Phytotoxin
Encyclopedia
Phytotoxin refers to a substance produced by a plant that is toxic or a substance that is toxic to the plant Many substances produced by plants are secondary metabolites and are the by-products of primary physiological processes. Some examples of phytotoxins are alkaloids, terpenes, phenolics, herbicides and substances produced by bacteria.
. They are medically important by interfering with components of the nervous system
affecting membrane transport
, protein synthesis, and enzyme
activities.
They generally have a bitter taste. Alkaloids usually end in -ine (caffeine
, nicotine
, cocaine
, morphine
, ephedrine
).
They often end in -ol (menthol
) and make the majority of plant essential oils.
Phenolics
Phenolics are made of a hydroxyl group bonded to an aromatic hydrocarbon
. Furanocoumarin
is a phenolic and is non-toxic until activated by light. Furancoumarin blocks the transcription and repair of DNA
. Tannins are another group of phenolics and they are important in tanning leather. Lignins, also a group of phenolics, is the most common compound on earth and helps conduct water in plant stems and fill spaces in the cell.
Alkaloids
Alkaloids are derived from amino acids, and contain nitrogenNitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
. They are medically important by interfering with components of the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
affecting membrane transport
Membrane transport
In cellular biology the term membrane transport refers to the collection of mechanisms that regulate the passage of solutes such as ions and small molecules through biological membranes namely lipid bilayers that contain proteins embedded in them...
, protein synthesis, and enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
activities.
They generally have a bitter taste. Alkaloids usually end in -ine (caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
, nicotine
Nicotine
Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
, cocaine
Cocaine
Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...
, morphine
Morphine
Morphine is a potent opiate analgesic medication and is considered to be the prototypical opioid. It was first isolated in 1804 by Friedrich Sertürner, first distributed by same in 1817, and first commercially sold by Merck in 1827, which at the time was a single small chemists' shop. It was more...
, ephedrine
Ephedrine
Ephedrine is a sympathomimetic amine commonly used as a stimulant, appetite suppressant, concentration aid, decongestant, and to treat hypotension associated with anaesthesia....
).
Terpenes
Terpenes are made of water insoluble lipids, and synthesized from acetyl CoA or basic intermediates of glycolysisGlycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
They often end in -ol (menthol
Menthol
Menthol is an organic compound made synthetically or obtained from peppermint or other mint oils. It is a waxy, crystalline substance, clear or white in color, which is solid at room temperature and melts slightly above. The main form of menthol occurring in nature is -menthol, which is assigned...
) and make the majority of plant essential oils.
- Monoterpenes are found in gymnosperms and collect in the resinResinResin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
ducts and maybe released after an insect begins to feed to attract the insect's natural enemies. - Sesquiterpenes are bitter tasting to humans and are found on glandular hairs or subdermal pigments.
- Diterpenes are contained in resin and block and deter insect feeding. Taxol, an important anticancer drug is found in this group.
- Triterpenes mimic the insect molting hormone ecdysoneEcdysoneEcdysone is a steroidal prohormone of the major insect molting hormone 20-hydroxyecdysone, which is secreted from the prothoracic glands. Insect molting hormones are generally called ecdysteroids. Ecdysteroids act as moulting hormones of arthropods but also occur in other related phyla where they...
, disrupting molting and development and is often lethal. They are usually found in citrus fruit, and produce a bitter substance called limonoidLimonoidLimonoids are phytochemicals, abundant in citrus fruit and other plants of the families Rutaceae and Meliaceae. Currently limonoids are under investigation for a wide variety of therapeutic effects such as antiviral or Viricide, antifungal, antibacterial, antineoplastic and antimalarial...
that deters insect feeding. - Glycosides are made of one or more sugars combined with a non-sugar like aglyconeAglyconeAn aglycone is the non-sugar compound remaining after replacement of the glycosyl group from a glycoside by a hydrogen atom. The spelling aglycon is sometimes encountered .Classes of phytochemicals found in the aglycone and glycosides forms :...
, which usually determines the level of toxicityToxicityToxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
. Cyanogenic glycosides are found in many plant seeds like cherries, apples,and plums. Cyanogenic glycosides produce cyanideCyanideA cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
and are extremely poisonous.Cardenolides have a bitter taste and influence NA+/K+ activated ATPases in human heart, they may slow or strengthen the heart rate. Saponins have lipid and water soluble components with detergent properties. Saponins form complexes with sterols and interfere with their uptake.
