KCN effect on DCPIP reduction of chloroplasts

Douglas Bielenberg dbielen at CLEMSON.EDU
Thu Feb 17 14:13:32 EST 2005

Hello all,
	Recently I ran a lab for a plant physiology course that involved the 
reduction of DCPIP by isolated chloroplasts from store bought
spinach.  This seems like a fairly robust lab and the two basic 
treatments work quite well.  Light resulted in the reduction of DCPIP by
chloroplasts.  DCMU completely inhibited this activity, as does boiling 
the chloroplasts.
	Another of the treatments I included was KCN.  My thoughts on this were 
that mitochondrial activity in the chloroplast prep may also reduce 
DCPIP, therefore inclusion of KCN would stop mitochondiral electron 
transport, and DCPIP reduction, if occurring.  Therefore either no 
effect of the KCN on rate of reduction or a slight decrease in rate of 
reduction would be expected.  Much to my surprise however the KCN 
treatments actually had an accelerated rate of DCPIP reduction.  To 
them, it appeared that KCN accelerates photosynthetic activity.  I was 
at a loss to explain this to my students.  Any ideas on what is 
happening here?

Many thanks for any replies,

Douglas Bielenberg
Department of Horticulture
Clemson University

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