Castor Bean Plant

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Noteworthy Plants For March 1999

The Castor Bean

A Plant Named After A Tick

Table Of Contents:

 1.   Introduction
 2.   Flowers & Fruits
 3.   Related Species
 4.   Chemistry of Oils
    Serum Cholesterol
 5.   Jojoba Oil (Wax)
 6.   Origin of Castor
 7.   Castor Oil in Paints
 8.   Castor Oil in Nylon
 9.   Castor Motor Oils
10.  Castor Oil Flavorings
11.  Ricin: A Deadly Protein
12.  Ricin In Medicine
13.  Castor Oil Elixirs
14.  References

1. Introduction

Probably everyone at one time in their life has had the rather unpleasant experience of taking castor oil. Attempting to disguise the disagreeable taste with peppermint or fruit juice often results in a permanent dislike for the flavor enhancer as well as the castor oil. Although it is native to the Ethiopian region of tropical east Africa, the castor bean or castor plant (Ricinus communis) has become naturalized in tropical and warm temperate regions throughout the world, and is becoming an increasingly abundant weed in the southwestern United States. Castor plants are very common along stream banks, river beds, bottom lands, and just about any hot area where the soil is well drained and with sufficient nutrients and moisture to sustain the vigorous growth. Although the seeds or beans are extremely poisonous, they are the source of numerous economically important products and are one of earliest commercial products. Castor beans have been found in ancient Egyptian tombs dating back to 4000 B.C., and the oil was used thousands of years ago in wick lamps for lighting. To many people the castor plant is just an overgrown, undesirable weed, and yet it produces one of nature's finest natural oils.

Castor bean plant (Ricinus communis) growing along the edge of San Elijo Lagoon in coastal San Diego County, California. The large, tropical, palmately-lobed leaves make this naturalized plant unmistakable.

The castor plant is a robust annual that may grow 6 to 15 feet (2-5 meters) in one season with full sunlight, heat and adequate moisture. In areas with mild, frost-free winters it may live for many years and become quite woody and tree-like. The large, palmately lobed leaves may be over 20 inches (50 cm) across and resemble a tropical aralia. There are several cultivated varieties with strikingly different foliage colorations, including black-purplish, dark red-metallic, bronze-green, maroon, bright green with white veins, and just plain green. Although it grows very rapidly with little care or insect pests and produces a mass of lush tropical foliage, its use in cultivation should be discouraged because of the extremely poisonous seeds or "beans." This is particularly true where small children might be attracted to the large, beautifully-mottled seeds which are produced in prodigious numbers.

Castor bean plant showing large, tropical, palmately-lobed leaf and cluster of spiny red fruits. On some plants the fruits are green.

2. Castor Bean Flowers & Fruits

Flowers occur most of the year in dense terminal clusters (inflorescences), with female flowers just above the male flowers. This species is clearly monoecious, with separate male and female flowers on the same individual. There are no petals and each female flower consists of a little spiny ovary (which develops into the fruit or seed capsule), and a bright red structure with feathery branches (stigma lobes) that receives pollen from male flowers. Each male flower consists of a cluster of many stamens which literally smoke as they shed pollen in a gust of wind.

Flower cluster (inflorescence) of castor bean (Ricinus communis). The upper spiny balls (ovaries) with red, star-shaped stigmas are the female flowers. The lower male buds open into whitish-yellow clusters of stamens. The wind-pollinated flowers have no petals.

The spiny seed pod or capsule is composed of three sections or carpels which split apart at maturity. Each section (carpel) contains a single seed, and as the carpel dries and splits open, the seed is often ejected with considerable force. Walking among large castor shrubs on a hot summer day can be quite an experience, with the sound of exploding carpels and seeds flying through the air and bouncing off road signs, sidewalks, and your head.

Castor bean fruit (Ricinus communis): The spiny, globose seed capsule (left) dries and splits into 3 sections called carpels (center). Each carpel (right) splits open and forcibly ejects a large seed. In the related Mexican jumping bean (Sebastiana pavoniana), a moth occupies each carpel and feeds on the seed tissue inside.

