5: Mineral Nutrition in Plants

surrounding water

The algal ancestors of land plants absorbed water, minerals, and CO2 directly from the

Stems

They serve as conduits for water and nutrients, and as supporting structures for leaves.

Phyllotaxy

the arrangement of leaves on a stem, is specific to each species

leaf area index

the ratio of total upper leaf surface of a plant divided by the surface area of land on which it growsSoil

mycorrhizae

Roots and the hyphae of soil fungi form symbiotic

associations called

diffusion or active transport

bulk flow

Transport occurs by short-distance ___________ and by long-distance ________.

selectively permeable membrane

The movement of substances into and out of cells is regulated by

transport proteins

Most solutes pass through _________ embedded in the cell membrane.

proton pump

The most important transport protein for active transport is the?

membrane potential

The voltage across a cell's plasma membrane.

Proton pumps in plant cells create a hydrogen ion gradient that is a form of potential energy that can be harnessed to do work. They contribute to a voltage known as a _____?

proton gradient and membrane potential

Plant cells use energy stored in the _____(2)____ to drive the transport of many different solutes.

"coat-tail" effect

The _______ of co-transport is also responsible for the uptake of the sugar sucrose by plant cells.

Cotransport

The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient.

a transport protein couples the diffusion of one solute to the active transport of another.

cell wall

cytosol

The plasma membrane directly controls the traffic of molecules into and out of the protoplast. It is a barrier between two major compartments, the _____ and the ______.

vacuolar membrane (tonoplast)

A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the vacuolar contents, called cell sap.

- regulates transport between the cytosol and the vacuole.

central vacuole

a large organelle that occupies as much as 90% or more of the protoplast's volume.

symplast

In plants, the continuum of cytoplasm connected by plasmodesmata between cells.

In most plant tissues, the cell wall and cytosol are continuous from cell to cell. The cytoplasmic continuum is called the _______.

plasmodesmata

The cytoplasm of neighboring cells is connected by channels called

apoplast

In plants, the continuum of cell walls and the extracellular spaces.

Transmembrane route

Water and minerals can travel through a plant: out of one cell, across a cell wall, and into another cell

Symplastic route

Water and minerals can travel through a plant: via the continuum of cytosol

Apoplastic route

Water and minerals can travel through a plant: via the cell walls and extracellular spaces

endodermis

It is the innermost layer of cells in the root cortex. It surrounds the vascular cylinder and is the last checkpoint for selective passage of minerals from the cortex into the vascular tissue.

transpiration-cohesion-tension mechanism

A transport mechanism that drives the upward movement of water in plants: transpiration exerts a pull that is relayed downward along a string of molecules held together by cohesion and helped upward by adhesion.

The movement of xylem sap against gravity is maintained by the?

translocation

The products of photosynthesis are transported through phloem by the process of?

Phloem sap

It is an aqueous solution that is high in sucrose (disaccharide). It travels from a sugar source to a sugar sink.

sugar source

an organ that is a net producer of sugar, such as mature leaves

sugar sink

A plant organ that is a net consumer or storer of sugar such as tuber or bulb. Growing roots, shoot tips, stems, and fruits are sugar sinks supplied by phloem.

Transfer cells

modified companion cells that enhance solute movement between the apoplast and symplast

positive pressure

In studying angiosperms, researchers have concluded that sap moves through a sieve tube by bulk flow driven by ?

pressure flow hypothesis

hypothesis that explains the method by which phloem sap is transported through the plant from a sugar "source" to a sugar "sink"

phloem

It allows for rapid electrical communication between widely separated organs. It is a "superhighway" for systemic transport of macromolecules and viruses.

negative pressure (tension)

Water and minerals are pulled up from the roots by _______ generated by evaporation from the leaves.

positive pressure

Sugars are pushed by __________ from where they are produced or stored to where they are needed. They can move both ways between leaves and roots.

autotrophic

An organism capable of synthesizing its own food from inorganic substances, using light or chemical energy. Green plants, algae, and certain bacteria are autotrophs.

Mineral

an inorganic element? It is 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

essential nutrient

It is a particular chemical element that is required for a plant to grow from a seed and complete the life cycle

C,H,O,N,P,K,Ca,Mg,S,Zn,Cu,Mn,Fe,B,Mo,Cl, and Ni.

