Flower senescence in daylily (Hemerocallis)

Abstract

Daylily (Hemerocallis hybrid cv. Cradle Song) flower development and senescence was categorised into seven stages, each separated by one day. As the bud developed (Stages I to III) its fresh and dry weight increased, but during flower opening (Stages III to IV) only the fresh weight increased, reaching a maximum when the flower was fully open (Stage IV). Fresh and dry weight declined as the flower senesced (Stages V to VII), and the petal tissue became water‐soaked. Flower respiration was relatively constant through Stages I to III, but during opening the CO2 production increased, then declined as the flowers senesced. Ethylene production was low throughout flower development, and there was a transient increase, up to 2.5 nl flower−1 h−1, as flowers senesced. Petal protein content per gram fresh weight decreased throughout flower development and senescence either on or off the plant. One‐dimensional SDS‐PAGE revealed a general gradual loss of protein bands during flower senescence and loss of some specific bands (e.g. at M, 30 000 and 40 000). Flowers, detached from the plant at Stage III, placed in deionised (DI) water for 7 h and then transferred to fresh DI water or actinomycin D (25 mg l−1), showed an increase in fresh weight up to a maximum at about 12 h after transfer, followed by a rapid decline. By 48 h the flowers had completely senesced, the tissue becoming watersoaked and free moisture appearing on the tips of collapsed petals. In contrast, senescence of flowers treated during opening with cycloheximide (1 mM) was greatly delayed, with little loss of fresh weight or reduction in flower diameter, even up to 181 h after transfer. When such flowers did finally senesce, they did not show the same pattern of senescence as seen with those in water or actinomycin D. Cycloheximide‐treated flowers wilted gradually and showed no water‐soaking and no free moisture at the petal tips. Cycloheximide treatment retarded the decline in protein content of the petals; and the protein population, as visualised by SDS‐PAGE, was maintained for up to 204 h after transfer to cycloheximide.