EFFECT OF LIGHT ON RESPIRATION 567 



respiration (as this was suggested by van der Paauw in 1932). If this 

 view is adopted, we may still ask whether illumination has any influence 

 on normal respiration as well (other than stimulation by accumulated 

 photosynthates) . The effect for which we are looking may consist 

 either in direct "photorespiration," i. e., a photochemical activation of 

 the respiratory system which sets in immediately upon illumination and 

 disappears abruptly upon return to darkness; or in an indirect stimu- 

 lation which sets in slowly in light and persists for some time in the dark. 

 The first effect is difficult to distinguish from decreased photosynthesis; 

 the second can easily be confused with accelerated respiration caused by 

 the accumulated products of photosynthesis. However, it was mentioned 

 on page 564, that Gessner (1939) concluded, from the effect caused by 

 ultraviolet light, that the "persistent" light stimulation of respiration, 

 is not — or not entirely — attributable to an accumulation of sugars. 

 The same conclusion was reached by Fockler, and Emerson and Lewis, 

 who also found that the dependence of light-stimulated respiration on 

 wave length is different from that of photosynthesis. 



Montfort and Fockler (1938) and Fockler (1938) noticed that the 

 respiration of nonchlorophyllous plant tissues, e. g., roots of Vicia faba, 

 shoots of asparagus, fruit skins, etc., is increased from 20 to 100% during 

 the first hour of illumination. On return to darkness, oxygen consump- 

 tion returned to its original level, sometimes quite rapidly. The respon- 

 sibility for this stimulation was found to lie with the radiations below 

 500 mM, a relation which indicates the participation of a yellow pigment. 

 No effects were observed in infrared light, whereas a vigorous effect 

 occurred in the ultraviolet. Fockler found a parallel between the 

 "action spectrum" of " photorespiration " and the absorption spectrum 

 of etiolated leaves as measured by Seybold (reproduced in Chapter 22, 

 Vol. II). 



Fockler thought that a similar direct effect of light on respiration 

 could be detected also in chlorophyllous tissues — where stimulated 

 respiration often is difficult to distinguish from inhibited photosynthesis 

 — by its dependence on wave length. However, in fully active green 

 tissues, photosynthesis is much too intense, compared with respiration, 

 to make such measurements possible. Fockler therefore inhibited the 

 photosynthesis (of Potomageton lucens) by narcotics in concentrations 

 which did not affect respiration (0.06% phenylurethan), and measured 

 the gas exchange in light of different colors. He found the strongest 

 oxygen uptake in blue light, and almost no uptake in green and red light. 

 One possible, but improbable explanation of these results is that photo- 

 synthesis is completely inhibited by 0.06% urethan, while respiration 

 is inhibited by red, and stimulated by blue light. A more probable 

 explanation is that the inhibition of photosynthesis by 0.06% phenyl- 



