Initiation and Control of Firefly Luminescence 



w. D. Mcelroy and j. w. Hastings 



McCollum-Prall Institute and Department of Biology, Tlie Johns Hopkins University, Baltimore, 



Maryland, and Department of Biological Sciences, Nortlnveslern University, 



Evanston, Illinois 



N' 



''UMEROUS STUDIES HAVE CLEARLY ESTABLISHED that the firefly flash is 

 _ initiated by way of a nerve impulse (3, 4). There remains some question 

 however, as to the precise mechanism involved. Two general theories, previously 

 discussed in detail by Buck (2), have been proposed. One, which may be called 

 the oxygen theory, proposes nervous control of a valve-like mechanism (the 

 tracheal end cell) in the tracheolar supply to the luminous organ. Since the 

 luminescent reaction requires oxygen, the firefly would presumably be able to 

 initiate or extinguish luminescence by the control of oxygen availability. The 

 second theory proposes that the nerve impulse stimulates the photogenic cell 

 directly. Recent studies with cell free extracts have suggested that the luminous 

 material (i.e., luciferase, luciferin and ATP and oxygen) is available, but 

 luminescence is prevented because of an inhibition of the enzyme (4). Presum- 

 ably the nerve impulse reverses the inhibition by splitting the inhibitory com- 

 plex, thus giving rise to active enzyme and a flash of luminescence. Evidence 

 has recently been obtained concerning this latter idea. 



FIREFLY FLASHES IN VIVO 



It is possible to obtain two types of flashes in the intact firefly. The flash 

 which occurs normally (fig. i) has a duration of not longer than 0.2 second 

 m rise time about 0.05 sec). This type of flash may also be induced by elec- 

 trical stimulation (i). The 'pseudo-flash,' reproduced in figure 2, occurs when 

 oxygen is readmitted to a firefly which has been placed temporarily under 

 partially anaerobic conditions (ca. i'2% O-.). In contrast to the normal flash, 

 the duration of the pseudo-flash is about 2 seconds (i 2 rise time about 0.5 sec). 



The fact that the pseudo-flash is approximately ten times slower than the 

 normal flash is not necessarily against the oxygen theory. It is possible that 

 the tracheal system immediately connected to the luminous gland has the 

 ability to rapidly change the oxygen tension locally. By placing the whole 

 firefly under anaerobic conditions, all of the tracheal system would lose oxygen 

 and considerable time might be required for recovery when the organism is 

 placed under aerobic conditions. Unfortunately, there is no information avail- 

 able concerning the physiology of the tracheal system and the special tracheal 

 end cells. 



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