The Cytocluomcs of Plant Tissues 



49i 



this dilTerencc is shown by Ihc following figures: substrate reduction of mung 

 bean particles; a + a.^, 93%; component 558, 43-6% and component 555, 

 40-8%. 



Microsomes 



The microsomal fraction, when reduced with dithionite, characteristically 

 shows an asymmetric band of maximum 559 m/^ (Fig. 10) or in some instances 



558.6 



MUNG BEAN 

 "MICROSOMES" 



580 



580 



,1(n 



520 550 

 X (nn>i) 



Fig. 11. The difference spec- 

 trum (at -190°C) obtained by 

 measuring the difference in 

 absorption between oxidized 

 mung bean microsomes and a 

 suspension of microsomes re- 

 duced with DPNH. 



Fig. 10. Difference spectra (at 

 — 190^^C) obtained from the mung 

 bean hypocotyl microsomal frac- 

 tion. The curves were obtained 

 from the difference in absorption 

 between aerated microsomal sus- 

 pensions and suspensions reduced 

 with dithionite (solid line) and 

 DPNH (dashed line). 



a two-peak spectrum of maxima 559 and 553 mfi. Reduction of this fraction 

 with DPNH gives a two banded spectrum at 558 and 552 mfi (Fig. 1 1). The 

 amount of 552 component varies among different plant species. 



Chloroplasts 



Cytochromes /and b^, the two haemoproteins that have been described as 

 chloroplast components, are always found in the reduced state; these two 

 components are not easily oxidized chemically (Davenport and Hill, 1954). 

 For this reason, difference spectra were difficult to carry out on isolated 

 chloroplasts. Before entering into a study of the low temperature spectra 

 of isolated chloroplasts it was thought advisable to obtain the low temperature 

 spectrum of cytochrome /, the one chloroplast component that has been 



