Mineral Nutrition Flashcards
Green Revolution
1960s
- adding minerals to crops increases productivity
- plant breeding for increased productivity
Ion uptake by roots
- roots absorb minerals from soil
Root anatomy:
- roots grow continuously
- roots can be 20-90% of plant biomass
- total root system can be miles long
- roots can be more extensive than canopy
Root growth
root growth depends on water and nutrient availability
adequate moisture and nutrients –> rapid growth
inadequate moisture and nutrients –> stunted growth
Types of root systems
taproot - one main root, axial roots
fibrous – roots branch and form fibrous network
root cap/ sheath
apical meristem – region of cell division (meristematic zone)
- elongation zone behind meristem pushes the root through the soil
- xylem and phloem
- root hairs
- most of root surface is root hairs
–> more surface area: more potential for water and nutrients to enter roots
Root cap serves to protect the root apical meristem
Soil and Nutrient Uptake
Soil is composed of
- colloids (suspended particles)
- clay (inorganic)
- humus (organic)
- -> Colloids and clay have high surface area
- serve as a reservoir of ions
Charge and pH are important
soil particles are negatively charged
- -> cations are reversible bound
- -> cations available for uptake by roots
anions not absorbed by soil particles
–> can be lost by water leaching (NO3-, PO4^-3)
root growth
root growth is favored by low pH (5.5-6.5) - slightly acidic soil
nutrients more soluble/available
Why is high pH not good for plants? Not enough protons, cations will be stuck at soil particles
Ion exchange in the soil
1) cations are absorbed to the negatively charged soil particles by electrostatic attractions
2) acidifying the soil increases the concentration of hydrogen ions in the soil. the additional hydrogen ions have a stronger attraction for the colloidal surface charges and so displace other cations into the soil solution
soil pH
soil pH drops from microbial metabolism
CO2 + H2O H2CO3 H+ + HCO3-
If the pH gets too low, adding lime to soil can improve nutrient availability. Why? lime (CaCO3) will help bring the pH back up
nutrients
- nutrients (ions: cations, anions) move into root by bulk flow with water or by transporters
–> nutrients taken up, soil locally depleted
–> roots grow to reach new areas of soil that are not nutrient depleted
essential elements
Essential elements (and light, CO2, H2O) allow plant to make everything that is needed
Criteria for essentiality:
(1) element required for plant to complete its life cycle (seed --> seed) (2) element has a demonstrable physiological role
–> many elements may play multiple roles in plant metabolism
The technique of hydroponics is a good way to determine which elements are essential to a plant.
Essential elements
H, C, O, N, P, S, Mg, Ca, K,
Mo, Cu, Zn, Mn, Fe, B, Cl
–> Na, Si, Se, Co considered beneficial
–> other elements may be found to be essential as our ability to measure them gets better
animals require: - -> Na, I, Co, Se, Si, Cr, Sn, Va, F - -> organic compounds
essential elements and their uses
N amino acids, nucleic acids P ATP, phosphorylated cpds K water potential S amino acids Ca pectin Mg chlorophyll, rubisco activation Fe P.E.T. Cu plastocyanin B phloem transport Mn water oxidation Zn N metabolism Mo N metabolism Cl water oxidation Ni ? Maybe N metabolism
nutrient transport
Xylem
–> minerals go up, generally transport
unidirectional
–> carry some amino acids (often made
in roots) and salts
–> passive: it is driven by transpiration
(water pulled up the plant)
Phloem
photoassimilates go down
transport can be bidirectional (up or
down)
80-90% sugar (sucrose – main
means for carbon to be transported
in the plant)
amino acids (glutamate, aspartate)
organic acids
plant hormones
polymers: protein, complex lipids
Phloem Anatomy
roots and stems are the same
sieve elements
major cell type, living cells
lose nucleus , vacuole, ribosomes
retain mito and ER
only primary cell wall
elongated, perforated end plates
(sieve plates) (end of the cells)
companion cells
secrete into sieve elements
numerous plasmodesmata
P Protein / callose
viscous
seals sieve plates during injuryPhloem Transport
transport is bidirectional
much slower than water movement
nutrients transferred from source to sink
three components:
source (eg: leaves – high [sucrose])
conduits (sieve elements)
sink (eg: roots or other tissues)
Phloem Loading
can be symplastic or apoplastic
symplastic: through plasmodesmata
sucrose can move by diffusion down gradient
apolplastic: through cell wall space
sucrose can enter apoplast
actively taken up into sieve element
requires energy (active transport)
Phloem Unloading
can be symplastic or apoplastic
symplastic:
sucrose moves down conc gradient by diffusion
apoplastic:
sucrose released into apoplast
hydrolyzed to glucose and
fructose
actively taken up into sink
sucrose actively unloaded into
apoplast
Mechanism of phloem transport
(pressure flow hypothesis)
based on water potential
water enters phloem with high [sugar]
and creates pressure
pressure at source moves sugar to
sink
sugar removed at sink
water returns via xylem
how can bidirectional transport occur? Presence of different columns of phloems allow for bidirectional transport to occur
does not require direct input of energy energy is used for loading and unloading
Summary
Water moves through plant based on difference in water potential
Water potential is composed of an osmotic potential and a pressure potential
Transpiration drives water transport in the plant
Xylem carries water and ions upward in plant
Phloem carries products of photosynthesis and is bidirectional
Xylem and phloem work together to move water and nutrients throughout the plant.
