L19 - Overview: Principles of Mineral Nutrition Flashcards
Give 4 points on why plant nutrition is important
1) Diversity
- Ability to access nutrients determines species presence. Also affected by presence of mineralising microbes + symbionts
2) Human Health
- Depends on plant nutrient uptake .
- Cereals low in key minerals Fe and Zn, millions nutrient deficient
- Biofortification through fertilisers could alleviate deficiencies
- Or produce plants with more efficient uptake
3) Sustainability
- NPK fertiliser production = GHG and run-off
- P reserves running out, <50% N recovered by plants
4) Bioremediation
- Hyperaccumulators can withstand otherwise toxic conc. of metals
- Could be deployed in land clean-up
Give the two basic properties of soil and what these properties depend on
1) Soil horizons
- Depends on bedrock, subsequent weathering/deposition + vegetation history
- Greater plant colonisation = greater humic content of topsoil
2) Cation exchange capacity (CEC)
- Negative soil particles bind cations and then exchange these w/ soil water. Then available to plant
Higher CEC:
- Clayey soils - larger particles than sandy soil (but prone to hypoxia + waterlogging)
- High humic content (also better draining)
How does soil mineral content influence plant yield?
- For many minerals, e.g. K more soil K = more leaf K
- More leaf K = higher yield
Sort the 14 major nutrients into four groups based on their functions
N, S: Assimilated into Organic Compounds
P,B: Energy storage and structural integrity
K, Ca, Mg, Cl, Mn: Remain as ions. Osmotic relations, signalling, enzyme cofactors
Fe, Zn, Cu, Ni, Mo: Redox reactions
Macronutrients are required in what amount?
1000 - 1500 mg/kg
Describe the general shape of the dose-response relationship for each mineral
Sketch the relevant diagram
- Flat ‘adequate zone’ supports max. growth
- Deficiency + toxicity on either side
- E.g. cork spot Ca deficiency or leaf tip necrosis B toxicity
How may the typical habitat of a plant influence its mineral uptake response?
- Plants grown on poor soil will grow better on low nutrients but growth response to increasing nutrients may saturate quickly
- Doesn’t have machinery to take up additional nutrients
- E.g. Avenella
- Plants on richer soil likely grows poorly on poor soil but growth rises more as nutrient content increases
- Could be desired in crossing for increased mineral content
- E.g. Urtica
Describe the three possible pathways for minerals to reach the root xylem
1) Apoplastic flow
- Travel in cell walls and intercellular spaces of root tissues
2) Symplastic flow
- Travel through cytoplasm of root cells, connected by plasmodesmata
3) Trans-cellular pathway
- Transport mediated travel through individual cells, crossing the cell membrane at each step.
How do roots change with age and how does this affect each pathway?
- Root apex has little suberin, allowing all transport - Apoplastic flow dominates
- Older regions undergo suberin deposition, especially at Caspian Strip in the endodermis
- Restricts apoplastic movement, forcing minerals through membrane into symplast
- More selective and regulated (due to membrane crossing)
Give two categories of transporters involved in the trans-cellular pathway
Describe each category
1) Low Affinity Transporters (LATS)
- High capacity, low efficiency
- Best for high nutrient conc.
- Includes Channels
2) High Affinity Transporters (HATS)
- Low capacity, high efficiency
- Best for low nutrient conc.
-Includes Antiporters and Symporters
- H+ gradient from ATP pump utilised for active transport
Give the two types of HATS and describe them
Antiporter:
- Moves two or more molecules in opposite directions across a membrane
- Involves the exchange of ions or molecules
Symporter:
- Moves two or more molecules in the same direction across a membrane
- Uses gradient of one molecule to drive transport of another molecule
How does transport protein activity change with environment?
- Nutrient starved plants show higher uptake rates
Once in the xylem how are nutrients distributed?
- Transpiration drives distribution through the xylem
Are nutrients distributed homogeneously in organs tissues or cells?
Give examples
- No
- E.g. K+ content in the barley root epidermis varies between the cytosol and the vacuole
- When tissue [K+] low, K+ moved from vacuole to cytosol for homeostasis
What are hyperaccumulators?
Why are they under threat?
What are their potential applications?
- Plants that can survive otherwise toxic levels of mineral nutrients or non-nutrient metals
- Under threat of extinction from mineral mining
- Bioremediation potential but dwarf and slow growing
- Could produce faster growing plants capable of withstanding toxicity
List 4 few ways in which roots adapt to nutrient supply
What hormone underpins many of these adaptations?
- Under nutrient depletion more assimilates invested in root (root:shoot weight increases)
- Proliferation of lateral roots in response to localised mineral supply
- Different complements of transport proteins
- Root hair length and number - increase under deprivation
All growth changes involve changes in auxin distribution
