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.

Ethylene‐insensitive floral senescence inSandersonia aurantiaca(Hook.)

“…Actinomycin D was ineffective in extending the vase life of Hemerocallis (Lay-Yee et al 1992). Individual sandersonia flowers weigh less than half the fresh weight of Hemerocallis flowers and their senescence occurs over a longer period of time, therefore there is greater opportunity for actinomycin D to reach the appropriate site of action and subsequently delay the senescence of sandersonia flowers.…”

“…Production of ethylene by the flowers was negligible (< 0.01 nl/g fresh weight per h) during the whole of the postharvest period regardless of the presence or absence of propylene. The production of ethylene by other flowers whose senescence is not regulated by ethylene, is also low (daylily < 1 nl/g fresh weight per h, Lay Yee et al 1992; chrysanthemum < 0.1 nl/g fresh weight per h, Singh & Moore 1992) when compared to the ethylene production of flowers whose senescence is known to be regulated by ethylene, such as Petunia (18 nl/g fresh weight per h, Whitehead et al 1984) and carnation (40 nl/ g fresh weight per h, Brandt & Woodson 1992). These data confirm that ethylene does not play a role in the senescence of sandersonia flowers.…”

“…The use of this inhibitor in the postharvest treatment of cut flowers can substantially improve vase life (Dilley & Carpenter 1975;Wulster et al 1982;Lay-Yee et al 1992;Jones et al 1994). The improved vase life of Gladiolus, Iris, Narcissus, Hemerocallis, and carnation following cycloheximide treatment was attributed to an almost complete inhibition of petal expansion and wilting (Wulster et al 1982;LayYee et al 1992;Jones et al 1994).…”

Identification of genes associated with perianth senescence in Daffodil (Narcissus pseudonarcissus L. ‘Dutch Master’)

“…This enhanced proteolytic activity most likely causes the changes in protein profiles and general decline in protein levels reported in senescing petals [34,29]. As well as having a role in recycling of nutrients, proteases may have important functions in inducing signals specific to programmed cell death by processing or releasing bioactive molecules or by activating cell surface receptors [35].…”

Programmed senescence of plant organs

“…Perianth senescence of some flowers occurs as part of a temporal program with the petals and sepals senescing strictly as a function of age. For example, daylily flowers senesce 12 ± 18 h after flower opening (Lukaszewski and Reid, 1989;Lay-Yee et al, 1992). The endogenous signals that regulate age-dependent petal senescence are completely uncharacterized, although the process is accompanied by the regulated expression of a suite of genes, some of which are functionally related to those associated with leaf senescence.…”