1 



578 



Jerome J, V/ollcen 



thicliness and an average chloroplast contains 21 such dense lay- 

 ers. The dense layer appears to be a composite, a double layer 

 with lamellae from 5^ to 100 A in thickness. Depending on the 

 fixatives used and the resolution of the electron microscope, as 

 many as 4 to 6 lamellae can be delineated (Fig. 6). However, we 

 associate only the two outer lamellae with the chlorophyll mole- 

 cules. Although chemical analyses of the chloroplast lamellae 

 have not yet been accomplished, the dense layers are talcen for 

 lipoproteins and lipids because of their affinity for fixing a- 

 gents such as OSO4 and the less dense spaces are aqueous proteins 

 enzymes, and dissolved salts. It was further envisioned that the 

 hydrophilic porphyrin "heads" of the ch3.orophyll molecijles extend 

 into the aqueous protein, and that the lipophilic phj^-fcol "tails" 

 reach to the lipid layer. 



1/hen Euglena are dark-gro\m, their chloroplast s are no longer 

 recognizable. These dark-f^proam Euglena cells contain chloroplast 

 remnants, proplastids^°^. Bleached cells, whether apx^earing by 

 dark-adaptation, streptomycin, heat, or u.v. light, all possess 

 proplastids. Gibor and Granickv-L'^^ll^ found tliat the proplastids 

 of some of these bleached strains were capable of sjTithesizing 

 porph;;>'rins in a standard culture medium. Others s^-nthesized por- 

 phyrins onJ-y after the 8-ddition to the medium of delta-aminolevu- 

 linic acid, a prec\;irsor to porphyrin synthesis ^--^^. Upon re-adap- 

 tation to light, the chloroplast development can be followed at 

 regTxLar time intervals. After as little as h hrs, in the light, 

 elongated bodies characteristic of chloroplast lamellae appear, 

 but these are thinner and not regularly packed. The lamellae, few 

 in number at first, increase progressively irith time in continu- 

 ous light, and by 72 hrs. (3-^1- generations under ovcc conditions) 

 the chloroplasts have the shape and lamellar organization describ- 

 ed for active phot osynthe tic Euglenas grown in light for many gen- 

 erations (Figs. 5 a-nd 6). Tlie number of lamellae tliat are formed 

 can be correlated with chlorophyll synthesis, and to the number of 

 chlorophyll molec\ales(-^^5). This kind of structure has the advan- 

 tage of bringing a large surface area necessary for the number of 

 cM.orophyll molec;ales in the chloroplast to be compressed into a 

 small vo3.ume. 



To see ho\7 much clolorophyll -vra-s available to the chloroplast, 

 and what area of the total lamellar surfaces irould be occupied by 

 the chlorophyll molecioles, the chlorophyll concentration per chl- 

 oroplast \rB.s determined and the number and thlclaiess of dense lay- 

 ers -vras statistically evaluated (Table l), 'Jihe validity for mono- 

 moleciJLar layers of ciilorophyll molecules on the surfaces of the 

 chloroplast lamellae \ra,s determined by ca^lculating the area avail- 



