Transcript Mineral Nutrition - ASAB-NUST

Plant Physiology
Mineral Nutrition
Mineral Nutrition in plants
• Plants are:
• Capable of making all necessary organic compounds
from inorganic compounds and elements in the
environment (autotrophic)
• Supplied with all the carbon, hydrogen, and oxygen
they could ever need (CO2, H2O)
• Required to obtain all other elements from the soil
so in a sense plants act as soil miners.
Mineral Nutrition in plants
• The study of how plants obtain, distribute,
metabolize, and utilize mineral nutrients.
• “Mineral”: An inorganic element
– Acquired mostly in the form of inorganic ions from the
soil
• “Nutrient”: A substance needed to survive or
necessary for the synthesis of organic compounds
Classifying mineral nutrients
• Amount required or present in plant tissue
• Metabolic need for the mineral nutrient
• Biochemical function(s) for the mineral
nutrient
• Mobility within the plant
Mineral macronutrients
Mineral micronutrients
Essentiality of mineral
nutrients
Essential: Universal for all plants
• – Absence prevents completion of life cycle
• – Absence leads to deficiency
• – Required for some aspect of mineral nutrition
• Beneficial: Often limited to a few species
• – Stimulates growth and development
• – May be required in some species
• – Examples: Na, Si, Se
Essentiality of mineral nutrients
• There are four basic groups:
• Group one:
– Forms the organic components of plants
– Plants assimilate these nutrients via biochemical
reactions involving oxidation and reduction
• Group two:
– Energy storage reactions or maintaining structural
integrity
– Present in plant tissue as phosphate, borate or silicate
esters
– The elemental is bound to OH group of an organic molecule
Biochemical functions of mineral
nutrients
Essentiality of mineral nutrients
• Group three:
– Present in plant tissue as either free ions or ions
bound to substrates such as the pectin component of
the plant cell wall
– Of particular importance are their roles as
– Enzyme cofactors
– In the regulation of osmotic potentials
Biochemical functions of mineral
nutrients
Essentiality of mineral nutrients
• Group four:
– This last group has important roles in reactions
involving electron transfer.
– Some also involved in the formation/regulation of plant
growth hormones – Zinc
– The light reaction of photosynthesis - Copper
Biochemical functions of mineral
nutrients
Techniques used to study
plant nutrition
Nutrient deficiencies
Mineral nutrient deficiencies occur when the concentration of a
nutrient decreases below this typical range
• Deficiencies of specific nutrients lead to specific visual, often
characteristic, symptoms reflective of the role of that nutrient in plant
metabolism
Chlorosis
Necrosis
Nutrient deficiency v. sufficiency
Patterns of deficiency
• The location where a
deficiency reflects the
mobility of a nutrient
• Nutrients are
redistributed in the
phloem
• Old leaves = mobile
• Young = immobile
Patterns of deficiency
Older leaves on celery turning yellow while the growing points in the center
remain green.
How are mineral nutrients acquired
by plants?
Uptake through the leaves
• Artificial: called foliar application. Used to apply
iron, copper and manganese.
• Associations with mycorrhizal fungi
• Fungi help with root absorption
• Uptake by the roots
The soil affects nutrient
absorption
• pH affects the growth of plant roots
and soil microbes
• Root growth favors a pH of 5.5 to
6.5
• Acidic conditions weathers rock
and releases potassium,
magnesium, calcium, and
manganese.
• The decomposition of organic
material lowers soil pH.
• Rainfall leaches ions through soil
to form alkaline conditions
The soil affects nutrient
absorption
• Negatively charged soil particles
affect the absorption of mineral
nutrients
• Cation exchange occurs on the
surface of the soil particle
• Cations (+ve charged ions) bind
to soil as it is –ve charded
• If potassium binds to the soil it
can displace calcium from the soil
particle and make it available for
uptake by the root
Plant roots – the primary route
for mineral nutrient acquisition
• Meristematic zone
– Cells divide both in direction of
root base to form cells that will
become the functional root and
in the direction of the root apex
to form the root cap
• Elongation zone
– Cells elongate rapidly, undergo
final round of divisions to form
the endodermis. Some cells
thicken to form casparian strip
• Maturation zone
– Fully formed root with xylem
and phloem – root hairs first
appear here
Root absorbs different mineral
ions in different areas
• Calcium
– Apical region
• Iron
– Apical region (barley)
– Or entire root (corn)
• Potassium, nitrate, ammonium,
and phosphate
– All locations of root surface
• In corn, elongation zone has max K
accumulation and nitrate absorption
– In corn and rice, root apex absorbs
ammonium faster than the
elongation zone does
– In several species, root hairs are the
most active phosphate absorbers
Why should root tips be the
primary site of nutrient uptake?
• Tissues with greatest need for nutrients
– Cell elongation requires Potassium, nitrate, and chlorine to increase osmotic
pressure within the wall
– Ammonium is a good nitrogen source for cell division in meristem
– Apex grows into fresh soil and finds fresh supplies of nutrients
• Nutrients are carried via bulk flow with water, and
water enters near tips
• Maintain concentration gradients for mineral
nutrient transport and uptake
Root uptake soon depletes
nutrients near the roots
• Formation of a nutrient
depletion zone in the region
of the soil near the plant root
– Forms when rate of nutrient
uptake exceeds rate of
replacement in soil by
diffusion in the water
column
– Root associations with
Mycorrhizal fungi help
the plant overcome this
problem
Mycorrhizal associations
• Not unusual
– 83% of dicots, 79% of monocots and
all gymnosperms
• Ectotrophic Mycorrhizal fungi
– Form a thick sheath around root.
Some mycelium penetrates the
cortex cells of the root
– Root cortex cells are not penetrated,
surrounded by a zone of hyphae
called Hartig net
– The capacity of the root system to
absorb nutrients improved by this
association – the fungal hyphae are
finer than root hairs and can reach
beyond nutrient-depleted zones in
the soil near the root
Mycorrhizal associations
• Vesicular arbuscular
mycorrhizal fungi
– Hyphae grow in dense
arrangement , both within the root
itself and extending out from the
root into the soil
– After entering root, either by root
hair or through epidermis hyphae
move through regions between
cells and penetrate individual
cortex cells.
– Within cells form oval structures
– vesicles – and branched
structures – arbuscules (site of
nutrient transfer)
– P, Cu, & Zn absorption improved by
hyphae reaching beyond the nutrientdepleted zones in the soil near the
Nutrients move from fungi
to root cells
• Ectotrophic Mycorrhizal
– Occurs by simple diffusion from the hyphae in the hartig
net to the root cells
• Vesicular arbuscular mycorrhizal fungi
– Occurs by simple diffusion from the arbuscules to the
root cells
– Also, as arbuscules are degenerating as new ones are
forming, the nutrients may be released directly into the
host cell
Manipulating mineral transport
in plants
• Increase plant growth and yield
• Increase plant nutritional quality and density
• Increase removal of soil contaminants (as in
phytoremediation)
Periodic table of plant mineral
nutrition
Vesicular-arbuscular mycorrhiza:Highly
colonized root of maize dyed with trypan
blue. Mycorrhizal formations are clearly
visible: 1) vesicles; 2) arbuscules
Ectomycorrhiza: root tip of Pinus
nigracolonised by ectomycorrhizal fungus