Final Exam - Plant Hormones Flashcards
What are the characteristics of meristems?
- perpetually undifferentiated tissues that allow a plant to have indeterminate growth
- active cell division
- cells are small and unexpanded
- plant development is plastic and represents responses to environment
What are the three basic plant organs?
- roots
- stems
- leaves
Where does primary growth of shoots occur?
from both the apical and axillary bud meristems
What are the major plant hormones?
- auxin
- cytokinins
- gibberellins
- abscisic acid
- ethylene
What is a tropism?
any response resulting in movement of organs toward or away from a stimulus
What is phototropism/
- cells on shaded side expand more than those on the side exposed to sunlight
- plants bend toward the light
What does most plant growth result from?
cell expansion due to the loosening of the cell wall
What is the acid-growth hypothesis?
- auxins stimulate acidification of the cell wall using proton pumps
- proton pumps lower the pH in the cell wall, activating expansins
- once the cellulose is loosened the cell can elongate
- turgor pressure expands the cell
How does auxin affect axillary and apical bud growth?
- inhibits axillary/lateral bud outgrowth
- promotes dominance of apical growth
What are the characteristics of apical meristems?
- generate primary growth
- growth in length through cell expansion
- dominant over other meristems
- responsible for vertical growth
What are the characteristics of axillary bud meristems?
- found above petiole/node junctions
- subordinate to apical meristems
What are the characteristics of root apical meristems?
-increase root length through cell expansion
What are the characteristics of cytokinins?
- stimulate cytokinesis
- produced in actively growing tissues
- stimulate growth of axillry/lateral buds
How do auxins and cytokinins work together?
- with auxin alone, cells expand but do not divide
- when auxin and cytokinin work together, cells expand AND divide
How do auxins and cytokinins play into apical dominance?
- auxins inhibit axillary bud growth, while cytokinins stimulate it
- competition between the two hormones contributes to apical dominance
What are the characteristics of gibberellins?
- variety of effects, including stem elongation and seed germination
- promote stem elongation via cell elongation and cell division
- dwarf varieties of plants are gibberellin-deficient
How does gibberellin deficiency occur in plants?
mutation in a gene which encodes a gibberellin biosynthesis enzyme
How do gibberellins play a role in germination?
- produced by embryos upon imbibition (initial water uptake)
- stimulates production of enzymes which digest complex carbohydrates to simple sugars
What is the main role of abscisic acid?
counteract the effects of other plant hormones
What are the two critical processes abscisic acid is involved in?
- seed dormancy
- drought tolerance
What are the characteristics of seed dormancy?
- ABA production occurs in dramatic increases during seed maturation
- ensures seed will germinate only in optimal conditions
- dormancy is broken when ABA is removed
How does ABA play a role in drought tolerance?
- ABA is the major hormone regulating the opening and closing of the stomata
- increased ABA will keep stomata closed
What are the characteristics of ethylene?
- simple, gaseous hormone
- associated with fruit ripening
