Organisms and Environment Revision 7: Responses to Environmental Challenges
how can we control crop parasites?
-"suicidal germination" - trigger premature seed germination w/ ethylene or strigol -antitranspirants --> reduce assimilate + water transfer --> parasite leaves overheat b/c no surface cooling --> blacken -genetic engineering to make host plant herbicide resistant -crop rotation to avoid continuous cropping of susceptible host -add nitrogen fertiliser (striga does best in N-starved soils)
examples of chemical defence
-orange: secretion of aromatic oils, insect-repellent -deadly nightshade: has berries (one will kill a grown man) contains poisonous alkaloid atropine which is a pupil dilator -gymnosperms + some woody angiosperms produce RESINS that seal wounds + deter insects -many plants release hydrogen cyanide upon tissue disruption (e.g. chewing) ----compartmentation prevents suicidal release of HCN if plant is intact
how else have carnivorous plants adapted to low nutrient availability + anoxia in soils?
-slow growth -efficient nutrient economy (N, P, K-reutilisation) -weakly developed root system ----weakly branched + short roots ----easy regeneration of new roots ----great metabolic + physiological activity of roots per unit biomass
when is chemical warfare resorted to?
A plant's exterior protection can be compromised by mechanical damage, which may provide an entry point for pathogens. If the first line of defence is breached, the plant must resort to a different set of defence mechanisms, such as toxins and enzymes. Secondary metabolites are compounds that are not directly derived from photosynthesis and are not necessary for respiration or plant growth and development. Many metabolites are toxic and can even be lethal to animals that ingest them. Some metabolites are alkaloids, which discourage predators with noxious odours (such as the volatile oils of mint and sage or repellent tastes (like the bitterness of quinine)
what is the most advanced method of "hunting" in carnivorous plants?
Active carnivores possessing snap, bladder, or catapult tentacle traps are the most advanced --> allow the plants to hunt even very mobile insects. Capture organs have mechanical and electrical sensors, which trigger rapid closure of the trap. prey touches the sensor --> viscoelastic energy stored in the open trap state is released
how do carnivorous plants resolve the conflict of interest: pollination vs nutrition
As flowering plants, carnivorous species need insect pollinators and some have very elaborate flowers In most insectivorous species, like sundew Drosera binata, the flowers are carried on tall pedicels, well above the potentially lethal sticky hairs, which in this species can easily entrap bumblebees
Camponotus sp.
One genus of ant (Camponotus sp. ) nests in hollow tendrils of Nepenthes bicalcarata in Borneo and feed on the pitcher's prey, which they haul out with their jaws. These ants may prevent the dangerous build up of excessive putrifying prey, so this could be a mutualistic association
what are pitchers?
Pitcher plants are several different carnivorous plants which have modified leaves known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. Some pitchers produce a sweet odour Many insects visit pitchers for nectar and escape unharmed. Pitcher plants may be an important nectar source in habitats where there are few flowers Some of the insect population "sacrificed" (especially evident in ants) in exchange for food source? Some insects breed safely in pitchers without harm (pitchers are temporary aquatic habitats - phytotelmata) - e.g. mosquito Wyeomyia smithii and midge Metriocnemus knabi. Some complex food webs established.
what are pitfall traps in carnivorous plants?
Pitcher plants, as another example, grow pitfall traps with a slippery rim to direct prey into a digestive moiety where gland cells take up prey-derived nutrients.
what are Oribatula tibialis?
Recent discovery of a mite (Oribatula tibialis) that can live safely amongst the glandular hairs of Pinguicula without touching them - scavenges fungi growing on dead prey carcasses
what did Darwin demonstrate?
SUNDEW PLANT the sticky hairs only closed over a struggling animal prey - and did not react to inanimate particles placed on their surface the response of the glandular hairs was triggered by organic nitrogen and that animal matter - e.g. egg albumen - was solubilised benefit of carnivory to the sundew plant, in terms of growth vigour, by feeding nitrogen via the leaves
what are passive traps in carnivorous plants?
Some species of carnivorous plants utilize passive traps, while others have evolved active traps to capture prey. Passive traps, of the flypaper type, have glandular hairs that produce a sticky glue-like substance to arrest their visitors.
what are lectins?
= non-enzymatic proteins and glycoproteins that bind to carbohydrates and exhibit a wide range of functions including disruption of digestion in insects and agglutination of blood cells in vertebrates Ricin is a powerful toxin produced in castor beans (Ricinus communis). It combines a lectin molecule with an N-glycoside hydrolase that enters animal cells and inhibits protein synthesis. Ricin is a highly potent toxin, having an average lethal dose of only 0.2 milligrams in humans!!
what are Flavonoids?
= one of the largest classes of phenolics
what are digestive enzyme inhibitors?
