Showing posts with label poisonous toxic and invasive plants. Show all posts

12:04 AM
Allelopathy refers to all the biochemical interactions, both beneficial and harmful, among all types of plants, including microorganisms.

For an allelopathic interaction to occur, chemicals must be released into the environment by one plant that will affect the growth of another. In this way allelopathy differs from competition, which involves removal of some factor from the environment that is shared with other plants. Allelopathy was recognized as early as Theophrastus (300 b.c.e.), who pointed out that chick pea plants destroy weeds growing around them.

Methods of Action

Avariety of different allelochemicals are produced by plants, usu- ally as secondary metabolites that do not have a specific function in the growth and development of the host plant but that do affect the growth of other plants. Originally plant physiologists thought these secondary products were simply metabolic wastes which plants had to store because they do not have an excretory system as animals do. Their various functions are now beginning to be understood.

One class of allelochemicals, coumarins, block or slow cell division in the affected plant, particularly in root cells. In thisway growth of competing plants is inhibited, and seed germination can be prevented. Several kinds of allelochemicals, including flavonoids, phenolics, and tannins, suppress or alter hormone production or activity in competing plants.


Other chemicals, including terpenes and certain antibiotics, alter membrane permeability of host cells, making them either leaky or impermeable. In some cases, membrane uptake can be enhanced, particularly for micronutrients in low concentration in the soil. Finally, a variety of allelochemicals have both positive and negative effects on metabolic activity of the affected plant.

Allelopathy in Agriculture

Most of the negative effects of weeds on crop plants have been attributed to competition; however, experiments using weed extracts have demonstrated that many weeds produce allelochemicals. Similarly, some crop plants are allelopathic to others and themselves, including wheat, corn, and rice. In these cases the residues of one year’s crop can interfere with crop growth in subsequent years.

This is increasingly important for farmers to consider who are incorporating low-tillage methods to reduce soil erosion. To minimize these effects, some of the traditional techniques of cover cropping, companion cropping, and crop rotation must be employed. Known allelopaths are also beginning to be used as biological control agents to manage invasive and weedy plant species.

Allelopathy in Nature

Several tree species, including black walnut, black locust, and various pines, are known to produce allelochemicals that inhibit the growth of understory species. In some cases this is a result of drip from the foliage or leachate from fallen leaves and fruit. In other cases, roots secrete allelochemicals that kill seedlings of other plants. Bracken fern (Pteridium aquilinum) is known to affect the growth of many other plants.
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9:27 PM
Biochemical Coevolution in Angiosperms
Biochemical Coevolution in Angiosperms
Flowering plants, or angiosperms, produce many compounds that are not directly related to growth and development. These secondary metabolites arise from primary metabolic pathways and act as antiherbivory mechanisms, allelochemicals, or attractants.

Secondary metabolites are biochemicals produced by plants in response to selection pressures. These pressures may be from herbivory, competition, or the need for pollination.

As plants produce compounds to enhance their survival, predators, competitors, and pollinators react and evolve means of adjusting to the plant’s efforts. Chemically simple secondary metabolites may be widespread throughout angiosperm (flowering plant) families, whereas more complex chemicals are often restricted to a single species.

Secondary metabolites are often under high selection pressures, causing individual compounds to have very limited distributions and making them useful in determining the evolutionary relationships between taxonomic groups. Presence of secondary compounds influences the activities of organisms interacting with the plants and, over long periods of time, influences evolution of those species.

Antiherbivory Mechanisms

Antiherbivory chemicals may have a wide range of effects on herbivores (plant-eating animals). Many compounds merely deter grazing. Crystals produced from calcium oxalate (raphides) may be ejected from the vacuoles of cells along with proteinaceous toxins, causing tissue swelling in the mouth of an offending herbivore.

Many monocotyledonous plant families, such as Liliaceae, Heliconiaceae, Rubiaceae, and Arecaceae, produce this type of antiforaging device. This type of defense is especially notable in young tissues that have not developed the toughness found inmature leaves as a herbivory deterrent. Red oaks produce tannins in response to gypsy moth attacks, reducing further herbivory.

