant to target and destroy ssRNA molecules
- Plant acquires immunity
What are the majority of plant viruses?
ssRNA
Describe Rhizobium radiobacter
Bacteria enters through wound. Develops tumour. Cons the plant into producing useful compounds - bacter can metabolise. Bacterial Ti plasmid inserted in the plants genome.