The shiny seeds of castor plants are a little larger than pinto beans and have very beautiful and intricate designs. At one end is a small, spongy structure called the caruncle, which aids in the absorption of water when the seeds are planted. Like human faces, finger prints or the spots on a leopard, no two seeds have exactly the same pattern. They are unquestionably among the most deadly seeds on earth, and it is their irresistible appearance that makes them so dangerous.

The many "faces" of castor seeds. Like the faces and fingerprints of people, the beautiful designs on castor seeds exhibit infinite genetic variation. The small structure on the end of each seed is a caruncle. The seeds superficially resemble the bodies of ticks, particularly ticks engorged with blood.

3. Related Members Of The Euphorbia Family

The castor bean or castor plant belongs to the Euphorbia Family (Euphorbiaceae), a diverse and economically-important family of flowering plants. Although the castor plant has a watery sap, many members of the family contain a poisonous milky sap or latex that exudes copiously from cut stems or leaves. In fact, the most important world source of natural rubber comes from several members of the Euphorbia Family, especially the para rubber tree (Hevea brasiliensis). Other economically important plants include tapioca from the large storage roots of the tapioca plant (Manihot esculenta), and tung oil from the seeds of the Chinese tung tree (Aleurites fordii). Tung oil is one of the world's finest and most durable finishes for wood. Another species of Aleurites (A. molucanna), is called the candlenut tree because the oil-rich seeds were used for candles in Hawaii and other Polynesian islands.

The seed of candlenut (Aleurites molucanna) contains about 50 percent oil and burns like a candle. The ancient Polynesians brought this tree to the Hawaiian Islands where it has become naturalized. The dried nuts were cracked open and the seeds were skewered onto the midrib of a coconut frond (or slender bamboo stem) and set on fire. [Since they contain about 50 percent unsaturated oil, the seeds ignite readily.] The Polynesians used them for candles that burned for about 45 minutes. Hawaiians also extracted the oil for many other uses: to shine and waterproof wooden bowls, to mix with charcoal to make black canoe paint, to burn as torches, and to burn in stone lamps for light.

The candlenut is also known as the kukui nut in Hawaii, and the large seeds are polished and strung into beautiful necklaces and bracelets. In fact, this tree has so many uses that it is the national tree of Hawaii. Throughout the islands the light green (silvery-gray) foliage decorates lush canyons and valleys. The light-colored foliage is easy to spot from the numerous vistas on these lovely islands.

The fruit and seeds of candlenut (Aleurites molucanna). In the Hawaiian Islands, the large seeds are polished and made into beautiful kukui nut necklaces and bracelets. The shiny black or dark brown seeds resemble polished gemstones.

See Article About Kukui Nuts & Tung Oil

There are many native members of the Euphorbia Family represented in the southwestern desert region of the United States and Mexico, including a shrub that produces the famous Mexican jumping bean (Sebastiana pavoniana) and the Arizona jumping bean (Sapium biloculare). Like the castor bean, the Mexican jumping bean also has capsules composed of 3 carpels, except some of these are occupied by a robust moth larva rather than a seed. A related roadside plant of southern Arizona and Mexico (Cnidoscolus angustidens) superficially resembles a young castor plant, except it is covered with very painful, stinging hairs (trichomes). Its appropriate name of male mujer or "bad woman" is quickly realized if one makes the mistake of touching it.

Go To The Mexican Jumping Bean Article

4. Chemistry Of Plant Oils

P lant oils are typically composed of triglyceride molecules (technically called esters) composed of a 3-carbon alcohol (glycerol) plus three 18-carbon (or 16-carbon) fatty acids. Unlike the saturated fatty acids of animal fats which are solid at room temperature, plant fatty acids are typically unsaturated and liquid at room temperature, with one or more double bonds between the carbon atoms (mono-unsaturated and polyunsaturated). [Note: The palm fatty acid palmitin is saturated and contains 16 rather than 18 carbon atoms.] The following table shows the structure of a typical plant fat molecule (triglyceride) composed of glycerol plus 3 fatty acids. Since it contains unsaturated fatty acids, it is liquid at room temperature and is often referred to as an oil. The fatty acids may be saturated (with all single bonds), mono-unsaturated (with one double bond) or polyunsaturated (with 2 or more double bonds):