Continued feeding on plants containing tannins would lead to slow starvation of a herbivore, as its digestive system could not absorb proteins. The same tannins are not deterrents to squirrels. Squirrels harvest acorns and bury them for later consumption, providing a food source for the squirrel and a dispersal mechanism for the acorn.

Beavers provide another example of the interaction between plant and animal evolution. Some of the beaver’s preferred foods include species that are unpalatable or toxic to other mammals, such as bracken fern, nettles, thistles, and skunk cabbage. This gives the beaver a largely uncontested food source that may involve a metabolic "cost" to the animal.

Other antiherbivory chemicals result in effects more severe than mere deterrence of feeding. Alkaloids such as caffeine, nicotine, and strychnine are potent anti herbivory mechanisms, causing convulsions, comas, and even death in herbivores. These effects may not occur in all herbivores.

Strychnine, for example, is produced by the fruit of some plants that may be eaten by birds without ill effects, but in mammals the same fruit causes failure of the central nervous system and induces seizures.The plant reduces herbivory by mammals, and the seeds get dispersed by birds that are able to detoxify the strychnine.

Grains and seed crops, such as wheat and peanuts, which are particularly attractive to animal and insect herbivores, often produce cyanogenic glycosides that release hydrogen cyanide as the tissues are digested. This compound inhibits cellular respiration, thus killing the herbivore. In each case members of a plant population are consumed by the herbivore, but future generations are spared by the loss.

Allelochemicals

Allelochemicals
Allelochemicals
Allelochemicals are compounds produced by an organism that interfere with the growth or development of another organism.Many phenolic acids act as allelo chemicals, inhibiting root growth of competing species. Many grains are known to release ferulic acid and caffeic acid into the soil, thus inhibiting the germination of weed species.

Phenolics may also act as antifungal compounds, increasing in concentration with fungal infection, thus protecting the plant from further attack. Phenolic compounds produced in tobacco and tomato leaves reduce the growth of these plants’ natural predator, tobacco hornworm, without affecting the growth or activity of the hornworm’s natural predator.

Allelochemicals produced in response to injury by herbivores may also attract predators of the herbivore.Wastes from many species of caterpillars induce the release of terpenoids from green leaves that attract parasitoid insects.

Production of specific combinations of volatiles on the part of the plant signals the predator, which will then reduce further herbivory. The plants have evolved the signal in response to herbivory, and the predators have evolved the ability to detect the signal indicating the location of their host.

Lectins are widely distributed carbohydrate-binding proteins, most commonly found in the Leguminoseae (legume) family. When found in the seeds, these compounds act as broad-spectrum insecticides, whereas in the roots of legumes they maintain bacterial relationships in nitrogen fixing nodules, providing the plant with a source of nitrogen unavailable to plants not producing nodules.

Attractants

Attractants
Attractants
Terpenoids and aliphatic compounds are often the components of essential oils of plants. The volatile nature of these compounds produces a distinctive odor that attracts pollinators. Composition of the volatile compounds often closely matches the natural pheromones produced by the pollinator, mimicking the chemical scent of a female insect in an attempt to attract male pollinators.

Pheromone mimicry is found primarily in members of the Orchidaceae, which are often dependent on single species of wasp for pollination. Other plants may mimic the odor of food. The smell of rotting flesh, attractive to flies, is produced via ammonia and alkylamines, such as cadaverine and putrescine. Methylesters may attract moth pollinators by mimicking the sweet smell of fruit.

Flavonoids often provide color to fruits and flowers and act as visual cues for pollination. Reds, blues, or yellows in varying patterns stand out against a background of green leaves, helping pollinators locate the flower.

Species may have minor chemical differences in their flavonoids that allow for the determination of identity, hybridization between species, and possible coevolution with pollinators. For example, tropical flowers tend to have a more intense red color from anthocyanins than do temperate flowers.

This difference correlates with differences in pollinator preferences, indicating a role by natural selection. Birds, such as hummingbirds, prefer red to yellow, whereas bees are not able to discern reds but are attracted to yellows. Carotenoids, such as xanthophyll and beta-carotene, give fruits and flowers distinctive yellow and orange colors.

Color patterns are also important in attracting pollinators. Butterflies are attracted to red/yellow color patterns. Flavonoid compounds not only impart color but also may modify color patterns by absorbing ultraviolet (UV) light.

