The chemical aspects of the circadian leaf movement known as "nyctinasty" are 
discussed in this paper. Each of the nyctinastic plants of five different genera 
so far examined contained a pair of factors, one of which induced leaf closure 
and another induced leaf opening. The relative contents of the closing and 
opening factors changed correlating with the nyctinastic leaf movement. The use 
of fluorescence-labeled and photoaffinity-labeled factors revealed that the 
factors bind to specific cells, the motor cells, present in the pulvini, and 
that the membrane fraction of the motor cells contained two proteins of 210 and 
180 kDa, which can bind to the factors.