Responses to Environmental Challenges Flashcards
How can strong light damage leaves?
Produces free radicals and reactive oxygen species (ROS)
Hoe can leaves protect themselves against reactive oxygen species?
- Xanthophylls cycle (preventing formation of ROS)
- Enzymatic destruction of ROS
- Rapid destruction and repair of D1 protein in PSII
What are photo-inhibition and photo-oxidation?
Photo-inhibition = damage due to strong light which is reversible via repair mechanisms
Photo-oxidaiton= irreversible damage
What are the relative capacities for damage repair in shade and sun leaves and why?
Shade leaves have a limited damage repair capacity and are more easily photo-oxidised
Sun leaves have a higher repair capacity (unless stressed by low temperatures) and do not usually become photo oxidised
Describe the xanthophyll cycle.
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How do chloroplast movements limit excess light absorption?
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What is dynamic photo-inhibition?
A method of temporarily diverting excess light absorption to heat whilst maintaining maximum photosynthetic rate
What are c3 and c4 plants
c3- cool season plants
c4- warm season plants
What is quantum yield? What is it dependent on and why?
Moles of co2 fixed/ moles of photons absorbed
Dependent temperature in c3 plants but nearly independent temperature in c4 plants, due to photosynthesis
What are the differences of photosynthetic capacities in c3 and c4 plants at different attitudes due to?
Due to reduced quantum yield and increased photorespiration
At which altitudes and attitudes does UV radiation decrease?
Higher altitudes and lower attitudes
How is UV radiation damaging to plants?
High quantum every damages. Long waveUV-A is photo oxidative. UV-B is photo-oxidative as well as causing photo lesions in biomembranes
Molecularly: UV breaks down disulphide bridges and dimerises thymine groups in DNA
What is dynamic photo inhibition?
The changes light response at different levels of light where a moderate level of excess light decreases the quantum efficiency without reducing the maximum photosynthetic rate
Describe dynamic photo inhibition and chronic photo inhibition compared to optimal photosynthesis
Moderate levels of excess light decreases quantum efficiency (reduced slope of the curve) without reducing maximum photosynthetic rate.
Whereas high levels of excess light
decreases quantum efficiency
and maximum photosynthetic
rate (chloroplast damage).
Give 4 ways in which leaves undergo photo protection as light flux increases.
- Decreased absorption
- Thermal energy dissipation
- Removal of ROS
- Inactivation/turnover of PSII (photosystem II)
What is the effect of co2 concentration leaf temperature?
Increased CO2 concentrations causes stomatal aperture to be smaller and therefore leaf temperature is higher as there is less transpirational cooling.
Describe the multilevel process of protection and repair of photo damage.
1) Suppression mechanisms e.g. using heat dissipation using the xanthophyll cycle
2) Detoxification- scavenging of ROS
3) repair mechanisms- synthesis of D1 protein
Describe the quenching process within photosystem II Why does this occur?
Violaxanthin is converted to an intermediate, antheraxanthin which is then converted into zeaxanthin (the fully quenched state)
This is done to use up excess energy that cannot be lost as heat or used in photosynthesis as converting between these forms uses energy
Describe the levels of zeaxanthin in evergreen leaves in winter compared to in summer.
Winter- high levels of Z maintained throughout day as they don’t know when they’ll have a cold day with high light intensities
Summer- levels of z rise and peak during the day to give more protection at noon
Why do birch trees grow a lot of bark?
To prevent fungal infections- they can just slough off the bark
How do grass species cope when there is an increase in vole population?
Produce new leaves with a higher silica content which has a lower C and N content and is more difficult to digest, causing the vole population to decrease
What do stinging nettles contain to protect from predators?
Stinging hairs containing formic acid, serotonin and histamine
What does the Primula auricula plant have to protect against insects and herbivores?
Farina wax layer which contains flavonoids which is an insect deterrent and an irritant on mammal skin
How do some plants (e.g. members of the spurge family produce and use latex to deter herbivores and insects?
Latex liquid produced by laticifers (specialised cells) dries to rubber and blocks herbivorous insects mouthparts
How do plants defend against mechanical damage which may provide an entry for pathogens ?
Using toxins and enzymes and secondary metabolites (compounds not directly derived from photosynthesis or for respiration or plant growth and development)
These metabolites can be toxic and lethal if ingested.Others such as alkaloids have noxious odours and therefore discourage predators.
What are terpenes and how do plants use them in chemical warfare?
Secondary metabolites and are usually volatile gases emitted during photosynthesis and can protect cell membranes from damage caused by high temperature or light
How are pyrethrins used in chemical warfare?
