Plant Foundations Flashcards
3 ways that plants are similar to animals
- Same stimuli (light, chemicals, touch)
- Have bulk flow systems (xylem and phloem)
- Need a way to perform gas exchange without water loss
Features of monocots
single cotyledon
paralell veins
mutiple main roots
SAM at base of plant
Feature of dicots
seed has two cotyledons (leafs)
tap roots branches with lateral roots
net type veins
SAM at apex of shoot
How do the survival strategies of monocots and dicots differ?
Monocots can let their above ground parts die becuase the SAM is protected
Dicots are able to grow their roots deeper so are more likely to keep ground parts
Features of model plant
Arabidopsis thaliana
- small genome
- fast life cycle
- self fertilising
- lots of seeds prodiced
- found accoss northern hemisphere so there is lots of genetic variation
How does plant and animal development differ?
- All animal development takes place at the start of life
- In plants, development is continuous throughout their life and is modulated by its environment (indiviudals can look very different)
2 key features of plants that must be established during development?
Polarity
Meristems
What are the two axes in plants?
Apical - basal: shoot to root
Radial: core to edge of stem
Why are meristems so important?
Allows plants to develop throughout their life and respond to environment
Means plants can remain sessile
What are the two classes of meristem?
Primary: contribute to plant height
Secondary: contribute to lateral growth
What are the three types of meristem?
Shoot apical meristem (SAM)
Auxillary meristems
Root apical maristem (RAM)
What is the function of the SAM
The souce of all above ground organs
3 zones:
- central zone that is source of all stem cells
- peripheral zone where stem cells leave and differentiate from
- rib zone produces central stem tissues
Key plant regulators in SAN size and new organ formation? - and their functions
Cytokinins - stabilise meristems
Gibberellins - not in meristems
Auxins - promote formation of new leaves
What is the function of auxillary meristems?
Allow the plant to recover from SAM removal
Found in leaves
How do auxillary meristems work?
They stay dormant until SAM removed - then auxin is sent as a signal to simulate development
Function of RAM?
Generates the axis of roots (not lateral roots)
Differences between SAM and RAM?
- Different organisation: RAM has quiescent centre, stem cells and a root cap to prevent mechanical injury by soil as it grows
- SAM generates axis and lateral organs (leaves) wheres RAM only generates axis
How does xylem/phloem develop?
secondary meristem: Vascular cambium - a distinct meristem is the source of xylem and phloem tissues
- cells displaced inwards to the stem develop into xylem
- cells displaced outwards develop into phloem
What plant growth regulators are used to develop xylem and phloem?
Auxin and cytokinin
What phytoreceptor detects red light?
Photochromes
What is the function of phytochromes?
Red and blue light are needed in photosythesis, so it is important for plants to detect where these are
Photochromes allow plants to grow away from shade and other plants
How do phytochromes sense light
Using its chromophore, existing in two states:
inactive (cis) and active
Activated by radiation/red light
Far red light caused chromophore to become inactive
How are do chromophores become inactive?
Far red light
Over time will regress - temperature dependent (faster at high temperatures)
What happens to active phytochrome?
Moves from cytoplasm to nucleus and interactes with transcriptional factors to mediate gene expression changes
What are phytochomes similar to in animals
Lipid soluble hormones
- enter the nucleus and alter gene expression
What effects can phytochromes have?
Seed germination, lead movement, synthesis of protective substances
How do lettuce seeds know when to germinate?
If in shade, and can only detect far red light, it will not germinate
If there is a flash of red light and germination is triggered, germination will stop after the detection of subsequent far red signals
What is blue light detected by?
Cryptochromes and phototopins and ZEITLUPE family
What do cryptochromes do?
Involved in developmental changes, growth responses and flower timing
How do cryptochromes work?
Light-sensitive chromophore
Absorption of photon causes confirmational change in protein
Enter nucleus and bind to transcription factors to change gene expression
How do phototropins work
Signalling through phosphoylation using a kinase domain (similar to GPCRs)?
What is buzz pollination?
Bee uses flight muscles to create a vibration that shakes pollen out of the anther
What are three potential functions of volatile signals?
- Recruit natural predators of herbivores
- Deter herbivores
- Warn other plants around them of herbivory
How is coordinated defense against herbivores work?
Jasmonic acid
- signals to plants to prime their own defense mechanisms
When might plants generate volatile compounds?
In response to wounding
How might volatile substances recruit predators?
Titan Arum plant mimics rotton flesh
Increased temperature is also through to recruit pollinators
How might a plant ‘tell the time’
Phytochromes and cryptochromes provide an input to the circadian clock of when it is light (as daylight times can change)
Then, some genes may be expressed just before dawn or dusk (eg. stomatal opening and closing, flower openint etc)
What is stress in plants
An condition that limit a plants full potencial
What are two possible responses to stress for plants
Input more energy into
- environmental growth - favoured by plants that live for many years
- reproductive efforts - favoured by annual plants
How might abiotic stress be sensed?
- Change in physical properties of plant
- Detection of misfolded proteins
- Detection of unusal or toxic chemicals
- Changes in DNA/RNA structure
- Sensing by specialised proteins
How are plant hormones different to animal?
Every plant cell is capable of producing PGRs, it is not limited to specific cell types/glands
How are PGRs similar to animal hormons
Need receptors to trigger a biochemical response to produce hormones and a response
(feedback loops)
Function of auxins?
Affect all aspects of plant development
- root development
- inhibition of shoot branching
Where are auxins produced?
Meristems
Function of cytokinins
Stimulate cytokinesis in response to nutrient levels
Also involved in meristem activity and aging
Function of gibberellins
“feel good factors”
released when times are good for plant (an increase in photosynthesis)
- flowering and fruit development
- seed germination
- cell elongation
upregulated by auxin
Function of abscisic acid
Stress factors - mainly responds to droubt and closes stomata to preserve water
- inhibit growth, germination and metabolism
Function of ethylene
Stress factor involved in
- wounding
- fooding
- UV-B radiation
these increase reactive oxygen species which increase ethylene release
Function of strigolactrone
Prevents shoot branching
Promotes symbiosis with fungi
Decrease with distance from root
Function of brassinosteriods
Similar to animal steriods
Cell elongation and differentiation
Germination and stress responses
Two hormones that are biotic stress responses
Salicyclic acid (pathogens)
Jasmonic acid (herbivores)
What is signalling by degregation?
ex: gibberallins
- in the absence of gibberellins, DLLA proteins interact with TFs so no transcription
- giberellins degredele della, so TPs can promote transcription
How does phosphorelay signalling work?
ex: cytokinin and ethylene
kinase sensor and relay of phosphorylation that ends with a nuclear response regulator transcrption factors
How is there communication between cells
Plasmodesmata allows the cytoplasm of cells to connect
- calcium ions can pass through plasmodesmata to propagate a signal through a tissue
When does calcium signallng happen?
Response to salt stress
Response to wounding
How does ROS signalling work?
ROS waves travel through a plant faster than diffusion
Allows whole plant acclimatisation to a local stress detection
How might nucleic acids signal in plants?
Long distance communication by small RNAs
- may be involved with RNA silencing
May be involved in the resposne to a range of stresses such as nutrient deprivation
What happens to a phosphate starved plant?
induction of small RNA in plant shoots, which moves to roots via phloem and signals to increase Pi uptake in roots
Calcium signalling experiment
Calcium sensor that flourses - know that it works
What may act as a signal in plants?
Hormones
Calcium
Nucleic acids
