Brief notes cont.

How humans exploit fungi for food and drug use.
Brewing baking and wine making all require yeasts, Sacchromyces cervisiae is probably the most commonly used. Yeasts are very active metabolically. The metabolism of the yeast produces CO2 that makes bread rise. It is a facultative anaerobe that ferments sugars to alcohol when forced to live without oxygen. Winemakers used to use the native yeasts growing on the grape skins for this purpose, but now they use domesticated strains. Brewers add yeast to water and hops to make beer.
Agaricus bisporus has been in cultivation for some time and is an important cash crop in some areas. Next in financial importance is shiitake and matsutake mushrooms, they are considered delicacies in the east, and were sometimes so expensive that they were sold singly. Recently they have been cultivated commercially and the price has fallen, but the market has increased. Truffles are the underground fruiting bodies usually found near oaks. In the areas around the French/ Italian border they provide additional income in rural areas. They have proved difficult to cultivate, but the French appear to have succeeded in inoculating the roots of some seeding trees with the mycelium.
Mushroom are very popular and wild ones always taste best, recently mushroom gathering has become so popular that in certain national forests in the US you have to buy a licence to collect them, and in some places they are considering banning mushroom picking altogether.
Various Penicillium spp. are used in the cheese industry, e.g. P. roquefortii is used in making Roquefort cheese. Aspergillus niger is used by the soft drinks industry for the fermentative manufacture of citric acid. Many fungi are used in medicine and research. Yeasts being unicellular are used in cytological and genetic research. Penicillium is an antibiotic, it hydrolyses the cell walls of certain bacteria. P. griseofulvum is used to produce an anti fungal antibiotic to treat ringworm diseases including athletes foot. Claviceps spp. causes ergot in cereals and is cultivated for medical use. C. purpurea is used in treating circulatory problems, low blood pressure, and in stimulation of post-natal uterus contraction.

Puccinia gramminis

Puccinia gramminis infects both barberry and wheat. On the upper surface of the barberry leaf the basidiospores germinate to form spermogonium, these must be cross-fertilized by insects for further development to proceed. A sticky, sweet exudate attracts the insects. Aecia are formed on the lower surface of the leaf, but the aeciospores cannot re infect the barberry, they must find a grass host.
On wheat the aeciospores germinate and uredia are formed. Urediospores are very small and light and can be blown 1000's of miles - from Canada down the side of the Rockies to Mexico, and from Spain and Portugal to the UK. This explains why P. gramminis can cause so much damage in the US, but less damage in Europe, as the mountains from east to west usually get in the way preventing the passage of urediospores.
Throughout the warm weather the urediospores re infect wheat. As the temperature drops telia are formed releasing teliospores. These are two celled and can overwinter if the temp is not too low - it usually is in UK. In spring the nuclei fuse (karyogamy), meiosis takes place followed by formation of basidia, then haploid basidiospores are released to infect barberry.
Control resistant varieties have been produced, this takes time and money, and the resistance does not persist because of the different strains of P. gramminis and its ability to mutate.
Fungicide application using predictions based on climatic conditions seems to be the best control. It is possible to forecast the likely incidence of epidemics, and this info used in conjunction with systemic fungicides, means the farmer can do minimum spraying for maximum effect.
Eradication of the barberry. As mentioned above, this can only be effective when the urediospores cannot persist because of low temp. In Mexico, US and Canada it is possible for asexual reproduction to continue throughout the year, so eradicating the barberry is not very effective.

Life cycle of Black rust (Puccinia graminis)

1. Spores called basidiospores are dispersed into the air in spring.
2. Basidiospores land on barberry leaves, germinate, then grow inside the leaf cells.
3. The fungal cells multiply producing structures in which pycniospores develop.
4. Pycniospores are picked up by insects and carried on the insect body from one infected site to another enabling fertilisation.
5. The fertilised cell develops on the underside of the barberry leaf and produces aeciospores.
6. The aeciospores are liberated into the air.
7. The aeciospores land on wheat stems or leaves and grow in through the stomata.
8. On the stem or leaf, structures producing uredospores develop. The uredospores are liberated into the air to infect other wheat plants.
9. Late in the summer teliospores are produced. These are inactive, resting spores which remain attached to the wheat stem during the winter months.
10. The teliospores germinate as the weather warms up in the spring and produce basidiospores.

