| Based on the characteristics of Cut rose (Rosa hybrida) in losing water from the cut flowers easily, and its weak tolerance to water deficit stress, 'Samantha'(Bridal Pink x Seedling), a stronger cultivar of tolerance chosen from 20 commercial cultivars tested, was used to investigate the role of superoxide dismutases (SODs) in protecting flowers under water deficit stress. Malondialdehyde (MDA) content, the specific activity and isoenzymes of SOD in the petals were determined when the flowers were subjected to 12~48h water deficit stress and 12h DDTC pretreatment under controlled conditions, relative humidity of 35%~40%,12h light:12h dark cycle with photosynthetic photon flux density of 80 uEm-2s-1,and 20C. The results showed as bellow:1. Opening process was delayed and flower senescence was promoted by water deficit stress. SOD specific activity and MDA content in the petals were increased sharply when exposed to water deficitstress.2. Compared with direct water deficit stress, 20mM DDTC pretreatment promoted dramatically senescence process, shortened vase life, increased bentneck rate, and decreased rewater rate significantly. It also increased obviously flowers mass loss, decreased flower water potentials, and increased MDA content.3. It was observed by SODs zymograms that there were three FeSOD isoforms, two Cu/ZnSOD isoforms and one MnSOD isoform in the control petals. By water deficit stress, three new FeSOD(FeSOD4, FeSOD5 and FeSOD6) and one Cu/ZnSOD isoenzymes in the petals were induced, and MnSOD was inhibited.4. Cu/ZnSOD and MnSOD bands disappeared, but FeSOD2 and SOD3 bands remained weakly in the petals of 20mM DDTC pretreatment when compared with control. However, the newly induced bands by water deficit stress above was not observed in the petals of DDTC pretreatment followed by water deficit stress.These results above suggested that tolerance to water deficit stress might be related to the increase of SOD activity in cut rose 'Samantha'.
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