Plant Hormones

what do plant hormones regulate?

growth, development, and response to the environment

hormones are produced in

small amounts

auxin

cell elongation, apical dominance, root formation, and fruit development

cytokinins

cell division, delay aging, shoot formation

ethylene

fruit ripening, abscission, stress responses

abscisic acid (ABA)

dormancy, drought response, stomatal closure

gibberellins (GA)

stem elongation, seed germination, bolting

brassinosteroids

cell elongation/division, vascular development, and stress resistance

auxin synthesis location

shoot apical meristems and young leaves

cytokinins synthesis location

mainy in the root tips

ethylene biosynthesis source

methionine

ABA biosynthesis

increases during drought

GA biosynthesis

high in immature seeds

brassinosteroid biosynthesis location

locally synthesized in organs

auxin transport

-polar

shoots: move downward (basipetal)

roots: move towards tip (acropetal)

cytokinin transport

in xylem from roots upward

ABA transport

moves root → shoot during drought through xylem

ethylene transport

gas hormone that diffuses easily

high auxin result

root formation

high cytokinin result

shoots or buds form

equal amounts of auxin and cytokinin result

undifferentiated callus cells

main natural auxin

indole-3-acetic acid

cell elongation

causes shoot growth and bending

phototrophism

plants bend towards the light because auxin redistributes and causes unequal elongation

apical dominance

promotes lateral and adventitious roots and used in rooting powder and tissue culture

vascular differentiation

helps form xylem, veins, and wound vascular tissue

fruit development

parthenocarpic fruit (seedless)

herbicides

synthetic auxin like 2,4-D kills weeds

basipetal

shoot from top to bottom

acropetal

roots towards root tip

AUX1

auxin influx carrier

PIN proteins

auxin efflux carriers

What do PIN proteins determine?

direction of auxin movement

delay senescence

keeps leaves green longer

cytokinin location

dividing tissues, seeds, fruits, and root tips

kinetin

synthetic cytokinin

zeatin

natural cytokinin from corn

ethylene fruit ripening

promotes softening, color change, and respiration burst

climacteric fruits

ripen with ethylene burst (tomatoes, bananas, peaches, apples)

nonclimacteric fruits

do not ripen with ethylene burst (grapes, citrus, strawberries)

abscission

promotes the dropping of leaves, flowers, and fruits

triple response

in dark grown seedlings: reduced elongation, increased thickening and horizontal growth

flood responses

in rice it stimulates internode elongation and increases air spaces

flower sex determination

in cucurbits ethylene promotes femaleness and glibberellins promote maleness

seed dormancy

prevents premature germination

ABA drought response

under water stress roots produce ABA, the stomata close, and water loss reduces

ABA stress response

helps defend against pathogens via stomatal closure

glibberellins stem elongation

stimulates cell division and elongation

seed germination in GA

breaks dormancy which can replace cold and light requirement

bolting in GA

rapid stem elongation in rosette plants

fruit development in GA

used in grapes for larger fruit and looser clusters

main roles of brassinosteroids

cell division and elongation, vascular differentiation, photomorphogenesis, flower and fruit development, stress resistance, and senescence regulation

important factors of brassinosteroids

required for normal plant growth, act locally near synthesis sites, most common form is brassinoide