Bees are capable of seeing in the UV range, so the presence of flavonoids may alter the bees’ perception of the flower. The patterns may also create cues as to the location of nectaries within the flower, guiding the pollinator to its reward.
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6:56 AM
Biological Invasions
Biological Invasions

Biological invasions are the entry of a type of organism into an ecosystem outside its historic range. In a biological invasion, the "invading" organism may be an infectious virus, a bacterium, a plant, an insect, or an animal.

Species introduced to an area from somewhere else are referred to as alien or exotic species or as invaders. Because an exotic species is not native to the new area, it is often unsuccessful in establishing a viable population and disappears.

The fossil record, as well as historical documentation, indicates that this is the fate of many species in new environments as they move from their native habitats. Occasionally, however, an invading species finds the new environment to its liking.


In this case, the invader may become so successful in exploiting its new habitat that it can completely alter the ecological balance of an ecosystem, decreasing biodiversity and altering the local biological hierarchy. Because of this ability to alter ecosystems, exotic invaders are considered major agents in driving native species to extinction.

Biological invasions by notorious species constitute a significant component of earth’s history. In general, large-scale climatic changes and geological crises are at the origin of massive exchanges of flora and fauna. On a geologic time scale, migrations of invading species from one continent to another are true evolutionary processes, just as speciation and extinction are.

On a smaller scale, physical barriers such as oceans, mountains, and deserts can be overcome by many organisms as their populations expand. Organisms can be carried by water in rivers or ocean currents, transported by wind, or carried by other species as they migrate seasonally or to escape environmental pressures.

Humans have transplanted plants since the beginning of plant cultivation in pre-Columbian times. The geological and historical records of the earth suggest that biological invasions contribute substantially to an increase in the rate of extinction within ecosystems.

Invasive Plants

Invasive Plants
Invasive Plants

In modern times, most people are not aware of the distinction between native plants and exotic species growing in their region. Recent increases in intercontinental invasion rates by exotic species, brought about primarily by human activity, create important ecological problems for the recipient lands. Invasive plants in North America include eucalyptus trees, morning glory, and pampas grass.

It would seem logical to assume that invading species might add to the biodiversity of a region, but many invaders have the opposite effect. In all ecosystems the new species are often opportunistic, driving out native species by competing with them for resources.

For example, Pueraria lobata, or kudzu, is a vine native to Japan. Introduced in the United States at the 1876 Philadelphia Exposition, kudzu was planted to control erosion on hillsides and for livestock forage. By the end of the twentieth century, it could be found from Connecticut to Missouri, extending south to Texas and Florida.

Kudzu covers everything in its path and grows as much as 1 foot (0.3 meter) per day. Similarly, English ivy (Hedera helix), a native of Eurasia, is considered a serious problem in West Coast states. It forms "ivy deserts" in forests and crowds out native trees and shrubs that make up essential wildlife habitat.

The invasion of an ecosystem by an exotic species can effectively alter ecosystem processes. An invading species does not simply consume or compete with native species but can actually change the rules of existence within the ecosystem by altering processes such as primary productivity, decomposition, hydrology, geomorphology, nutrient cycling, and natural disturbance regimes.

Invasive Insects and Microorganisms

The invasion of native forests alone by nonnative insects and microorganisms has been devastating on many continents. The white pine blister rust and the balsam woolly adelgid have invaded both commercial and preserved forest lands in North America. Both exotics were brought to North America in the late 1800’s on nursery stock from Europe.

The balsam woolly adelgid attacks fir trees and causes their death within two to seven years from chemical damage and by feeding on the trees’ vascular tissue. The adelgid has killed nearly every adult conebearing fir tree in the southern Appalachian Mountains.

The white pine blister rust attacks five-needle pines; in the western United States fewer than 10 pine trees in 100,000 are resistant. Because white pine seeds are an essential food source for bears and other animals, the loss of the trees is having severe consequences across the food chain.

Since the 1800’s the deciduous trees of eastern North America have been attacked numerous times by waves of invading exotic species and diseases. One of the most notable invaders is the gypsy moth, which consumes a variety of tree species. Other invaders have virtually eliminated the once-dominant American chestnut and the American elm.

