OXYGEN EXCHANGE DURING THE SHORT INDUCTION PERIOD 1317 



no such qualitative changes of metabolism occur, the recovery of full photo- 

 synthetic efficiency may require much longer than the usual 1 to 3 minutes 

 (c/. ch. 13, and sect. 6 below). Both types of abnormal induction must be 

 due to the influence of the products of dark anaerobic metabolism on the 

 catalytic mechanism of photosynthesis. This influence may be nonspecific, 

 due to reducing properties, or the acidity of the fermentation products; 

 but it may also involve specific inhibition effects. 



2. Oxygen Exchange during the Short Induction Period 



The short induction was discovered by Warburg in 1920, in the first 

 precise manometric study of photosynthesis in Chlorella. (Osterhout and 

 Haas, 1918, in their earlier description of induction phenomena, probably 

 dealt with a combination of "short" and "long" induction; cf. section 5.) 

 Working in a buffer solution ([C'Oa] = 9.1 X 10"^ mole/1.) Warburg found 

 that, in strong light (10-20 klux), the integrated oxygen production in 10 

 minutes decreased when the illumination was subdivided into ten periods of 

 1 minute each: by 10% when the dark intervals lasted 1 minute, and by 75 

 or 85% when they lasted 5 minutes. Further extension of the intervals had 

 no effect. 



This was indirect evidence of the existence of an induction period, fully 

 developed after 5 minutes of darkness. Warburg could not observe the 

 induction directly, because of the inertia of the manometric system {cf. 

 fig. 29.1); but, from experiments in which light periods of varying length 

 followed dark periods of 5 minutes each, he estimated that the induc- 

 tion lasted for about 2 minutes in strong light; no signs of induction were 

 found in weak light (400-800 lux). 



The observation that induction disappears in weak light justified the use of short 

 illumination periods in Warburg and Negelein's experiment's on the quantum yield of 

 photosynthesis (page 1086). However, the absence of induction was derived from experi- 

 ments in alkaline buffers, in which oxygen evolution alone was measured; whereas the 

 quantum yields were measured in nonbuffered solutions, in which carbon dioxide con- 

 tributed markedly to pressure changes. McAlister (19.37) found that carbon dioxide 

 consumption also shows no induction in weak light (cf. fig. 33.8); but his results were 

 obtained with comparatively low concentrations of carbon dioxide (0.03 to 0.3%), 

 whereas Warburg and Negelein used 4 or 5%. Emerson and Lewis (1941) found that 

 in the one case not covered by either Warburg or McAlister — that of carbon dioxide 

 exchange in an atmosphere of high carbon dioxide content — significant induction effects 

 may occur even in weak light. More recently, measurements by Emerson and co- 

 workers (1954) have confirmed this observation and revealed that transient phenomena 

 of great complexity can occur in an atmosphere of high carbon dioxide content. 



Van der Paauw (1932) studied the induction in another unicellular green 

 alga, Hormidium flaccidum, and found that it lasted 1.5 minutes at 26° C, 