Structure Of A Fat Molecule:

  H  C#    1  2  3   4   5   6   7   8  9  10  11  12  13  14  15  16  17 18 
H-C-OH HOO-C-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 Stearic
H-C-OH HOO-C-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH=CH-CH2-CH=CH-CH2-CH2-CH2-CH2-CH3  Linoleic

Glycerol                      3 Fatty Acid Molecules

  Glycerol + Three Fatty Acids = A Fat Molecule (Triglyceride).
  Linoleic Acid Polyunsaturated: 2 Double Bonds In The Molecule.
  Stearic Acid Saturated: All Single Bonds Between Atoms Of Carbon.
  Oleic Acid Monounsaturated: 1 Double Bond Between Carbons 9 & 10.
  H2O (HOH) Formed When Fatty Acid Bonds To Each Carbon Of Glycerol.

Cis and Trans Fatty Acids

Fatty acid isomers containing double bonds may have the cis or trans configuration. In cis fatty acids, all the hygrogen atoms adjacent to the double bonds are on the same side of the longitudinal carbon axis. In trans fatty acids, the hygrogen atoms adjacent to the double bonds occur on alternate sides of the main axis. To illustrate the difference between cis and trans configurations, see the following illustration of the 18-carbon fatty acid called linoleic acid :

Polymers of linoleic acid: The trans and cis configurations of C18H32O2

In the trans configuration, the four hydrogen atoms adjacent to the double bonds occur on alternate sides of the main carbon axis (two on one side and two on the opposite side). The trans configuration is chemically more stable. It is typically produced during partial hydrogenation of polyunsaturated vegetable oils. In the cis configuration, all four hydrogen atoms adjacent to the double bonds occur on the same side of the carbon axis.

When polyunsaturated vegetable oils are partially hydrogenated to improve their texture, trans fatty acids are produced. Trans fatty acids tend to raise the level of low density lipoproteins (bad LDLs) and lower the level of high density lipoproteins (good HDLs). These changes in blood lipids (cholesterol levels) may increase the risk of heart disease (atherosclerosis) in some people. Dieticians generally recommend the use of mono-unsaturated, unhydrogenated oils such as canola or olive oil whenever possible, and the avoidance of trans fatty acids found in french fries, donuts, chips, cookies and crackers.

Omega-3 and Omega-6 Fatty Acids

In the above illustration, the first double bond is located on carbon #6, counting backwards from right to left. [The first carbon is at the end opposite the carboxylic or COOH group.] Therefore, this is an omega-6 fatty acid. Unsaturated fatty acids found in plant oils and seeds are typically omega-6 fatty acids. In omega-3 fatty acids, the first double bond in on carbon #3, counting back from right to left on the above illustration. Omega-3 fatty acids are prevalent in fish oils and flax seeds (Linum usitatissimum).

Blood Triglycerides and Cholesterol

Cholesterol is a complex lipid and vital precursor of sex hormones, vitamin D and bile salts. It is produced by the body, although some dietary cholesterol comes from animal products. Cholesterol is carried to sites in the body by low-density lipoprotein molecules (LDLs). High-density lipoproteins (HDLs) remove cholesterol from these sites and deliver it to the liver for breakdown. Excessive levels of cholesterol in the blood can lead to fatty deposition in blood vessels (arteries) called plaque. For example, damage to a blood vessel wall (by injury or strain) causes cells underlying the internal wall to divide. White blood cells (macrophages) accumulate in the area to ingest particles of damaged cells. LDLs carrying cholesterol gather in the area to provide materials for repairing the wall. While waiting to be used, the cholesterol molecules can become oxidized, causing them to be engulfed by macrophages. After engulfing several oxidized molecules, the macrophages die and become deposited as fatty "foam cells" in the area of the wall being repaired. A buildup of these fatty deposits mixed with fibrous muscle cells is called plaque, which can narrow the diameter of an artery and seriously impede the blood flow. This can be life threatening if the blood vessel happens to be a coronary artery that supplies the heart muscle with oxygen-rich hemoglobin. Plaque formation in the carotid arteries can impede oxygenated blood flow to the brain, often resulting in a stroke. Even without injury, plaque can form in arteries if cholesterol levels in the blood are high enough, particularly if they become oxidized and are engulfed by roving macrophages. The condition or disease in which blood vessels become clogged with plaque is called atherosclerosis.

