Plant Behaviour Flashcards
What must all living organisms be able to do?
» Organise biological molecules on a higher level
» Access and use energy
» Grow
» Respond to their environment
» Make more of themselves
- In order to stay alive, plants and animals must be able to detect and respond to changes in their external environment
Define behavior
» The way in which an organism responds to an external stimulus
» In general terms, animals respond with movement, plants with growth
What are the effects that determine the way a plant grows
- All plants grow and move in response to environmental information
» Stem and leaves towards the sun
» Foraging roots towards nutrients in the ground
» Root elongation slows down and root hairs spread out in areas of high nutrients
» Slow, so we generally don’t see it
How do plants behave?
- Plants can detect a variety of external stimuli, and respond appropriately
How do plants detect light and environmental factors?
- Photoreceptors: » Light - Mechanical stimulation » Wind, herbivory » Physical environment (eg, support structures)
How do plants detect nutrients and physical forces of nature like temperature?
- Physical environment
» Gravity, temperature, soil water, salt, CO2 - Chemical receptors:
» Nutrients
» Scents (eg, dodder vine can detect tomato smell)
» Chemical messages from other plants (eg, smell of freshly cut grass )
Why is light an especially important environmental factor for plants
» Required for photosynthesis
» Triggers key events in plant development (“photomorphogenesis”)
» Allows plants to measure the passage of days and seasons
What about light can plants detect?
» Presence/absence of light, but also
» Direction
» Intensity
» Wavelength (especially blue and red)
How is blue light received in plants and what is it used for?
- Blue light receptors (cryptochromes)
- Blue light initiates a range of responses in plants:
» Phototropism (growth towards light)
» Light-induced opening of stomata
» Light-induced slowing of elongation of the juvenile shoot (hypocotyl) after it breaks ground
How is red light received in plants and what is it used for?
- Red light receptors (phytochromes)
- Plants use red light as a measure of light quality (and competition)
» Measure ratio of far red (730 nm, NOT absorbed by overhanging leaves) to red (660 nm, absorbed by overhanging leaves)
» This occurs because phytochromes change shape depending on the presence of red, far red, or no light
What are the responses t red light?
- Seed germination » Seeds have limited food reserves, so many seeds germinate only when light environment (and other conditions) are optimal (eg, death of a shading tree) - Shade avoidance » Stimulates branching » Inhibits vertical growth - Setting of internal clock - Flowering
What are biological clocks?
- Biological systems (plants and animals) exhibit cyclic activity patterns (“circadian rhythms”)
» circa- = approximately, -dies = day
» Opening and closing of stomata, sleep (orientation of leaves in legumes)
How does light effect biological clocks?
- Biological clocks are internal
» Still being researched, but appear controlled by alternating feedback loops of transcription of “clock genes” - But those internal clocks are not perfectly aligned to 24h (vary between 21-27h) … to avoid desynchronisation, they are constantly re-set by light cues (both red and blue)
How does photoperiod effect plants?
- Plants also use the changing of the length of day (“photoperiod”) over a year to adapt to different seasons
» Eg, to avoid producing leaves in winter (for deciduous trees) - The photoperiod is a critical determinant of flowering → ensure flowers are produced when the right pollinators are present
What are long-day plants?
- “Long-day plants” (spinach, lettuce, irises …) flower only when the photoperiod is more than 14h, ie in spring/summer
» Measure is very accurate (just a minute can make the difference!)
» Actually controlled by length of darkness rather than day length )
What are short-day plants?
- “Short-day plants” (chrysanthenums, soybeans …) flower only when the photoperiod is less than a specific number of hours, ie in autumn/winter
» Measure is very accurate (just a minute can make the difference!)
» Actually controlled by length of darkness rather than day length)
How does gravity effect plants?
- Shoots grow upwards, roots grow downwards even in the absence of light because plants can detect gravity
What are Statoliths?
- Statoliths: dense components within the cytoplasm of sensor cells that settle at the bottom of the cell, with gravity (≈ balance in animals)
What are the types of Environmental stresses plants face?
- Environmental stresses can be biotic (living, eg herbivores) and abiotic (non living, eg water, temperature) - plants respond to both
What are the types of water stress?
- Drought
- Flooding
What are the effects of a drought?
» Water is needed for photosynthesis …
» Water deficit causes stomata to close → greatly reduces transpiration
» Other responses within different species
• Grass roll into tubelike shape to reduce exposure to dry air
• Other shed leaves in response to seasonal drought
» All reduce photosynthesis, but at least the plant survives
What are the effects of flooding?
» Flooded soils have no air space (thus less oxygen for cellular respiration)
» Some have adapted specialized aerial roots (eg mangroves)
» Others produce ethylene in response to flooding, which kills some cells in the root cortex, creating an air tube (≈ snorkel)
What are the effects of salt on plants?
- Salt stress affects plants for two reasons:
» Excess soil sodium decreases water potential of the soil, thus causing a deficit in net movement of water to the plant
» Sodium is toxic to plants at high concentrations - Some plants can produce organic compounds to counter-act these negative effects (to a certain extent …)
What are the types of temperature stress
- heat
- cold
