Circadian Rhythm In Neurospora

Life is a cyclical chemical process that is regulated in four dimensions. We distinguish parts of the cycle: development describes the changes from single cell to adult, and aging the changes from adult to death. Birth to death, a cycle, and there are cycles within cycles—circannual rhythms, menstrual cycles, semilunar cycles, and daily 24 hr or circadian cycles.

Jay C. Dunlap (1999)

The fungi are a richly diverse collection of sessile poikilotherms. They extract what they can from their immediate environment, and are subject to the extreme conditions of nature. Thus, there is an obvious selective advantage for possessing an endogenous timing system with which to anticipate the regular, daily changes in temperature, humidity, and light.

M. Merrow, T. Roenneberg, G. Macino, and L. Franchi (2001)

Virtually all forms of life, from unicellular bacteria to multicellular organisms including humans, exhibit the daily cycles known as circadian (from latin: circa, about; diem, a day). A critical feature of circadian rhythms is their self-sustained nature; that is, under constant environmental conditions they continue to repeat the daily cycle. For example, when conidia of Neurospora crassa (Chapter 5) are inoculated at one end on an agar growth medium in a race tube (Figure 11.6), the surface mycelium begins to grow toward the other end and after 21.6 hours the mycelium produces aerial hyphae once a day that form conidia. This cycle repeats in a regular manner every 21.6 hours. Thus, after a few days, the culture in the race tube exhibits conidiating bands alternating with undifferen-tiated surface growth. The time between bands (period length) is close to 24 hours

Point of inoculation


One circadian cycle

One circadian cycle

Cotton plug


Side view

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