Plant Behaviour

Question 1

What must all living organisms be able to do?

Answer 1

» 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

Question 2

Define behavior

Answer 2

» The way in which an organism responds to an external stimulus
» In general terms, animals respond with movement, plants with growth

Question 3

What are the effects that determine the way a plant grows

Answer 3

• 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

Question 4

How do plants behave?

Answer 4

• Plants can detect a variety of external stimuli, and respond appropriately

Question 5

How do plants detect light and environmental factors?

Answer 5

- Photoreceptors:
» Light
- Mechanical stimulation
» Wind, herbivory
» Physical environment (eg, support structures)

Question 6

How do plants detect nutrients and physical forces of nature like temperature?

Answer 6

• 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 )

Question 7

Why is light an especially important environmental factor for plants

Answer 7

» Required for photosynthesis
» Triggers key events in plant development (“photomorphogenesis”)
» Allows plants to measure the passage of days and seasons

Question 8

What about light can plants detect?

Answer 8

» Presence/absence of light, but also
» Direction
» Intensity
» Wavelength (especially blue and red)

Question 9

How is blue light received in plants and what is it used for?

Answer 9

• 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

Question 10

How is red light received in plants and what is it used for?

Answer 10

• 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

Question 11

What are the responses t red light?

Answer 11

- 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

Question 12

What are biological clocks?

Answer 12

• 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)

Question 13

How does light effect biological clocks?

Answer 13

• 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)

Question 14

How does photoperiod effect plants?

Answer 14

• 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

Question 15

What are long-day plants?

Answer 15

• “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 )

Question 16

What are short-day plants?

Answer 16

• “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)

Question 17

How does gravity effect plants?

Answer 17

• Shoots grow upwards, roots grow downwards even in the absence of light because plants can detect gravity

Question 18

What are Statoliths?

Answer 18

• Statoliths: dense components within the cytoplasm of sensor cells that settle at the bottom of the cell, with gravity (≈ balance in animals)

Question 19

What are the types of Environmental stresses plants face?

Answer 19

• Environmental stresses can be biotic (living, eg herbivores) and abiotic (non living, eg water, temperature) - plants respond to both

Question 20

What are the types of water stress?

Answer 20

• Drought

- Flooding

Question 21

What are the effects of a drought?

Answer 21

» 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

Question 22

What are the effects of flooding?

Answer 22

» 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)

Question 23

What are the effects of salt on plants?

Answer 23

• 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 …)

Question 24

What are the types of temperature stress

Answer 24

• heat

- cold

Question 25

What are the effects of the heat temperature stress?

Answer 25

» Heat denatures proteins
» Transpiration helps plants cool down (by evaporative cooling)
» But if it is also dry, plants close their stomata, which stops this cooling, so plants also synthesize heat-shock proteins (HSPs; ≈ animals), which acts as scaffolds around proteins to help maintain their shape

Question 26

What are the effects of the cold temperature stress?

Answer 26

» Cold decreases membrane fluidity, altering transport across the cell membrane → plants increase proportion of unsaturated fat in membrane when exposed to low temps (which helps maintain fluidity)
» Plants in cold climates also secrete extra sugar to protect against frost

Question 27

How do plants respond to mechanical stimulation?

Answer 27

• Plants respond to touch » Plants that are touched grow more slowly
  » Vines coil rapidly around support, to climb upwards towards a forest canopy
• Most plant responses are mediated by hormones (chemical messengers of the endocrine system), but a few are similar to an action potential in the nervous system

Question 28

How do animal and plant communication systems differ?

Answer 28

• Plants do not have a nervous system, but they use chemical communication to coordinate their multicellular activity
• Endocrine communication in plants

Question 29

How does the endocrine system in plants work?

Answer 29

• Plant hormones regulate virtually all aspects of growth and development
  » Plant hormones can have different effects in different tissues and the developmental stage of the plant
  » Multiple hormones often interact to control growth and development

Question 30

What are signal transduction pathways

Answer 30

• The chains of molecules that relay signals inside a cell

Question 31

What are the steps of signal trasnduction?

Answer 31

1) Reception
2) Transduction
3) Response

Question 32

Draw and label the diagram of signal transduction

Answer 32

Google Doc

https://docs.google.com/document/d/1BpabtfqIj5MGsWdBTMRokVNMhJZjMkFjHpc7UqK5cCk/edit?usp=sharing

Question 33

Provide examples for four types of plants hormones

Answer 33

• Auxin
• Cytokinins
• Giberellins
• Ethylene

Question 34

What is Auxin and what is it used for?

Answer 34

- Chemical messenger produced mainly by shoot, involved in
» Cell elongation (increases cell size)
» Stem elongation
» Enhances apical dominance
» Formation of lateral and adventitious roots
» Regulates development of fruit
» Phototropism (response to light)
» Gravitropism (response to gravity)

Question 35

Where is synthetic Auxin used?

Answer 35

• Uses of synthetic auxins
  » Useful in vegetative propagation of plants by cuttings (stimulates formation of adventitious roots)
  » Monocots can rapidly degrade auxins, but eudicots cannot … application of synthetic auxins (eg, herbicide 2,4-D) kills eudicots by hormonaloverdose

Question 36

What is Cytokinins?

Answer 36

• Chemical messenger produced mainly in roots, involved in
  » Cell division (thus works in concert with auxin for elongation)
  » Antagonises the apical dominance action of auxin

Question 37

What is Giberellins?

Answer 37

• Chemical messenger
• Also involved in stem elongation
• With auxin, involved in fruit development
  » Use of synthetic giberellin sprays to make fruit bigger
• When combined with water, triggers seed germination

Question 38

What is Ethylene?

Answer 38

• When tip of growing seedling meets obstacle, ethylene is produced → “triple response” (enables the shoot to avoid the obstacle):
  » Slowing of stem elongation
  » Thickening of the stem (makes it stronger)
  » Curvature (causes the stem to grow horizontally)

Question 39

What are some function that Ethylene is used for?

Answer 39

» Senescence (programmed cell death)
» Leaf abscission (loss of leaves from deciduous trees)
» Fruit ripening: initiates enzymatic breakdown of cell wall and conversion of acids and starches to sugars to make the fruit sweet and attract animals
• Commonly used in commercial fruit production

Question 40

What is the first piece of evidence that proves plants have intelligence?

Answer 40

• Plants communicate with other lifeforms
  » Other plants
  » Animals (eg, plants attacked by herbivorous insects release “help” chemicals that attract carnivorous insects)

Question 41

What is the second piece of evidence that proves plants have intelligence?

Answer 41

• Just like animals, plants interact and compete with each other to capture sunlight and nutrients
  » “Pushing and shoving” towards the sun
  » Some even release of toxins and conduct chemical warfare underground

Question 42

What is the 3rd piece of evidence that proves plants have intelligence?

Answer 42

• Plants also collaborate …
  » Can recognise relatives (by chemical signatures), and reduce root growth when near siblings to reduce competition
  » In forests, trees are connected underground by huge mycorrhizal network through this network, trees share carbon with fungi and with each other!
  • Expose one tree to 14CO2, and a few days later you’ll find that 14C in seedlings around it → seedling are being nurtured by larger plants
  • Dying trees can send food (and alarm signals) to neighbours from a different species