SUMMARY: Although sporangiospores of do not swell or produce germ-tubes in distilled water, when they are suspended in heavy water the water in the spore is exchanged with heavy water in the medium. Spores swell and some produce germ-tubes in a glucose solution. Maximum germination occurred in the presence of utilizable carbon and nitrogen sources and suitable compounds containing phosphate, sulphate, potassium and magnesium ions. Germination was accompanied by a considerable increase in oxygen uptake and by the time the germ-tube emerged, the dry weight had increased by about 500%. Respiratory inhibitors (2,4-dinitrophenol, sodium azide, potassium cyanide) inhibited germination; sodium azide inhibited both the oxygen uptake and the dry weight increase.

Electron microscope studies showed structural changes in germinating spores similar to those reported in other Rhizopus species: a new inner wall layer was formed, and changes in form and probably number of mitochondria occur. The effects of either anaerobic conditions or media containing sodium azide, on fine structure of germinating spores were similar; mitochondrial multiplication ceases, mitochondrial cristae became a disorganized collection of undulating ‘plates’, and the nuclear membrane became split in places, thus giving rise to small vacuoles between the two electron-dense layers of the membrane.


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