Plant defences are those mechanisms employed by plants in response to herbivory and parasitism. According to Hanley et al. (2007), “the tissues of virtually all terrestrial, freshwater, and marine plants have qualities that to some degree reduce herbivory, including low nitrogen concentration, low moisture content, toxins or digestibility-reducing compounds”. The type of chemical defence may be species specific (Scott 2008). The defences that plants possess may be in the form of chemical production or in the form of physical defences such as thorns or spikes and even through reinforced, rigid leaves. “The compounds that are produced in response to herbivory can either have a direct effect on the attacker itself (e.g. toxins or digestibility reducers), or serve as indirect defenses by attracting the natural enemies of the herbivores” (Bezemer & van Dam 2005). This essay will focus on chemical plant defences and in particular the effects of terpenes, phenolics, nitrogen-based defences as well as allelopathy in plants. The first group of chemical compounds to be discussed are terpenes. Terpenes are a very comprehensive group of metabolites which are known to contain essential oils that produces well-known scents in herbs belonging to the Lamiaceae plant family (Scott 2008). These scented compounds are usually found in the trichomes of basil, rosemary, lavender, etc. (Scott 2008). Electron micrograph images of these trichomes can be seen below. According to Keeling & Boltmann (2006), there are about 30 000 known types of terpenes which originated from structures created from terpene synthases. These terpene synthases can be broken up into three groups, monoterpene synthases, sesquiterpene synthases, and diterpene synthases (Keeling &... ... middle of paper ... ...n-toxic, but becomes toxic once it reacts with air or soil compounds to become the allelopathic hydrojuglone (Appleton et al. 2009). Once this compound reaches the soil, it can affect neighbouring plants by “root contact, leakage or decay in the soil, falling and decaying leaves, or when rain leaches and drips juglone from leaves and branches onto plants below” (Appleton et al. 2009). This process is illustrated below. This essay has therefore discussed the most popular classes of plant chemical defences, namely terpenes, phenolics, nitrogen-based defences and allelopathy. The effects of these defences on herbivores has also been touched on. Many of these compounds produced by plants have later been extracted by humans for use as insecticides. Compounds such as tannins are also used in the wine industry. These chemicals thus have a very strong economic influence.
A population of Plantago lanceolata (ribwort plantain) on the path was found to have higher trampling tolerance than populations away from the path; this reflected the sharp differences in the conditions of the plant at these sites. Ribwort Plant had generally a higher tolerance to trampling than any other plants as more were found on the path, but there were less compared with other plants as distance increased from the path. These results suggest that the competition level found on the path was sufficient enough to impose a selection pressure for the evolution of tolerance in a sensitive species, but in some areas the distribution of Ribwort Plantain were the same. This provides that other conditions affect the tolerance of trampling for Ribwort Plantain.
Dr. May Berenbaum, an entomologist at University of Illinois, has conducted over 40 years of research on parsnips and the parsnip web worm. During her lecture on March 22nd, she explained how parsnips are invasive weeds that are full of toxic furanocoumarins. Interestingly, the parsnip webworm only eats the parsnips and is able to process the toxin very well. The interactions between the web worm and parsnips cause the parsnips to select for plants with a higher amount of furanocoumarins in order to defend themselves from the worms. When the worms are not there, i.e. in New Zealand, the parsnip plants grow taller and develop more ways to attract pollinators, and they do not put energy into having as many furanocoumarins
“(Silent Spring) spells out in memorable detail through out the book the effects of synthetic insecticides and herbicides on water, soil, plants, wildlife, fish and human beings. But in the book’s final chapter she suggests alternative courses of action for mankind —- a way out of this march toward death.” (Holmes, Pg. 123)
The location of secretory structures and the presence of essential oils and alkaloids were investigated (Corsi and Biasci, 1998).The consumption of varying parts of the plants (leaves, fruits) can cause different degrees of clinical effects and there appears to be different susceptibility to toxicity between species. The primary time of year for poison hemlock is spring; often when there is insufficient forage available. At this time the plant may also be more palatable. The toxicity increases throughout the growing season and the roots become toxic only later in the year. Once dried, the toxicity is considered to be reduced but not eliminated. The plant causes different signs and lesions in different species of animals (Dougall and Maureen,
Theophrastus Bomabastus Von Hoheneheim (Paracelsus) said “sola dosis facet venenum,” translated as, “all things are poisonous and nothing is without poison.” (Wink & Wyk, 2008) For people living in the Great Lakes regions of Northern Michigan, it often feels the opposite, “in everything there is medicine and nothing is without medicine.” Undoubtedly, some plants can externally or internally irritate the body affecting homeostasis, including instances of photo-sensitization and allergies; but generally these symptoms are not life threatening. According to herbalists and toxicologists, it is important to “distinguish between poisons that can kill in minute amounts, toxins that are less toxic than poisons, and toxicants that are toxic in high concentrations only.” (Wink & Wyk, 2008).
