216 CONTROL MECHANISMS IN CELLULAR PROCESSES 



tification. This handle was firmly seized in 1959 bv Butler, Norris, 

 Siegelman, and Hendricks, all at Beltsville. Using special spectro- 

 photometric techniques, they haye been able to show the actual 

 occurrence of the expected reyersil^le change in absorption in vivo, 

 and then in tissue extracts as well. Their work has already been 

 confirmed elsewhere (Bonner, 1960), and the purification and iden- 

 tification of the reyersible pigment itself is thus in sight, although 

 it may be a considerable task. It is either a protein or intimately 

 bound to protein; naturally both speculations and inyestigations on 

 its enzymatic actiyity will be yigorously pursued. In the past, many 

 metabolic roles for the red, far-red system haye been suggested, 

 including the possibility that it controls plant growth by affecting 

 either auxin or gibberellin leyels, or both, but such effects seem likely 

 to be highly indirect ( see, e.g., Hillman, 1959 ) . The possibility that 

 it may act by controlling the rate of oxidatiye phosphorylation has 

 been raised (Gordon and Surrey, 1960) but is also far from being 

 demonstrated as yet. 



Let us now leaye the higher plants to consider two related ques- 

 tions. These are whether photoperiodism in other organisms is 

 mediated by the red, far-red reyersible pigment and whether, in fact, 

 the pigment occurs in other organisms at all. The short answer is 

 that we don't know, as yet, but this is hardly explicit enough. 



Both photoperiodism and the red, far-red system probably occur 

 in most of the lower green plants, although there has been yery little 

 work of this kind, and particularly little with the unicellular forms, 

 which would make yaluable experimental material. It is known 

 that certain algae fail to grow heterotrophically in darkness, eyen if 

 supplied with sugars (e.g., Killam and Myers, 1956), Recently, 

 studies with a strain of the Cyanophyte Nostoc haye shown that low 

 light intensities are not only required for rapid growth but also exert 

 profound morphogenetic effects (Lazaroff, 1960). A crude action 

 spectrum suggests the possible actiyity of the red, far-red system. 



Among the fungi most of the relatiyely few light effects studied 

 show action maxima in the blue or near ultrayiolet, with red light 

 equiyalent to darkness (see Cantino and Turian, 1959; Cochrane, 

 1958). There appear to be exceptions, howeyer. One is that the 

 sporulation of certain brewer's yeasts is reported to be photoperiodi- 

 cally controlled, there being both long- and short-day strains. The 

 red region of the spectrum appears to be the most eff ectiye ( Oppen- 



