DIURNAL CHANGES IN PIGMENT CONTENT AND 



IN THE PHOTOPERIODIC EFFICIENCY 



OF RED AND FAR RED 



ERWIN RUNNING 



Department of Botany, University of Tiibingen, Germany 



With Hyoscyamus we observed some time ago a remarkable effect of 

 light on chlorophyll formation. If the plant is offered a 3-hr hght 

 break within a prolonged dark period, the effect of this hght break 

 on the chlorophyll content depends on the time of day at which it is 

 offered (Fig. 1). Within a 63-hr dark period, there are two periods 



35r 



Fig. 1. Hyoscyamus niger. Chlorophyll production in 9: 63-hr light- 

 dark cycles. During the dark period, 3 hr light breaks. Controls without 

 light breaks. Abscissas, time of light break (Clauss and Rau, 1956). 



of time with an optmium effect of the hght which are 24 hr apart. 

 Between these maxima the hght break even makes the chlorophyll 

 content decrease (Clauss and Rau, 1956). 



Continuing these experiments, we found that significant diurnal 

 fluctuations in the chlorophyll content of seedlings can interfere with 

 those effects. This reminds us of observations published by Sironval 

 (1957), Wendel (1957), and others. In addition, our experiments 

 with Perilla demonstrated the continuation of these changes for at 

 least 4 days (Fig. 2). 



Of course, chlorophyll itself is not the light-absorbing pigment in 

 photoperiodism. But what about those substances which must increase 

 or decrease in quantity along with the changes in chlorophyll content? 



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