1370 INDUCTION PHENOMENA CHAP. 33 



induction" was observed by Shiau and Franck, following the secondary 

 induction wave (fig. 33.18B). A similar and sometimes even stronger per- 

 manent decline of oxygen production was produced by adding cyanide 

 (10-^ M HCN, in the presence of 20 mm. CO2). The decline from the 

 peak of oxygen production to the final steady level was more pronounced 

 the longer the preceding dark period; after several hours in the dark, the 

 rate in the first minutes of illumination was three to eight times higher than 

 in the subsequent steady state. 



There is a parallelism between these results and the fluorescence induc- 

 tion curves obtained in the presence of cyanide (fig. 33.39). In both cases, 

 the initial part of the induction curves is unaffected ; a depression of photo- 

 synthesis and enhancement of fluorescence appear only after the "second 



wave." 



In interpreting the phenomenon of "inverse induction" Franck and 

 co-workers noted that it occurs under conditions of inhibited carbon dioxide 

 supply (low carbon dioxide, presence of cyanide). The carbon dioxide 

 supply deficiency is not so important at the beginning of illumination, after 

 the carboxylation of the acceptor has had time to be completed in the dark. 

 The insufficient rate of replacement of the carbon dioxide used up by photo- 

 synthesis begins, however, to be felt after one or several minutes of illumina- 

 tion. 



Some more recent observations of the effect of oxygen deficiency on in- 

 duction can be mentioned here. 



Van der Veen (1949") found that the induction curves of Holcus lanatus 

 did not change substantially by substituting (instead of air) nitrogen con- 

 taining only 0.3% oxygen (with unchanged content of carbon dioxide), ex- 

 cept that the preparatory dark period was lengthened. (The induction 

 curve was, for example, the same after 30 minutes dark incubation in 0.3% 

 O2 as after 2 minutes incubation in air.) This seems to indicate that the 

 "de-adaptation" in the dark (which causes induction) is an autoxidation. 

 When oxygen was removed altogether from the nitrogen atmosphere dur- 

 ing the incubation period, the rate of steady photosynthesis of Holcus 

 leaves remained low for hours afterwards. The effect was noticeable even 

 after 1 minute anaerobiosis in darkness; after 30 minutes the steady rate 

 was only a few per cent of normal. It could be completely restored by 

 aerobic incubation in darkness. 



The capacity for carbon dioxide uptake and release by heat-inactivated Holcus 

 leaves was also destroyed by anaerobic incubation. In Chlorella, no gas gulps or bursts of 

 any kind appeared in an atmosphere of pure oxygen or hydrogen without carbon dioxide. 

 A small amount of oxygen was produced in light in the hydrogen atmosphere. 



Higher plants, placed in pure hydrogen, produced an oxygeri gush, followed by a 

 steady, slow oxygen production. Van der Veen suggested that this gush originated 