PhenolicsPolyphenolPolyphenols are a structural class of natural, synthetic, and semisynthetic organic chemicals characterized by the presence of large multiples of phenol structural units...
Phenolics are made of a hydroxyl group bonded to an aromatic hydrocarbonHydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
. Furanocoumarin
Furanocoumarin
Furanocoumarins, or furocoumarins, are a class of organic chemical compounds produced by a variety of plants. They are biosynthesized partly through the phenylpropanoid pathway and the mevalonate pathway, which is biosynthesized by a coupling of dimethylallyl pyrophosphate and 7-hydroxycoumarin...
is a phenolic and is non-toxic until activated by light. Furancoumarin blocks the transcription and repair of DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
. Tannins are another group of phenolics and they are important in tanning leather. Lignins, also a group of phenolics, is the most common compound on earth and helps conduct water in plant stems and fill spaces in the cell.
Herbicides
Herbicides usually interfere with plant growth and often imitate plant hormones.- ACCase Inhibitors kill grasses and inhibit the first step in lipid synthesis, acetyl coA carboxylase,thus affecting cell memebrane production in the meristems. They do not affect dicots plants.
- ALS Inhibitors affect grasses and dicots by inhibiting the first step in some amino acid synthesis, acetolactateAcetolactateα-Acetolactic acid is a precursor in the biosynthesis of the branched chain amino acids valine and leucine. α-Acetolactic acid is produced from two molecules of pyruvic acid by acetolactate synthase. α-Acetolactic acid can also be decarboxylated by alpha-acetolactate decarboxylase to produce...
synthesis. The plants are slowly starved of theses amino acids and eventually DNA synthesis stops. - ESPS Inhibitors affect grasses and dicots by inhibiting the first step in the synthesis of tryptophanTryptophanTryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...
, phenylalaninePhenylalaninePhenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form...
and tyrosineTyrosineTyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
, enolpyruvylshikimate 3-phosphate synthase enzyme. - Photosystem IIPhotosystem IIPhotosystem II is the first protein complex in the Light-dependent reactions. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. The enzyme uses photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce...
Inhibitors reduce the electronElectronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
flow from water to NADPH2+ causing electrons to accumulate on chlorophyllChlorophyllChlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
molecules and excess oxidation to occur. The plant will eventually die. - Synthetic AuxinAuxinAuxins are a class of plant hormones with some morphogen-like characteristics. Auxins have a cardinal role in coordination of many growth and behavioral processes in the plant's life cycle and are essential for plant body development. Auxins and their role in plant growth were first described by...
mimics plant hormones and can affect the plant cell membrane.
Bacterial Phytotoxins
- TabtoxinTabtoxinTabtoxin, also known as wildfire toxin, is a simple monobactam biotoxin produced by Pseudomonas syringae. It is the precursor to the antibiotic tabtoxinine β-lactam....
is produced by Pseudomonas tabaci that may cause toxic concentrations of ammoniaAmmoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
to build up. This build up of ammonia causes leaf chlorosis. - Glycopeptides are produced by a number of bacteria and have been indicated in disease development. A glycopeptideGlycopeptideGlycopeptides are peptides that contain carbohydrate moieties covalently attached to the side chains of the amino acid residues that constitute the peptide. Over the past few decades it has been recognised that glycans on cell surface and those bound to proteins play a critical role in biology...
from Corynebacterium sepedonicum causes rapid wilt and marginal necrosisNecrosisNecrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
. A toxin from Corynebacterium insidiosum causes plugging of the plant stem interfering with water movement between cells. Amylovorin is a polysaccharidePolysaccharidePolysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
from Erwinia amylovora and causes wilting in rosaceous plants. A polysaccharide from Xanthomonas campestrisXanthomonas campestrisXanthomonas campestris is a bacterial species that causes a variety of plant diseases. Available from the NCPPB,and other international Culture collections such as ICMP, ATCC, and LMG in a purified form, it is used in the commercial production of a high-molecular-weight polysaccharide - xanthan...
obstructs water flow through phloemPhloemIn vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
causing black rot in cabbage. - Phaseotoxins prooduced by Pseudomonas phaseolicola and Pseudomonas glycinea can cause starchStarchStarch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
accumulation, decrease cell permeabilitySemipermeable membraneA semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...
in swiss chard and inhibit bean callus tissue growth. - Rhizobiotoxine produced by Rhizobium japonicum causes the root nodules of some soy bean plants to become chlorotic.