CHLOROPHYLL CONTENT AND YIELD IN FLASHING LIGHT 1277 



rived from P^ll'., the saturation rate in continuous light, agrees with the 

 product of the values [Eb] and [/cb] derived separately, from the saturation 

 yield in flashing hght and the flash yield dependence on the length of the 

 dark intervals, respectively. The agreement supports strongly the as- 

 sumption that saturation in continuous light and the maximum flash yield 

 are determined by the same "bottleneck" reaction, brought about by a 

 finishing catalyst present in a concentration of the order of 10 ~^ mole/1. 

 (~0.1% of fChlJo) and having an "action period" of the order of 1/50 

 second (at room temperature). 



No flashing Hght experiments have been carried out with objects for 

 which abnormal assimilation numbers had been found in continuous hght, 

 such as aurea leaves, etiolated seedlings or autumn leaves. If the hypothe- 

 sis that the rate-limiting reaction is the same in continuous and in flashing 

 light applies to all of them (which is not necessarily true, because under 

 abnormal conditions the limiting role may be taken over by a different re- 

 action), then the plant objects showing exceptionally high assimilation 

 numbers, pa, should exhibit also exceptionally high values of the ratio r. 

 In Myers' (1946) experiments with Chlorella cells grown in light of different 

 intensity, the saturation rates per unit chlorophyll amount (and thus also 

 the ratios va) varied by a factor of 4 as the culture light increased from 6 

 to 360 foot-candles, and the chlorophyll concentration within the cells 

 dechned by a factor of 5. In table 32.1, Emerson and Arnold's figures 

 show no significant change associated with chlorophyll concentration 

 changes by a factor of 2, produced in a similar way {i. e., by changes in 

 illumination during the growth of the algae). However, only experiments 

 performed on the same algae in both steady and flashing light could pro- 

 vide truly significant information as to the correlation between va and t. 



In chapter 34 we will describe experiments by Tamiya and co-workers 

 in which flash yields far exceeding the Emerson-Arnold hmiting value of 

 5 X 10~^ [Chi] have been obtained by further increasing the energy of the 

 flashes and by prolonging the dark intervals beyond the Emerson-Arnold 

 limiting duration of about 0.02 sec. For reasons to be presented there, we 

 are reluctant to consider these experiments as sufficient to cast aside all 

 the conclusions based on the observations of Emerson and Arnold; but a 

 renewed experimental study of flashing light saturation seems necessary. 



In identifying the hmiting catalyst with the catalyst Eb in schemes 

 28.1 and 28.11, we follow Franck and Herzfeld. In their scheme, (7.VA), 

 Eb was supposed to act (with equal efficiency) on four (different) intermedi- 

 ate products "on the reduction side" and four (identical) intermediate 

 products "on the oxidation side." The assumption of several processes 

 on the reduction side, all catalyzed by Eb, can be avoided by postulating 

 only one photochemical reduction process, followed by catalytic dismuta- 



