crop physiology / summer semester 1 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 reactions Mo Constituent of nitrogen reducing enzymes B Involved in sugar metabolism and transport Mn, Cl Involved in water splitting in photosynthesis Fe Constituent of cytochromes, ferrodoxin K Involved in maintenance of ionic balance O Terminal electron acceptor in respiratory energy exchange C, H, O Constituents of stored energy in seeds, fruits, tubers, etc Mg Constituent of chlorophyll P Inorganic nutrient involved in metabolic energy transfers N, S, C, H, O, P Constituents of proteins, enzymes, nucleic acids C, H, O, Ca Constituents in plant structure Element Role Essential Plant Nutrients 60,000 H 2 O H Hydrogen 40,000 CO 2 C Carbon 30,000 O 2 , CO 2 O Oxygen 1,000 NO 3 - , NH 4 + N Nitrogen 250 K + K Potassium 125 Ca 2+ Ca Calcium 80 Mg 2+ Mg Magnesium 60 H 2 PO 4 - , HPO 4 2- P Phosphorus 30 SO 4 2- S Sulfur Conc. in DM mmol/kg Available form Chem. Symbol Element Macronutrients
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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
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.
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Hydroponic Culture and Essential Elements
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Hydroponic Farming
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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
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Deficiency Symptoms
• Chlorosis– N, Mg, S, Fe,…
• Necroses– K, …..
• Stunting– Ca, B, ……
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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
* 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
---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