Plant Nutrition and Transport

1
Plant Nutrition and Transport

• Smith
• Chapter 27

2
Plant Nutritional Requirements

• Nearly all plants are photoautotrophs
• Require carbon dioxide, water, minerals

3
Nutrients Essential for Plant Growth

• Macronutrients
• Carbon
• Hydrogen
• Oxygen
• Nitrogen
• Potassium
• Calcium
• Magnesium
• Phosphorus
• Sulfur

• Micronutrients
• Iron
• Boron
• Manganese
• Zinc
• Copper
• Chlorine
• Molybdenum

4
Why is the soil in a tropical forest not suitable
for agriculture?
5
Many aspects of plant structure are responses to
low concentrations of these vital resources in
the environment
6
Carnivorous Plants

• Plants that capture animals to supplement their
  nutrient intake
• Venus flytrap lures insects with sugary bait
  closes on victim
• Cobra lily lures insects down a one-way passage

7
Specialized Absorption Structures

• Root hairs
• Root nodules
• Mutualism
• Nitrogen fixation

8
Nutrient Uptake at Root Nodules of Legumes
Nitrogen-fixing bacteria
9
Mycorrhizae

• Symbiosis between a young plant root and a fungus
• Fungal filaments may cover root or actually
  penetrate it
• Fungus absorbs sugars and nitrogen from the plant
• Roots obtain minerals absorbed from soil by
  fungus

10
How will Mycorrhizae effect plant growth and why?

11
Why doesnt carbon enter the plant through its
roots?
12
Water Use and Loss

• Plants use a small amount of water for metabolism
• Most absorbed water lost to evaporation through
  stomata in leaves
• Evaporation of water from plant parts is the
  result of transpiration

13
How Do Stems and Leaves Conserve Water?

• Cuticle
• Waxes
• Stomata
• Guard cells
• Turgor pressure
• Swollen - Open
• Collapsed - Closes stoma

14
How is Water Transported Through Plants?

• Transpiration
• Evaporation
• Cohesion-tension theory
• Transpiration causes water in xylem to be pulled
  upwards
• Cohesion of fluid columns
• Hydrogen bonds
• holds one water molecule to another

15
Water Transport

• Water moves through xylem
• Xylem cells are tracheids or vessel members
• Both are dead at maturity

vessel member
16
Xylem and Phloem
17

TranspirationOnly 2 of water taken into a plant
at the roots is used for photosynthesis and other
plant functions
18
Cohesion-Tension Theory of Water Transport

• Hydrogen-bonded water molecules are pulled upward
  through xylem as continuous columns

19
The Role of Hydrogen Bonds

• Hydrogen bonds attract the hydrogen of one water
  molecule to the -OH group of another
• Hydrogen bonds make water cohesive water
  molecules stick together inside the narrow xylem
  walls as the molecules are pulled upward
• If water concentration of soil drops, inward
  movement stops, plant wilts

20
Transpiration Drives Water Transport
Water evaporates from leaves through stomata
This creates a tension in water column in xylem
21
Replacement Water is Drawn in Through Roots
22
Osmosis and Wilting

• Water responds to solute concentrations moves
  osmotically into plant cells
• When water loss is balanced by osmotically
  induced movement inward, plant is erect

23
Transpiration
Only 2 of water taken into a plant at the roots
is used for photosynthesis and other plant
functions
24
Cuticle

• Translucent coating secreted by epidermal cells
• Consists of waxes in cutin
• Allows light to pass though but restricts water
  loss

25
Stomata

• Openings across the cuticle and epidermis allow
  gases in and out
• Guard cells on either side of a stomata open and
  close it

26
How are Organic Compounds Distributed?

• Phloem
• Translocation
• Pressure Flow Theory

27
Pressure Flow Theory
28
translocation
29
Phloem

• Carry organic compounds
• Conducting tubes are sieve tubes
• Consist of living sieve-tube members
• Companion cells
• Lie next to sieve tubes
• Help load organic compounds into sieve tubes

30
TransportableOrganic Compounds

• Sugars travel through the phloem as sucrose
• Carbohydrates are stored as starches

31
Transport through Phloem
sieve plate
companion cell
sieve tube member

• Driven by pressure gradients
• Companion cells supply energy to start process

32
Loading at Source

• Small soluble organic compounds loaded into
  phloem

33
Where is the most common site for the source in
summer? Where would the source be in the winter?
The sink is going to be ?
34
Translocation

• Fluid pressure is greatest at a source
• Solute-rich fluid flows away from the
  high-pressure region toward regions of lower
  pressure

Section from a stem
35
Unloading at a Sink

• Region where compounds are being stored or used
• Solutes are unloaded into sink cells and water
  follows

Section from a root
36
Interdependent Processes
ATP formation by roots
absorption of minerals and water by roots
transport of minerals and water to leaves
respiration of sucrose by roots
transport of sucrose to roots
photosynthesis
37
In Conclusion

• A vascular plant depends on the distribution of
  water, mineral ions, and organic compounds to all
  of its cells
• Root systems take up water and nutrients
• Distribution of water and mineral ions occurs
  through xylem
• Plants lose water through transpiration
  evaporation of water from leaves and other parts
  exposed to air

38
In Conclusion

• Most plants have a waxy, water impermeable
  cuticle covering their aboveground parts
• Stomata open and close at different times
• Plants distribute organic compounds through
  sieve tubes

39
In Conclusion

• The pressure flow theory states that
  translocation is driven by differences in solute
  concentration and pressure between source and
  sink regions
• developed by M. Roig