PLANT RESPONSES Flashcards
Directional growth
=tropism
Controlled by plant hormones
Non-directional growth
=nastic response
Fast + controlled by temporary changes (e.g. plant turgidity- osmosis)
Example of non-directional growth response
Daisies:
Open during day for pollination, close during the night for protection
Physical responses to herbivores
Thorns
Spiny leaves
Tough fibrous tissue
Chemical responses to herbivores
Alkaloids- bitter + toxic (e.g. nicotine), increase production in response to damage
Tannins- bitter + bind to digestive enzymes of animals + inactivate them
Terpenoids- toxic + smell deters insects
Pheromones (response to herbivores)
Chemical produced by an individual to affect behaviour of another
Example of pheromone
When plant is damaged, release chemicals causing nearby plants to release chemicals
Chemicals attract parasites to kill attacker (e.g. caterpillar)
Thigmonasty (response to herbivores)
Response to touch
Responses to abiotic stress
Leaves fall off due to low temps (no photosynthesis, so wasting energy)
Antifreeze production- stops ice crystals forming in cytoplasm (e.g. carrots)
Stomatal closure to reduce transpiration (drought)
Types of tropisms
Geotropism (gravity)
Phototropism (light)
Chemotropism
Thigmotropism (touch)
State some roles of plant hormones
Produced in variety of tissue
Move via AT, diffusion + mass flow in phloem + xylem
Slow response
Permanent changes
Work synergistically + antagonistically with other hormones
Auxin effect
E.g. IAA
Promote cell elongation
Inhibits growth of side shoots
Inhibits leaf abscission
Cytokinins effect
Promote cell division
Works synergistically with auxin
Gibberellins effect
Stem elongation
Seed germination
Absicic acid effect
E.g. ABA
Seed dormancy
Stimulates stomatal closure (guard cells= flat + flaccid)
Stimulates anti-freeze production
Ethene effect
Promote fruit ripening
Leaf abscission
Conclusions to plant hormone experiments
Shows shoots grow towards light
Tip is needed to grow + bend
Light sensors must be in tip of shoot
Auxin diffuses down shaded part of plant
How does auxin work
Made in meristem cells near tips of roots + shoots
Causes cell elongation
Binds to receptors on cell surface membrane + promote AT of H+ into cell wall (=acidic)
Reduces pH= weakens cellulose bonds + activates enzymes to break cellulose bonds
Osmosis, elongation is permanent as cellulose cell wall is weakened
Plant ages + destroys auxin, cellulose cell wall; becomes rigid= permanent change
Auxin + phototropism
Cells in tip contain phototropin in cell membrane
When hit by light they become phosphorylated
This causes auxin produced in shoot + tip to move to shaded side (via transporter proteins)
Cell elongates- shaded side bends
Explain how roots are +ve geotropic + -ve phototrophic
Gravity causes auxin to move to lower side of roots + shoots
- in root auxin inhibits cell elongation. Cells on lower side elongates less + root grows downwards
- in stem auxin promotes elongation. Cells on lower side elongate + stem grows upwards
Apical dominance
Region near top of terminal bud contains apical meristem = dominance over lateral buds= plants grow straight without wasting energy on side branches, allows them to compete for light (photosynthesis)
If tip of plant is cut off, lateral buds start growing + plant bushes out
Control of apical dominance
Auxin made in aphical bud where it causes cell elongation
Auxin diffuses down lateral buds, where it inhibits them
Why will lateral buds grow if plant is upside down?
Upside down= diffusion of auxin upwards against gravity, therefore auxin to lateral buds + growth
Gibberellins + stem elongation
Produced in young leaves + seeds
Causes growth in cell internodes
Auxin + Gibberellin can be…
Synergistic- grow tall
Antagonistic- gibberellins stimulate lateral shoots, auxin inhibits them
Gibberellin + germination (Barley seed)
When seed absorbs water embryo releases gibberellins
Gibbs travel to aleurone layer (membrane) of endosperm (food store)
This switches on genes which code for amylase + protease (hydrolytic enzymes)
Stored starch hydrolysed to glucose (using enzymes)
This provides substrate for respiration so embryo can grow
Why does leaf abscission occur
Less light in winter (shorter days, lower intensity) + lower temps reduces photosynthesis
Water lost through leaves, fungal infections + frost= damaged plant= leaf loss
Wastes energy
Leaf abscission in deciduous plants
Auxin produced in young leaves, inhibits abscission
Reduce light= reduced auxin concentration
Ethene produced as leaves age
To balance shift between two hormones, leaf abscission starts (aux + eth= antagonistic)
Abscission layer of leaf have thin walls (weakened by enzymes), breaking cellulose bonds
At same time- Suberin develops underneath for protection
Vascular bundle sealed off
Leaf blown away with wind
When is absicic acid produced
Under abiotic stress (e.g. temp)
Causes stomata to close, reducing transpiration
Absicic acid + stomatal closure
ABA binds to receptors on cell surface membrane of guard cells
Ca2+ enters cell causing other ions to exit (e.g. K+ + Cl-)
Water potential of cell increases
Water leaves cell via osmosis
Guard cells= flaccid (straight)= closed stomata
Commercial use of auxin
Selective weed killer
Rooting powder
Pathonocarpy fruit development without pollination
Commercial use of gibberellins
Improve fruit shape
Delay fruit dropping
Bring forward seed production
Stopping= shorter plants= saves resources + reduces wind damage
Commercial use of cytokinins
Promote cell division
Stops ageing (reduced waste)
Promote shoot growth in tissue culture
Commercial use of ethene
Fruit ripening
Fruit dropping at same time (easier harvesting)
Speed up ripening
Promote growth of female flowers (for pollination)
Stopping increase CO2 which reduces ethene= delay fruit ripening
