THE EFFECT OF AUXIN AND CALCIUM-ANTAGONISTS ON TRACHEARY ELEMENT DIFFERENTIATION IN PHASEOLUS-VULGARIS L

Auxin induced the formation of tracheary elements in bean seedlings wh en applied for 24 h to a point source in the hypocotyl. Differentiated tracheary elements appeared basipetally to the application point. Ver apamil, a Ca2+ channel blocker, and LiCl, a reported inhibitor of Ca2 release from intracellular stores, both inhibited tracheary element d ifferentiation when applied after auxin. However La3+, an inhibitor of Ca2+ uptake, was without effect on auxin-induced tracheary element di fferentiation. The results are discussed in relation to xylogenesis in tissue culture, which requires Ca2+, and vascular strand formation in whole plants, which requires polar auxin transport. It is concluded t hat Ca2+ is necessary for auxin-induced vascular strand differentiatio n in the intact plant.