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Dry weight, water content, soluble carbohydrate content, and carbohydrate composition of daylily (Hemerocallis hybrid cv Cradle Song) flower petals were monitored in the 3 d leading up to full opening and in the first day of senescence. Timing of events was related to the time (hour O ) when flower expansion was 60% complete. Petal dry weight increased linearly from hour -62 (tight bud) to hour 10 (fully developed flower), then fel1 rapidly to hour 34 as senescence advanced. lncrease in water content was proportional to dry weight increase from hour -62 to hour -14, but was more rapid as the bud cracked and the flower opened, giving an increase in fresh weight/dry weight ratio. Soluble carbohydrate was 50% of petal dry weight up to hour 10, then decreased during senescence to reach 4% by hour 34. Up until hour -14, fructan accounted for 80% of the soluble carbohydrate in the petals, whereas hexose accounted for only 2%. Fructan hydrolysis started just prior to bud crack at hour -14, reaching completion by hour 10 when no detectable fructan remained, and fructose plus glucose accounted for more than 80% of the total soluble carbohydrate. l h e proportion of sucrose remained constant throughout development. Osmolality of petal cell sap increased significantly during fructan hydrolysis, from 0.300 to 0.340 osmolal. Cycloheximide applied to excised buds between hour -38 and hour -14 halted both fructan hydrolysis and flower expansion. l h e findings suggest that onset of fructan hydrolysis, with the concomitant large increase in osmoticum, is an important event driving flower expansion in daylily.attention away from the equally dramatic bud and flower growth that occurs during the 3 to 4 d leading up to full bloom, with the size doubling about every 30 h to reach a maximum flower weight of 5 to 10 g fresh weight (depending on cultivar), and with the actual opening process from bud to fully expanded flower taking only 5 h (Lay- Yee et al., 1992). This study documented the growth that took place during this rapid flower expansion, and explored some of the underlying physiological events in the petals that were associated with the expansion, in particular the changes in carbohydrate composition and content. MATERIALS AND METHODS Plant MaterialHemerocallis hybrid cv Cradle Song plants were grown in a glasshouse (27OC day, 21OC night) under natural light supplemented with incandescent lighting between 4:OO PM and 12:OO AM (Lay-Yee et al., 1992), and flowers were harvested according to Bieleski and Reid (1992). Stages of flower development are shown in Figure 1. Timing of events is reported in relation to the time at which flower expansion is 60% complete (midnight), denoted hour O (see Bieleski and Reid, 1992). Petal Fresh Weight and Dry WeightModern daylilies are hybrids that have been developed over the past century from crosses involving up to 12 species of the Asian genus, Hemerocallis, within the family Liliaceae (Munson, 1989). They are rapidly becoming a feature of gardens in temperate regions by virtue of their...

~~During senescence, petals of attached daylily (Hemerocallis hybrid cv Cradle Song) flowers lost 95% sugar and 65% dry weight over the first 24 h, with 30% of dry weight loss coming from nonsugar components. Detaching flowers did not delay senescence, but halted loss of carbohydrate and amino acid, suggesting that loss in the intact state was due to phloem export. Peta1 autolysis occurred mainly in the interveinal parenchyma, causing vascular strands to begin separating from the petal mass. Such vascular strands still stained with tetrazolium and accumulated sucrose, indicating a retained viability. Their sucrose accumulation rates were high in comparison with those of other plant tissues, and the accumulated product was mainly sucrose. Sucrose synthesis took place in the senescent petal, and sucrose was the principal sugar in phloem exudate, whereas hydroxyproline and glutamine were the main transport amino acids. ['4ClSucrose applied t o attached senescent flowers was rapidly translocated t o other parts of the plant, particularly developing flower buds. Thus, onset of phloem export allowed most of the soluble carbohydrate and amino acid in the senescing flower t o be retrieved by the plant. Additional salvaged material came from proteins and possibly from structural carbohydrate. Over a 12-h period, the flower switched from acting as a strong carbohydrate sink during expansion t o become a strong source during senescence. This rapid reversal offers potential for phloem transport studies.The daylily, Hemerocallis hybrid cv Cradle Song, has been useful for studying development and senescence processes in flowers. First, its ephemeral flower has been shown to have severa1 features of senescence common to other, slower-declining plant tissues . When the first physical signs of senescence begin to appear (wilting, then onset of autolysis in the petal tips, later extending over the whole petal), there is a small but well-defined respiration climacteric, an increase in apparent free space, an increase in efflux of sugars and ions, and a change in the phospholipid pattern. Rather surprisingly, the ability of petals to accumulate phosphate and to maintain phosphate ester synthesis (along with a high energy charge) survives well into senescence. Second, the daylily does not respond to ethylene nor to ethylene inhibitors in its senescence and produces only traces of ethylene, leading to the conclusion