XVI International Botanical Congess
Tracheary element differentiation requires strict coordination of secondary cell wall (2oCW) synthesis and PCD to produce a functional cell corpse. The execution of cell death involves an influx of Ca2+ into the cell, and is manifest by rapid collapse of the large hydrolytic vacuole and cessation of cytoplasmic streaming. This precise means of effecting cell death is a prerequisite for postmortem developmental events including autolysis and chromatin degradation. A 40-kDa serine protease is secreted during 2oCW synthesis which may be the coordinating factor between 2oCW synthesis and PCD. Specific proteolysis of the extracellular matrix is necessary and sufficient to trigger Ca2+ influx, vacuole collapse, death, and chromatin degradation, suggesting extracellular proteolysis plays a key regulatory role during PCD. We present a model in which 2oCW synthesis and cell death are coordinated by the concomitant secretion of the 40-kDa protease and 2oCW precursors.