Produced by chrysanthemum plants and act as insect neurotoxins
What are anthocyanins?
Colourful water-soluble flavonoids pigments produced by plants to protect foliage from the damaging effects of ultraviolet radiation
What are Phytoalexins?
Isoflavonoids with antibiotic and antifungal properties- they are produced in response to pathogen attack
Why do some fruits secrete aromatic oils?
Secretion of aromatic oils from fruit walls are thought to be insect repellent
Give an example of a poisonous alkaloid and from which plant it comes from.
Deadly nightshade (Atropa belladonna) contains atropine- used to slow heart rate and reduce saliva production during surgery
How are cyanogenic glycosides and cyanolipids used in chemical warfare? How is suicidal release of HCN prevented?
When tissue is disrupted, these natural produces are hydrolysed liberating the respiratory poison hydrogen cyanide.
Cyanogenic glycoside is converted to cyanohydrin by ß-galactosidase which is then converted to hydrogen cyanide by hydroxynitrile lyase
Compartmentalisation prevents release of HCN within the intact plant
Describe the origin of cyanogenic glycosides
Derived from the five hydrophobic protein amino acids tyrosine, phenylalanine, valine, leucine, and isoleucine.
Cleavage of the carbohydrate by beta galactosidase yields cyanohydrin
How is caffeine (an alkaloid) used in chemical warfare?
It is toxic to insects and fungi
How do plants use protease inhibitors to prevent subsequent attack by herbivores?
After herbivore feeding, a series of molecular signalling processes are triggered that induce systemic production of protease inhibitors (inhibits enzymes such as trypsin and chymotrypsin) which contributes to the protection of undamaged plant parts from subsequent attacks.
How do insects exploit plant chemical defences for their own benefit, using an example.
Larvae of monarch butterfly feed milkweed which contains cardenolides and therefore the butterflies cannot be eaten by blue jays as they will become violently sick.
The viceroy butterfly mimics the appearance of the monarch and therefore avoids predation by the blue jays.
What is allelopathy?
When a plant produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms
Give 4 examples of allelochemicals which could be produced when a pant is damaged by UV light, wounding or pathogen attack.
- Long chain fatty acids
- Simple acids
- Terpenes
- Phenolic compounds
What is a glycoside?
A molecule in which a sugar is bound to another functional group through a glycosidic bond.
What is juglone? Describe its allelopathic effects.
A allelochemical which is present in the roots, leaves and green peel of nuts (e.g. black walnuts) and is toxic against the plants and inhibits germination. It is a respiration inhibitor. This ensures that when they fall from the tree, they prevent growth of new plants too close to the original which would compete for resources.
Describe how plants can use other organisms for defence mechanisms (mutualistic defence).
Myrmecodia species have chambered roots and hollow stems or inflated thorns that provide ready made homes for ants which can feed on herbivorous insects that attack the leaves.
What is polyphyletic evolution?
When a trait is evolved many times in unrelated families.
What are the differences between plants and their parasites in terms of carbon, nutrient and water acquisition? Why are these differences necessary?
- Water relations of root and shoot hemiparasites are very distinct from those of their hosts
- Parasitic plants have lower water potentials and higher rates of transpiration
-They facilitate the acquisition of water and organic and inorganic solutes from the host
What is a hemiparasite and a holoparasite?
Hemiparasite- obtains some nourishment from its host but still photosynthesises.
Holoparasite- obtains all its nutrients from the host.
Describe the parasitic reduction syndrome in holoparasites (combination of repeated traits in may groups of parasitic plants).
- Loss of leaves (reduced to scales)
- Small plant size (no need for large plants to hold leaves)
- Loss of roots (reduced to stumpy projections called haustoria)
- Loss of chlorophyll
- Loss of genes needed for photosynthesis
- Fast gene evolution in genes which are not lost
What is the purpose and function of haustorium?
- They are specialised organs for attachment, penetration and solute transfer from the host.
- They are metabolically active and process the host’s assimilates as they are transferred
- Haustorium establishes xylem continuity with the host
How do parasites identify host produced germination stimulants?
Recognise allelopathic chemicals secreted by roots which may be natural defence mechanisms which the parasite has evolved to use as a germination stimulant. OR a co evolution signalling system where the parasite responds to the presence of the host.
Other parasites secrete enzymes onto host tissues which causes the release of 2,6-DMBQ which triggers haustorium production.
Which signals can be produced when the parasite comes into contact with the host surface?
-Terpenoids released by host trigger haustorium formation