Tree species that continue to decline because of new invaders include the American beech, mountain ash, white birch, butternut, sugar maple, flowering dogwood, and eastern hemlock. It is widely accepted that the invasion of exotic species is the single greatest threat to the diversity of deciduous forests in North America.

Effects on Humans and Humans as Invaders

Some introduced exotic species are beneficial to humanity. It would be impossible to support the present world human population entirely on species native to their regions. Humans, the ultimate biological invaders, have been responsible for the extinction of many species and will continue to be in the future.

At the beginning of the twenty-first century, the United States was spending $4 billion annually to eradicate invasive plant species, a figure that does not take into account loss of biodiversity or wildlife habitat.
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9:37 PM
Biological Weapons
Biological Weapons
Biological weapons are biological agents that can be used to destroy living organisms. This general definition includes the use of virtually any kind of microorganism (bacterium or fungus) or biological agent (mycoplasma like organism, virus, viroid, or prion) to destroy any biologically important plant or animal.

There are two basic ways of using biological weapons against humanity. The first is to attack the food or water supply. This would produce hardship and the possible death from starvation of many individuals. In developed countries such as the United States, total devastation due to such an attack would likely be avoided, as there are considerable stores of food, in dispersed locations, that would mitigate against crop failure of moderate proportions.

In addition, most experts agree that the amount of biological contaminant required to overcome the effects of dilution and time in most water reservoirs makes poisoning of water supplies impractical, although not impossible.

The other way of using biological weapons against humanity is to attack individuals directly, using pathogens. Numerous known pathogens could be used, but the most effective biological weapons would creep upon the population with stealth. Naturally occurring agents that have promise as biological weapons are pathogens, which can infect and colonize a host. A pathogen causes disease, an alteration in the metabolism of a host.


In order for disease to occur, it is necessary to have a virulent pathogen, that is, one that is capable of causing disease; a susceptible host, able to be infected; and an environment that is favorable to both the host and the pathogen. When these occur together, disease occurs.

For the disease cycle to begin, it is necessary for propagules of the pathogen to come in contact with the susceptible host. Propagules include those that cause initial infections, called the primary inoculum.

As the disease cycle progresses, the host may release other propagules, considered the secondary inoculum. When only one progression of disease occurs during a prolonged span of time, the disease is termed monocyclic. When more than one cycle of disease takes place in a growing season, the disease is called polycyclic.

Monocyclic Diseases

An example of the monocyclic disease cycle occurs with corn smut. The primary inoculum is released in the spring, as the tassel and silk of the corn appear. Infection occurs, symptoms of large black galls develop on the ears, and new inoculumis produced for the following growing season.

This kind of disease produces a single cycle during a growing season. The potential for problems depends on the amount of inoculum present at the beginning of the disease cycle. In order to use corn smut as a biological weapon, the initial amount of inoculum must be sufficient to reach all of the plants that are targeted.

This is the same general case as with anthrax. Anthrax is a disease of animals that is caused by the bacterium Bacillus anthracis. The bacterium is able to survive in nature as small spores that are able to resist extremes of climate and time.

These microscopic spores are produced at any time when environmental conditions are unfavorable for growth of the bacterium. The spores are less than 2 microns in diameter, and if they become suspended in the air, they will hang indefinitely. Such small particles are called PM 10 (particulate matter less than 10 microns in size).

These particles are of extreme importance, as they are not filtered out by common filters and must be removed by HEPA (high-efficiency particulate-arresting) filters, which can remove particles smaller than a micron. When these particles are inhaled, they cause disease of the lung tissue, which will result in destruction of the lungs and the resultant death of the host.

The reasons that Bacillus anthracis could be a biological weapon are that it is easily concealed and disseminates quickly as an invisible, airborne powder. The small particle size allows it to be inhaled, after which it lodges in the lungs and begins the process of infection. The infection begins like that of a common chest cold.

By the time the host determines that anthrax might have been contracted, the condition is normally fatal. One of the features of anthrax as a biological weapon is that it is not contagious. Spores are not produced until the host is dead, at which time the spores are not placed back into the air currents. This permits anthrax to be used against a specific target.

