mineral nutrition & nutrient uptake by plants - agri...

crop physiology / summer semester

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Mineral Nutrition & Nutrient Uptake by Plants

Plants and Inorganic Nutrients

17 essential plant nutrients• In its absence plant is unable to complete

normal life cycle• Element is part of some essential plant

constituent or metabolite• Element cannot be replaced by other element• Deficiency cannot be corrected by the

addition of similar elements of factors.

Nutrient Roles in Plants

Cu, Zn, Mn, Zn, Fe

Other essential elements involved in enzyme reactionsMoConstituent of nitrogen reducing enzymesBInvolved in sugar metabolism and transportMn, ClInvolved in water splitting in photosynthesisFeConstituent of cytochromes, ferrodoxinKInvolved in maintenance of ionic balance

OTerminal electron acceptor in respiratory energy exchange

C, H, OConstituents of stored energy in seeds, fruits, tubers, etcMgConstituent of chlorophyllPInorganic nutrient involved in metabolic energy transfersN, S, C, H, O, PConstituents of proteins, enzymes, nucleic acidsC, H, O, CaConstituents in plant structureElementRole

Essential Plant Nutrients

60,000H2OHHydrogen40,000CO2CCarbon30,000O2, CO2OOxygen

1,000NO3-, NH4

+NNitrogen250K+KPotassium125Ca2+CaCalcium

80Mg2+MgMagnesium60H2PO4

-, HPO42-PPhosphorus

30SO42-SSulfur

Conc. in DMmmol/kg

Available formChem. Symbol

Element Macronutrients


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Essential Plant Nutrients

3.0Cl-ClChlorine2.0BO3

3-BOBoron2.0Fe2+, Fe3+FeIron1.0Mn2+MnManganese0.3ZN2+ZnZinc0.1Cu2+CuCopper0.05Ni2+NiNickel0.001MO4

2-MoMolybdenum

Conc. in DMmmol/kg

Available formChem. Symbol

Element Micronutrients

Beneficial Elements

• Sodium - Na, required for C4 plants, perhaps pyruvate transport

• Silicon - Si, strengthens cell wall in grasses, helps fight fungi, lodging

• Cobalt - Co, essential for legumes, really for N2-fixing bacteria

• Selenium - unknown role

Critical Concentration of Nutrients

What is the critical concentration?

• A tissue concentration below which growth is limited by 10%.

• A toxic concentration can be defined as the concentration above which growth is limited.

• Nutrient concentrations in between critical and toxic are termed adequate.


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Nutrient Uptake from Soil

• Interception--contact exchange between root surface and soil particles

• Mass flow--nutrients in solution move to root surface along a water potential gradient

• Diffusion-- nutrients move down a concentration gradient from areas of high to lower conc.

Soil Water and Minerals

Factors Affecting Mineral Nutrient Availability

• Soil moisture• Organic matter• Soil texture• Soil temperature• Soil pH

pH and Mineral Nutrient

Availability


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Hydroponic and aeroponic systems for growing plants in nutrient solutions in which composition and pH can be automatically controlled. (A) In a hydroponic system, the roots are immersed in the nutrient solution, and air is bubbled through the solution. (B) An alternative hydroponic system, often used in commercial production, is the nutrient film growth system, in which the nutrient solution is pumped as a thin film down a shallow trough surrounding the plant roots. In this system the composition and pH of the nutrient solution can be controlled automatically. (C) In the aeroponic system, the roots are suspended over the nutrient solution, which is whipped into a mist by a motor-driven rotor.

Lab slide

Lab slide

Hydroponic Culture and Essential Elements

Lab slide


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Lab slide

Hydroponic Farming

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Lab slide

Nutrient deficienciesNutrient deficiencies

•• Mineral nutrient deficiencies occur when the Mineral nutrient deficiencies occur when the concentration of a nutrient decreases below the concentration of a nutrient decreases below the critical deficiency content (CDC) critical deficiency content (CDC)

•• Mineral nutrient deficiencies are another Mineral nutrient deficiencies are another conceptual example of the conceptual example of the ““Law of the minimumLaw of the minimum””–– Nutrient deficiency and CDC values determined from a Nutrient deficiency and CDC values determined from a

variety of studies variety of studies –– Greenhouse Greenhouse –– HydroponicHydroponic

Lab slide


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Deficiency Symptoms

• Chlorosis– N, Mg, S, Fe,…

• Necroses– K, …..

