Hormones Flashcards
Physiological roles of auxin (4)
-cell elongation, concentration dependent inhibition of growth, apical dominance and tropisms
Physiological roles of Gibberellins (4)
Parthenocarpy, seed germination, stem elongation and juvenile-adult transitions
Physiological roles of ABA (2)
Seed dormancy, water stress stomatal closure
What is senescence?
Aging of plant or plant parts due to degradation of chlorophylls, DNA, RNA and proteins is called as senescence
Why is ABA a stress hormone?
ABA is called a stress hormone because it closes the stomata to prevent water loss in drought conditions
What does an auxin mutant look like?
Dead
What does a pin mutant look like?
Tall, with no lateral growth (leaves, branches, flowers, etc.)
Physiological roles of Cytokinins (4)
Delays leaf senescence, promotes movement of nutrients, greening of tissues and chloroplasts, reverses apical dominance
How do CK’s counteract apical dominance?
Cytokinins alter the dormancy in lateral buds, and their relative concentration to auxin will stimulate growth. When the SAM is removed, CK is synthesized to activate a lateral bud which will become the new SAM. Lateral growth is stopped when auxin levels are greater than CK
How do CK’s delay leaf senescence?
CK’s are linked to the greening of leaves and chloroplasts, and source and sink relationships. By extending the periods of growth, senescence is delayed.
Physiological roles of Ethylene (4)
Fruit ripening, leaf/flower senescence, leaf abscission and breaking seed/bud dormancy
Where is ethylene synthesized?
Ethylene can be synthesized in all parts of the plant
How does leaf abscission occur?
Ethylene causes the degradation of cell walls by destroying enzymes (relevant to fruit dropping and senescence)
How is ABA transported?
Drought conditions create increased alkalinity in the apoplast, favouring the anionic form of ABA. In this form, ABA does not readily cross the membranes of mesophyll cells and thus more ABA molecules reach the guard cells to close them (and preserve water)
