Transcript Plant Mineral Nutrition

Plant Physiology talk Four
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
Mineral Nutrition
How plants acquire and use
mineral nutrients
• Why is mineral nutrition important?
• What are the essential mineral nutrients?
• classification systems
• Mineral nutrients in the soil
• nutrient availability
• adsorption to soil particles
• effects of pH
• Roots and mineral nutrient acquisition
• root structure
• depletion zones
• Mycorrhizae
• Nitrogen - the most limiting soil nutrient
Why is mineral nutrition important?
Fertilization increases crop production
Crop
Yield,
tons/hecta
re
Fertilizer used, kg/hectare
Why
is mineral
nutrition
Add more
fertilizer nitrogen,
get moreimportant?
crop production.
Fertilization increases crop production
Crop
Yield,
tons/hect
are
Nitrogen added, kg/hectare
Plants require nine
macronutrients and at least
eight micronutrients
• An essential nutrient is a particular
chemical element that is required for a
plant to grow from a seed and complete
the life cycle.
– 17 elements are essential nutrients
Essential plant nutrients
The symptoms of a mineral deficiency depend on
the function and mobility of the nutrient in the
plant
• For example, a magnesium deficiency, an ingredient of
chlorophyll, causes yellowing of the leaves, or
chlorosis.
• Iron may also be a culprit.
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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
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
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
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 of plant
growth hormones – Zinc
– The light reaction of photosynthesis - Copper
Biochemical functions of mineral
nutrients
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
•
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
nutrient-depleted zones in the
soil near the root
Mycorrhizal
associations
Minerals get taken up with Water
• Root hairs increase surface
area of root to maximize
water absorption.
• From the epidermis to the
endodermis there are three
pathways in which water can
flow:
• 1: Apoplast pathway:
• Water moves exclusively
through cell walls without
crossing any membranes
– The apoplast is a continuous
system of cell walls and
intercellular air spaces in
plant tissue
Minerals get taken up with Water
• 2: Transmembrane
pathway:
• Water sequentially enters a
cell on one side, exits the
cell on the other side,
enters the next cell, and so
on.
• 3: Symplast pathway:
• Water travels from one cell
to the next via
plasmodesmata.
– The symplast consist of the
entire network of cell
cytoplasm interconnected by
plasmodesmata
Minerals get taken up with Water
• At the endodermis:
• Water movement through
the apoplast pathway is
stopped by the Casparian
Strip
– Band of radial cell walls
containing suberin , a waxlike water-resistant material
• The casparian strip breaks
continuity of the apoplast
and forces water and
solutes to cross the
endodermis through the
plasma membrane
– So all water movement
across the endodermis occurs
through the symplast
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)
Leaf senescence and withdrawal of
nutrients to the plant
Senescence
•Term for the collective
process leading to the
death of a plant or plant
part, like a leaf.
•Leaf senescence is a part
of the process by which a
plant goes into dormancy
and is induced by a change
in day length.
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Changing leaf color
• As day length decreases, the plants
ability to synthesize chlorophyll
becomes reduced.
• Yellow and orange carotinoids and
xanthophylls, always present within
the leaf, begin to show.
• Water and nutrients are drawn into
the stems and from the leaves.
• Senescing cells also produce other
chemicals, particularly anthocyanins,
responsible for red and purple colors.
• Some species, particularly oaks,
contain high quantities of tannins in
the leaves which are responsible for
brown colors.
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Nutrient retention during senescence
• In deciduous tree species
some 60 – 70% of N, 60 –
70% of P, 30% of K, 25% of
Mg, and 15% of Ca are
withdrawn from leaves prior
to them being shed.
• Storage is in the bark and
elements are re-mobilized in
spring
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Leaf Abscission
• The final stage in leaf
senescence is abscission
("cutting off")
• Abscission is controlled by a
special layer of cells at the
base of the petiole, the
abscission layer.
• This layer releases ethylene
gas that stimulates
production of cellulase.
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Leaf Abscission
• This in turn breaks down cells
walls so that eventually the leaf is
held on to the plant only by xylem
fibers.
• Wind eventually weakens these
and leaf falls
• Another special layer of cells
adjacent to the abscission layer
produces cells impregnated with
suberin.
• These form a protective layer,
which is seen as the leaf scar
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Essential plant nutrients
Let Us Sum Up
Seventeen elements are considered
as essential plant nutrients for
higher plants.
They are generally classified based
upon their relative concentration in
plants.
They are also classified based upon
their biochemical behaviour and
physiological functions.
Mineral nutrients (14) are taken up by
plants in ionic forms.
Plant nutrients can also be classified
based on their biochemical behaviour
and physiological functions in plants.
Periodic table of plant mineral
nutrition
The End.
Any Questions?