Effects of Trehalose and Sucrose on the Vase Life and Physiology of Cut Astilbe (Astilbe x arendsii Arends) Flowers

The postharvest physiology of cut astilbe inflorescences (Astilbe x arendsii), which consist of many small florets with a short vase life, was studied in response to treatments to extend their vase life. Exogenous ethylene treatment at 0.3 mu L.L-1 for 7 h did not affect the senescence of inflorescences or leaves of five cultivars and 0.2 mM silver thiosulfate for 2 h did not improve the quality of inflorescences of three cultivars, which indicated that ethylene is not a critical factor for senescence in astilbe florets. Continuous treatment with 2% sucrose or 2% trehalose solutions prolonged the cut inflorescence vase life of one or two of five astilbe cultivars, respectively. Pulse treatment with 2% trehalose in combination with 6% sucrose increased total soluble sugar contents from 11.4 to 57.6 mg.g(-1) FW and raised the respiration rate of inflorescences from 15.3 to 28.4 mu mol CO2.h(-1).g(-1) FW at 2 days after harvest (DAH) in the cultivar 'Gloria Purpurea'. However, the effects of pulse treatment diminished at 4 DAH and extended the vase life from 4.0 days to a maximum of 5.6 days, which suggested that pulse treatments were inadequate to maintain sugar contents and respiration activity. Continuous treatment with 6% sucrose extended the vase life from 4.3 to 10.0 days and raised the chroma (C*) value of florets from 28.7 to 54.9 at 8 DAH. Continuous treatment with 2% trehalase + 4% sucrose markedly prolonged the vase life to 11.5 days and increased the C* value to 53.9 at 8 DAH. Under stereomicroscopic observation, continuous treatment with 2% trehalase + 4% sucrose maintained more vivid pink color of petals, styles, filaments and receptacles than those in control florets at 9 DAH. Combined treatment with 2% trehalose and 30 AM validamycin A, a potent inhibitor of trehalose metabolizing activity, induced severe wilting of florets and necrotic spots on leaves. Exogenous trehalose may be hydrolyzed by trehalose metabolizing activity in cut astilbe inflorescences. The results suggest that continuous treatment with trehalose and sucrose solutions is effective to maintain development and delay senescence of florets to extend the vase life of cut astilbe inflorescences.