The location of secretory structures and the presence of essential oils and alkaloids were investigated (Corsi and Biasci, 1998).The consumption of varying parts of the plants (leaves, fruits) can cause different degrees of clinical effects and there appears to be different susceptibility to toxicity between species. The primary time of year for poison hemlock is spring; often when there is insufficient forage available. At this time the plant may also be more palatable. The toxicity increases throughout the growing season and the roots become toxic only later in the year. Once dried, the toxicity is considered to be reduced but not eliminated. The plant causes different signs and lesions in different species of animals (Dougall and Maureen,
Coevolution may be defined as an evolutionary change in a trait of the individuals in one population in response to a trait of the individuals of a second population, followed by an evolutionary response by the second population to the change in the first (Janzel, 1980). Plant animal coevolution is a very broad topic with many different areas and examples therefore this essay will be focused on the evidence of coevolution between grasses and herbivores. Key questions explored will be how is coevolution studied,
In a study conducted by Appel and Cocroft at the University of Missouri, it was found that some small plants (Arabidopsis thaliana) have chemical defenses against predators, specifically caterpillars (Pieris rapae). These plants can sense when a predator is near and can communicate with others about the impending danger. When a caterpillar is near the plant can “hear” the vibrations and change it’s chemical makeup. By changing the chemicals in the leaves the plant creates a bitter taste in the caterpillar's mouth to stop the caterpillar from feasting on any more leaves. The experiment consisted of a large sample of Arabidopsis thaliana as well as Pieris rapae (caterpillars).
...icot stem. Label and sketch its parts. Take note of the position of the vascular bundle.
Invasive plant species such as Ailanthus altissima (Tree of heaven), Allaria petiolata (garlic mustard), and once again Celastrus orbiculatus, use allelopathy to deter away competitors surrounding a plant species to make room for it to grow and expand. What allelopathy does is produce chemical compounds that change the soil and not allow other species of plants to grow, intake nutrients or germinate (Pisula & Meiners 2010). A net benefit is created when chemical compounds are released in the soil because it leaves more nutrients or resources available to the invasive plant species when native plants aren’t
Qualitative and quantitative difference exists among plant allelochemicals in plant species. Moldenke et al. (1983) focused on the induction effect of three monoterpenes found in peppermint on the sixth instar of Peridoia saucia; pulegone, menthone and menthol. These phytochemicals were fed to the Peridoia saucia at 0.01% - 0.1% of diet. There was no significant difference in the level of induction caused by the three allelochemics; probably due to their closeness in chemical nature. Furthermore, the mixture of the three compounds did not yield greater P450 induction. This is also suggestive that qualitative difference among plant allelochemics might also have effect on induction of P450 and other detoxification enzymes.
Interactions in between plant species are of great importance and often result in fierce competition within the community. Over the past decades, increasing in human activity and movement allowed certain species to migrate beyond their origins and vastly expand in population, plants being one of the most complicated organisms on earth were highly involved in such activity. This enabled invasions by alien plants which poses serious threats and may inflict negative impacts to native species of plants in an certain ecosystem. Due to this nature, it may be concluded that there are certain traits and characteristics in these plants that allowed for the dominance to occur. It is crucial to be able to identify these traits to prevent
The condensed tannins are even further categorized into many different sub-types pertaining to the compounds structure and linkages of their flavonoid groups (Barbehenn and Constabel 2011). Plant species with secondary or woody growth have been found to contain generous amounts of condensed tannins (Hattenschwiler and Vitousek 2000). Conversely, these condensed tannins are generally absent within the herbaceous plants (Hattenschwiler and Vitousek 2000).
Zimmerman, H. G. and Neser, S. 1999. Trends and prospects for biological control of weeds
Plant extracts are commonly referred to as plant botanicals and are the secondary plant metabolites synthesized by the plant for protective purposes. Some of these compounds are toxic to insects. These plant compounds are called botanical pesticides, plant pesticides or simply botanicals. Many of the plant botanicals are used as insecticides both in homes, in commercial as well as in subsistence agriculture by small-scale farmers. They may be contact, respiratory or stomach poisons. Botanicals are not very selective because they target a broad range of insect pests. Plant insecticides act in several ways: as repellents by driving the insects away due to smell or taste, as anti feedants which cause insects on the plants to reduce their food intake and hence starve them to death; as oviposition deterrents, by preventing insects from laying egg; or as inhibitors by interfering with the life cycle of the insects. Plant insecticides