1754 CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP. 37A 



resonance shift is to be expected, although its extent cannot be estimated 

 without much better knowledge of the packing density. 



Another criterion of the state of chlorophyll in vivo is its fluorescence — 

 assuming that it is not due to a small fraction of the pigment present 

 in a special state. Rodrigo's protein-chlorophyll complex was fluorescent, 

 while artificial monomolecular layers of chlorophyll, as well as chlorophyll 

 crystals, do not fluoresce. However, fluorescence may perhaps be acti- 

 vated by a protective coating of chlorophyll monolayers with lipide mate- 

 rials (which probably exists in the chloroplasts), so that new model experi- 

 ments are needed before it can be asserted that the fluorescence of chloro- 

 phyll in vivo proves that chlorophyll molecules are attached individually 

 to protein molecules and do not form monomolecular layers with a resonance 

 interaction within them. (See, in this connection, Krasnovsky's data in 

 table 37C.IIIB.) 



{d) Location of A ccessory Pigments 



Not much, if any, new information has been developed on the location 

 of accessory pigments, carotenes and phycobilins, in relation to chloro- 

 phyll and other cell constituents, since Hubert's scheme (Vol. I, fig. 46) 

 tentatively placed the carotenoids between the phytol chains in the lipoid 

 layers of the chloroplasts. 



Particularly in need of clarification is the question of the location of the 

 phycobilins. Several sets of observations seem to be difficult to reconcile. 

 Microscopic observations (of some red algae, at least) seems to indicate 

 that the red pigment is spread over the whole chloroplast while chlorophyll 

 is concentrated in small "grana"; in ultracentrifugation experiments with 

 blue-green algae, described in section 3 of this chapter, chlorophyll has 

 been observed to precipitate in a large-particle fraction, while the phyco- 

 bilins precipitated much later (c/. also Calvin and Lynch, 1952). 



These experiments seem to indicate a spatial separation of green from 

 the red (or blue) pigments in the natural state. 



Experiments on sensitized fluorescence and action spectra of photo- 

 synthesis (Chapters 24 and 32) indicates on the other hand, a close associa- 

 tion between the phycobilins and the chlorophylls, permitting a highly 

 efficient energy transfer. 



The ultracentrifuge experiments could perhaps be explained by a 

 leaching out of the chromoproteids during the maceration of the cells. 

 McClendon and Blinks (1952, 1954) found that chloroplasts of red alga 

 Griffithsia pacifica easily loose their phycoerythrin when the plants are 

 crushed in a distilled water, highly saline solution (up to 1.5 M) or sucrose 

 solution (up to 2 M). In polyethylene glycol (Carbowax 4000, molecular 

 weight 2,400) and other equally high-molecular solvents, on the other hand, 

 the plastids do not swell and retain their red pigment. It seems that sol- 