= proteins that block the normal digestion and absorption of nutrients by vertebrate and invertebrate herbivores
what are defensins?
= small cysteine-rich proteins that display broad anti-microbial activity and were first isolated from the endosperm of barley (Hordeum vulgare) and wheat (Triticum aestivum).
what is horizontal gene transfer (HGT)?
=the transfer of genes between two different organisms. Normally, genes are passed down from parents to offspring. In horizontal gene transfer, DNA is transferred in a different way and the swap often occurs between two separate species. Bacteria and other microbes are known for this ability. Although rare, there are some cases of HGT in eukaryotes, including certain plants
what is special about the sticky hairs of sundew (Drosera)?
Stickly droplets act like fly paper Glandular hairs with mucopolysaccharide secretions Hairs fold over prey in Drosera to form a "temporary stomach" The glandular head of the structure is multifunctional, secreting mucilage (arrowed) and enzymes and facilitating rapid absorption of digestion products Fluorescent histochemical staining with fluorescein diacetate reveals hydrolytic esterase enzymes in the stalked digestive glands and in glandular trichomes on the leaf surface.
how is it possible for parasitic plants to achieve HGT?
already engaged in cellular contact w/ the host
what is Juglone?
an allelochemical present in roots, leaves, and green peel of nuts in the species Black Walnut (Juglans nigra) -toxic against other plants (inhibits seed germination) -bound in glycoside -also a respiration inhibitor
what are Phenolics?
another large class of secondary metabolites produced by plants to defend themselves against pathogens. They are produced primarily via the shikimic acid and malonic acid pathways in plants, and include a wide variety of defense-related compounds including flavonoids, anthocyanins, phytoalexins, tannins, lignin, and furanocoumarins.
what are Anthocyanins?
are colorful water-soluble flavonoids pigments produced by plants to protect foliage from the damaging effects of ultraviolet radiation. Anthocyanins are responsible for the showy colors of many plants and are present in high concentrations in flowers, fruits, and the leaves of deciduous plants in fall.
how many times has carnivory evolved in plants?
at least 5 times, separately about 650 spp. of carnivorous plants (out of about 300,000 spp. of vascular plants) there are carnivorous plants in 8 families, 550 species
what is apoplastic transport?
between cell membrane and cell wall
what would happen to carnivorous plants if there was too much nitrogen?
carnivorous plants lose their advantage in their habitats pitchers stop forming at a certain point
holocarnivory
carnivorous plants secreting their own digestive enzymes
hemicarnivory
carnivorous plants that do not secrete their own digestive enzymes
what do carnivorous plants do?
catching or trapping of prey (traps) absorption of metabolites from prey utilization of these metabolites in their growth and development
what is symplastic transport? how is it used in these plants?
cell-cell Symplastic transport via the glandular head and the leaf cells occurs via two concentric layers of cells (arrowed) with very rapid cytoplasmic streaming Rapid cell-cell communication occurs between adjacent glandular hairs; stimulation of one will cause others in its vicinity to curl towards it, within a few seconds of stimulation
what are obligate hemiparasites?
contain chlorophyll, so only need water and mineral salts from host. But rates of photosynthesis may be low, respiration is high and radiotracer work shows that they need CHOs from host to support growth (esp carbon) Reduction in parasite PS may reduce its demand for nitrogen - advantage in nitrogen-starved soils
what are Pyrethrins?
monoterpenoid esters produced by chrysanthemum plants that act as insect neurotoxins. Many commercially available insecticides are actually synthetic analogues of pyrethrins, called pyrethroids, including the insecticides permethrin and cypermethrin.
what is the relationship between the Myrmecodia plant and ants?
mutualistic relationship: chambered roots, hollow stems or inflated thorns provide ready-made homes (domatia) for ants. Ant colonies that establish in the plant feed on herbivorous insects that attack its leaves.
do carnivorous plants have roots?
not true roots — instead leaves are modified to accommodate a trap function on either aerial or underground/submersed parts.
what are Terpenoids (terpenes)?
occur in all plants and represent the largest class of secondary metabolites with over 22,000 compounds described. The simplest terpenoid is the hydrocarbon isoprene (C5H8), a volatile gas emitted during photosynthesis in large quantities by leaves that may protect cell membranes from damage caused by high temperature or light.
why would parasites steal host plants' genes?
to help them invade/infect and get past host defenses some of the genes may also help the parasitic plants avoid infections
how is seed germination triggered in plant parasites?
triggered by root secretions of host after being spread by birds/dropping/wind/explosive fruits that shoot seeds everywhere
what are protease inhibitors?
