Quiz 7: Growth Hormones Flashcards
what are 2 ways cell can grow?
- enlargement
2. division
describe cell enlargement
- softening of cell wall
- cytoplasmic swelling due to water uptake
- cells elongate in length
describe cell division
- single parent cell forms 2 complete identical daughter cells- mitosis
- occurs at meristems
what hormone is active during mitosis
cytokinin
requirements for growth
- water
- oxygen
- nutrients
- sunlight
- location
- temperature
what is a tropisms
- growth or movement in response to external stimuli controlled by hormones
Phototropism
- response to light
heliotropism
-diurnal response to sunlight
geotropism
response to earth or gravity
thigmotropism
response to touch ex vines
what characteristics will a plant in proper light have
- full stems
- short internodes
- closely spaced leaves
what characteristics will plants have grown in too much shade
- long internodes
- poorly developed leaves
what characteristics will plants have grown in complete darkness
-thin colourless stems with pale underdeveloped leaves (etiolation)
give a common example of when phototropism - inside and outside
- inside: bend toward the windows
- outside: sun moves across sky , if blocked for part of the day plant appears one sided
what is heliotropism
- diurnal movement of plant parts in response to the direction of the sun
- track the sun’s motion moves across sky
- reverts to neutral position
Diaheliotropism
-tracking sun (max amount if direct solar radiation leaf receive
Paraheliotropism
avoiding the sun
t or f heliotropism is a growth movement
- false: rapid reversible movements in response to turgor changes in cells in an organ at base of leaf petiole
geotropism
grow in same or opposite direction of gravity
negative geotropism
-opposite direction of gravity ex stems
positive geotropism
- in direction of gravity
ex roots
diageotropism
-horizontal growth of rhizomes, stolons and some roots
what hormones affect geotropism
- auxon and gibberelins
Thigmotropism
response to touch
ex tendrils grasp supportive objects
what hormones involved in thigmotropism
-uneven distribution of auxin
describe nastic movement
- controlled by hormones but not in direct response to external stimuli
- non directional ex seed germination, flowers opening and closing
- combo hormones at various levels and []
what does hormone mean in greek
to set in motion
what do hormones do in plant
- initiate biochem activities resulting in observable, physiological responses
what is other word word for plant hormones
- Plant Growth Regulators
what are 5 principle hormones studied ( 3 growth, 2 decay)
- Auxin
- Gibberellins
- Cytokinin
- Abscisic acid
- ethylene
what is greek word for auxin
to increase
principle function of auxin
- stimulate increase in cell length (esp near stem and root tips)
cell elongation directly prop. to [auxin]
what is IAA
-natural auxin in plants ;
-indole- 3- acetic acid
produced in apical meristem –> apical dominance
-moves downward, decreasing []
t or f shade plant display lots of phototropism
false
what hormone is responsible for adventitious root
- auxin
what is gibberellins
what is it related to
hormone controls growth of internodes
- light intensity
- high light = restrained
- low light= active, increase internode length
what are 4 functions of Gibberellins
- growth at internodes
- trigger seed germination
- breaking bud dormancy
- induce flowering
t or f ; absence of gibberellins results in dwarfism
true
what is bolting, what hormone involved
- stimulation of flowering/ seed production in crops grown for leaves
- gibberellins
what is greek breakdown of cytokinin
kytos= container/ cell kinesis= movement
what is primary role of cytokinin
promotion and regulation of cellular division
what ratio promotes root formation
high ratio auxin and cytokinins
what ratio promotes shoot formation
low ratio auxins to cytokinins
what hormone promotes lateral bud growth in flowering plants
- cytokinin
what does senescence mean in latin
to grow old
t or f once begun, senescence can be reversed
false
what is senescence controlled by , what is it responsible for
hormones
- ripening of fruit
- ageing flowers
- leaf drop
what hormones inhibit senescence
- auxin, gibberellins, cytokinin
what triggers production of abscisic acid and ethylene
environmental cues
which hormone has the most control on leaf abscission
ethylene
what is purpose of abscisic acid
- syn of terminal buds and leaves
- suspend primary and secondary growth and trigger bud scale to protect bud over winter
- stimulate closure of stomata
- inhibits shoot growth (not roots)
- induce seeds to syn storage proteins
- inhibits gibberellins
- induction and maintenance of dormancy
- induces cell growth in response to wounding
what is syn of terminal buds and leaves stimulated by?
-stresses, water shortage, low temp
describe leaf abscission
- breakdown of chlorophyll
- movement of sugars from leaf to body of plant
- weakening of cell walls at base of petiole
what cues abscission
low temp and short days cue reduction of auxin and increase production of ethylene
what is ethylene
-gas hormone
what characteristics does amount of ethylene vary in species
- amount varies on species
- tissue
- stage of development
what 5 things does ethylene stimulate
- release of dormancy
- shoot and root growth differentiation –> triple response
- stimulate leaf and fruit abscission
- stimulates flower opening
- stimulates flower and leaf senescence
- stimulate fruit ripening
what is the triple response
- stunting of growth
- twisting of plants
- abnormal thickening of stems
what is the colour ripening in fruit a result of
- chlorophyll breakdown
what 3 things occur during fruit ripening
- colour changes from chlorophyll breakdown
- sugar content rises
- cell walls and membranes soften
describe apical dominance
controlled by growth hormones in apical meristem
what does removal of meristem cause
- reduction [ auxin]
- allows axillary buds to develop
what are adventitious roots? how are they controlled ?
- stimulation of root development on stems
- auxins
