IB Bio Plant Hormones & Responses to Stimuli

plant hormones

produced by special cells & influence physiology of cells

most common hormone

auxin (IAA)

auxin (IAA)

promotes plant growth by facilitating elongation of developing cells

where is auxin produced?

@ root & shoot tips (apical meristems)

how does auxin lead to growth?

increases H+ ion --> loosens primary cell wall --> wall expands due to increased turgor pressure

gibberellins (gibberellic acid)

group of plant hormones that promote cell growth; 2nd-most common

how many variations do gibberellins have?

60 variations (GA1, GA3)

where are gibberellins produced?

in young leaves, roots, & seeds but may be transported to other plant parts

how do gibberellins cause growth?

increase levels of GA --> rapid shoot growth (bolting)

cytokines

group of hormones that stimulate cytokinesis (division of cytoplasm)
- produces lateral (horizontal) growth & delays senescence (aging) of leaves

cytokines are a variation of...

nitrogen base adenine

where are cytokines produced?

in roots & transported throughout plant

what are cytokines often coupled w/?

coupled w/ auxin

ethylene

gas that promotes ripening of fruit & stimulates production of flowers

ethylene + auxin -->

inhibits lengthening of roots, stems, & leaves

why is the role of ethylene opposite of cytokines?

ethylene influences leaf abscission (dropping of leaves)

abscisic acid (ABA)

growth inhibitor

what is abscisic acid role in buds?

delays growth & causes formation of scales

what is abscisic acid role in seeds?

maintains seed dormancy

what is dormancy interrupted by?

interrupted by gibberellins