FRUCTAN HYDROLYSIS DRIVES PETAL EXPANSION IN THE EPHEMERAL DAYLILY FLOWER

Dry weight, water content, soluble carbohydrate content, and carbohydr ate composition of daylily (Hemerocallis hybrid cv Cradle Song) flower petals were monitored in the 3 d leading up to full opening and in th e first day of senescence. Timing of events was related to the time (h our 0) when flower expansion was 60% complete. Petal dry weight increa sed linearly from hour -62 (tight bud) to hour 10 (fully developed flo wer), then fell rapidly to hour 34 as senescence advanced. Increase in water content was proportional to dry weight increase from hour -62 t o hour -14, but was more rapid as the bud cracked and the flower opene d, giving an increase in fresh weight/dry weight ratio. Soluble carboh ydrate was 50% of petal dry weight up to hour 10, then decreased durin g senescence to reach 4% by hour 34. Up until hour -14, fructan accoun ted for 80% of the soluble carbohydrate in the petals, whereas hexose accounted for only 2%. Fructan hydrolysis started just prior to bud cr ack at hour -14, reaching completion by hour 10 when no detectable fru ctan remained, and fructose plus glucose accounted for more than 80% o f the total soluble carbohydrate. The proportion of sucrose remained c onstant 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 h alted both fructan hydrolysis and flower expansion. The findings sugge st that onset of fructan hydrolysis, with the concomitant large increa se in osmoticum, is an important event driving flower expansion in day lily.