Structure and Reproduction of Rhizopus sp.,

Crisp and clear information about the species Rhizopus. Arranged data for the purpose of exam preparation.

1. Rhizopus Presented by Irfan M

2. What is Rhizopus ? 2 Rhizopus is a type of fungus which belongs to the class  Zygomycetes  because of the fact that it produces zygospore in its sexual reproductive phase. It also refers to  bread ,  black  or  pin mould . There are around  8-10 known species  of Rhizopus. The name Rhizopus was first named by  Ehrenb  in  1820 . 

3. Classification Kingdom :  Fungi Division :  Mycota Sub-division :  Eumycotina Class :   Zygomycetes Order :  Mucorales Family :  Mucoraceae Genus :  Rhizopus 3

4. Features of Rhizopus The mode of nutrition is  saprophytic  and  parasitic  in Rhizopus where a majority of them are saprophytic and few are parasitic viz. R.artocarp , R.arrhizus etc. In Rhizopus, the  mycelium  is coenocytic , tubular, multinucleated , vacuolated and consist of cytoplasmic materials like Golgi body, mitochondria etc. The reserve food material is in the form of  glycogen  and  oil droplets .

5. A cell wall of the thallus is  non-cellulose  and made of chitin. The hyphae of Rhizopus differentiates into three distinctive parts namely  stolon  (intermodal region),  rhizoids  (nodal region) and  sporangiophores . For the growth of Rhizopus, the most important factor is  moisture  or water availability. These are the opportunistic fungi which can commonly cause “ Zygomycosis  or  Mucormycosis ”.

6. Structure of Rhizopus 6 Hyphae Stolon Rhizoids 2. Cell- wall 3. The protoplasm Columella Sporangium Sporangiospores

7. Hyphae : Rhizopus consists of two kinds of hyphae namely  vegetative  and  reproductive   hyphae . Vegetative hyphae differentiate into two types namely  Stolon and rhizoids Stolon : It is the intermodal region which also refers to Runner. A stolon is the aerial hyphae which grow horizontally and is found attached to the substratum. It is aseptate , branched and lacks cross walls. Rhizoids : It is the nodal region which forms when the stolon touches the surface of the substratum. Rhizoid is the much-branched structure that forms under the substratum. Its main function is to invade all the nutrients from the substratum. 7

8. Reproductive hyphae consist of  sporangiophores  which grow vertically from the stolon . Sporangiophores are unbranched , elongated, columellate and give rise to the reproductive structures refers to sporangiospores . Cell- wall : The cell wall of hyphae is composed of chitin chitosan , lipids, proteins etc . The protoplasm : It consists of many nuclei, mitochondria, endoplasmic reticulum and other cytoplasmic inclusions like the ribosome, oil droplets, vacuoles etc. 8

9. Columella : It arises from the sporangiophore which is generally dome or umbrella-shaped. The surface of columella can be smooth or rough. The columella is hygroscopic in nature which the main function is water absorption . Sporangium : It connects with the columella and a long sporangiophore . The shape of the sporangium is spherical or globose in shape. It carries the reproductive structures refers as sporangiospores . The size of the sporangium is 0.2mm . Sporangiospores : These are the asexual spores which are globose to ovoid and unicellular. The colour of sporangiospores is hyaline to brown. 9

10. General cultural characteristics Growth : The growth of mycelium is very fast- growing. Appearance : Dense cottony colonies Colour : The colour of mycelium is generally white and after sporulation turns grey or golden brown

11. Reproduction in Rhizopus It reproduces by  vegetative ,  asexual  and  sexual  methods 11

12. “ Sometimes the thallus of the Rhizopus breaks accidentally or some other factors into few fragments where each fragment give rise to a new thallus on favourable conditions . Vegetative reproduction 12

13. The asexual reproduction can take place through both sporangiospores and chlamydospores . Asexual reproduction 13 Asexual reproduction through sporangiospores First, the vegetative hypha grows to form sporangiophore that is long and slender. Then the sporangiophore develops and enlarges at the apical region to form columella which is of variable shape and size.

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15. This columella gives rise to the large, round sporangium by pushing cytoplasmic material to the peripheral wall. After that, differentiation of sporangia takes place wherein between sporangia and columella , spore sac is present which carries the sporangiospores . The structure of Sporangiospores is oval, unicellular, multinucleate and non-motile. These sporangiospores multiply their number in the spore sac and in extreme conditions, it ruptures the sporangial wall and releases out of the wall. In the environment, the sporangiospores remains in a dormant state or in a resting state. When favourable conditions return, these sporangiospores form germ tube and undergo germination to form a vegetative hypha .

16. 16 Asexual reproduction through chlamydospores

17. During unfavourable condition like insufficient food material and water, the protoplasm is surrounded by a thick and nutrient-rich wall . This chlamydospore then detaches from the vegetative hyphae and remains in the resting phase. When this chlamydospore gets moisture then it forms a germ tube which then germinates into a new thallus .

18. In Rhizopus, the sexual reproduction occurs by the method of “ Gametangial conjugation”. S exual reproduction 18

19. First, the (+) and (-) thallus comes in contact with each other. Then conjugation occurs between the positive and negative thalli by the means of outgrowth developed by positive and negative thalli . The septum develops between the progametangium and plasmogamy occurs that results in the formation of “ Coenogametes ”. Then karyogamy occurs by which the gametes of both the  (+) and (-) thallus  fuse with each other to form “ Zygote ”.

20. The zygote undergoes the maturation phase and surrounds by a thick-walled structure called “ Zygospore ” which covers by an outer layer and inner layer. The zygospore undergoes a resting phase for some time. On favourable conditions, zygospore forms germ tube and germinates by forming a new vegetative body .