Fungi: Pigments, Luminescent and Fossil | Botany

In this article we will discuss about:- 1. Pigments of Fungi 2. Luminescent Fungi 3. Fossil Fungi 4. Behaviour of Compatible Nuclei 5. Spore Dissemination. 

Pigments of Fungi:

Many fungi are beautifully pigmented. This character has often been used in classification of certain groups of fungi. Again certain wood-attacking fungi cause staining in wood. The pigments that are produced in the fungi themselves or in the wood that is attacked by the fungi are linked up with the metabolic activities of the fungi. Their specific role in the fungal cell is still answerable.

Pigments of variable chemical nature have been isolated from different fungi, some of them are indicated below:

Phycornyces blakesleeanus, Mucor hiemalis, Allomyces javanicus and Piobolus sp. contain —carotine. Erythroglaucin, auroglaucin and flavoglaucin have been obtained from Aspergillus glaucus. Citromycetin and citrinin have been extracted from Penicillium glabrum and P. citrinum. Helminthosporium gramineum, H. cynodontis, and H. catenarium contain helminthosporin.

Ceratocystis ulmi causes blue stain of elm wood. Verticillium sp. produces green dis­colouration of maple wood. Stored wood may be stained by the growth of the fungi like Mucor, Rhizopus, Aspergillus, Penicillium, Alternaria and many others by growing on the surface of the wood.

Luminescent Fungi:

Some fungi give out light, sometimes cause the attacked wood or leaves to become luminous. Some of them are: Panus incandescens, Pleurotus incandescens, P. igneus—pilei are luminescent; Clitocybe illudens—fruit body and mycelium are luminescent; the rhizomorphs of Armillaria mellea and the sclerotia of Collybia tuberosa and C. cirrhata give out light; Omphalia flavida and Xylaria hypoxylon—mycelium is luminous.

Luminosity in these fungi is due to the action of an enzyme luciferase on a sub­stance known as luciferin present in the fungal cells in presence of oxygen.

Fossil Fungi:

The constitution of the fungi has not given much scope for being fossilized. The most common kind of fossil fungi is by incrustation with calcium carbonate. Some­times fungi inhabiting leaves and stems remain as impressions’. These impressions are formed when the plant parts along with fungi are deposited in the siliceous or calca­reous matrix.

Gradually the matrix hardens and sets, and the impressions often clearly portray the details of fungi. Besides these, fungi may also be preserved in masses of Baltic amber.

According to James (1893), fossil fungi may be traced back in the Devonian period. This was partly supported by Seward (1933), who felt that the existence of fungi may be looked from the Devonian period onwards and representatives of some of the parasitic and saprophytic fungi may be anticipated to have existed even in a more remote age.

The generic names of the fossil fungi are expressed with the addition of the suffix ites to the present-day genera of fungi with which their resemblance is indicated. Saccardo in his Sylloge Fungorum (1882) included 350 names of fossil fungi, their fruit bodies (very infrequently with spores) on or with fossil leaves or stems.

Some of the fossil fungi are: Peronosporites gracilis Renault, Mucorites cambrensis Renault, Phycomycites Jrodinghamii Ellis, Erysiphites metilli Pamp., Penicillites curtipes Berk., Pezizites candidus Gopp et Ber., Polyporites bowmanii Lindley et Hutton, Agaricites wardianus Mesch., Puccinites cretaceous Velen.

Behaviour of Compatible Nuclei in Fungi:

After the compatible nuclei are brought together by the methods discussed above, they may fuse with each other immediately without any delay, or their fusion may be delayed. Where the fusion between the compatible nuclei takes place-immediately after they are brought together without any delay, a diploid cell (zygote) is formed.

Subse­quent stages of development of the zygote follow any one of the following ways:

1. The zygote remains active for a short period, then develops a thick wall, goes to rest and germinates to produce zoospores or gametes, during which meiosis takes place.

2. The zygote becomes active to produce a diploid thallus bearing two types of zoosporangia. In some of these zoosporangia, diploid zoospores are formed which give rise to diploid thalli; in others, haploid zoospores are developed by meiosis. These haploid zoospores produce haploid thalli exhibiting an alternation of generations.

3. The zygote develops thick wall and goes to rest. Under favourable conditions depending on the nature of fungi, it germinates in various ways, during which meiosis takes place. Such a thick-walled zygote is oospore when it is formed from a female gamete through fertilization. Whereas, a zygote which results from the fusion of two isogametangia or isogametes is a zygospore.

But where the fusion between the compatible nuclei is delayed there is establish­ment of a dikaryophase, when the compatible nuclei without fusing, either pair or remain close to each other. This dikaryophase is usually very much prolonged. Ultimately dikaryophase is followed by diplophase, when karyogamy of the com­patible nuclei takes place. Karyogamy is immediately followed by meiosis resulting in the formation of haploid nuclei around which spores are developed.

Thereby, haploid condition or haplophase is re-established of these spores, mat are formed endogenously in a sac-like structure known as ascus (pl. asci), are the ascospores. Whereas, others borne exogenously on a more or less club-like structure called basidium (pl. basidia), are the basidiospores.

Spore Dissemination in Fungi:

Survival of species is very much conditioned by dispersal of spores into habitats where food is available. In most species of fungi special mechanisms for spore dis­semination are lacking. In them mature spores remaining on the conidiophores or in the ruptured fruit body are removed by air currents or other agency.

Many fungi, however, exhibit special and often intricate mechanisms for the more or less violent dis­charge of the mature spores, very interestingly exhibited by the genus Sphaerobolus.

Turgour often provides the necessary energy as in the sporangial discharge of the genus Pilobolus or the ascospore discharge of many Ascomycetes. Other mechanisms include the fluid drop-excretion-mechanism of the Basidiomycetes and those in which the kinetic energy of rain drops is utilized by the ‘splash cup’ of the Nidulariaceae, or by the bellows effect of rain drops falling on the mature fruit body of the genus Lycoperdon.

In many aquatic Phycomycetes spore dissemination is effected by self-motile zoospores.

In terrestrial fungi the most important agencies for spore dissemination are air currents, insects and animals.

The dissemination of spores of Puccinia graminis may be cited as one of the important examples of air currents as a factor in dispersal of spores. The transport of Ceratocystis ulmi, pathogen of the Dutch elm disease by bark beetles may be cited as a classical example of insects as agencies for dissemination of spores.

A number of fungi, parti­cularly the coprophilous ones, such as the species of Pilobolus, Ascobolus, Sordaria, and Coprinus, their spores are disseminated by herbivorous animals like horses, cattle, sheep and goats. These animals swallow the spores and herbage together.

After having been eaten the spores pass through the alimentary tract of the animals and by the time they pass out with the feces, the animals may transport them for miles. After being discharged from the animal body along with the feces the spores develop into new fungi.