TRACHEARY-ELEMENT DIFFERENTIATION IN SUSPENSION-CULTURED CELLS OF ZINNIA REQUIRES UPTAKE OF EXTRACELLULAR CA-2+ - EXPERIMENTS WITH CALCIUM-CHANNEL BLOCKERS AND CALMODULIN INHIBITORS

Tracheary-element (TE) differentiation in suspension cultures of Zinnia elegans L. mesophyll cells was inhibited by blocking calcium uptake in three ways: 1) reducing the [Ca2+] of the culture medium, 2) blocking calcium channels with the non-permeant cation La3+, and 3) blocking calcium channels with permeant dihydropyridine calcium-channel blockers. Calcium-channel blockers were effective when added at any time between 0 and 48 h after culture initiation; after 48h, calcium sequestration and secondary cell-wall deposition began. In contrast, calmodulin antagonists inhibited TE differentiation when added at the beginning of culture, but not when added after 24h. These results indicate that TE differentiation involves at least two calcium-regulated events: one calmodulin-dependent and occurring shortly after exposure to inductive conditions, and the other calmodulin-independent and occurring just prior to secondary cell-wall deposition. © 1990 Springer-Verlag.