INVOLVEMENT OF CALMODULIN AND CALMODULIN-BINDING PROTEINS IN THE DIFFERENTIATION OF TRACHEARY ELEMENTS IN ZINNIA CELLS

Inhibitors of the action of calmodulin, such as trifluoperazine, chlorpromazine and tetracaine, prevented the differentiation of tracheary elements in isolated mesophyll cells of Zinnia elegans L. but did not prevent cell division. Differentiation was also completely inhibited by W-7, while cell division was inhibited by only 40%. Results of pulse-treatment with trifluoperazine indicated that the inhibitory effect of trifluoperazine on differentiation was maximal immediately before the formation of secondary walls. A calmodulin-overlay method revealed the presence in Zinnia cells of calmodulin-binding proteins whose levels increased in a hormone-dependent manner during differentiation. In particular, calmodulin-binding proteins of 28 and 27 kDa appeared abruptly immediately before the formation of secondary walls. The dramatic appearance of the binding proteins required the presence of both auxin and cytokinin. Levels of calmodulin were also found to increase rapidly between 36 and 48 h of culture, prior to the formation of secondary walls. Since both auxin and cytokinin are prerequisites for the induction and progression of the differentiation of tracheary elements (Fukuda and Komamine, 1980, Plant Physiol. 65, 57-60), our results suggest that calmodulin and calmodulin-binding proteins play important roles in the progression of the differentiation of tracheary elements immediately before the formation of secondary walls.