Any substance that lowers the LDLs and increases the HDLs tends to reduce the probability of plaque formation and a heart attack. Lowering the intake of saturated animal fats can reduce the total cholesterol level but does not alter the ratio of lipoproteins. Saturated fats in red meats and tropical palms can increase the amount of LDLs in the blood; however, margarines can also raise the level of LDLs. Trans fatty acids in margarines and shortenings made from partially hydrogenated plant oils have been linked to the epidemic of heart disease in the U.S. that began in the 1930s and 1940s. Oils containing trans fatty acids increase LDLs ("bad" cholesterol) and depress HDLs ("good" cholesterol). At this time, the best type of fatty acids for a healthy balance of LDLs and HDLs are the monounsaturated fatty acids found in olive oil (Olea europea) and canola oil (Brassica napus).

In addition to the benefits of monounsaturated olive and canola oils, omega-3 fatty acids prevalent in fish oils and flax seeds (Linum usitatissimum) may actually help to reduce levels of LDLs in the blood and lower the risk of atherosclerosis. Diets rich in polyunsaturated oils have be correlated with an increased risk of certain cancers because of highly reactive carbon fragments from the breakdown of fatty acids. These carbon fragments have unpaired electrons and are powerful oxidizing agents known as free radicals.

  See Olive Fruits (Olea europea)  

Sometimes diet and exercise are not enough to reduce the LDLs and the risk of heart disease. This especially true in older adults who are genetically predisposed to excessive LDL production, and who are at risk for plaque formation in their blood vessels (atherosclerosis). A class of chemicals called statins has been developed to reduce the production of cholesterol. Statins work by blocking a key enzyme in the liver that is necessary for cholesterol production. Once this metabolic pathway is blocked, the level of LDLs decreases dramatically. Statins also increase the liver's ability to remove the LDLs already in the blood. There are six statins currently prescribed by physicians as of 2005: Lipitor® (Atorvastatin), Lescol® (Fluvastatin), Mevacor® (Lovastatin), Pravachol® (Pravastatin), Crestor® (Rosuvastatin), and Zocar® (Simvastatin).

Losing Weight By Eating Saturated Fats?

The popular "Atkins diet" named after the physician Dr. Robert Atkins results in substantial weight loss by consuming fat-laden red meats with little are no carbohydrates. The normal primary source for energy-rich ATP molecules is the aerobic oxidation of glucose derived from complex carbohydrates. When carbohydrates are in short supply the body breaks down fat resulting in ketone bodies known as acetoacetic acid and beta-hydroxybutyric acid. This process is known as ketosis. Ketones are a fuel alternative for glucose in most cells. The ketones are converted into acetyl coenzyme A (acetyl-CoA) which enters the citric acid cycle for ATP production. Acetone, which gives off the pecular breath odor of ketosis, comes from acetoacetic acid. When an animal stops eating, free fatty acids are released into the blood stream and are processed by the liver. Ketosis occurs during prolonged starvation, uncontrolled diabetes and the Atkins diet. Although the Atkins diet recommends vegetables plus vitamin and mineral supplements, some dieticians are skeptical about this extreme method of weight reduction. There is ample evidence that high protein diets increase the risk of gout and kidney stones. Extra calcium is also taken from bone tissue. Some physicians question whether the brain can function properly during prolonged periods of ketosis. There can be a dramatic weight loss when the body uses dietary fat and protein as an energy source, but anyone on the Atkins diet should be eating plenty of fruits and vegetables and probably should be taking vitamin and mineral supplements.

