The chromist algae are those algae in the Kingdom Chromista. These are often referred to as the Stramenopiles. The 'true' Chromista are defined both on the basis of genetics and physiology. They include such algae as: Phaeophyta (brown seaweed), Bacillariophyta (diatoms), Xanthophyta (yellow algae) and Chrysophyta (golden algae). Cryptophyte and haptophyte algae are sometimes included in this group. The chloroplasts of these algae resemble those of the red algae. Possibly the chromists obtained their chloroplasts by incorporating entire eucaryotic alga. Chromista includes some protists lacking chloroplasts, such as: Labyrinthula (slime net protozoa) and Oomycota (water moulds).

Chromista are members of the Super-Group Chromalveolata. The Chromalveolata is an even broader group that includes the telonemias, ciliates and dinophytes. The Chromalveolata, as a whole, share a common ancestor with the green plants and red algae.

Organelles

Organelles are tiny bodies that do much of the metabolic work for the eukaryotic cells that host them. The mitochondria, for example, are involved in eukaryotic respiration. Mitochondria have their own genes, apart from those in the nuclei of the host cell. Mitochondria are much closer genetically to certain bacteria than they are to their own host cell! Chloroplast are the organelles that contain the photosynthetic machinery of the cells of plants, seaweed and algae. Strangely, chloroplast genes are more closely related to those in cyanobacteria than to their own host cell's genes! It has long been noticed that organelles reproduce inside their host cells - as if they are separate organisms.

In the 1970s Lynn Margulis revived the hypothesis that some organelles really used to be bacteria. Genetic studies have since amply confirmed this suspicion. Probably chloroplasts and mitochondria were originally symbiotic bacteria that became incorporated into protozoan cells. It is even possible that this symbiosis first occurred back when eukaryotes had not yet differentiated from archaebacteria (Collins & Jegalian 1999, Doolittle 2000 ).

There are plausible analogues of how chloroplasts may have developed. Some ciliates harbour phycobionts for use as makeshift chloroplasts. In some cases these symbiotic algae must be captured anew in each generation. However, a few of the ciliates pass their phycobionts on to their daughter cells.

It is now suspected that the origin of chloroplasts is vastly more interesting that anyone had hitherto suspected. It is highly probable that chloroplasts were not all domesticated in the same way (Lee 1999). The Glaucophyta algae have ‘cyanelles’ that seem only slightly different from cyanobacteria. In some species these cyanelles have peptidoglycan walls which are very much like remnants of bacterial cell walls. The Cryptophyta algae have chloroplasts which strongly resemble entire eukaryotic algae. Each chloroplast has its own plastids, and it also has a little ‘nucleomorph’ inside it. This nuceomorph appears to be a remnant of the nucleus of an entire eukaryotic alga. Euglenoid and dinoflagellate algae have genetically diverse chloroplasts. These appear to have been ‘stolen’ from other algae. Seemingly their ancestors kept and cultivated the chloroplasts from their food items. Algae have therefore seemingly obtained their chloroplasts through separate routes

References

Adl, Sina M. et al. 2005. The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists. Journal of Eukaryotic Microbiology. 52(5): 399-451.

Bhattacharya, D. and Medlin, L.K. 2004. Dating Algal Origin Using Molecular Clock Methods. Protist. 155: 9-10.

Cavalier-Smith, Thomas. 2004. Only six kingdoms of life. Proceedings of the Royal Society, London. (B): 1251-1262.

Collins, Francis S. and Jegalian, Karin G. 1999. Deciphering the code of life. Scientific American. 281 (6): 86-91.

Doolittle, W. Ford. 2000. Uprooting the Tree of Life. Scientific American. 282, (2): 90-97.

Lee, Robert Edward. 1999. Phycology. 3rd Edition. Cambridge University Press. Cambridge.

Margulis, Lynn and Schwartz, Karlene V. 1982. Five Kingdoms - an illustrated guide to the phyla of life on Earth. 2nd Edition. W.H. Freeman and Company. New York.

Tudge, Colin. 2000. The Variety of Life. Oxford University Press. Oxford.

Nearly everywhere there are truffle-like fungi. The genera Elaphomyces, Gymnomyces and Rhizopogon all produce truffle-like bodies. Some truffle-like fungi are edible, others are tough in texture, and yet others engulf the sand in which they grow. Some are sporocarps, and others are spore-less resting bodies. Even the morel mushrooms produce truffle-like bodies for over-wintering.

Most pseudo-truffles are ascomycetes, but some are basidiomycetes. The conifer forest false truffles (Truncocolumella spp.) are a club fungi. The bolete false truffles (Gastroboletus spp.) produce bolete-like mushrooms which do not usually break through the leaf litter. Many false truffles appear to be derived from above ground toadstools. They are structured very much like toadstools in an ‘aborted’ form, they remain in the budding stage without opening their caps. Most of these basidiomycete false-truffles are more common in the western conifer forests.

