Physiological Events Associated with Petal Development and Senescence of Hibiscus syriacus L. 'Parangsae'

To characterize the physiological changes during the development and senescence of Korean hibiscus (Hibiscus syriacus L. 'Parangsae') flowers, chronological stages were determined and soluble sugar content, osmolality, respiration, ethylene production, and abscisic acid (ABA) content in petals were determined. An increase in cell sap osmolality from 351 mmol to 411 mmol at stage IV (fully open flower) in Korean hibiscus coincided with an increase in soluble sugar content by over 2-fold and fresh/dry weight ratio changed from 4.0 to 8.4. During subsequent senescence and collapse of the flower, there was a rapid loss of fresh and dry weights and a reduction in the fresh/dry weight ratio. Wilting was characterized as early senescence and maximum respiration rate was found in fully open flowers. Ethylene production remained extremely low until petals started to open and ethylene production, ACC synthase activity and ACC content increased as flower fresh weight started to decline. Petal fresh weight decreased while considerable increase was shown in ethylene production when flowers were wilted and rolled. Moreover, corolla diameter was reduced and ABA was increased prior to and during senescence. Pre-senescence petal tissue was characterized by an increase of soluble sugar, which may regulate turgidity, and a continuous increase of ABA, which may be a constituent of signal transduction leading to programmed cell death.