Mineral Nutrition in Plants I

When one tugs at a single thing in nature, (s)he finds it attached to the rest of the world.

John Muir

USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 2: 619.

Oplopanax horridusDevils Club

• Ethnobotany,

– Medicinal uses,

– Sacred uses,

– herbalgram.org

• Modern uses,

– Empirical studies,

NCBI.

NPR

Assimilation

• Every organism is an open system connected to its environment by a continuous exchange of energy and nutrients....

• …in the energy flow and chemical cycling that keep an ecosystem alive, plants…perform the key step of transforming inorganic compounds into organic ones.

• …and to synthesize organic matter, plants also requires raw materials in the form of CO2 H2O and a variety of mineral present

as inorganic ions in the soil.

…prelude to Chapter 37 (old edition), Campbell and Reece.

Sessile and Dainty

…stationary,

…growth and development are a plant’s version of locomotion,

– primary and lateral roots exploit new space,

– axilary buds grow new stems, yielding new leaves, that in turn build mesophyll cells, etc.

Dainty?

- generally, no excretory organs.

Where does it go?

• Exclusion;

– selective permeability of the plasma membrane (keep out),

• active transport of unwanted substances (kick out),

– secreted plant products take unwanted substances out of solution,

• Sequestration;

– most metabolic waste products and toxic substances are transported to the vacuole, some to other compartments (i.e. ER),

• Apoptosis and Abscission (+);

– programmed cell death and programmed organ death, (i.e. leaf drop).

vacuole

Programmed Cell Death

Plant Nutrition and Mineral Transport

• What elements are found in plants?

• How and where do they function?

• Phytoremediation?

• Nutrient Deficiencies?

Relative Elemental Analysis of Plants

H2O or CO2

Soil

Essential Nutrients

• Essential mineral nutrients:

– one whose absence prevents a plant from completing its life cycle (classic definition),

– or, one that has a clear physiological role (current modification of classic definition).

• Macronutrient: required in relatively large amounts,

• Micronutrient: required in relatively small amounts.

Use for reference, but we’ll organize the nutrients according to biochemical function.

Group 1. Nutrients that are part of carbon compounds.

Group 2. Nutrients that are important in energy storage or structural integrity.

Group 4. Nutrients that are involved in redox reactions.

Group 3. Nutrients that remain in ionic form.

See Table 38.1

Structural Elements, Covalently Bonded IGroup 1: Nutrients that are parts of carbon compounds...

• N: amino acids, proteins, nucleic acids, co-enzymes, etc.

• S: cysteine, methionine and proteins; lipoic acid and coenzyme A, etc.

Plants assimilate these nutrients via biochemical reactions involving oxidation and reduction.

low S high S

RootCell

MesophyllCell

Uptake;Secondary Active

Transport

Storage

Some assimilation into cysteine in the root,

Transport in the xylem sap to leaves.

Storage

Assimilation in leaves;

• cysteine,

• glutathione.

Sulfur Compounds

…hormone.

…antioxidant.

Phytochelatins• Chelate: a complex in which a metal ion is bound by a ligand,

– chelation: to remove (a heavy metal, such as lead or mercury) from solution by means of a chelate,

Traditional Heavy Metal Pollution Treatments

• remove, and/or • encapsulate (with concrete or asphault),

Phytoremediation,

• plants uptake, chelate and sequester metals, • harvest plants, dry, dispose (less mass).

Phytoextraction Phytostabalization

Phytodegredation

Accumulation in harvestable

shoot tissue.

Metal ions or toxins

Phytoremediation

• P: sugar phosphates, ATP, phospholipids, also nucleic acids, proteins,

• Si: deposited as amorphous silica in cell walls, contributes to cell wall mechanical properties,

– “essential” for life cycle in only a few species in hydroponic experiments,

– however, in the field, probably essential for survival of many more plants.

Structural Elements, Covalently Bonded II Group 2: Nutrients important for energy storage or structure...

Equisetum hyemale

Si obligate

• B: nucleic acid synthesis?, transport?, chlorophyll biosynthesis?,

– and cell wall function.

Rhamnogalacturonan II

11 different sugar monomers,

> 21 enzymes required for synthesis.

