98 MACROMOLECULAR COMPLEXES 



formation of lamellae, globules accumulate in large masses, and the 

 chloroplast function appears to be arrested. The pigment concen- 

 tration in the mutant indicates that there is a greater accumulation 

 of chlorophyll b, and that the pigments are probably located in the 

 globules. In older stages of the plastids in this mutant, the globules 

 are broken down with further breaks in the inner structure, along 

 with a decrease in pigment concentration. 



The picture of chloroplast development still remains inconclusive, 

 and more experimental work is necessary. However, in order for the 

 plant to carry on photosynthesis, an ordered lamellar structure is 

 necessary. As already noted, the chloroplast contains nucleic acid. 

 It is very suggestive that nucleoproteins are involved in the synthesis 

 of the lamellar lipoproteins of the chloroplast, and that the synthe- 

 sis of chlorophyll and the lamellae proceed simultaneously. 



Chloroplast Function as Related to Structure 



What does the chloroplast structure tell us about how the chloro- 

 plast functions in photosynthesis? That is, how does the conversion 

 of light energy to chemical energy take place via chlorophyll? The 

 chloroplast is a polyphasic system comprising a stacked array of 

 layers of lipids and proteins separated by monolayers of chlorophyll. 

 Experimentally in Eii galena it has been found that any physical or 

 chemical forces (i.e., light, temperature, drugs) that affect the syn- 

 thesis of either chlorophyll or the chlorophyll-complex will disrupt 

 the lamellar structure (Wolken et ah, 1955; Wolken, 1956a). This 

 change was associated with the removal of Mg++ from the chloro- 

 phyll molecule. Is the chloroplast, then, like an emulsion, which is 

 stabilized by the chlorophyll molecules? Levitt (1954) suggests 

 that the magnesium atom is the necessary part of the molecule and 

 that any theory of the conversion of light energy into chemical en- 

 ergy via chlorophyll has to take into account the valence changes of 

 the magnesium ion. 



Resonance studies indicate that the chloroplast has properties of 

 a crystal and, together wih the evidence of an ordered structure 

 from electron microscopy, permit an analogy to a photobattery— 

 a semiconductor (Calvin, 1958). The assumption is that we are 

 dealing with an electron-transfer phenomenon through many mole- 

 cules by a conduction-band mechanism. Films of both chlorophyll 

 a and methyl chlorophyllide a deposited from organic solvents have 



