Plant Responses to Internal

1
Plant Responses to Internal External Stimuli
2
I. Etiolation vs. De-etiolation

• A. Etiolation are the adaptations/responses
  plants have towards growing in complete darkness
• Short stubby roots, unexpanded leaves, pale stems
  
• B. De-etiolation when a plant(shoot) reaches
  light also known as greening
• Stem elongation slows, leaves expand, roots
  elongate, shoot produces chlorophyll
• Through Etiolation De-etiolation we will
  discuss how plants response to a signal and then
  transduce a response

3
(No Transcript)
4
(No Transcript)
5
II. Signal Transduction pathway

• A. It occurs in 3 steps
• 1. Reception (receptors)proteins along the cell
  membrane or cytoplasm change shape due to a
  specific stimulus
• 2. Transduction if the signal is weak secondary
  messengers inside the cell amplify the signal and
  transfer it from the receptors to other proteins
  that carry out the response Ex. Ca2 and cyclic
  GMP
• 3. Response 2 ways either post-translational
  modification (modifying preexisting enzymes) or
  transcriptional regulation (increase/decrease
  synthesis of mRNA encoding specific enzymes by
  binding to specific DNA sequences
  (transcriptional factors)

6
(No Transcript)
7
II. Plant Hormones

• A. Hormones signaling molecule that is produced
  in tiny amounts in one part of the body and
  transported to other parts where it binds to a
  receptor and triggers a response.
• 1. In plants some work together to influence one
  response, others can regulate several processes
• 2. The first hormone discovered was when watching
  a plants growth toward/away light
  (phototropism) by auxin (IAA) indoleacetic acid

8
(No Transcript)
9
II. Plant Hormones

• B. Survey of Plant Hormones
• 1. Auxin
• 2. Cytokinins
• 3. Gibberellins
• 4. Brassinosteriods
• 5. Abcisic Acid (ABA)
• 6. Strigolactones
• 7. Ethylene

10

• 1. Auxin always moves from shoot tip downward
  (polar transport) and allows cells to elongate,
  promotes formation of lateral roots, regulates
  development of fruit, enhances apical dominance
• a. By way of expansins that break cellulose
  microfibrils due to a low pH by uptake of H ions
  in the cell walls

11

• 2. Cytokinins stimulate cell division, apical
  dominance, differentiation of cells and aging
• a. produced in growing tissues (roots, embryos
  fruits)
• 3. Gibberellin stem elongation, fruit growth
  seed germination (break dormancy)
• a. mostly found in young roots an leaves, work
  with auxin to help fruit develop and can increase
  the size of fruit

12

• 4. Brassinosteroids promote cell expansion and
  cell division in shoots, root growth in low
  conc., promote xylem growth
• 5. Abscisic Acid (ABA) slows growth, inhibit
  germination in young seeds and allows seeds to
  withstand dehydration, causes stomata to close

13

• 6. Strigolactones stimulate seed germination,
  help establish mycorrhizal associations and
  control apical dominance
• 7. Ethylene promotes ripening of fruit, and the
  triple response in seedlings (inhibit stem
  elongation, promotion of lateral expansion and
  horizontal growth), leaf abscission