PLANT PHYSIOLOGY , Vol 103, Issue 1 213-219, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Fructan Hydrolysis Drives Petal Expansion in the Ephemeral Daylily Flower
R. L. Bieleski
The Horticulture and Food Research Institute of New Zealand Ltd., Mt. Albert Research Centre, Private Bag 92-169, Auckland, New Zealand
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 0) when
flower expansion was 60% complete. Petal dry weight increased linearly from
hour -62 (tight bud) to hour 10 (fully developed flower), then fell rapidly
to hour 34 as senescence advanced. Increase 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. The 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. The findings
suggest that onset of fructan hydrolysis, with the concomitant large
increase in osmoticum, is an important event driving flower expansion in
daylily.