Structure is conserved in the cell walls of all higher plants,

– boron links two Rhamnogalacturonan II monomers,

– contributes to cell wall function through cross-linking with cellulose microfibrils and other cell wall components.

Salts, Co-factors, and Redox Reagents Group 3,4: Nutrients that remain in ionic form...

• Salts and Co-factors:

– K, Ca, Mn, Zn, Na, Mg,

• K: co-factor for > 40 enzymes, and is the principle cation for establishing cell turgor and control of membrane potential,

• Ca: contributes to cell wall structure, membrane structure, and acts in signal transduction,

• Mg: co-factor in enzymes required for phosphate transfers, and a component of chlorophyll.

• Redox Reagents:

- Fe, Cu, Mo, Mn.

Dose Response Curves

threshold

saturation

toxicity

Nutrient Deficiencies

Mineral deficiencies are relatively easy to identify in controlled conditions.

Hydroponics

Chronic and acute deficiencies of several nutrients may occur simultaneously,

Deficiencies (or excess) of one element may induce deficiencies (or excess of another element.,

Pathogens often induce symptoms similar to nutrient deficiencies.

Difficult in Soils

Recognizing Deficiencies

Leaf Clues;

– if an essential nutrient is relatively mobile, symptoms generally appear first in older leaves,

– deficiencies in relatively immobile nutrients generally appear in young leaves.

Nutrients classified based on their tendency to re-translocate

during deficiencies.

1. K+ is transported across the root cell plasma membrane,

2. K+ is transported from the root symplast to the xylem,

3. K+ is transported via xylem sap to the older leaves,

– diffuses to the apoplast and is transported into the mesophyll cells,

- or, K+ diffuses into, or out of the phloem.

5. Moves in source-sink direction.

K+ Transport

Deficiency Characteristics Group 1: Nutrients that are parts of carbon compounds...

• N (mobile) is most often the limiting nutrient in natural systems,

– it is a critical components in many plant cell components (especially proteins) and deficiencies quickly limit growth,

– the most typical deficiency characteristic is chlorosis (yellow leaves),

• slowly developing deficiencies produce short, woody stemmed plants,

• anthocyanin production (red pigment).

Means for using excess

carbohydrates.

• S (immobile) is generally available,

– deficiencies (especially proteins) quickly limit growth,

– similar general characteristics as seen in N deficiencies.

Deficiency Characteristics Group 2: Nutrients important for energy storage or structure...

• P (mobile) can be a limiting nutrient in natural systems (esp. at high pH),

– it is a critical components in respiration and photosynthesis as well as a key component of the phospholipids that make up membranes,

– the most typical deficiency characteristics are stunted growth and dark green leaves,

• necrotic lesions may occur,

• anthocyanin production (red pigment).

• Si (mobile) is usually available,

– lodging (falling over) and prone to fungal infections.

• B (immobile) lots of deficiency characteristics, especially necrosis (cell death) in expanding cells.

pH and Nutrient Availability

• The pH of the soil affects the availability of all elements,

• Plants adapt to the soil pH,

– directly modify soil pH,

– adapt mechanisms to operate in extreme conditions.

Width of bar corresponds to relative availability

Deficiency Characteristics Group 3: Nutrients that remain in ionic form...

• K (mobile) deficiencies,

– mottled or marginal chlorosis, veins retain their color, necrosis at margins, thin stems, short internodes,

• Ca (immobile) deficiencies,

– Necrosis in areas of cell division and rapid expansion (meristems), leaf primordium, etc.

• Mg (mobile) deficiencies,

– chlorosis, beginning especially between veins,

– old leaves, or young leaves?

Deficiency Characteristics Group 4: Nutrients that are involved in redox reactions...

• Fe (immobile) can undergo Fe2+ <--> Fe3+, are are important in electron transfer reactions,

– chlorosis, especially between veins,

– would you expect to see it in older or younger leaves first?

• Zn (mobile) deficiencies,

– dwarfism, extreme cases display chlorosis.

• Cu (immobile) deficiencies,

– dark green leaves, necrotic spots appearing at the tips of young leaves.

Wednesday

• Quiz

• Through assigned reading.