See a comprehensive evaluation of the Atkins Diet and other low-carb diets:

Johnson, P. 2004.  "The Skinny On Fat:  A Skeptical Evaluation
of the Atkins and Other Low Carb Diets." Skeptic 10 (4): 66-73.

5. Jojoba Oil: A Liquid Wax

Another high quality oil comes from the jojoba plant (Simmondsia chinensis). Although this native shrub of the southwestern United States was once placed in the Euphorbia Family, it is now placed in its own monotypic family, the Simmondsiaceae. It was once thought to have originated in China, hence, the specific epithet of chinensis. Jojoba seeds contain a liquid wax rather than an oil. Like plant oils, jojoba oil is composed of an alcohol plus fatty acids; however, it has a long-chain alcohol (with more than 3 carbon atoms) and many fatty acids (more than three). It is therefore not a triglyceride, and is considered a true wax. Unlike most animal and plant waxes (including beeswax, ear wax and the cuticle coating on leaves and fruits), jojoba wax is liquid at room temperature because of its unsaturated fatty acids. Jojoba oil has qualities similar to sperm whale oil, and is a renewable resource that could replace the needless slaughter of these magnificent mammals. Perhaps genetic engineers will find a way to transplant the gene for jojoba oil into a fast-growing seed plant, thus providing an efficient and cost-effective method of jojoba oil production.

Seeds and liquid wax of jojoba (Simmondsia chinensis), a native shrub of the southwestern United States. The white, solid wax is produced by hydrogenation of the unsaturated liquid wax. This process involves the addition of hydrogen to the fatty acids under heat and pressure.

The seed capsules of jojoba (Simmondsia chinensis), a native shrub of the southwestern United States. Each capsule contains one oily seed, the source of jojoba "oil" which is technically an unsaturated liquid wax.

See A Honeycomb Made Of Beeswax
See The Sad Saga Of A Drone Honey Bee

6. Derivation Of The Name Castor

It is interesting to trace the origin of the name "castor." Castor is the generic name of the North American beaver (Castor canadensis) and one of the brightest double stars in the constellation Gemini. In Greek and Roman legend, Castor was one of the twin sons of Jupiter and Leda. According to E. A. Weiss, writing in Castor, Sesame and Safflower (1971), the name "castor" has nothing to do with beavers, luminous stars, or offspring of Greek and Roman Gods. Castor was apparently coined by English traders who confused it with the oil of another shrub, Vitex agnus-castus, which the Spanish and Portuguese in Jamaica called "agno-casto." Although it is commonly known as the castor bean plant, the seed is really not a true bean and it is not related to the Bean or Legume Family (Fabaceae). There are many other examples of "beans" that are technically not beans, such as Mexican Jumping "beans" and coffee "beans."

The scientific name for the castor plant, Ricinus communis, has a much more logical derivation. Communis means common in Latin, and castor plants were already commonly naturalized in many parts of the world when the eighteenth century Swedish naturalist Carolus Linnaeus (Karl von Linné) was giving scientific first and last names to plants and animals over 200 years ago. Ricinus is the Latin word for tick and is the specific epithet for the Mediterranean sheep tick (Ixodes ricinus). Apparently Linnaeus thought the seeds looked like ticks, particularly large ticks engorged with blood.

A western wood tick (Dermacentor occidentalis). The mottled body of certain ticks superficially resembles a castor bean seed (especially when the tick is engorged with blood), and the tick's head resembles the caruncle of a castor bean seed.

Compare This Tick With Castor Bean Seeds

7. Castor Oil In Paints

The castor plant has many uses, particularly the thick, yellowish or almost colorless oil obtained from the seeds. There are an astonishing number of industrial applications for castor oil and its derivatives, and new ones are continually being discovered. When dehydrated, castor oil is converted into a quick-drying oil used extensively in paints and varnishes. In fact, one of the largest single markets for castor oil in the United States is in the paint and varnish industry. Some experts say that dehydrated castor oil has qualities superior to linseed oil and tung oil, two of the most important drying oils. Castor oil is one of the world's most versatile natural products. Its water resistant qualities make it ideal for coating fabrics and for protective coverings, insulation, food containers, and guns.

