BFG Ch 7 Flashcards
Name the five major plant hormones
auxin gibberellin cytokinin ethylene abscisic acid
What is phototropism
When plant stems grow towards the light. Common response in sun loving species. Shade lovers do not do this
Where are plant hormones made
Cells of general organs such as stems, leaves, roots and flowers
what happens to seedlings that grow up in darkness
They have been colorless stems and undeveloped leaves. this is called etiolation
Etiolation
when a seedling grows up without light and doesn’t develop colored stems and has undeveloped leaves.
What does gibberellin do primarily?
Promote stem growth at internodes
results in space at the leaves
more active in low light (of high-light lovers)
shade-loving sp. don’t show elongation sensitivities
etiolated plants use gibberellin to try to reach the sun.
What is geotropism? What hormone controls this?
When a part of the plant responds to gravity’s force
Stems have negative geotropism (grow UP), roots have positive geotropism (grow DOWN)
Auxin controls it.
-cell elongation to turn stems up (accumulates in lower side of stems)
roots respond to lower amounts of auxin in upper cells to allow growth downward
What is thigmotropism?
The response to touch. Controlled by auxin; mechanisms unknown
What are nastic movements?
controlled by hormones but not the direct result of outside stimulus like geotropism, phototropism, and thigmotropism
Cell growth at changing positions across the stem tip
seen in twiners; ivy; opening/closing flowers; fly traps
all movements require growth and are expensive and essentially irreversible.
What does auxin as a plant hormone do?
The hormone stimulates an increase in cell length. Especially near stem and root tips
Distribution changes in response to light; allows plants to elongate toward the sun.
senesence
irreversible plant ripening
it is closely regulated by opposing hormones: Ethylyne gas; abscisic acid promote it
Auxin/gibberellin/cytokinin inhibit senesence
What hormones oppose senesence
Auxin
Gibberellin
Cytokinin
Cytokinin
plant hormone that stimulates cell division
What hormones promote senesence
Ethylene gas: used to commercially ripen fruit.
Abscisic acid
coupled with external environmental cues such as shorter days.
What changes occur during fruit ripening?
Chlorophyll breakdown (color change) tannins switch to sugars = promote predation membrane softening and cell breakdown (via ethylene) fungi growth on overripe things
Describe leaf senesence prior to abscission
chlorophyll breakdown, weakening cell walls at base of petioles (“abscission zone”)
decrease auxin, increase ethylene
- due to low night temps and shorter days
- ethylyne=enzymatic breakdown of cellulose and pectin in walls of middle lamellae
similar process in evergreens, fruits, and flowers that undergo periodic abscission
What is apical dominance? What hormone controls it?
apex growth suppresses the growth of axillary buds
Auxin controls this- it suppresses growth of axillary buds
How do adventitious roots occur?
after cutting or layering
grow on cut stems/leaves; controlled by auxin
sometimes they’ll cut the plant and leave it on the parent plant while the adventitious roots draw nutrients until it’s good to go for moving. (this is called layering)
Synthetic growth regulators
defoliants: promote leaf abscission
disbudders: cause flower buds to fall off (rid them of unwanted future fruits)
growth retardents: production of dwarfed potted plants
herbicides: weed killers
What is plagiotropism?
when branches grow oblique to gravity
What is diageotropism?
when branches/roots grow horizontal to gravity
Additional roles of gibberellin
controls seed germination
revives plants from winter sleep
non-universally increases flower formation and fruit size
Additional roles of ethylene
stem thickening (esp in seedlings) initiates flowers (pineapple, not universal)
Abscisic acid
promotes dormancy as well as aids in ripening and abscission