What are the 17 essential plant nutrients

chlorosis

the yellowing seen on the leaves of plants when they cannot make chlorophyll due to a lack of magnesium ions

N, K, Mg, P, Cl, Na, Zn, Mo

What elements are considered mobile nutrients in mineral deficiency in plants (mobile means it occurs in old leaves)

Ca, S, Fe, B, Cu

What elements are considered immobile nutrients in mineral deficiency in plants (immobile means it occurs in young leaves)

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

• E.g. Na, Si, Se

Group 1: Part of carbon compounds

Group 2: Important in energy storage or structural integrity

Group 3: Remain in ionic form

Group 4: Involved in redox reactions

The four basic groups of Essentiality of Mineral Nutrients

Group 1: Part of carbon compounds

(N,S)

• Forms the organic components of plants

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

Group 2: Important in energy storage or structural integrity

(P, Si, B)

• Energy storage reactions or maintaining structural integrity

• Present in plant tissue as phosphate, borate or silicate esters

Nitrogen

What element?

Function:

• Serves as a constituent of many plant cell components, including amino acids and nucleic acids.

Symptoms of deficiency:

• Chlorosis

• Stunting of growth

• Slender and woody stems

• Anthocyanin accumulation = purple coloration in leaves, petioles and stems of some plants

Sulfur

What element?

Function:

• Constituent of several coenzymes and vitamins essential for metabolism.

Symptoms of deficiency:

• Chlorosis

• Anthocyanin accumulation

• Stunting of growth

Phosphorus

What element?

Functions:

• Integral component of sugar-phosphate intermediates of respiration and photosynthesis, and the phospholipids that make up plant membranes

• Component of nucleotides (ATP, DNA, RNA)

Symptoms of deficiency:

• Stunted growth in young plants and dark green coloration of leaves, which may be malformed

• Contain necrotic spots (small spots of dead tissue)

• Anthocyanin accumulation

• Slender (but not woody) stems

• Death of older leaves

• Delayed maturation of plant

Silicon

What element?

Functions:

• Deposited primarily in ER, cell walls, and intercellular spaces as hydrated, amorphous silica

• Forms complexes with polyphenols = lignin alternative in reinforcement of cell walls

• Can ameliorate the toxicity of many heavy metals

• Enhanced growth and fertility

Symptoms of deficiency:

• Lodging (falling over)

• Fungal infection

Boron

What element?

Functions:

• Cell elongation

• Nucleic acid synthesis

• Hormone responses

• Membrane function

Symptoms of deficiency:

• Black necrosis of young leaves and terminal buds

• Stems may be stiff and brittle

• Apical dominance may be lost = plant becomes highly branched and soon necrotic

• Fruit, fleshy roots, and tubers may also exhibit necrosis

Group 3: Remain in ionic form

(K, Ca, Mg, Cl, Mn, Na)

• 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

Potassium

What element?

Functions:

• Regulation of osmotic potential of plant cells

• Activates many enzymes in respiration and photosynthesis

Symptoms of deficiency:

• Mottled or marginal chlorosis -> necrosis

• Stems may be slender and weak with abnormally short internodal regions

• Increased susceptibility to root-rotting fungi in corn -> lodging

Calcium

What element?

Functions:

• Synthesis of new cell walls

• Used in mitotic spindle during cell division

• Functions as second messenger (calmodulin-calcium complex) that regulates many metabolic processes

Symptoms of deficiency:

• Necrosis of young meristematic regions (tips of roots or young leaves)

• General chlorosis and downward hooking of young leaves

• Deformed young leaves

• Brownish, short and highly-branched root system

• Severe stunting if meristematic regions die prematurely

Magnesium

What element?

Functions:

• Activation of enzymes involved in respiration, photosynthesis, and DNA/RNA synthesis

• Also a part of the ring structure of the chlorophyll molecule

Symptoms of deficiency:

• Chlorosis between leaf veins

• Leave may become yellow or white if deficiency is extensive

• Premature leaf abscission

Chlorine

What element?

Functions:

• Required for water-splitting reaction of photosynthesis through which oxygen is produced

• May be required for cell division in leaves and roots

Symptoms of deficiency:

• Wilting of leaf tips -> chlorosis and necrosis

• Reduced growth of leaves

• Leaves may take on a bronze-like color (bronzing)

• Stunted and thickened roots near the tips

Manganese

What element?

