9.3 Growth in plants Flashcards
What are meristems?
Meristems are tissues in a plant consisting of undifferentiated cells capable of indeterminate growth
Why are meristems different to totipotent stem cells?
They have specific regions of growth and development
What can meristematic tissue cause?
Plants to regrow structures or even form new plants
What are the two types of meristems?
Apical meristems and Lateral meristems
Where do apical meristems occur?
At shoot and root tips
What are apical meristems responsible for?
Primary growth (plant lengthening)
Where do lateral meristems occur?
At the cambium
What are lateral meristems responsible for?
Secondary growth (plant thickening/ widening)
What do apical meristems produce?
New leaves and flowers
What do lateral meristems produce?
Bark
What causes the growth of apical meristems at the tips of the roots and shoots?
A combination of mitosis and cytokinesis
What does differentiation of the dividing meristem cause?
A variety of stem tissues and structures like leaves and flowers
Where does growth occur in the the stem?
In the nodes
What happens to the remaining meristem tissue?
They form an inactive axillary bud
What do lateral axillary buds have the potential to do?
Form new branching shoots, compete with leaves and flowers
What controls the growth of the stem and formation of new nodes?
Plant hormones
Where are the plant hormones released from?
The shoot apex
What are auxins?
One of the main groups of plant hormones involved in shoot and root growth
What happens when auxins are produced by the shoot apical meristem?
It promotes growth in the shoot apex via cell elongation and division
What does the production of auxin prevent?
Apical dominance - growth in lateral axillary buds
What does apical dominance do?
Makes sure that a plant uses its energy to grow up towards the light in order to outcompete other plants
What happens when the distance between the terminal bud and axillary bud increases?
The inhibition of the axillary bud by auxin diminishes
What will different species of plants show?
Different levels of apical dominance
What can auxin efflux pumps set up?
Concentration gradients within tissues which change the distribution of auxin within the plant
What can auxin efflux pumps control and how?
The direction of plant growth by determining which regions of plant tissue have high auxin levels
Why can auxin efflux pumps do?
Change position within the membrane due to fluidity
Be activated by different factors
In shoots what does auxin do to cell elongation?
Stimulates it
What does high concentration of auxin in shoots do?
Promotes growth
In roots what does auxin do to cell elongation?
Inhibit it
What does high concentration of auxin in roots do?
Limit growth
How does auxin influence cell growth rates?
By changing the pattern of gene expression within a plants cells
Why are auxins mechanism of action different in shoots and roots?
As different gene pathways are activated in each tissue
In shoots how does auxin promote plant growth via cell elongation?
By increasing the flexibility of the cell wall
What does auxin activate in the plasma membrane?
A proton pump which causes the secretion of H+ ions into the cell wall
What does the decrease in pH caused by auxin result in?
Cellulose fibres within the cell wall to loosen by breaking the bonds between them
What does auxin upregulate?
The expression of expansins which increase cell wall elasticity
As the cell wall is more flexible what does that cause?
An influx of water causing the cell to increase
What is tropisms?
The growth or turning movement of a plant in response to a directional external stimulus
What is phototropism?
A growth movement in response to a unidirectional light source
What is geotropism/gravitropism?
A growth movement in response to gravitational forces
What is hydrotropism?
A growth movement in response to a water gradient
What is thigmotorpism?
A growth movement in response to a tactile stimulus
What are both phototropism and geotropism controlled by?
The distribution of auxin in the plant cells
Where will auxin accumulate in geotropism and why?
On the lower side of the plant in response to the force of gravity
What triggers auxin in phototropism?
Light receptors called phototropins
What do phototropins trigger?
The redistribution of auxin to the dark side of the plant
What happens on the dark side of the shoot in phototropism?
The dark side of the shoot elongates and shoots grow towards the light
What happens on the lower side of the shoot and the roots in phototropism?
The lower side of the shoot elongates and roots grow away from the ground
What happens on the dark side of the root in phototropism?
The dark side of the root becomes shorter and the roots grow away from the light
What happens on the light side of the root in phototropism?
The lower side of the root becomes shorter and the roots turn downwards into the earth
Where does negative phototropism occur?
The roots
Where does positive phototropism occur?
The shoots
What is micropropagation?
A technique used to produce large numbers of identical plants
Why can plants reproduce asexually from meristems?
Because they are undifferentiated cells capable of indeterminate growth
What is vegetative propagation?
When a plant cutting is used to reproduce asexually in the native environment
What is it called when plant tissues are cultured in the laboratory in order to reproduce asexually?
Micropropagation
What is selected during the micropropagation?
Specific plant tissue from a stock plant which is then sterilised
What is the explant?
The tissue sample
Where is the tissue sample during micropropagation grown?
On a sterile nutrient agar gel
What is the explant treated with and why?
It is treated with growth hormones to stimulate shoot and root development
What happens to the growing shoots in micropropagation?
They can be continuously divided and separated to form new samples
During micropropagation, what happens once the root and shoot developed?
The cloned plant can be transferred to soil
Why is micropropagation used?
To rapidly produce large numbers of cloned plants under controlled conditions
What are the three reasons to use micropropagation?
Rapid bulking
Virus free strains
Propagation of rare species
Why are desirable stock plants cloned via micropropagation?
To conserve the fidelity of the selected characteristics
Why is micropropagation more reliable than selective breeding?
Because new plants created are genetically identical to the stock plant
How do plant viruses spread through infected plants?
Via the vascular tissue
How can propagating plants prevent viruses?
Propagating plants from non infected meristems allows for the rapid reproduction of virus free plant strains
What does micropropagation do for rare species?
Increases the number of them
Why does micropropagation help orchids?
Because they are difficult to breed sexually
What helps increase numbers of species commercially in demand?
Micropropagation