• Stunting– Ca, B, ……

Lab slide

Factors influencing susceptibility to Factors influencing susceptibility to nutrient deficienciesnutrient deficiencies

•• Plant factors Plant factors –– Species Species –– Developmental Developmental

stage stage –– Tissue or organ Tissue or organ

type type •• Environmental Environmental

factors factors –– Temperature Temperature –– Light Light

•• Soil factors:Soil factors:–– moisturemoisture–– NutrientNutrient--specific specific

factors factors –– External supply External supply –– Bioavailability Bioavailability –– Phloem mobility Phloem mobility

(next slide)(next slide)–– Nutrient interactions Nutrient interactions –– Soil pH Soil pH

Lab slide

Ion Mobility

• Ions can be delivered anywhere for utilization – Some can be redistributed from older tissues if

needed (deficiency symptoms in old tissues) – Example: N from enzymes/proteins

Mg from chlorophyll • Some are not redistributed (deficiency

symptoms in new tissues) – Example: Ca and Fe

Mobility of Plant Nutrients

Molybdenum, NickelZinc

Manganese*SodiumCopperChlorineBoronPhosphorusIronMagnesiumSulfurPotassiumCalciumNitrogenImmobileMobile

* Deficiencies may occur on older or younger leaves depending on species ` and growth rate


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Solute Transport• Membrane Potential

– For uncharged solutes---conc. gradient determines the chemical potential

– Charged solutes or ions will also diffuse in response to an electrochemical gradient

• ie., positively charges ions will be attracted to regions dominated by negative charge

Transmembrane Potential

Combination of Concentration differences and charge differences contributes to the electrochemical gradient

EquationNernst• States that at equilibrium the difference in conc.of

an ion between two compartments is balanced by the voltage difference between the two compartments.

• DEn = -2.3 RT/ zF log [C]i /[C]o– when DE = the electrical potential difference for ion

(Eo-Ei); z = valence of ion; e.g. K+ = +1; C = conc. of a charged species (mM, mM or M). T = 25 C or 298 K; F = 23 cal/mV. mole; R = 1.987 cal/mole.deg

• -zDEn = 59 log [C]i /[C]o

• Using the Nernst equation, 7 of the textbook; En = - 2.3 RT X log Ci

zF Co

and a gas constant (R) of 8.31441 J K-1mol-1, a Faraday constant (F) of 96,400 J V-1 mole-1, and remembering that 0°K is -273°C; for an external concentration of 1 mM and an internal concentration of 75 mM K+, what is the membrane electrical potential from outside to inside the membrane that is contributed by the K+, at 20°C?


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• The Nernst equation is presented by the following equation -zEn = 59 log Ci

Co If a tenfold difference of concentration existed across the membrane, inside higher than outside, for a univalent ion such as K+, what would be the electrical potential across the membrane due to this ionic concentration difference?

Mineral Uptake

• Roots and Leaves • In ionized form

– (NH4+, NO3

-, K+, Ca++, Cl-) • Transport:

– Passive (diffusion) or – Active (pumped)

Nutrient uptake determined by membrane transport

Model for Membrane Transport


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Passive Transport

• Dependent upon the electrical potential across membrane (+ or -)

• Most cells are negatively charged on inside• Soil particles are also negatively charged• So positive ions (cations) are more readily

bound to soil particles and transported across membranes than negatively charged ions (anions)

Active Transport

• Uses energy usually as ATP • Pumps against an electrochemical gradient • More anions (-) use active transport that

cations (+). Why? Because the cytoplasm is more negative than the apoplast

Active Transport

• Driven by ATPase proton pumps---hydrolyzes ATP and uses negative free energy to drive protons against an electrochemical gradient---proton gradient and membrane potential contribute to proton motive force with tendency to move protons back across membranes

ATP-ase Proton Pump and Solute Exchange


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Proton Motive Force

Primary source of energy for:• Active transport of cations, anions, amino acids,

and sugars• Regulation of cytoplasmic pH• Stomatal opening and closing• Sucrose transport ---[phloem loading]

Hypothetical steps in transport of a cation

Secondary Active Transport Coupled to Proton Gradient

Model for Secondary Active Transport—Symport


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Cell to Cell Transfers of Ions and Solutes---Plasmodesmatal connections

Ion Movement

• Ions track water movement from root hairs to the xylem and upward

• Symplastic movement (cell to cell, via plasmodesmata)

• Apoplastic movement (intercellular spaces)

Ion Movement Through Roots


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Nitrogen Fixation

• N is one of the more plentiful nutrients but not in the available form (N2)

• Several bacteria “fix” N in plant roots (primarily legumes: beans, peas, soybeans, alfalfa, clover, etc.)

