Penicillia are common and cosmopolitan genus; commonly know as green and black-molds. These are found frequently on citrus and other decaying fruits, or on cheese. The conidia of penicillia are found everywhere in the air and in soil. In the biological laboratory they contaminate cultures. Contamination of Fleming’s bacterial culture by Penicillium notatum led to the discovery of penicillin, this wonder drug.

Plant body ___Structure
The Mycelium: the mycelium is well developed and is profusely branched. It is composed of colorless, slender, tubular, branched, and septate hyphae. Some of the hyphae may invade the substratum to absorb nourishment from the substratum, whereas the other spread on the surface of the substratum. Some of the hyphae may interwine to form rhizophores. In some species, mycelium may develop into a sclerotium. The mycelium becomes coloured when the fungus enters reproductive phase.
Cell structure: the hyphae are septate and each cell is uninucleate. The cell wall is microfibrillar and in Penicillium notatum it is reported to consist of three or four layers, the outer most layer is composed of glucans, the next of proteins, the third of chitin fibrils embedded in a granular matrix, and the inner most of pectic or hemicellulosic material. The plasma membrane surrounds the cytoplasm in which mitochondria, ribosomes and endoplasmic reticulum is embedded.
LIFE CYCLE: The Penicillia reproduce vegetatively, asexually, and asexually. The perfect state of form –genus Penicillium is assigned to two different genera, the Eupenicillium and Talaromyces.
Vegetative Propagation: The vegetative reproduction takes place by fragmentation during which the hyphae break up into short fragments, which grow by repeated division into a new mycelium.
Asexual Reproduction: The asexual reproduction is by formation of non-motile, asexual spores, the conidia, and produce at the tip of special, erect, hyphae called conidiophores. Many crops of conidia are produce during a growing season.
Conidiophores: The mycelium produces simple, long, erect, conidiophores that branch two third of the way to the tip, in characteristic broom like fashion. The branches of conidiophores end in a group of conidiogenous cells, the phialides that produce conidia at their tips in chain.
Structure and development of conidia: The conidia are tiny, uninucleate, spore like structures which may be globose to avoid in form. The spore wall is pigmented and is differentiated into two layers, an outer thick, ornamented layer, the exine; and inner smooth and thin layer, the intine. The conidia are detached from the conidiophores and are carried by wind to a suitable substratum where they germinate by forming a germ tube. The germ tube elongates, becomes septate to form a new hyphae.
Sexual Reproduction:  The perfect state of Penicillium is assigned to two different genera, the Eupenicillium and Talaromyces. All the species are homothallic. In Penicilllium vermiculatum the sexual reproduction is oogamous. The male sex organs are antheridia and female sex organ are ascogonia.
Ascogonium: A mature ascogonium is a long erect, multinucleate, tubular structure with curved upper end. It arises from uninucleate, septate hyphae as a finger like, lateral outgrowth which elongates into an ascogonium. The nucleus of the ascogonium divides many times mitotically to produce 32 or 64 nuclei.
Anteridium: while the ascogonium is developing a uninucleate branchoriginates from a cell of the same hyphae adjacent to the developing ascogonium, or from neighbouring hyphae. This is the antheridial branch. It grows up band coils around the ascogonium. The tip of the antheridial branch swells up and is cut off from rest of the branches to form a uninucleate antheridium.
Fertilization: The tip of the antheridium comes in contact with the walls of the ascogonium and the walls of contact between the two dissolves to form a pore. The protoplast of the gametangia comes in contact with each through this pore. The antheridial and ascogonial nuclei arrange themselves in pairs. Each pair is called a dikaryon.
Development of Ascus and Ascospores: The stimulus of plasmogamy results in septation of ascogonium into binucleate cells. Some of these segments usually those present in the middle, produce outgrowth called ascogenoum which develop into ascogenous hyphae composed of binucleate cells. The tip cells of these hyphae act as ascus mother cells which develop either simply by elongation, or by crozier formation into ascus. Karyogamy takes place in the ascus mother cell and this diploid uncleus undergoes meiosis to produce four haploid nuclei. A mitotic division results in the formation of eight haploid nuclei. These are transformed into ascospores by free cell formation. The ascus are globose or pear-shaped and the unicellular, uninucleate and lens-shaped with a groove around the edge.

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