Plant Responses to Internal and External Signals Flashcards
What is etiolation? What would this look like?
These are morphological adaptations for growing in the dark.
A plant may have pale stems, stubby roots, and unexpanded leaves.
Can etiolation be reversed? how would you do this and what is this called?
YES
by exposing the plant to light regularly
de-etiolation
What are the three stages of cell signal processing and what does this look like?
Reception - receptors (usually proteins) change shape in response to a stimulus or hormone, these are often found on the plasma membrane.
transduction - secondary messengers amplify signals produced and transfer singnal to intracellular proteins to carry out response
response - cellular response is activated and cellular activities are regulated as a result.
Describe the cell signal processing pathway in regards to de-etiolation (reception, transduction, and response).
Reception - light would be the stimulus in this case that binds to receptor PHYTOCHROME RECEPTOR that responds to light by: opening Ca2+ channels to increase cytosol concentration of calcium and activating enzyme that produces cGMP
Transduction - second messengers include: Ca2+ and cyclic GMP (cGMP), second messengers above transfer signal to protein kinases.
Response - Protein kinases are activated and generate response by activating transcription factors that regulate expression of specific genes (like ones for de-etiolation). de-etiolation response begins: chemical precursors to chlorophyll produced, photosynthesis, regulate levels of different plant hormones that regulate growth.
How are already existing proteins modified to become activated or deactivated?
phosphorylation and dephosphorylation
What is the difference between a protein kinase and a phosphatase?
protein kinase - are directly activated by cGMP and Ca2+. ALSO PHOSPHORYLIZE transcription factors, turning them on.
phosphatase - TURN OFF TRANSDUCTION PATHWAYS BY DEPHOSPHORYLATION.
What are the 4 characteristics of plant hormones we discussed in class?
- they are chemical signals that modify or control one of more physiological process within a plant
- are produced in veyr low concentrations but have profound effect on growth and development.
- have multiple effects, also multiple hormones can effect a single process.
- effect plant responses based on the amount or concentration of specific hormones and often the combination of hormones present.
What are the 8 different hormones we discussed in class and where are they made?
auxin - young leaves, apical meristem, seeds and fruit
cytokinins - roots, embryos, and fruits
gibberellins - meristems of apical buds and roots, young leaves, developing seeds
abscisic acid - EVERYWHERE
ethylene - EVERYWHERE
brassinosteroids - EVERYWHERE
jasmonates - not specified
strigolactones - root
What is the function of auxin (8)?
Stem elongation
Phototropism - curvature towards light
Prevents leaf abscission
Apical dominance
Phyllotaxy (arrangement of leaves on the stem)
Leaf venation
Development of fruit
Promotes formation of lateral and adventitious roots (used in vegetative propagation - using cutting to grow new plants)
What is the coleoptile and how does it relate to auxin?
This is the sheath that covers the young shoot.
Experiments done that realized grass seedlings only bend towards light if the tip of the coleoptile were present. It is suspected that auxin moved from the tip to the region of elongation to promote this response.
What is the eacid-growth hypothesis and how does it relate to auxin?
Auxin stimulates the proton pumps of cells (pumping more H+ protons into the cell wall) in the region of growth which increases the membrane potential and lowers the pH.
Expansins located in the cell wall have their cross-links to cellulose microfibrils and other components broken in response to this increase in proton numbers, THIS LOOSENS THE WALLS FABRIC
At the same time the increase in membrane potential is causing ions to flow inside the cells and with them water travels with them causing increased turgor of the cell.
this increase in turgor and increased plasticity of cell wall causes the cell to elongate.
What is a practical use for auxins?
synthetic auxins can kill plants in high doses, so they can be used as a HERBICIDE
What are the functions of cytokinins (4)?
Increase cell division (CYTOkinesis)
Delays senesence (Inhibiting protein breakdown)
Seed germination
Apical dominance - counters auxin and stimulates axillary bud growth, cytokinins comes form roots, explains why lower parts of plants tend to have longer axillary growth towards bottom.
What are the functions of giberellins (3)?
Stem elongation and cell division
Fruit growth (used in spraying seedless grapes)
Gemrination and development of seeds (see starch breakdown card)
Describe how gibberellin brekas down starch during germination.
- seed imbibes water, stimulated gibberellin release to aleurone (thin outer layer of endosperm)
- aleurone releases enzymes such as amylase that breaks down starch
- sugars absorbed by scutellum (cotyledon) and consumed during growht of seedling
