742 A. M. Mayer and A. Poljakoff-Mayber 



in water extracts prepared from the seeds. But the amount of each 

 of these enzymes, or their activity, is rather Hmited and increases dur- 

 ing germination. The Hberation, or the activation, of many enzymes 

 is known to be closely linked with proteolytic cleavage of enzymogens 

 or protein complexes of some kind. If such liberation of enzymes is 

 a prerequisite for germination and growth, then some of the in- 

 hibitory action of coumarin might be the direct result of its inhibition 

 of proteinase activity. 



Ron and Mayer (69) have shown that coumarin at a concentration 

 of 1.4 X 10"^ ^t completely prevents the growth of cultures of Chlor- 

 ella vulgaris. A somewhat lower concentration (6.85 X 10'^ '^^) ^^oes 

 not prevent cell multiplication but causes an increase in cell diam- 

 eter. The diameter of the controls was 5 ix while that of cells grown 

 in coumarin was 6.8 fx. This represents an increase by a factor of ap- 

 proximately 21/2 in cell volume. The increase of cell size was paralleled 

 by an increase in oxygen uptake per cell. However, when calculated 

 per unit of dry weight, coumarin caused a decrease in oxygen uptake 

 as the dry weight of cells grown in coumarin increased. Substances 

 that induce an increase in oxygen uptake are usually considered as 

 potential uncouplers of oxidative phosphorylation. There is a ten- 

 dency to consider the coumarin derivatives as uncouplers; this is 

 mainly based on the uncoupling action of dicoumarol (30), although 

 dicoumarol differs from the naturally occurring coumarins, especially 

 in the steric configuration near the double bond of the lactone. Ron 

 and Mayer do not ascribe such an uncoupling action to the coumarin 

 effect in Chlorella, but an uncoupling action of coumarin may be 

 hinted at by the work of Levari (31) who showed that coumarin 

 stimulates the respiration of lettuce seeds (variety 'Progress') during 

 the first six hours of germination, and by the fact that coumarin 

 slightly increased (20 per cent) the oxygen uptake of mitochondria 

 (59). But in all these cases the results do not permit any conclusions, 

 as they were not always calculated on a protein or a nitrogen unit, 

 and no direct measurements of phosphorylation were made. 



Aloni (1) studied the ability of lettuce mitochondria to liberate 

 inorganic phosphorus from ATP (adenosine triphosphate). Atldi- 

 tion of coumarin to such reaction mixtures did not cause any signifi- 

 cant increase in jihosphorus liberation. Apparently coumarin did 

 not affect the ATPase activity of lettuce mitochondria. 



The effect of coumarin on jihosphorus metabolism of the seeds 

 is especially interesting. Half of the phosphorus in dry lettuce seeds 

 is present in the form of phytin. The breakdown of this phytin be- 

 gins immediately with the onset of germination and phytin has dis- 

 appeared (onipletely in lettuce seedlings germinated for three days 



