module 5 - 16.2 and 16.3 plant responses to abiotic stress and herbivory Flashcards
which main 2 abiotic factors to plants face?
- temperature fluctuations due to seasons
- light due to fluctiations in daylight hours
how do the seasonal changed affect rate of photosynthesis?
- plants need to make enough glucose and triose phosphate from photosynthesis to meet demand of respiration and synthesis of molecules
- plants hibernate if rate of photosynthesis is too low
what is photoprediodism?
plants responding to lack of light
what are the responses a plant does in response to lack of light?
- loss of leaves
- breaking of leaf bud dormancy
- timing of flowering
- tuber formation for over-wintering
what is the process of abscission in plants?
- falling light levels leads to lower auxin concs
- leaves respond by increasing production of ethene
- ethene causes genes to switch on in separation layer of abscission zone, enzymes made to digest cell wall of separation layer
- vascular bundles in petiole are sealed off
- cells in protective layer of abscission zone make suberin and lignin to waterproof and protect the car when leaf falls off
- plant cells at abscission zone take in large amounts of water, swell, and eventually burst, making leaf fall off
how is freezing in plants prevented?
molecules are produced called ‘anti-freeze’ to lower the melting point of water and prevent water freezing
- can be sugars, polysaccharides, amino acids and proteins
- produced when genes switch on due to prolonged fall in temp and reduced daylight
what is the mechanism for day to day stomatal opening?
- proton pump drives protons (H+) from guard cells
- guard cells become increasingly negative
- negative charge opens potassium voltage gates channels so uptake of K+ ions occurs
- increase in K+ conc lowers WP inside cell so water diffuses into cell by osmosis
- this increases cell’s volume and turgor pressure
- rings of cellulose microfibrils only allow extra turgor pressure to elongate guard cell causes an open pore for gas
what is the hormonal control of stomatal closure?
- when roots begin to sense water shortage in soil ABA is released from roots
- ABA binds to receptor proteins in guard cell’s membrane
- cause concentration of free Ca2+ to increase due to influx of guard cells
- causes Cl- ions to exit guard cell (chloride shift)
- this stops uptake of any further K+ ions into guard cells
- loss of K+ ions causes increased WP, so water diffuses out cell
- makes cell plasmolysed so stomata closes
what are the 4 groups of plant responses to herbivory?
- physical defences
- chemical defences
- pheromones
- folding on touch (mimosa pudica)
what are examples of physical defences?
prickles, thorns, spines, stings
what are examples of chemical defences?
tannins
alkaloids
terpenoids
what are tannins?
- have a bitter taste - puts animals off eating them
- toxic to insects - binds to digestive enzymes & inactivates them
what are alkaloids?
- bitter tasting, nitrogenous compounds found in many plants
- act as drugs affecting metabolism of animals
- e.g. nicotine and caffeine
what are terpenoids?
compounds produced often form essential oils but also often act toxic to insects and fungi that might attack the plant
what are pheromones?
- chemicals affecting social behaviour of other membranes
- they warn other plants of herbivores and stimulating them to synthesise toxic chemicals like tannins