Although not always classed with truffles, very similar kinds of fruiting-bodies can occurs in the archaemycete pin-moulds. Some people consider the pin-moulds in the genus Endogone to be tiny truffles. Rodents eat these bodies, and this aids in the dispersal of the endogones' spores. In other words, they must be considered at least a kind of false-truffle, or perhaps trufflettes.

There are other false-truffles for which the bulb is not a sporocarp, but a mass of hyphae (sclerotium). A sclerotium is a means by which a fungus survives drought or winter. While many toadstools have sclerotia, some of the false-truffles have truly gigantic ones. For example, the sclerotium of the ‘tuckahoe’ (Wolfiporia cocos) looks very much like a truffle. It can be be as large as a coconut. These tuckahoes were eaten by the Algonquins and other Amerindian peoples. The actual sporocarp of the tuckahoe is a polypore toadstool, which is rarely seen. A related species, the Polyporus tuberaster, is also known as a tuckahoe. Its sclerotium tends to be more sandy and less edible. The toadstool of this polypore is more commonly seen than the regular tuckahoe's. The Australian version of the tuckahoe (Mylitta australis) is very similar. This fungus was also once used as a food source. Giant hypogeous sclerotia are fairly common in dry environments, such as the American prairies and the Australian outback.

American hypogeous (underground) fungi were spread by flying squirrels, skunks, armadillos, peccaries and other creatures. European truffles may originally have been adapted to diaspora by the wild pig. They produce an odour which is especially attractive to pigs. Truffle spores can survive passage through an animal's digestive tract. The spores produce mycelia which spread from the dung to the soil, seeking out a mychorrhizal association with plants. The spores of the various pseudo-truffles are, or were, spread by different animals in different habitats. American flying squirrels are especially fond of both the deer truffles and the true truffles. In some places hypogeous fungi are a significant part of the flying squirrel's diet (Loeb et al 2000).

Masses of the honey mushroom’s mycelium can glow eerily on dark nights. Mostly this mycelial mat is hidden under bark, but on occasion it is noticeable. Jack-o’-lantern toadstools also can glow in the dark. In this case, a whole group of fungal fruiting bodies may be seen glowing feebly on dark nights. In both cases, the chemical reaction radiates a bluish-green light. The glow is ‘cool’, except perhaps at a micro-molecular level. Of course, immobile glowing fungi cannot explain all will-o’-the-wisp sightings. Some spook lights move, and hence must have another explanation.

The adaptive function of fungal bioluminescence is not fully known. It is most common in wood rotting fungi. In many cases bioluminescence seems to be a side effect of oxygen respiration. The light producing enzymatic reactions are also involved in the creation of metabolic water. In some species, the glowing tissues may attract insects, which help to disperse the spores. In actual fact, even though the biochemical process is fairly well understood, its full biological role is still an enigma.

I remember my first encounter with luminous fungi, probably a soil Mycena. When I was a child I found a glowing patch in the grass. At the time I tried to convince myself that it was a glowworm. However, when I went to grab it, I fetched up an off-centre glowing segmented structure. Apparently, these segments were the gills of the toadstool!

Endophytes belong to several fungal taxonomic groups, but most are ascomycetes. Many of the needle cast fungi (e.g. Phomopsis spp. & Lophoderma spp.), have endophytic relatives. Even some of the leaf spot diseases (e.g. Rhytisma spp.) have endophytic relations. Most of the endophytes which infect pines are members of the Rhytismataceae family. Since there are rhytismataceous parasites, mycologist have wondered if endophytes are not just the old familiar parasites in dormancy mode. Genetic studies show that the rhytismataceous endophytes are not the same as their pathogenic cousins. They are members of the same genera, but they are not identical species (Ganley et al 2004). Endophyticity seems to be a niche different from parasitism. Possibly this mode of life developed from true parasitism.

In theory parasites can evolve to become ever more benign to their host. If a parasite does not harm its host, it has a more secure food supply than if it weakens the host. Severe plant diseases may often be due to parasites in novel hosts. Novel hosts may lack resistance to the ‘new’ parasite. In the long run, both host and parasite may co-evolve into an asymptomatic relationship. Probably a fungus would evolve quicker than a long-lived tree. Highly virulent strains of a parasite would have an initial advantage in its new frontier. The advantage would become a detriment after the contagion’s food supply is consumed. Natural selection would then favour the less virulent strains of the parasite. This co-evolution seems to have happened in many cases. Dutch elm disease (Ceratocystis novo-ulmi) was relatively benign in Asian elms. But when it reached Europe and the Americas, it encountered hosts which were not equipped to deal with the fungus. Similarly, the potato blight (Phytophthora infestans) is relatively harmless to the potatoes of the Andes. When potatoes were cultivated in Europe they lost their tolerance of the fungoid. When the fungoid was introduced to Ireland in the 1840s, the results were devastating. There are many other examples of diseases which only become problems for host species which have not co-evolved mutual tolerance.

