The Cytochiomes of Plant Tissues 481 



The year 1939 was a vintage year in the study of plant cytochromes because 

 of the work of three separate groups in Japan, England and America. 



Okunuki (1939), continuing investigations initiated in 1937, pubUshed 

 three papers devoted to pollen derived from ten different kinds of plants. 

 The cytochrome spectrum of pollen is intense, showing absorption maxima 

 at 605, 561 and 550 m/^. Okunuki did not comment on the difference in 

 maxima of the pollen b component (561 mfi) and that of yeast and muscle 

 (564 m^i). Okunuki also studied the effect of carbon monoxide on the 

 respiratory rates of the pollen under investigation and in most instances 

 found a photoreversible inhibition. Remarkably, there were some instances 

 where carbon monoxide had little effect on the respiratory rate, an observa- 

 tion Okunuki interpreted as being due to species variation in carbon monoxide 

 affinity. 



Okunuki, in 1939, was successful in preparing and concentrating cell-free 

 pollen extracts which contained a number of dehydrogenases and which were 

 capable of catalysing the rapid oxidation of succinate to fumarate. It is 

 unfortunate that these remarkable contributions of Okunuki have largely 

 been passed over. 



Okunuki was primarily interested in the oxidative characteristics of 

 particulate cell-free preparations from pollen. During the same time and 

 using very similar techniques. Hill and Bhagvat (1939) showed that particulate 

 cell-free preparations could be obtained from a variety of flowering plants. 

 Such preparations contained the bulk of the plant cytochromes, observed at 

 that time as components a, b and c, and these cytochromes were observed to 

 undergo reversible oxidation and reduction in plant preparations. Hill and 

 Bhagvat (1939) also observed that their preparations oxidized succinate, and 

 that this oxidation was promoted by the addition of soluble cytochrome c 

 and was found to be inhibited by cyanide and azide. The first brief report of 

 Hill and Bhagvat (1939) was elaborated in a later paper (Baghvat and Hill, 

 1951) in which they stated that components a, b and c could be observed in 

 every tissue studied by them. In each case the cytochromes were associated 

 with cytochrome oxidase and succinic dehydrogenase activities. Bhagvat and 

 Hill (1951) concluded : 'the cytochrome system in plants behaves in the same 

 way as that of yeast and animal tissues, thereby showing the presence of a 

 respiratory mechanism identical with that characteristic of animal tissues'. 

 This very sweeping generalization needs some modification in the light of 

 our present knowledge, much of which has been subsequently contributed by 

 Hill and his colleagues. 



Marsh and Goddard (1939) used a different approach for studying the 

 cytochromes of plant tissues. Their approach was to investigate the effects 

 of cyanide, azide, and carbon monoxide on respiratory rates of carrot slices 

 and leaves. By determining the ratio of affinity of the enzymes which mediate 

 the respiration of carrot tissues and young carrot leaves for oxygen and 



