Chemical Control Systems In Plants Flashcards
What 3 main parts can plant growth be divided into?
Cell division
Cell elongation
Cell differentiation
What is tropism?
The movement of part of a plant in response to and directed by an external stimulus
What is positive tropism?
Towards stimulus
What is negative tropism?
Away from stimulus
Synergy
Hormones interact together
Antagonism
Hormones have opposite effects
Growth factors: auxins
Promote cell elongation, inhibit the growth of side shoots, inhibit lead abscission
Growth factors: gibberellins
Promote seed germination and growth of stems
Growth factors: cytokinins
Promote cell division
Role of gibberellins
- seed absorbs water and swells
- embryo secretes G which diffuses into the aleurone layer
- G stimulates aleurone layer to produce amylase which diffuses into endosperm and breaks down food store for embryo
Evidence for gibberellins role in stem elongation
When G is applied artificially to dwarf plants they can stimulate stem elongation
What are photoreceptors?
Structures or pigments sensitive to light of specific wavelengths
Phototropins
Group of photoreceptors responsible for triggering phototropism
Where is indoleacetic acid made
Shoot apex
Positive phototropism involving IAA
Photoreceptors detect light
Auxin diffuses to shaded side of stem
Cells elongate by loosening structure of cell walls involving hydrogen ions
Positive phototropism as cells ok shaded side bend
How does auxin stimulate cell growth?
Bind to specific receptor sites on the cell-surface membrane
Activates the active pumping of hydrogen ions into cell wall spaces
Alters the hydrogen concentration which means low pH of cell walls for the enzymes that break bonds between adjacent Celulose microfibrils also mean cells are flexible
Absorb water by osmosis means turgor pressure and cell walls stretch leading to cell elongation
Auxins destroyed by enzymes
Apical dominance
The growth of the main central stem of a plant which reduces production of lateral shoots
Evidence that apical dominance is controlled by auxin
When the shoot apex is pruned (the apical bud) lateral branches grow higher up the plant
Example of antagonism in this process of apical dominance
Cytokinins made in roots and travel upwards to promote lateral growth whereas auxin travels downwards inhibiting lateral growth
Germination and wavelength: red light
Stimulates germination
Germination and wavelength: far red light
Inhibits it
Photomorphogenesis
Development of structure driven by light
Phytochromes
Pigments that control photomorphogenesis which has 2 Interconvertible forms pfr and pr
Role of Pr
Absorbs red light- there is no response
Role of pfr
Absorbs far red light= response- in darkness pfr is converted into Pr slowly
Short day plants
Red light inhibits flowering
In long periods of darkness pfr levels fall to allow flowering
Long day plants
High levels of pfr stimulate flowering
Short nights means little pfr converted to Pr
Flower growth
Florigen
Migrates through vascular system to apical meristem to promote floral initiation
Evidence that florigen spreads through grafted plants via plasmodesmata
- Graft and keep under long days and short nights
- Leaf is induced by long nights and short days
- If the leaf on the end of the chain is subjected to long nights all plants will flower
Etoliation plants
Kept in the dark:
Grow rapidly to reach light
Use food reserves
Grow tall with no chlorophyll
Pfr as a transcription factor
When Pr is converted into pfr in light it moves into nucleus
Binds to nuclear protein phytochrome interacting factor 3 (PIF3) which is a transcription factor
PIF3 only activates gene transcription and forms mRNA when it is bound to pfr
