Chapter 41 Plant hormones

Phototrophism: photochromes absorb blue and red light.

Phototropic responses occur due to blue light receptors

Photomorphogenic responses occur due to red light receptors

Pr absorbs a photon of red light (660nm) à converting it to Pfr

Pfr absorbs a photon of far red light (730nm) à converting it to Pr

Pfr is biologically active part / Pr is inactive

Gravotropic:

Gravity perceived by cell

Signals form in cell

Signal is transduced in and out of cell

Differential cell elongation occurs

Auxin differential concentration in lower part of stem, bending upward during growth

Thigmotrophism:

Auxins and ethylene cause plant tissue to respond unequally to touch generating unequal growth curving the stem structure.

Plant Hormones:

1. Auxins: stem elongation, growth, inhibits abscission of leaves, promotes cell division with cytokinins, causes ethylene production, promotes lateral bud dormancy

Where: apical meristem

Method: cell wall plasticity effecting young cells w/o secondary cell wall

(makes cells transport H into cell wall space decreasing pH which activates enzymes that breakdown cell wall fiber)

2. Cytokinis: stim cell division, promote chlorplast devel., delay senescence, promote bud formation.

Where: root apical meristem, immature fruits

Method: stimulate production of proteins needed for mitosis.

3. brassinosteroids: additive effect to auxin/gibberellins, elongation, membrane polarization, delayed senescence.

where: pollen, immature seeds, shoots, leaves

4. oligosaccharins: pathogenic degense,

where: cell wall

method: breakdown of cell wall components incuding oligosaccharides signal defense mechanisms

5. ethylene: control abscission, promote fruit ripening

where: root shoot, leaf node, aging flowers, ripening fruit

Method: auxins cause ethylene production, ripens fruit, causes leaves to die.

6. abscisic acid: inhibits bud growth, stomatal closure, seed dormancy, ihhibitor of other hormones.

Where: leaves, fruits, root cap, seeds.

7. gibberellins: promote stem elongation, stim enzymes in germinating seeds

where: roots, shoots, young leaves, seeds.