Mineral Nutrition

Question 1

Green Revolution

Answer 1

1960s

• adding minerals to crops increases productivity
• plant breeding for increased productivity

Question 2

Ion uptake by roots

Answer 2

• 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

Question 3

Root growth

Answer 3

root growth depends on water and nutrient availability

adequate moisture and nutrients –> rapid growth

inadequate moisture and nutrients –> stunted growth

Question 4

Types of root systems

Answer 4

taproot - one main root, axial roots

fibrous – roots branch and form fibrous network

Question 5

root cap/ sheath

Answer 5

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

Question 6

Soil and Nutrient Uptake

Answer 6

Soil is composed of

• colloids (suspended particles)
• clay (inorganic)
• humus (organic)
• -> Colloids and clay have high surface area
• serve as a reservoir of ions

Question 7

Charge and pH are important

Answer 7

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)

Question 8

root growth

Answer 8

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

Question 9

Ion exchange in the soil

Answer 9

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

Question 10

soil pH

Answer 10

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

Question 11

nutrients

Answer 11

• 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

Question 12

essential elements

Answer 12

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.

Question 13

Essential elements

Answer 13

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

Question 14

essential elements and their uses

Answer 14

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

Question 15

nutrient transport

Answer 15

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

Question 16

Phloem Anatomy

Answer 16

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 injury

Question 17

Phloem Transport

Answer 17

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)

Question 18

Phloem Loading

Answer 18

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)

Question 19

Phloem Unloading

Answer 19

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

Question 20

Mechanism of phloem transport

Answer 20

(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

Question 21

Summary

Answer 21

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.