herbivory and medicinal plants Flashcards
how do plants protect themselves
1) mechanical protection on the surface
2) reduction in digestibility
3) phytotoxins
give an example of mechanical protection seen in plants
1) spines e.g. cacti or thistles
2) thorns e.g. brambles or roses
both deter large animals
what are trichomes and what sort of animals do they deter
a form of mechanical protection, they are small hairs which deter smaller animals such as insects
how does the stinging nettle (urtica dioca) mechanically protect itself
has sharp, stinging hairs which release substances into the skin causing irritation
give some examples of dosage dependant (need alot to show affect) substances which reduce digestability
1) cellulose
2) pectin
3) ligins
4) cutins and waxes
5) tannins
6) silica
what are phytotoxins
secondary metabolites which exhibit qualitative effects (only a small amount is needed)
what is secondary metabolism
when compounds formed in primary metabolism such as the formation of lipids, amino acids etc from carbon/nitorgen assimilation are used to form new compounds in the plant
what do lipids form after secondary metabolism
1) steroids
2) terpenoids
what do amino acids produce after secondary metabolism
1) alkaloids
2) nitroaliphatics
3) cyanogenic compounds
what are some nitogen based phytotoxins
1) cyanogenic glycosides
2) glucosinolates
3) alkaloids
4) proteins
what are some non nitrogen based phytotoxins
1) iridoids = intermediate in the synthesis of alkaloids
2) terpenoids
3) saponins
4)isoflavonoids
give an example of some plant toxins
1) nicotine - alkaloid
2) strychnine - alkaloid
3) cyanogenic glycosides
outline the use of phytotoxins in milkweeds, omarch butterflies and bluejays to aid protetcion
1) milk weed produces several cardiac glycoisdes which are very toxic
2) monarch catepillars ingest the milkweed tissue therefore sequestering the toxin within their own tissue
3) this toxin survives into the adult butterfly stage
4) which when eaten by blue jays exhibits its effect so blue jays learn to avoid butterflies
outline how ragworts and the cinnabar moth use phytotoxins to avoid ingestion or damage
1) ragworts contain phytotoxin pyrrolisidine alkaloids
2) cinnabar moths are resistant to this phytotoxin so ingest ragworts and sequester toxin into their own tissues for protection
what are the different theories as to why animals eat some plants but not others
1) classical plant defence theory = ehrilich and raven
2) the plant apparency theory= feeny
3) resource availability theory
outline the plant apparency (likelihood of being found by a herbivore) theory
long lived, late successional plants are more apparent (easy to find) so must employ more generalist stratergies so use quantitative methods such as increased lignin, cellulose, tannins
compared to short lived plants which are not as east to find, therefore use more specalist stratergies = qualitative methods
what compound does clover or members of the pea family make
hydrogen cyanide
how does clover and members of the pea family make hydrogen cyanide
1) within the leaves there is a secondary metabolite (cyanogenic glycoside) which contains a triple bond which is energentically expensive
2) in a seperate compartment of the leaf is the enzyme glucosidase
3) when something eats the leaf the enzyme and compound react producing an unstable product which breaks down forming a ketone and hydrogen cyanide
what are the two genes which control if clover or members of the pea family produce hydorgen cyanide
1) G = synthesis of the secondary metabolite cyanogenic glucoside
2) E= synthesis of the enzyme glucosidase
only when both genes are dominant (GE) will the plant produce hydrogen cyanide
what is meant by doctrine of signatures
the old philosophy that herbs which resemble various parts of the body can be used to treat ailments of that part of the body
give some examples of plant based medicines which can be brought over the counter
1) rubiaceae = cough mixture
2) cassia = laxatives
3) eucalyptus = inhalers
4) papayer and salix = pain killers
give some examples of powerful drugs extracted directly from plants
1) atropine = pupil dilation
2) morphine = pain killer
3) quinine= antimalarial
4) vincristine = antitumour
outline how vincristine and vinblastine are used in medicenes
plants native to madagascar with powerful anti-cancer properties
1) vinblastine = used to increase survival in childhood leukaemia from 10-95%
2)vincristine used to treat hodgkins disease
what are some stratergies for surveying plant world for mediciens
1) screen everything
2) systematic approach
3) ethnopharmacological approach based on ethnobotany
what is ethnopharmacy
an interdisciplinary science which investigates the perception and use of pharmaceuticals within a human society
evaluate the approach of screening everything to explore plant medicene
= nearly impossible
= expensive
outline the systematic approach
based on phytochemistru where certain types of chemicals can only be found in certain plants
