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Plant Physiology

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Title: Plant Physiology


1
Plant Physiology
  • Mineral Nutrition

2
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.

3
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

4
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

5
Mineral macronutrients
6
Mineral micronutrients
7
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

8
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

9
Biochemical functions of mineral nutrients
10
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

11
Biochemical functions of mineral nutrients
12
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

13
Biochemical functions of mineral nutrients
14
Techniques used to study plant nutrition
15
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
16
Nutrient deficiency v. sufficiency
17
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

18
Patterns of deficiency
Older leaves on celery turning yellow while the
growing points in the center remain green.
19
How are mineral nutrients acquiredby 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

20
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

21
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

22
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

23
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

24
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

25
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

26
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

27
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 nutrient-depleted zones in
    the soil near the root

28
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

29
Manipulating mineral transport in plants
  • Increase plant growth and yield
  • Increase plant nutritional quality and density
  • Increase removal of soil contaminants (as in
    phytoremediation)

30
Periodic table of plant mineral nutrition
31
Vesicular-arbuscular mycorrhizaHighly 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
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