The column of flowers treated with ethylene also showed an
increase in the transcript abundance of the isolated cysteine peptidase,
accompanied by an increase in peptidase activity. The
ethylene treatment was also associated with a decrease in waterinsoluble
protein levels, whereas no decrease was observed in the
level of water-soluble protein, similar to the effects in petals. The
time lines of these processes were similar in both columns and
petals (although a large increase in DenCys1 transcript abundance
occurred later in columns than in petals, and the increase in protease
activity also came later in the column). In several species
ethylene treatment induced senescence and death in many cells
of the style (Wu and Cheung, 2000). The same might be true for the
stylar part of the column in Dendrobium flowers. If so, the column
might participate, just as the petals, in nourishing other cells, after
pollination. As noted in Section 1, our unpublished data indicated
that the column of Dendrobium flowers is the main source of the
increase in ethylene production following pollination. The present
data suggest the idea that this increase in column ethylene production
might induce senescence (cell death) in column cells. Wu
and Cheung (2000) described that in many plant species pollination
induces programmed death in cells of the central stylar tissue.
Thus after pollination cell death was restricted to the area where