Download Bio426Lecture11Feb17

Ectomycorrhiza
Inside root
• Intercellular hyphae
• Does not enter cells
Outside root
• Thick layer of hyphae around root
• Fungal sheath
• Lateral roots become stunted
• Hyphae
•Mass about equal to root mass
Forms extensive network of hyphae
even connecting different plants
Ectomycorrhizal root tip
Mantle
Hyphae
Hartig Net
Why mycorrhiza?
• Roots and root hairs
cannot enter the smallest
pores
Why mycorrhiza?
• Roots and root hairs
cannot enter the smallest
pores
• Hyphae is 1/10th
diameter of root hair
• Increased surface area
Root hair
Smallest hyphae
•Surface area/volume of a
cylinder:
SA/vol ≈ 2/radius
Why mycorrhiza?
Not inoculated
with
mycorrhizae
Inoculated with
mycorrhizae
• Roots and root hairs
cannot enter the smallest
pores
• Hyphae is 1/10th of root
hair
• Increased surface area
• Extension beyond
depletion zone
Why mycorrhiza?
• Roots and root hairs
cannot enter the smallest
pores
C – C – NH2 --> C – C + NH3
• Hyphae is 1/10th of root
hair
• Increased surface area
• Extension beyond
depletion zone
• Breakdown of organic
matter and transfer of its N
to host plant.
Are mycorrhizae always beneficial?
Probably not!!
Mycorrhizal interaction continuum
(Nancy Johnson & Co)
Mutualistic
Neutral
Parasitic
What conditions influence where on the continuum a
given interaction falls?
Mycorrhizal response (MR) of various plant
species at ambient and elevated CO2.
MR > 0 means better growth with AM than without AM
MR < 0 means better growth without AM than with AM
Plant growth is reduced by a full soil community that includes
mycorrhizal fungi (filled bars) compared to the partial community
(open bars). Added N significantly reduces the stunting of plant
growth by the full soil community.
Are soil organisms competing with plants for nitrogen?
Total plant mass, g
6
Agropyron repens
5
- Nitrogen
+ Nitrogen
Full
Full
4
3
2
1
0
Full Partial
Partial
Soil Community
Partial
Full
Partial
Summary on mycorrhizae
• Symbiosis with mycorrhiza allows greater soil exploration,
and increases uptake of nutrients (P, Zn, Cu, N, water)
• Mycorrhiza gets carbon from plant
• Great SA per mass for hyphae vs. roots
• Not all mycorrhizal associations benefit the plant!
• Two main groups of mycorrhiza – Ectomycorrhiza and VA-mycorrhiza
For us
more on nitrogen nutrition
•Why is N so important for plant growth?
•What percentage of the mass of plant tissues is N?
•What kinds of compounds is N found in?
•Why is there a strong relationship between the N
concentration of leaves and photosynthesis?
Nitrogen - the most limiting soil nutrient
Evidence - factorial fertilization experiments (N, P, K, etc.)
show largest growth response to N.
1.
Required in greatest amount of all soil nutrients
2. A component of proteins (enzymes, structural proteins,
chlorophyll, nucleic acids)
3. The primary photosynthetic enzyme, Rubisco, accounts
for a 25 to 50% of leaf N.
Photosynthetic capacity is strongly correlated with
leaf N concentration.
4. Availability in most soils is low
5. Plants spend a lot of energy on N acquisition - growing
roots, supporting symbionts, uptake into roots, biochemical
assimilation into amino acids, etc.
The inorganic forms of nitrogen in soils.
1. NH4+, ammonium ion. A cation that is bound to clays.
2. NO3-, nitrate ion. An anion that is not bound to clays.
Nutrient “mobility” in soils refers to the rate of diffusion,
which is influenced by nutrient ion interactions with soil particles.
Would you expect NH4+ or NO3- to diffuse more rapidly?
Would you expect a more pronounced depletion zone for NH4+ or NO3-?
The Nitrogen Cycle
N2
Atmospheric N2
Plant N
N Fixation
NO, N2O
Denitrification
NH4+ uptake
NH4+
NO3-uptake
Nitrification
NH4+
immobilization
Mineralization
Soil
Organic N
NO3NO3immobilization
Leaching
Solute Transport (Ch. 6)
1. The need for specialized membrane transport systems.
2. Passive vs. Active Transport
3. Membrane Transport Mechanisms
Why the need for specialized transport systems?
Fig. 1.4
Fig. 1.5A
That the permeability of biological membranes differs
from that of a simple phospholipid bilayer indicates
that transporters are involved.
Fig. 6.6
Passive vs. Active Transport
Passive transport requires no energy input, DG < 0
Active transport requires energy, DG > 0
Hydrostatic
Whether active or passive transport is required is
determined by the chemical potential of a solute on
either side of a membrane.
We can use the DG concept to understand the chemical
potential.
Chemical potential difference
1. Concentration component
2.3 RT log (Cji/Cjo)
What is the concentration influence on where
the solute will tend to move spontaneously?
2. Electrical component
zjFE
What is the electrical influence on where
the solute will tend to move spontaneously?
Movement along electrical and concentration gradients
(from Lecture 3)
DG = zF DEm + 2.3 RT log(C2/C1)
At equilibrium (DG = 0) can rearrange this as:
DEm = -2.3(RT/zF) log(C2/C1)
Nernst potential
•The difference in electrical potential (voltage)
between two compartments at equilibrium with
respect to a given solute.
•The membrane electrical potential at which the
concentration and electrical influences on a solute’s
movement are exactly balanced, so there is no net
movement.
DEj = 2.3RT (log Cjo/Cji)
zjF
•At equilibrium, the difference in concentration of
an ion between two compartments is balanced by
the voltage difference between the compartments.
Cj
o
Cji
Plasmamembrane and the tonoplast are sites
of much ion transport.
Fig. 6.4
Maintenance of cell membrane potential
requires energy produced by respiratory metabolism
Fig. 6.7
Fig. 6.8
Transport of a solute against its concentration gradient can
occur by coupling it to proton transport with its concentration
gradient.
Fig. 6.9
even