The clear, yellowish oil and attractive (but deadly) seeds of the castor plant (Ricinus communis). Castor oil is one of the world's most useful and economically important natural plant oils.

8. Castor Oil In Nylon

Castor oil is the primary raw material for the production of sebacic acid, which is the basic ingredient in the production of nylon and other synthetic resins and fibers. Approximately three tons of castor oil are necessary to produce one ton of nylon. Sebacic acid is a 10-carbon dicarboxylic acid with a carboxylic group (C-OOH) at each end of the molecule. It is reacted with 1,6-hexanediamine, a 6-carbon molecule with an amino group (C-NH2) at each end. The free carboxylic and amino ends of these molecules begin bonding together in a chain reaction called condensation polymerization, in which a water molecule is produced at each link. The resulting nylon polymer is called Nylon 6,10 to denote the 6-carbon diamine and 10-carbon sebacic acid.

9. Castor Bean Motor Oil

The superior "oiliness" of castor oil and its ability to "cling" to very hot moving parts make it an outstanding racing oil for high performance engines. In fact, it is the basic ingredient of Castrol-R racing motor oil for high speed automobile and motorcycle engines. Castor oil is a popular fuel additive for two cycle engines, and imparts a distinctive aroma to the exhaust of these engines. Castor wax, a hard wax produced by the hydrogenation (chemical combination with hydrogen) of pure castor oil, is used in polishes, electrical condensers, carbon paper, and as a solid lubricant.

10. Fruit Flavors From Castor Oil

Although castor oil is rather malodorous and distasteful, it is the source of several synthetic flower scents and fruit flavors (esters), such as jasmine, apricot, peach, plum, rose, banana, and lemon. The chemicals (esters) responsible for these flavors and aromas are obtained from ricinoleic acid, one of the important ingredients of natural castor oil. In fact, ricinoleic acid comprises about 90% of the total triglyceride fatty acids of castor oil. Castor oil is also used in making soap, inks, and plastics; for preserving leather; as an illuminant; in Turkey red oil for dyeing and finishing textiles; and in brake fluids and certain insecticidal oils. Even after the oil has been removed, the poisonous crushed seeds or oil cake (pomace) makes an excellent fertilizer.

Structural Formula Of Ricinoleic Acid


Brazil and India are two of the major world producers of castor oil, although the plants are grown commercially in many other countries, including the United States (New Mexico, Texas, and the midwestern United States). It has been estimated that the world production of castor seeds was nearly one million tons in 1970. In terms of total production, castor oil is one of the world's most important industrial vegetable oils.

11. Ricin: A Deadly Protein

The active poison in castor seeds is ricin (RYE-sin), a very deadly protein called a lectin. Ricin is found in the meal or cake after the oil has been extracted. Those who occasionally take castor oil may be assured that ricin does not occur in the pure oil. When a gram of ricin is compared with equivalent weights of other toxic substances, it turns out to be one of our deadliest natural poisons. It has been estimated that, gram for gram, ricin is 6,000 times more poisonous than cyanide and 12,000 times more poisonous than rattlesnake venom. Ricin mixed with food and used as bait is highly toxic to certain pest animals, such as some rodents and insects. E. A. Weiss (1971) states that a dose of 0.035 milligram (approximately one millionth of an ounce) may kill a man, and even small particles in open sores and in the eyes may prove fatal. According to the Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (1997), a dose of ricin weighing only 70 micrograms or two millionths of an ounce (roughly equivalent to the weight of a single grain of table salt from a salt shaker) is enough to kill a 160 pound person. As few as four ingested seeds can cause death in an adult human, and lesser amounts may result in symptoms of poisoning, such as vomiting, severe abdominal pain, diarrhea, and convulsions. Of course the degree of poisoning depends upon the amount ingested and the age and general health of the individual. There are numerous documented cases of ricin poisoning and death when horses, livestock, and poultry accidentally ate castor seeds or meal.