• Symbiotic relationship between bacteria and plant

Molecular Biology of Root Nodule Formation


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Development of Root Nodule

Development of Root Nodule

Roots of soybean Fig 26-10 Raven et al

Root nodules on legumesMycorrhizal Fungi Facilitate Nutrient

Uptake

• A mutualistic relationship between soil fungi and plant root---83% of dicots---79% of monocots---all gymnosperms

• Absent from roots in very dry, saline, and flooded soils

• Absent where soil fertility is very high or low• Composed of fine, tubular filaments---hyphae• Hyphal mass form mycelium


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Mycorrhizae

EndomycorrhizaeEctomycorrhizae

Mycorrhizal Fungi

• Ectomycorrihzal fungi---thick sheath or mantle of fungal mycelium

---cortical cells not penetrated, but surrounded---Hartig net

---mass can be equal to root mass

---infects trees and woody angiosperms

Mycorrhizal Fungi

• Endomycorrihzal fungiVA—vesicular arbuscular mycor.

---hyphae are less dense---penetrate cells of cortex---vesicles within cells---arbuscules—site of

nutrient transfer---facilitates uptake of P, Zn, Cu

Tree Nutrition

Pinus strobus (White pine) without and with mycorrhizae. Raven et al Fig 13-38


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Mineral Nutrient Assimilation• incorporation of mineral elements into

organic molecules• Nutrients are assimilated directly into

organic molecules, e.g. C, H and O into sugars, N into amino acids, S – into amino acids, P into ATP

• Cation nutrients (K, Ca, Mg, Fe, Mn Cu, Co, Na, Zn) exist in complexes with organic molecules via nonconvalent bonds:

Mineral Nutrient Assimilation– Coordination bonds (several oxygen or nitrogen atoms share

electrons) to form a bond with a cation nutrient

Mineral Nutrient Assimilation– Electrostatic interactions – charge group attraction,

e.g., Ca2+ for carboxylate groups in pectin (Ca2+-pectate)

Mineral Nutrient Assimilation– C, H and O assimilation – photosynthesis and

respiration– Nitrogen

• NO3- assimilation involves a series of reductions to higher energy forms; nitrite (NO2

-, nitrate reductase w/NAD(P)H as the electron donor) → ammonium (NH4

+) (nitrite reductasew/ferrodoxin as the electron donor)

• NH4+ is assimilated into glutamine (glutamine synthase,

glutamate + NH4+ = glutamine)

• 12 ATP/N assimilated• Glutamine (2N/5C) is converted to asparagine (2N/4C),

which is the primary form for transport and storage. • NO3

- is transported to the shoot and most assimilation takes place in leaves; except when NO3

- levels are low, then assimilation occurs in the roots


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Mineral Nutrient Assimilation

• N2 (N≡ N, molecular nitrogen), nitrogen fixing bacterial symbionts in roots (primarily legumes), convert N2 to ammonia (NH3) (nitrogenase), which at physiological pH is converted to NH4

+. • Some legumes assimilate NH4

+ into ureides, which are by-products of uric acid.

Mineral Nutrient Assimilation• Sulfer – absorbed by roots as sulfate (SO4

2-) by co-transporters

• Assimilation of sulfate (SO42-) into cysteine, consumes

about 14 ATP/S • SO4

- is assimilated into 5’-adenylsulfate/adenosine-5’-phosphosulfate (SO4

- + ATP → APS + Pi, reaction catalyzed by ATP sulfurylase

• APS is then reduced to produce SO32-(APS reductase),

then SO32- is reduced to sulfide (S2-, sulfite reductase,

ferrodixin), which condenses with O-acetylserine (OAS) (S2- + OAS → cysteine) to form cysteine

• Assimilation occurs more in leaves than roots (because photosynthesis produces reduced ferrodoxin and photorespiration generates serine), SO4

- is transported to leaves

Mineral Nutrient Assimilation

• Phosphorous/phosphate - HPO42- is the

form absorbed by roots• Assimilation primarily into ATP (high

energy bonds) but it is incorporated into almost everything, transport form (to leaves) is primarily HPO4

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mineral nutrition & nutrient uptake by plants - agri...

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