1948 KINETICS OF PHOTOSYNTHESIS CHAP. 37D 



ena affect the calculated quantum yields most strongly if the cells are kept 

 in an unsteady state throughout the measurement by exposing them to 

 intermittent illumination. Manometric measurements of Emerson and 

 co-workers, to be described in section (h), and polarimetric studies by 

 Brackett et al, summarized in section (c) below, gave evidence of the actual 

 occurrence, variety and long duration of such transients. 



The above summary of War})urg's 1950-52 papers, as well as the re- 

 view of the related findings of other investigators in parts (h), (c) and (d) 

 of this section, have been written down in 1953. Since then, Warburg's 

 long "road to perfection" proved to lead beyond the "end" he assumed to 

 have reached in 1951. Two new unexpected vistas opened in 1952 and 1954, 

 respectively. First, Warburg, Krippahl, Schroder and Buchholz (1952), 

 and Warburg, Krippahl, Buchholz and Schroder (1953), described cul- 

 tures of Chlorella pyrenoidosa, capable of many hours of sustained photo- 

 synthesis with a quantum requirement of 3-4, in steady light of an intensity 

 sufficient to compensate respiration 30 or 40 times over, i. e., under condi- 

 tions where the respiration correction (and the possible contribution of 

 transients) are practically insignificant! Then, Warburg, Krippahl, Schro- 

 der, Buchholz and Theel (1954) found that a very small "photocatalytic" 

 amount of blue-green light enhances strongly the efficiency of photosynthesis 

 in light of other colors, fully replacing in this respect the (relatively strong) 

 white "background illumination" previously used by Warburg et al 



Unfortunately, Warburg's description of the way in which the new, 

 exceptionally efficient Chlorella cultures have been grown does not indicate 

 anything markedly different from the ways such cultures have been gener- 

 ally grown in the past (unless growing at a window with northern exposure, 

 and supplementing natural light with light from a xenon arc, has a special 

 effect on photochemical efficiency). One procedure used in the new experi- 

 ments, which may be important (although it, too, has not remained untested 

 by other observers in the past, and was said by Warburg in 1951 to lead to 

 poorer yields), was to measure the quantum yield directly in the culture 

 solution (rather than in a buffer, or in distilled water— we recall that the lat- 

 ter was recommended by Warburg in 1951). Warburg et al. (1954) used 

 either the same medium in which the cells had been grown, or a fresh me- 

 dium, to resuspend the cells after centrifugation. The growth medium was 

 distilled water with a complete assortment of nutrient elements, including 

 vanadium (as recommended by Arnon). 



Dilute suspensions were used in these studies, and the whole vessel was 

 illuminated uniformly by means of a mirror shaken together with the ves- 

 sel ; the two procedures combined to give as uniform an illumination of all 

 cells as possible, and thus to create the most favorable conditions for ex- 

 tensive linearity of the light curve. Nevertheless, it seems remarkable 