With the exception of certain pathogenic bacteria, lectins include some of the most insidious plant toxins affecting people. In addition to ricin from castor bean seeds, another very poisonous lectin called abrin occurs in the seeds of rosary bean (Abrus precatorius), a common tropical vine in the Legume Family (Fabaceae). According to the Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals, 1983), one thoroughly masticated seed of rosary bean can cause fatal poisoning. Brightly colored rosary beans are commonly strung for seed jewelry in Mexico and Central America. Sometimes the seeds are boiled in order to facilitate the piercing of their hard seed coats, and this heating would undoubtedly denature the toxic proteinaceous lectins inside. Of course, the undisputed record for the deadliest natural toxin goes to the anaerobic bacterium of spoiled food (Clostridium botulinum). A fascinating article on botulism appeared in Scientific American, April, 1968. So deadly is the toxin (even deadlier than strychnine, arsenic and snake venoms), that an amount equal to the weight of ink in a printed period in a textbook is enough to kill 30 adult humans. One ounce could theoretically kill 30 million tons of living matter and one pound could kill the entire human population. However, even an innocuous coconut can be a lethal weapon if you stand under a heavily laden palm. The odds of this unfortunate event is considerably greater than winning the jackpot in the California State Lottery. [In fact, the chance of being struck by lightning is actually greater than winning the California Lottery.]

The poisoning mechanism of castor beans is very complicated. It causes clumping (agglutination) and breakdown (hemolysis) of red blood cells, hemorrhaging in the digestive tract, and irreparable damage to vital organs such as the liver and kidneys. It is most toxic when taken intravenously or inhaled as fine particles. In fact, the possibilities of ricin dust in chemical warfare are horrendous. There are even documented cases of castor bean poisoning in murders by paid assassins.

At the cellular level, ricin is known as a "ribosome-inactivating protein" or Type 2 RIP, one of the most potent cytotoxins in nature. It is synthesized in the endosperm cells of maturing seeds. Ricin is composed of two complex 3-dimensional molecular subunits, a 267 amino acid globular protein called the A chain (RTA) and a 262 amino acid protein called the B chain (RTB). The two polypeptides are held together by a single disulphide bond. The RTA and RTB proteins do not become deadly until the disulsulfide bond is broken and they are separated from each other. Once inside the cell, RTA becomes a deadly enzyme that catalyzes the depurination (loss of purine bases) from ribosomes. When ribosomes lose specific purine bases, such as adenine, they no longer function and protein synthesis shuts down.

In summary, ricin is a potent cytotoxic protein is that is lethal to eukaryotic cells by inactivating the organelle sites of protein synthesis called ribosomes. Just one single ricin molecule that enters the cytosol of a cell (the semifluid medium between the nucleus and plasma membrane) can inactivate over 1,500 ribosomes per minute and kill the cell.

The agglutination of red blood cells has been atributed to a powerful hemagglutinin in castor beans called ricinus communis agglutinin (RCA) and not ricin. Ricin is a potent cytotoxin but a weak hemagglutinin. Poisoning by the ingestion of castor beans is due to ricin, not RCA, because RCA does not penetrate the intestinal wall, and does not affect red blood cells unless given intravenously. If RCA is injected into the blood, it will cause the red blood cells to agglutinate and burst due to hemolysis.

For More Information:
  1. Robertus, J.D. 1991. "The Structure and Action of Ricin, A Cytotoxic N-glycosidase." Seminar in Cell Biology 2: 23-30.

  2. Vitetta, E.S. and P.E. Thorpe. 1991. "Immunotoxins Containing Ricin or its A Chain." Seminar in Cell Biology 2: 47-58.

  3. Wiley, R.G. and T.N. Oeltmann. 1991. "Ricin and Related Plant Toxins: Mechanisms of Action and Neurobiological Applications." In: Handbook of Natural Toxins (Vol. 6). Edited by R.F. Keeler and A.T.Tu. Marcel Dekker, Inc., New York.

