1426 INDUCTION PHENOMENA CHAP. 33 



exchange with the medium (and not merely release carbon dioxide as inert 

 final product of oxidation) ; and signs have been found that setting into 

 motion or stopping the anabolic photochemical mechanism of photosyn- 

 thesis affects the course and rate of the catabolic thermal processes more 

 immediately than one could expect if their relation were due merely to the 

 one process supplying substrates (sugars and carbon dioxide, respectively) 

 for the other. These relationships will be discussed in chapter 36. 



The other reason for considering the interlocking of photosynthesis with 

 other metabolic processes lies in kinetic findings, in particular the occur- 

 rence of inverse induction, in which bursts of photochemical activity, con- 

 siderably in excess of the steady rate, have been observed at the beginning 

 of the illumination period (while bursts of nonphotochemical gas exchange 

 have been observed in the initial periods of darkness, or reduced illumina- 

 tion). As mentioned before, the concept of photosynthesis as a closed re- 

 action sequence could account for inverse induction if it meant starting 

 photosynthesis at full normal rate and then going into a temporary slump, 

 or if it meant starting at a higher-than-normal rate of exchange of one gas 

 (O2 or CO2) but lower-than-normal rate of exchange of the other one (to 

 readjust the proper balance of the oxidized and the reduced forms of the 

 photosynthetic catalysts and intermediates). It seems, however, that the 

 various observed bursts and gulps of oxygen and carbon dioxide cannot all 

 be explained in this way, and require the assumption that the pools of 

 photosynthetic intermediates communicate with other metabolic pools 

 and reservoirs, and that the levels to which these pools are filled depend on 

 the rates of both the photochemical and the nonphotochemical metabolic 

 processes. Every time one of these rates is suddenly changed, through an 

 increase or decrease of illumination, all the pools and reservoirs are partly 

 drained, or filled up, to a new stationary level, and this readjustment can 

 be accompanied by evolution or absorption of either oxygen, or carbon 

 dioxide, or both gases. This is obviously a generalization of the picture in 

 which the filling of the pools of intermediates was considered as a matter of 

 photosynthesis alone. Superimposed on these changes in the amounts of 

 intermediates — such as various organic acids, perhaps also peroxides (or 

 other intermediates in the exchange with molecular oxygen) — ^is the re- 

 adjustment of catalysts, which may involve the oxidation or reduction of 

 intermediate redox systems (such as the cytochromes, c/. above section 

 B7). 



The attribution of gas "bursts" and ''gulps" in the first minute of illu- 

 mination to the filling up of the photosynthetic pools by respiration inter- 

 mediates was first suggested by Franck (1949) as interpretation for the 

 rate measurements by Warburg and co-workers in intermittent hght. As 

 stated before in this chapter, Burk and Warburg (1951) suggested that the 



