THE NATURAL STATE OF PROTOCHLOROPHYLL 407 



Variations occur also in the holochrome from a single plant. Proto- 

 chlorophyll holochrome extracted by glycerine at al)out 5°C. from 

 etiolated barley leaves usually has a broad absorption band with an 

 indistinct maximum lying somewhere between 6-45 and 650 m^. If 

 this extract is allowed to stand at room temperature in the dark for 1 

 or 2 hours its absorption maximum gradually shifts to between 630 

 and 635 m/x (5). 



The absorption maximum of the chlorophyll-a holochrome shows 

 similar shifts in position. The chlorophyll-a holochromes derived 

 from protochlorophyll holochromes with absorption maxima near 

 650 m^^ have absorption maxima that lie near 680 ni/z, whereas those 

 derived from protochlorophyll holochromes with absorptions at 630 

 to 635 ran usually have absorption maxima near 672 m/x. Further- 

 more, the chlorophyll-a holochrome produced by illumination of dark- 

 grown barley leaves at about 5°C. and extracted in the cold with 

 glycerine had an absorption maximum at 678 m^u. When the ex- 

 tract was kept at room temperature for 3 hours the absorption maxi- 

 mum shifted to 670 m^u. Fully greened barley leaves, however, when 

 extracted with glycerine at room temperature yield an extract whose 

 absorption maximum is close to 680 m/x. The cause of these changes 

 is not known. 



A shift in the position of the absorption maximum of chlorophyll a 

 from 670 to 677 or 678 mju during its accumulation in leaves was 

 reported by Krasnovskii and Kosobutskaya (6) who attributed the 

 shift to the change from a monomeric to a coUoidally aggregated form 

 of chlorophyll during greening (6,7), Om- experiments do not support 

 this interpretation for the shift in the absorption maximum of chloro- 

 phyll a during greening. When fully greened barley leaves were ex- 

 tracted at room temperature with glycerine we obtained an absorp- 

 tion maximum at 680 m^l. We have also obtained the absorption 

 maximum at 680 m^u for the chlorophyll-a holochrome newly formed 

 from protochlorophyll holochrome extracted with cold (»5°C.) 

 glycerine from etiolated barley leaves and squash cotyledons. These 

 results show that, even without the increase in chlorophyll con- 

 centration caused by greening of the leaf, the absorption maximum 

 of chlorophyll a lies at 680 m;u — a position comparable to that of 

 chlorophyll in fully greened leaves (8). When the glycerine ex- 

 tracts of newly formed chlorophyll stand at room temperature for 

 some hours, the absorption maxima shift to shorter wavelengths, 