typically produced in response to herbivore attack and inhibit digestive enzymes including trypsin and chymotrypsin. They occur widely in nature but have been well studied in legumes, solanaceous plants, and grasses. Herbivore feeding often triggers a series of molecular signaling events that induce systemic production of these compounds in distal tissues that contribute to the protection of undamaged plant parts from subsequent attacks by a wide range of herbivore pests
when is carnivory a useful adaptation?
unfavourable conditions, mostly low nutrient availability in wet, acid soils Ecological factors in terrestrial habitats of carnivorous plants: -wet bog and fen organic soils (peat) -soil hypoxia or anoxia, low redox potential, phytotoxins, high Fe2+ and Mn2+ .........many of these plants don't have a cuticle so they need wet environments so they don't lose too much water -mostly acid soils (pH 3-6) -low available mineral nutrient content in soils -high air humidity BUT large energy cost
what was the big debate after Darwin? What was the solution?
whether insectivorous plants were saprophytes or true carnivores i.e. did they break down prey with their own enzymes or did they depend on contaminating bacteria to do the job for them? Sterile tissue culture techniques and enzymological studies resolved the issue - some plants are true carnivores, although microbial decay also plays a role
what is allelopathy?
= chemical inhibition of one plant (or other organism) by another, due to the release into the environment of substances acting as germination or growth inhibitors. allelochemical = a chemical produced by a living organism that exerts a detrimental physiological effect on individuals of another species when released into the environment
What about the changing environment is a threat to carnivorous plants?
Increased nitrogen deposition and eutrophication of low nutrient environments are a threat to carnivorous plants. Botanical carnivory is associated with plants that master survival in nutrient-poor habitats lacking nitrogen, phosphate, sulphur and minerals.
how do parasites acquire water compared to their hosts?
1. higher rates of transpiration 2. lower water potentials --> net flow of water + assimilates to parasite WHY? to facilitate acquisition of water PLUS inorganic + organism solutes from the host the driving force is maintained by accumulation of carbon- or nitrogen-containing compounds which act as osmoticants
examples of plants' physical defences
= Morphological, anatomical and biochemical defences against pests and diseases -bark layer of trees - dead material that is waterproof, tough, self-repairing but must also expand annually and allow gas exchange -grasses producing more silica to bring down vole population -thorns (energy consuming) to protect from grazing mammals -holly: thick cuticle ---> leaves survive 2 or 3 years, are much less spiky towards top of tree (safe from herbivores) -stinging nettles: high N consumption to grow quickly, protect itself w/stinging hairs that snap and release chemicals; if shoots are grazes, the regenerated versions develop denser covering of stinging hairs
what are alkaloids?
= a large class of bitter-tasting nitrogenous compounds that are found in many vascular plants and include caffeine, cocaine, morphine, and nicotine. They are derived from the amino acids aspartate, lysine, tyrosine, and tryptophan, and many of these substances have powerful effects on animal physiology CAFFEINE is toxic to insects + fungi
what are holoparasites?
= a parasitic plant that derives all of its fixed carbon from the host plant NEED transfer of mineral nutrients + carbohydrates
what are hemiparasites?
= a plant parasitic under natural conditions, but photosynthetic to some degree -almost always parasites when found growing in natural vegetation -have a pre-parasitic autotrophic phase which may last from a few hours to several months -angiosperm parasites in general have reduced root systems, few or no root hairs and no mycorrhizae, so rely on host for mineral acquisition. Many hemiparasites have poorly developed root systems and lack root hairs - use host root system to forage for nutrients Experiments show that phosphorus may be most important ion supplied by host.
what is a haustorium?
= an organ for attachment, penetration and solute transfer from the host, that is highly variable morphologically and physiologically -also metabolically active (enzymes process host's assimilates as they are transferred) -establishes xylem continuity but there is no clear evidence of phloem continuity between host and parasite, although phloem does differentiate in haustorium -very rapid growth (24h) All angiosperm parasites are attached via this Always xylem continuity between host and parasite.
How did carnivory evolve?
Carnivory developed independently in different plant families. Today, over 630 species from more than a dozen genera have been identified that can live on an animal diet To reconstitute the emergence of carnivorous plants, genomes of more green flesh-eaters — primitive and advanced — must be investigated. Of particular interest are the genomes of the most advanced hunters Dionaea musciplula, its aquatic sister Aldrovanda vesiculosa and the closely related Drosera species. The secretome of Dionaea is dominated by a mixture of different hydrolases and antimicrobial proteins. In terms of homologies to non-carnivorous plants, these genes and their expression patterns exhibit strong similarities to plant defence responses. Plants defend themselves against pathogenic fungi and herbivores by wound-induced jasmonates that trigger defence gene production (including chitinase secretion). Plants in nutrient-poor habitats appear to have turned the sword, modifying their ancient defence mechanisms for feeding on chitin-bearing herbivores.
how does the Venus flytrap capture prey?
