1730 



CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP. 37A 



structure reappeared after 4 hours exposure to light. At first, the laminae were thinner 

 and wider-spaced than in fully light-adapted cells; the original structure was restored 

 only aftei- 72 hours in light. Spectroscopic observations showed that some chloro- 

 phyll remained in the cells after complete dark adaptation; the pigment content de- 

 clined during the first few hours in light, and only then began to grow, particularly 

 rapidly on the second day of the exposure. This shows that the formation of the lam- 

 inae is not related to the synthesis of chlorophyll. 



Fig. 37A.18a. Layered structure of grana in chloroplasts of a higher plant. Sectioned 

 parallel to the large cross-section of the chloroplasts (Palade 1953). 



Leyon (19530 showed that the same species may e.xhibit both granular 

 and laminated chloroplasts. He investigated chloroplasts from Beta 

 saccharifera and Aspidistra elatior, fixed, embedded in plastic, and sec- 

 tioned. On cross sections normal to the large plane of the chloroplast, the 

 layers sometimes appeared continuous, interrupted only by starch de- 

 posits (fig. 37A.17). Yet, the same plant produced also typical "money 

 rolls" of disc-shaped lamellae, consisting of 50 or 60 discs of equal diameter, 

 apparently originating from a granum. This suggested that a change from 

 granular to laminated structiu'e (or vice versa) may be the result of aging. 



