THE ALCOHOL-SOLUBLE AND INSOLUBLE FRACTIONS OF THE PHOTOSTNTHETICALLY 

 FIXED CARBON IN NATURALLY OCCURRING MARINE PHYTOPLANKTON POPULATIONS 



by 

 William H. Thomas 



Chemical analyses of phytoplankton cells may- 

 give information valuable in determining the 

 nutritive value of such cells to their 

 predators. Such analyses are most easily 

 carried out with laboratory-cultured cells, 

 but such cells may not truly represent those 

 occurring in nature. This paper reports 

 experiments made at sea with naturally 

 occurring populations in which determinations 

 of the alcohol-soluble fraction of marine 

 phytoplankton were made. These determina- 

 tions may give an indication of the gross 

 chemical composition of photosynthesizing 

 cells . 



Because of the small numbers of algal cells 

 present per unit volume of pelagic water, 

 attempts to harvest these cells for purposes 

 of chemical analyses by the usual chemical 

 means would be extremely time consuming. 

 Fortunately the use of the C-^ technique of 

 labeling the organic matter produced by 

 phytoplankton greatly increases the 

 sensitivity of a chemical extraction pro- 

 cedure so that only relatively small volumes 

 of water need to be handled. 



In these experiments a sample of surface 

 water was taken with a plastic bucket. 

 Aliquots of this sample were added to 250-ml. 

 ground-glass-stoppered bottles, C^^was added 

 to each bottle, and the bottles were 

 illuminated at 1200-1^00 foot-candles at the 

 surface sea-water temperature in a glass- 

 bottomed water bath. After incubation, 

 aliquots of the water were filtered through 

 HA Millipore filters (0 .^5 H pore size) to 

 determine the total activity fixed. Another 

 aliquot was filtered through a sintered-glass 

 filter. The residue on this filter was 

 extracted with boiling 80°/o ethanol. An 

 aliquot of the combined extracts was 



evaporated on a steel planchet to determine 

 the extractable activity. A linear 

 relationship between volume of extract and 

 activity showed that self -absorption 

 corrections were not necessary when volumes 

 no larger than 0.50 ml. were evaporated on 

 the planchets. The proportion of extract- 

 able material in the cells was determined 

 by dividing the activity extracted by the 

 total activity in the cells. The assumption 

 is made that after this long period of 

 incubation all chemical entities in the 

 cells are labeled with Cl^ to the same 

 extent and that the ratio of extractable 

 activity to total activity truly represents 

 the proportion of alcohol soluble in all 

 materials. It is further assumed that no 

 losses of Cl^ occurred during evaporation 

 of the extract on the planchets. 



Considering the speed of the photo synthetic 

 cycle as shown by Buchanan et _al. (1952), 

 (steady-state labeling of sugar phosphates 

 after about 15 minutes) the first assumption 

 seems reasonable (cf. also Fogg, 1956). 

 Compounds appearing in the extract would 

 include sugars, amino acids, sugar phosphates, 

 pigments (less their protein moieties) and 

 lipids. Substances remaining behind would 

 include proteins, polysaccharides, and 

 nucleic acids. 



An initial preliminary experiment was 

 performed at Station 0-1, 50 miles west of 

 Baja California (30 8 01' N latitude and 

 ll6°l*-9' W longitude). In this experiment 

 only four bottles were incubated (for eight 

 hours) and the activity recovered in the 

 extract was only 92 cpm. above background In 

 10 ml. of extract. The total activity on the 

 millipore filter was 619 cpm. Thus about 

 15°/o of the activity was extracted. Because 



113 