Taste discrimination in blowflies

Flies taste with their feet, and on the last tarsal segment they have gustatory bristles and taste hairs. These hairs have a pore at the end into which a stimulus can enter to reach the sensory cells. There are five sensory cells in each hair; one mechanoreceptor which detects bending, two which respond to salts (one to anions the other to cations), one responds to sugar, and one to water (Barth 1991). The feet perform preliminary tasting of substances. If these substances are acceptable as food or water then the fly will extend its proboscis. This preliminary tasting prevents the fly from tasting harmful substances with its proboscis as the fly doesn't actually take in any food until it has passed the chemical tasting of its tarsal hairs and also the hairs around the edge of the labellum, which work in the same way as the tarsal taste hairs.
Barth, F.G. 1991. Insects and flowers, the biology of a partnership. Princeton University Press, New Jersey, USA.

How mosses obtain, retain, and transport water

Mosses are poikilohydric, there are two main growth habits, acrocarpous and pleurocarpous.
Acrocarpous have an upright growth form. They are endo hydric, which means that most of their water intake passes up the centre of the stem through rudimentary vascular tissue. This can be seen at its most advanced in Polytrichum spp. which has hydroids, sort of primitive tracheids. These are dead at maturity, and like tracheids have inclined end walls. Acrocarpous mosses also have a thin cuticle to help prevent water loss, the cuticle is also water repellant. However some water can be lost by evaporation, to minimize such losses mosses grow together in clumps creating their own microclimate. Fine hair points roughen up the outline of a clump increasing boundary layer resistance as the air stream passes over it. Water storage ability is 200-600% dried weight. Pleurocarpous e.g. Hypnum cupressiforme have a prostrate growth form. they are ectohydric, and so take in most of their water straight from the outside, because of this they have no cuticle. They are usually branched and have overlapping leaves, and can often be found growing in dense mats; and they have capillary structures. All of these features make it easy for them to absorb water in moist situations, and also to minimise water loss during drier times. The have less water transportation ability than acrocarpous forms, but they have less need, as absorption can occur over the whole surface of the plant. Their water storage ability is greater than acrocarpous, being 600-1200% their dried weight. Sphagnum spp. in addition to the above has special water storage cells. These large water-filled cells account for the pale colour of Sphagnum.


Is believed to have first occurred when an anaerobic heterotroph ingested an aerobic heterotroph, but did not digest it. This may have happened as the O2 began to increase in the atmosphere, and this symbiosis would have enabled the two organisms to survive. This is believed to have happened around 1900-1200 MYA, and was the origin of the eukaryotes. Symbiosis is the organisation of two or more organisms for the mutual benefit - though it is not clear what benefit the mitochondrion got - perhaps just a controlled environment. Today mitochondria still have their own DNA and divide in two when the cell does, though they depend on the nucleus for instructions, and cannot exist on their own. Flagella are believed to originate from motile anaerobes that formed a symbiotic relationship the with the anaerobic heterotroph and mitochondrion. These three plus photoautrotriphic cells combine in various combinations to form the different types of organisms that exist today. Nostoc (a blue-green alga) is often found living in a symbiotic relationship with a liverwort. Nostoc can fix nitrogen, and the liverwort provides a protective environment. About 4/5 of all vascular plants have a symbiotic relationship with mycorrhizae. Lichens are fungi and algae in a symbiotic relationship, first reported by Beatrix Potter. And one of the most fascinating symbiotic relationships is that between ants and acacias. The ants obtain their food from the plant and in return kill any insects that attempt to feed on the acacia and attack other plants that touch it.

Alternation of generations refers to the manner in which in a life cycle the sporophyte is succeeded by the gametophyte and then in turn by the sporophyte. In the life cycle of Mnium hornum, and all other bryophytes, the haploid gametophyte is the visible plant, the diploid sporophyte being dependant on the gametophyte for nutrition etc. The main means if dispersal is when the haploid spores are blown by the wind, the sperm are motile, but fertilisation and transportation requires water. In Pinus, e. g. Pinus sylvestris, and most other plants, it is the diploid sporophyte that is visible, the megaspore stays attached to the tree, and is dependant on it for nutrients. The diploid seed falls to the ground whilst still in the cone, further dispersal can occur by animals. The microspores are tiny and may be dispersed great distances by wind.