Functions:

• Activates several enzymes in plant cells

• Decarboxylases and dehydrogenases involved in the Krebs Cycle are activated by manganese

• Photosynthetic reaction through which oxygen is produced from water

Symptoms of deficiency:

• Intervenous chlorosis associated with development of small necrotic spots

• Chlorosis may occur on younger or older leaves, depending on plant species and growth rate

Sodium

What element?

Functions:

• Vital for regeneration of phosphoenolpyruvate (substrate for the first carboxylation in the C4 and CAM pathways

• Stimulates growth through enhanced cell expansion

• Can partly substitute for potassium as an osmotically active solute

Symptoms of deficiency:

• Chlorosis and necrosis

• Fail to form flowers

Group 4: Involved in redox reactions

(Fe, Zn, Cu, Ni, Mo)

• This last group has important roles in reactions involving electron transfer

• Some also involved in the formation of plant growth hormone

• The light reaction of photosynthesis

Zinc

What element is involved in the formation of plant growth hormone

Copper

What element is involved in the light reaction of photosynthesis

Iron

What element?

Functions:

• Component of enzymes involved in the transfer of electrons (redox reactions) such as cytochromes

Symptoms of deficiency:

• Appearance of intervenous chlorosis on younger leaves

• Veins may become chlorotic, causing the whole leaf to turn white under extreme or prolonged deficiency

Zinc

What element?

Functions:

• Required by many enzymes for their activity

• May be required for chlorophyll biosynthesis in some plants

Symptoms of deficiency:

• Reduction in internodal growth = rosette habit of growth in which leaves form a circular cluster

• Small and distorted leaves, with leaf margins having a puckered appearance

• Intervenous chlorosis and development of white necrotic spots in some species

Copper

What element?

Functions:

• Associated with enzymes involved in redox reactions like iron

Symptoms of deficiency:

• Production of dark green leaves which may contain necrotic spots

• Twisted and malformed leaves

• Leaves may abscise prematurely under extreme deficiency

Nickel

What element?

Functions:

• Urease is the only known nickel-containing enzyme in higher plants

• Required by nitrogen-fixing microorganisms for the enzyme that reprocesses some of the hydrogen gas generated during fixation (hydrogen uptake hydrogenase)

Symptoms of deficiency:

• Urea accumulation in leaves -> leaf tip necrosis

Molybdenum

What element?

Functions:

• Components of several enzymes, including nitrate reductase (catalyzes the reduction of nitrate to nitrate during its assimilation by the plant cell) and nitrogenase (converts nitrogen gas to ammonia in nitrogen-fixing microorganisms)

• Small additions to such soils can greatly enhanced crop or forage growth

Symptoms of deficiency:

• General chlorosis between veins and necrosis of older leaves

• In some plants (e.g. cauliflower, broccoli), leaves may not become necrotic but appear twisted and subsequently die (whiptail disease)

• Flower formation may be prevented or may abscise prematurely

• Uptake through the leaves (Artificial = foliar application)

• Associations with mycorrhizal fungi (fungi helps)

• Uptake by the roots

How are mineral nutrients acquired by plants?

5.5 - 6.5

potassium, magnesium, calcium, manganese

- Root growth favors a pH of _______

- Acidic conditions releases ....

Apical region

The root absorbs different mineral ions in different areas: calcium

Apical region (barley)

Entire root (corn)

The root absorbs different mineral ions in different areas: iron

• 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

The root absorbs different mineral ions in different areas: Potassium, nitrate, ammonium, and phosphate

These ate 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

Why should root tips be the primary site of nutrient uptake?

• Increase plant growth and yield

• Increase plant nutritional quality and density

• Increase removal of soil contaminants (as in phytoremediation)

How does Manipulating Mineral Transport in Plants beneficial?

Senescence

• Term for the collective process leading to the death of a plant or plant part, like a leaf.

• this is a part of the process by which a plant goes into dormancy is induced by a change in day length.

Senescing cells

These cells produce other chemicals, particularly anthocyanins, responsible for red and purple colors.

Leaf Abscission

• The final stage in leaf senescence. It means cutting off

• It 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.