Examples of Endophytic Fungi

A rather typical example of an endophytic symbiont is a fungus which grows in the seeds of darnel grasses. This Gloeotinia temulenta is apparently a symbiont in darnel grasses. It appears to be a helpful endophyte on wild darnel grass (Lolium temulentum). Grazing animals apparently learn to recognise the darnel, probably by taste, and avoid eating it. Darnel ryegrass, or ‘tares’, of the Old World was a scourge of cereal farmers and haymakers alike. In the early days wheat, and other grains, were often contaminated by the seeds of wild grasses. But darnel seldom infests cereal crops nowadays, as seed-corn is cleaner now than it was in yesteryear. Darnel is still considered a pest by forage farmers. It is difficult to reduce the darnel without killing other forage grasses. Now it is known that darnel's toxicity actually hails from the fungus, not the grass itself.

The darnel fungus can be a pathogen, if it occurs in a different host species. In these hosts it tends to form ascomata fruiting bodies on the seeds. (Endoconidium temulentum is the asexual anamorph.) Darnel's endophytic relatives are not always benign either. Gloeotinia granigena can be pathogenic to certain species of ryegrass and fescue. In these grasses it causes the ‘blind seed’ disease. This disease causes both the abortion of the seed embryo, as well as making the grain toxic. Gloeotinia spp. are not the only blind seed fungi, nor are they the only fungal genus with an ambiguous pathogenicity.

Certain species of the Epichloë fungus can harm plants, while other species in the genus are asymptomatic. (The asexual anamorph form of the fungus is called Neotyphodium.) The mutualistic versions of these Epichloë fungi do not harm their hosts, at least noticeably. However, they do make the host plant distasteful to herbivores. This protective role could be considered a mild form of symbiosis.

One interesting example of a symbiotic endophyte is the fungus Taxomyces andreanna. The fungus lives in several species of yew (Taxus). The endophytic fungus produces a chemical called Paclitaxel in the inner bark of the yew trees. This compound has been found to slow the replication of cells. Probably its symbiotic role is to inhibit competing parasites in its host. Paclitaxel has been found to be a useful, to us humans, as a chemotherapy agent! It can be used, with a regimen of other drugs, for fighting certain kinds of tumours. Originally the drug was obtained by harvesting wild yews. This exploitation is no longer necessary.

References

Coder, Kim D. 2004. Foxfire - secret lights in the chipper box. I.S.A. Arborist News. 13 (5): 5-8.

Corliss, William R. 1983. Hand Book of Unusual Natural Phenomena. Anchor Press. Garden City New York.

Ganley, Rebecca J., Brunsfeld, Steven J. and Newcombe, George. 2004. A community of unknown, endophytic fungi in western white pine. PNAS, July 6, 101 ( 27):| 10107-10112

Heinrich, Bernd. 1997. The Trees of My forest. Cliff Street Books. New York.

Holliday, Paul. 1989. A Dictionary of Plant Pathology. Cambridge University Press. Cambridge.

Lee, Robert Edward. 1999. Phycology. 3rd Edition. Cambridge University Press. Cambridge.

Loeb, S.C., Tainter, F.H. and Cazares, E. 2000. Habitat associations of hypogeous fungi in the southern appalachians: Implications for the endangered northern flying squirrel (Glaucomys sabrinus coloratus). America Midland Naturalist. 144(2):286-296.

McLoughlin, Stephan and Vajda, Vivi. 2005. Ancient wollemi pines resurgent. American Scientist. 93 (6): 540-547.

Meijer, G. and Leuchtmann, A. 1999. Multistrain infections of the grass Brachypodium sylvaticum by its fungal endophyte Epichloë sylvatica. New Phytologist, 141: 355-368.

Schardl, C. L., Leuchtmann, A., Chung, K.-R., Penny, D., and Siegel, M. R. 1997. Coevolution by common descent of fungal symbionts (Epichloë spp.) and grass hosts. Molecular Biology and Evolution. 14: 133-143.

Schwarze, F.W.M.R., Engels, J. and Mattheck, C. 2004. Fungal Strategies of Wood Decay in Trees. Springer. Berlin.

Thomas, William S. 2003. Field Guide to Mushrooms. Sterling Publishing Co., Inc. New York.