LIGHT INDUCED OPTICAL CHANGES IN GREEN LEAVES 

 Walter Bonner and Robert Hill 



INTRODUCTION 



In a previous account of some work by the present authors (1) 

 accumulated evidence was presented suggesting that light init- 

 iated oxidation-reduction reactions in higher plants involved 

 cytochromes f^ and b^. As yet, there are no unequivocal data 

 relating to rapid changes in the oxidation states of cytochromes 

 f and b^ on illumination of green leaves or isolated chloroplasts. 

 Light induced optical changes, which have been said to correspond 

 to cytochromes, have been described in isolated chloroplasts of 

 higher plants by Lundegardh (2), James and Leach (3), and Muller, 

 et. al_. (4), The present paper describes the rapid oxidation of 

 cytochrome f which occurs on illumination of green leaves and, 

 in addition7 some observations pertaining to cytochrome b(,. An 

 abstract of some of this work has been published (5). 



METHODS 



Etiolated leaves of mung bean ( Phaseolus areus ) were obtained 

 from seedlings grown in the dark at 25°. Spinach leaves were 

 obtained from locally grown plants; spinach chloroplasts were pre- 

 pared by standard procedures. Optical measurements were per- 

 formed either with a double-beam differential spectrophotometer 

 or with a rapid scanning split-beam spectrophotometer; both of 

 these instruments were similar to ones already described (6), 

 Leaves were mounted on a specially constructed rack which fitted 

 into a moist chamber and suspensions of chloroplasts or algae 

 were placed directly into the moist chamber. The basic design 

 of the moist chamber has been described previously (7). Actinic 

 light was provided with a Unitron Koehler illuminator equipped 

 with suitable inCerference filters. In all experiments the 

 photomult ipler of the spectrophotometer was shielded from the 

 actinic light with suitable filters. The visual optical obser- 

 vations were performed with a low-dispersion microspectroscope; 

 the optical path of the comparison prism was equipped with two 

 wedged troughs. 



RESULTS 



Cytochromes f^ and b^ are easily observed in acetone extracted 

 chloroplasts and in etiolated leaves (1). It is also apparent 



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