Variability in the response to ethylene of cut flowers of three Vanda orchid cultivars

Ethylene plays an important role in the senescence of most cut flowers - including members of the family Orchidaceae - but sensitivity to ethylene varies among species and cultivars. Therefore, we compared ethylene sensitivity in cut flowers of three Vanda orchid cultivars: 'Pure Wax', 'Pachara Delight', and 'Sansai Blue'. The flowers were exposed to air (control), 10 mu L L-1 ethylene for 24 h, or 0.2 mu L L-1 1-methylcyclopropene (1-MCP; an ethylene inhibitor) for 6 h. Ethylene reduced the vase lives of all three cultivars by approximately 50%, and 1-MCP extended their vase lives, but each cultivar had a different response to ethylene regarding pigmentation. The anthocyanin content of 'Pure Wax' was almost unaffected by ethylene, except at the bud stage, whereas in 'Pachara Delight' it was partially reduced after 2 days, mainly in the full bloom stage. The anthocyanin content of 'Sansai Blue' was completely reduced during this period after exposure to only 1 mu L L-1 ethylene. The ethylene-treated 'Pure Wax' and 'Pachara Delight' flowers exhibited increased wilting and sleepiness compared to the control flowers. In contrast, the ethylene-treated 'Sansai Blue' flowers immediately discoloured, and the faded flowers did not wilt during the subsequent 7 days. Anthocyanin breakdown in 'Sansai Blue' was related to its comparatively high sensitivity to ethylene. Examination of changes in other quality parameters of the 'Sansai Blue' flowers over 2 days following ethylene treatment revealed that ethylene significantly reduced their fresh weight, but not their water uptake rate, ion leakage, and amino acid and protein contents. However, as expected, the rates of ethylene evolution and respiration increased slightly in response to ethylene treatment. All three cultivars are sensitive to exogenous ethylene, but their ethylene-induced colour-fading responses differ. In cut 'Sansai Blue' flowers, ethylene first promotes petal anthocyanin degradation, then other typical senescence-related processes.