Unit 11: Signals in plants/responses

• etiolation: the process of growing less than normal in size, especially because of lack of light
• de-etiolation: the process of removing the inhibition of photosynthesis by light and plant undergoes profound changes.
• photoreceptors: light-sensitive cells in the retina that convert light energy into electrical signals
• what is guanylyl cyclase?

  an enzyme that produces the second messenger cGMP
• what is phyotchrome?

  a photoreceptor responsible for light detection during de-etiolation
• how does phytochrome work during de-etiolation?


  releases Ca+ into cytosol then causes phytochrome to change shape, leading to the activation of guanylyl cyclase -> cGMP
• what is post translational modification?

  pre-existing proteins are modified by phosphorylation and 2nd messengers, altering protein's shape and function
• what is transcriptional regulation?


  Control of gene expression through the binding of transcription factors to DNA.
• what are activators in transcriptional regulation?


  proteins that increase translation
• what are repressors during transcription?


  proteins that decrease transcription
• what are the two main pathways involved in responses in plants?

  post translation modification and transcriptional regulation
• what is true of plant hormones?

  active at LOW concentrations
• tropism: growth response curving toward or away stimuli
• phototropism: growth of shoots toward/away from stimuli
• what is polar transport?


  Movement of molecules within a cell in a specific direction.
• what role does auxin play?


  stimulates cell growth (elongation) by binding to a receptor, BUT high concentrations of auxin hinders growth
• what is acid growth hypothesis?

  auxin stimulated proton pumps that increases voltage across membrane and lowers pH in the cell wall. This activated expansins that break hydrogen bonds in the cell wall to enhance ion uptake, osmosis, and turgor leading to elongation.
• phyllotaxy: arrangement of leaves on a stem
• what is the affect of polar transport?

  controls spatial organization: branching patterns, phyllotaxy, and vein patterns
• what is the role of cytokinins?


  produced in growing tissues to promote cytokinesis and cell division
• what is a terminal bud: bud that is located at the apex of a stem (aka apical buds)

  
• what is apical dominance?


  ability of apical buds to suppress the development of axillary buds
• what are axillary buds?


  lateral buds of the stem
• what is the direct inhibition hypothesis?

  auxin is transported from shoot to axillary bud: inhibiting growth, but cytokinins enters shoot system through roots and signals growth.
• polar flow of auxin down shoots triggers synthesis of strigolactones (repress bud growth)
• what other roles does cytokinins have on plants other than cell division?

  inhibits protein breakdown, and stimulated RNA/protein synthesis in order to slow the aging of plant organs
• what is the role of Gibberellins?


  stem elongation, fruit growth, and seed germination
• how does gibberellin act in plants?

  • enhances elongation and cell division
  • fruit growth requires both auxins and giberellins
  • plant seed embryos are rich in gibberellins
  • water surrounding a seed causes gibberellin to break dormancy and germinate
• what role does abscisic acid (ABA) play?

  precedes bud dormancy and leaf abscission

  • slows growth, functions in seed dormancy and drought tolerance
  • high levels lead to germination inhibition and protein production
  • germination occurs when ABA is moved or inactivated
• what is seed dormancy?


  germination only occurs in optimal environmental conditions (to ensure that the seed doesn't die)
• what is one response in plants to drought tolerance?


  wilting causes increased ABA causes stomata to close OR open potassium channels that lead to loss of water and cause stomata to close
• what is the role of ethylene?


  produced in response to stress, fruit ripening, senescence (deterioration), leaf abscission
• how does ethylene affect stress in plants?


  instigates growth maneuver (triple response) that causes shoot to avoid obstacle

  • ex: slow stem elongation, strengthen stem, or adds curvature
• what are ein mutants?


  ethylene insensitive mutants fail to undergo triple response (lack of receptor)
• what are eto mutants?


  ethylene-overproducing mutants produces higher rates of ethylene -> add inhibitors
• what are ctr mutants?

  constitutive triple-response under triple response but ignores the inhibitors of ethylene
• senescence: programmed death
• how does ethylene influence leaf abscission?


  loss of leaves prevents loss of moisture (desiccation)

  • detachment occurs at base of parenchyma cells (where nutrients are stored and recycled for other leaves) and enzymes come in to hydrolyze cell wall
• how does ethylene influence fruit ripening?


  ethylene triggers ripening (which triggers ethylene production -> positive feedback) and organic molecules are converted to sugars
• what role does brassinosteroid play?


  cell elongation, division, slow leaf abscission