12. Ricin In Cancer Research

Although it is a very potent poison, ricin has been shown to possess antitumor qualities and has been used in cancer research and chemotherapy during recent years. One of the most promising uses of ricin is in the production of immunotoxins, where the protein ricin is joined to monoclonal antibodies. The antibodies are produced in a test tube (in vitro), and have protein receptor sites that recognize the specific target cells of a tumor. The resulting ricin-antibody conjugate is called an immunotoxin. By arming these antibodies with ricin, the deadly toxin can be carried directly to the site of the tumor in a cancer patient. Thus, ricin can destroy the tumor cells, without damaging other cells in the patient.

To produce monoclonal antibodies, B-lyphocytes (plasma cells) from mice are exposed to a specific tumor antigen so that they can produce antibodies against the tumor. The plasma cells are then fused with myeloma (cancer) cells, producing rapidly-dividing hybridoma cells that are essentially "immortal." The hybridoma cells divide rapidly in a test tube and continue to produce the same type of anti-tumor antibodies, called monoclonal antibodies.

13. Castor Oil As A Cure-All Elixir

Castor oil has been used medicinally in the United States since the days of the pioneers. As Americans moved west after the Civil War, settlers were very attracted to Indian medicines and popular "cure-all" remedies. The stronger smelling and the more vile tasting the concoction, the better, and some medical historians have described the latter part of the 1800's as the "age of heroic cures." Traveling medicine men peddled their elixirs throughout towns of the west, and often their products contained up to 40 percent (80 proof) alcohol. Castor oil was one of the old-fashioned remedies for everything from constipation to heartburn. It is indeed a very effective cathartic or purgative (laxative) and is still used to this day; however, there are milder, less drastic methods of inducing regularity. Castor oil is also used as personal lubricant: It is sometimes applied externally as a soothing emollient for dry skin, dermatitis, other skin diseases, sunburn, open sores, and it is the primary ingredient of several brand name medications. Several additional little-known uses for castor oil include hair tonics, ointments, cosmetics, and contraception creams and jellies. One remarkable old remedy mentions administering castor oil to induce labor during pregnancy.

One of the reasons castor plants have become so successful is their extremely viable seed that germinates readily in a variety of soils. In fact, desperate vegetable gardeners have been known to place the poisonous seeds in the burrows of gophers and moles, thus propagating and dispersing the plant. Because of its ability to grow wild and reseed itself, castor plants are recognized by botanists as naturalized weeds throughout the southwestern United States.

Since many towns in the southwestern United States have wild castor plants growing near residential areas, children should be taught to recognize its very dangerous seeds. It is doubtful that any large scale campaign to eradicate this hardy plant will ever be completely successful. Unless the southwest experiences another ice age, castor plants will continue ejecting their beautiful but deadly seeds by the millions, and will be with us for many generations to come. Although it is usually classified as a weed in the southwestern United States, one can't help admiring this valuable oil-producing plant in an energy-hungry world.

Castor Bean References

  1. Armstrong, W.P. 1982. "Not Beavers, Stars or Sons of Jupiter." Environment Southwest No. 496: 4-7.

  2. Hill, A.F. Economic Botany. 1952. McGraw-Hill, New York.

  3. Lewis, W.H. and M.P.F. Elvin-Lewis. 1977. Medical Botany: Plants Affecting Man's Health. John Wiley & Sons, New York.

  4. Robinson, T. 1964. The Organic Constituents of Higher Plants: Their Chemistry and Interrelationships. Burgess Publishing Co., Minneapolis, Minn.

  5. Schery, R.W. 1972. Plants For Man. Prentice-Hall, Inc., Englewood Cliffs, New Jersey.

  6. Simpson, B.B. and M.C. Ogorzaly. 1986. Economic Botany: Plants in Our World. McGraw-Hill, New York.

  7. Weiss, E.A. 1971. Castor, Sesame and Safflower. Barnes & Noble, New York.

  8. Windholz, M., S. Budavari, R.F.Blumetti, and E. S. Otterbein (Editors). 1983. The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals. Merck & Co., Inc., Rahway, New Jersey.

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