Polycyclic Diseases

Some kinds of biological weapons can be termed weapons of mass destruction. These biological weapons are able to self-perpetuate and thereby create great amounts of destruction. They are polycyclic in nature.

A plant-based example of this is the epidemic of potato late blight,which caused the Irish Potato Famine of the mid-1840’s. Most of the people living in Ireland at that time depended on their own harvests for food. During a two-year period, the climate became especially cool and damp, conditions favorable for the spread of potato late blight.

Because potatoes are planted from vegetative parts, there was genetic uniformity of the crop, which was highly susceptible. The pathogen is extremely virulent, with the capacity to destroy a single plant overnight. Total crop failure resulted in the reduction of Ireland’s population from about six million to about two million people.

About one-third of the people emigrated to other lands, and about one-third of the population died from starvation. All of this destruction could have started from a single fungal propagule that infected a plant and then spread. This fungus is still problematic world wide. However, regular sprays with fungicide reduce the risk of crop destruction.

Pathogens that occur at low levels in any given area are called endemic and may, when conditions are favorable, produce a widespread surge of disease in that area. This is called an epidemic. Epidemics that occur over wide geographic ranges, such as two or more continents, are called pandemics. The endemic potato late blight fungus caused an epidemic, and because it also spread into Europe and North America, the situation could be called a pandemic.

A similar concern is expressed with regard to the disease smallpox. Smallpox is caused by a virus that is easily passed from an infected individual to a healthy one. The smallpox virus no longer occurs in nature (is not endemic) anywhere in the world. The last reported case of smallpox in nature occurred in the late 1970’s. As a result of a concerted vaccination effort among many nations, this normally fatal disease was eradicated.

The last stores of smallpox virus are housed at the Centers for Disease Control (CDC) in Atlanta, the U.S. Army Biological Weapons Research Unit in Fort Detrick, Maryland, and the Russian Academy of Sciences in Moscow. Some people fear some of the inoculum from one of these storehouses could be transported into unconfined areas of the outside world.As such, small pox would become a very formidable biological weapon.

Smallpox is highly contagious and spreads easily from person to person. Should an infected person walk the streets of a highly populated urban area, it would be possible to infect millions of people within the span of a week or two. Within several weeks, especially in this age of global travel, the infection could spread around the world.

Vectors

One method of spreading disease is through the use of vectors.Vectors are arthropods or other invertebrates that have the ability to transmit a pathogen from one host to another. The most famous vector is the mosquito, which can transmit malaria, dengue fever, West Nile virus, and many other diseases.

The corresponding vector in plants is the aphid, which can transmit a host of viruses and mycoplasmas (bacteria that lack cell walls). In order for transmission to occur, it is necessary for a vector to first come in contact with an infected host, feed upon that host, and then pass the pathogen to an uninfected host.

The most notable vector-borne disease is plague, which is passed from infected animals to humans by fleas. This disease, which was once responsible for hundreds of thousands of deaths, is now readily controlled by the use of insecticides to kill off the vector.

Designer Weapons

With twentieth century advances in technology, the manipulation of the genetics of a pathogen to make it a "super pathogen" is possible. The creation of a genetic code which could be pathogenic is also possible. So-called designer weapons are those that may be envisioned by someone who feels he or she has a need to make a more destructive or more "targeted" weapon. These weapons could then be used on a specific population or area.

The creator of the designer weapon would have an advantage, as he or she would also be able to create a vaccine against the designer weapon, which could be administered to a specific group of individuals. Designer weapons, like all biological weapons, work best when there is an abundant supply of susceptible hosts and when the genetics of these hosts do not vary greatly.

Pathogen Dispersal

There is considerable opportunity for the use of any pathogen as a biological weapon. Most pathogens can be cultured with standard laboratory equipment; however, the difficulty is in creating a system of dispersal that will effectively spread the inoculum over an area of susceptible hosts.

There are innumerable systems that could be used; these include spraying particles into the air, mailing them in an envelope, or placing them into a bomb. One of the less sophisticated methods of dissemination is the use of aircraft that are used for agricultural spraying. These aircraft could spray inoculum over large areas, with the potential of infecting large populations.
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