the pollen tubes were transmitted. The cell death process apparently
facilitated the passage of the pollen tubes, and nourished the
pollen tubes. Whether or not there is senescence (cell death) in the
Dendrobium column, following pollination, and whether or not this
aids in nourishing the pollen tubes and/or the ovary, remains to be
elucidated.
In conclusion, treatment with ethylene resulted in an early
increase in the transcript abundance of a senescence-associated
cysteine peptidases in the petals, in an early rise in peptidase activity,
and in a later decrease in water-insoluble protein levels. The
delay of petal senescence by a specific inhibitor of cysteine peptidases
(E-64) indicates that the activity of this class of peptidases is
limiting the processes leading to visible petal senescence. As E-64
does not permeatemembranes, the resultsmight suggest an effect
on an extracellular cysteine peptidase. Treatment of the flowers
with 1,10-phenanthrolin, a metal chelator, also doubled the time
to ethylene-induced visible petal senescence. However, this compound
might have several effects other than on metallopeptidases