THE CHLOROPLAST STRUCTURE IN PliOTCSrilTIIESIS 

 Jerome J. V/ollcen 



The chemistry and molecular structure of the chloroplast must 

 he linJced to its function as an energy capturing, storing, and 

 transferring device in photosynthesis. An organism ideally suit- 

 ed for the study of the cliloroplast chemistry and structure is 

 Euglena, which is photos ;yrithetic in the light and "chemosynthe- 

 tic" in the dark. In these light< ^>dark adaptations, biochemi- 

 cal changes are accompanied by structural changes of the chloro- 

 plast. In addition, grcarth at elevated temperatures above 32°C. 

 and drug action (e.g., streptomycin, antihistamines, etc.) inter- 

 fere -vrith the organism's photometabolism and hence with chloro- 

 phyll synthesis, bringing about structural changes of the chloro- 

 plast and resulting in chlorophyll- less mutant fortTis(l). 



THE CIELOROPLAST 



The precise ccanposition and chemistry of active chloroplasts 

 is still unlcnown; gross analysis of isolated chloroplasts indi- 

 cates from 35^ to 55fa protein, l8/a to 37^ lipids, mostly phospho- 

 lipids, and 5^ "to 8^ inorganic material on a dry weight basis. 

 Nucleic acids, RNA. and DIIA, have been identified, with estimates 

 from 0.3/0 to yjo on a dry weight basis. ^^^^ Tlie chJ.oroplast pig- 

 ments, the chlorophylls average about Sjo and the carotenoids 2^. 

 In Euglena, the chloroplast chlorophvlls constitute about 855^ 

 chlorophyll a and 15^/3 chlorophyll b ^-'■''. The major carotenoids 

 are p-carotene, lutein, and neoxanthin. However, in Euglena^ in- 

 stead of lutein, 80^ of the carotenoids present were identified 

 as antheraxanthin, 11^ p-carotene, and 7^ neoxanthin^ 0, In addi- 

 tion, ^k-carotene, crytoxanthin, echinenone, and two new caroten- 

 oids, euglenanone and hydroxy-echinenone irere identified. 



The chlorophyll and carotenoid syntheses can be followed, and 

 their concentrations calculated frou the absorption spectra. For 

 example, from such spectra, 1,0 x 10^ chlorophyll molec\i3.es were 

 calculated for an average chloroplast ^5 ^ . It is now possible to 

 obtain the absorption spectruia of a ^i,ngle in vivo cliLoroplast by 

 techniques in microspectrophotcmetry^'^^. A recorded absorption 

 spectrum of a Euglena chloroplast is illustrated in Fig, 1, Fig, 



5 75 