In the Venus flytrap Dionaea muscipula — the Darwin Plant — the leaf tip develops into a bilobed snap trap, each trap lobe equipped with three sensory hairs. When visitors inadvertently bend these trigger hairs, mechano-receptor cells are stimulated to fire an electrical impulse, which travels as an action potential along the entire trap surface. A second action potential triggered within 20 seconds of the first shuts the snap trap.
What genes are required for the carnivory syndrome?
Stimulated by prey animals, carnivores that operate active traps translate mechanical touch into an all-or-nothing travelling nerve-like impulse This action potential is based on the sequential activation of ion channels that transiently depolarize the membrane potential. Recently, the genomes of the first carnivorous plants Utricularia gibba and Genlisea aurea were identified. Despite their tiny size, these genomes accommodate the typical number of genes found in other plants, lacking genes encoding animal nerve cell-type ion channels. Interestingly, the ion channel profile of the excitable carnivore U. gibba is not much different from that of non-carnivores. Furthermore, there is no evidence that either U. gibba or G. aurea have hijacked genes from their animal victims to build traps capable of catching fast moving animals. Given that no carnivore-specific genes have been identified so far, flesh-eating plants apparently gained their carnivorous syndrome from how they assemble the proteins that exist in all plants.
what is parasitic reduction syndrome?
THESE ARE HOLOPARASITES 1) Loss of leaves - leaves reduced to scales 2) Small overall size of plant - no need for large plants to hold leaves 3) Loss of roots - reduced to short, stumpy projections with haustoria 4) Loss of chlorophyll 5) Loss of genes needed for photosynthesis 6) Fast gene evolution in genes which are not lost
what are the most advanced hunting skills?
The hunting skills of active carnivores possessing snap, bladder, or catapult tentacle traps are the most advanced. These sophisticated capture organs allow the plants to hunt even very mobile insects. Capture organs have mechanical and electrical sensors, which trigger rapid closure of the trap. When prey touches the sensor, viscoelastic energy stored in the open trap state is released within a blink of an eye.
what is polyphyletic evolution?
Trait evolved many times, in unrelated families parasitic plants are an example of this (3000 spp in 17 families, 1% of all angiosperms)
How do these plants process their prey?
entrapped struggling animal repeatedly touches the mechano-sensors --> triggering trains of action potentials --> mechano-electrical stimulation of the trap initiates the synthesis of jasmonate-type touch hormones --> the closed trap seals hermetically and floods the forming green stomach with a lytic enzyme cocktail insect flesh is covered by a chitin shell --> hydrolases in the green stomach of Dionaea degrade the chitin polymer coat (chitinases), as well as proteins, nucleic acids, glycans and lipids from the prey into their respective monomers and dissociate the nitrogen, phosphate and sulphate side groups (the latter, together with minerals such as potassium, are the macronutrients required for plant growth, which in non-carnivorous plants are usually taken up from the soil by transport proteins in the roots of the plant when in contact with trapped animals, traps express and operate root-type transporters to efficiently absorb prey-derived nutrients. Dionaea gland cell transporters shuttle nutrients released by the decomposition of the animal food --> Dionaea glands are able to take advantage of the steep proton gradient that powers proton-driven solute transporters --> mining the animal food source to the trace level
what do plant parasites have that's an example of convergent evolution?
evolution of an absorptive organ occurring many times over in unrelated groups of flowering plants
What are Saponins?
glycosylated triterpenoids (triterpenoids with attached sugar groups) that are present in the cell membranes of many plant species. These substances have detergent (soap-like) properties and disrupt the cell membranes of invading fungal pathogens. The wheat pathogen Gaeumannomyces graminis is unable to infect oats that contain avenacins, a class of triterpenoid saponins. However, some fungal pathogens have developed counter-measures to these plant defenses: Botrytis cinerea, Fusarium oxysporum, and Septoria lycopersici are all capable of degrading saponins and causing disease in susceptible saponin-producing plants.......an ever ongoing arms race of co-evolution........
what is special about Pinguicula (Butterwort)?
has sticky hair traps Enzyme-secreting glands are densely cytoplasmic, multicellular structures embedded in the epidermis Fluorescent histochemical staining with fluorescein diacetate reveals high concentrations of hydrolytic esterase enzymes in the digestive glands Some slugs are kleptoparasites, stealing prey from Pinguicula traps
why do parasites have high assimilate demand?
high respiration rates
what are Phytoalexins?
isoflavonoids with antibiotic and antifungal properties that are produced in response to pathogen attack. These toxic molecules disrupt pathogen metabolism or cellular structure but are often pathogen specific in their toxicity. Examples include MEDICARPIN produced by alfalfa (Medicago sativa), rishitin produced by both tomatoes and potatoes (the Solanaceae family), and CAMALEXIN, produced by Arabidopsis thaliana.
