546 



R. A. Olson 



partial orientation of the porphyrin oscillators in the plane of the lamellae. 

 While the studies of anisotropic optical properties of in vivo chloroplasts have 

 not ruled out the possibility of the molecular orientation of chlorophyll, they 

 have not appeared to provide conclusive evidence thereof in any of the spectral 

 regions investigated. The question is reopened, however, by the recent discov- 

 ery of a far-red absorbing form of chlorophyll capable of accepting excitation 

 energy from accessory pigments and from ordinary cUorophyll . ( ^^' This chlo- 

 rophyll demonstrates a maximum absorption near 705 m/i and a maximum 

 emission near 7Z0 m/x; this spectral region is at longer wave lengths than that 

 considered in the investigations mentioned above. While conventional visual ob- 

 servations are limited by the poor spectral response of the human eye, suitable 

 visual observations can be effected through use of the nnodern infrared image 

 converter (the first observations reported from our laboratory were made with 

 a surplus World War II "snooperscope"). In live Euglena cells a bifluorescence 

 at wave lengths greater than 690 mfi was noted and in a later publication a di- 

 chroic ratio of 4.00 at 695 mjx was reported . ^ ^ ^ ' ^''' Using selected chloroplast 



fragments, Sauer and Calvin measured an electro-dichroism as high as 1.Z7 at 



f 13) ■ 



695-700 m^. ^ ' The relation between these two observations awaits an under- 

 standing of the attachment site of the chlorophyll molecule. Current studies in 

 our laboratory have been directed toward characterizing the in vivo oriented 

 chlorophyll in detail. 



EXPERIMENTAL 



Dichroism 



Euglena provides a most striking example of chloroplast dichroism in the 

 far-red spectral region. Photomicrographs demonstrating this property pre- 

 sent the conventional appearance of the organism in which the positions and 

 spacial relationships of the chloroplasts are clearly indicated with respect to 

 the cell outline. While the Euglena cell varies in shape from spheroid at rest 

 to teardrop-like or prolate when actively swimming, the discoid chloroplasts 

 are usually located peripherally, more or less facing the limiting cell nnembrane 

 or pellicle. This arrangement of the chloroplasts in the cell permits the simul- 

 taneous observation, in the same preparation of numerous aspects of chloroplast 

 orientation varying from the circular face view to the more linear edge view. 

 It also permits a wide observational choice of edge viewed chloroplasts in nu- 

 merous azinnuthal aspects in the specimen plane. 



The azimuthal dependence of dichroism in Euglena is demonstrated in 

 Plate I A and B. The cells are photographed in unpolarized transmitted light 

 from a monochromator at 695 m^ through a Nicol prism mounted behind the ob- 

 jective. Edge viewed chloroplasts show maximum absorption when the electric 

 vector of the transnnitted light lies in the plane of the lamellae and minimum 

 absorption when the electric vector lies perpendicular to the plane of the lamel- 

 lae. They show minimum absorption when the electric vector of the transmitted 

 light lies perpendicular to the lamellar plane. This indicates that the oscillators 

 of absorption lie in or very close to the plane of the lamellae. Chloroplasts 



