LIGHT SCATTERING BY CHLOROPLASTS IN THE UV 

 William F. Prickett, F. Dudley Bryant, and Paul Latimer 



Scattering spectra of biological materials which contain light absorbing 

 compounds are closely related to the absorption spectra. Several green plant 

 materials and red blood cells have been studied in the visible spectrum. How- 

 ever, the present study^^' seems to be the first of a biological material in 

 which a scattering spectrum is measured in the important near ultraviolet. 



The method is described in detail elsewhere^^' ^'. Briefly, scattering 

 spectra are determined from the difference between two "absorbance spectra" 

 of a given sample measured with a standard spectrophotometer (we used the 

 B & L 505). In one case the optics of the instrument are used in the normal 

 configuration; in the other diffusing plates are placed after the sample and 

 blank vessels. From particle (chloroplast) concentration, particle size, and 

 other information, absolute scattering coefficients are calculated. While only 

 light scattered at small angles, 5 - 49°, is observed, these coefficients are 

 extrapolated to describe total scattering (assuming that light scattered in all 

 directions has the same spectral properties). The scattering coefficient, S , 

 is the fraction of the incident light striking the geometrical cross section of 

 the particle which is scattered. From the above experimental information and 

 using the equations and method of Latimer and Eubanks, we also calculate the 

 absorbance, E' (corrected for scattering losses) of a single particle (E' = 

 log lo/I). 



Spinach chloroplasts in 0. 5 M sucrose buffered at pH 7. were obtained 

 with a blender, washed twice, and resuspended for measurements in standard 

 1 cm^ silica vessels. To cancel out errors caused by dissolved proteins and 

 small particles in the sample vessel, supernate of the stock suspension was 

 added to the blank medium in the appropriate concentration. We made UV dif- 

 fusing plates by grinding Corning No. 7910 glass on both sides with No. 100 

 carborundum. 



The results of two consistent runs were averaged to obtain the given 

 spectral curves. The average particle diameter was 3. ji, average particle 

 concentration, N, was 1.35 x lO'^/ml (P = 0.94, see Ref. 3). Experimental 

 suspension absorbances were in the range 0. 1 - 0. 4 depending on sample, 

 wavelength, and type of measurement. 



The particle scattering and absorbance curves are given below in Fig. 1. 

 Of particular interest is the scattering shoulder at about 280 - 305 m^ corres- 

 ponding to the broad absorbance band of proteins and nucleoproteins at 255 - 



711 



