The Relationship Between Superoxide Dismutase (SOD), Ascorbate Peroxidase (APX) And Tolerance To Water Deficit Stress In Cut Rose 'Samantha'

It has been reported that tolerance of plants to environmental stresses is closely related to regulation of anti-oxidant system in plants themselves. This experiment was aimed to investigate the relationship between key enzymes in anti-oxidant system, superoxide dismutase (SOD) and ascorbate peroxidase , (APX) and tolerance to water deficit stress in cut roses (Rosa hybrida). Flowers of 'Samantha' were pretreated with enhancement reagent or/and inhibitors of the two key enzymes for 12 h, water deficit stressed for different period, and vased for later observation. The result showed:1. Compared with non-stressed control flowers, water deficit stress increased significantly bent neck rate, reduced water recovery rate, inhibited flower opening process and shortened vase life of flowers. Water deficit stress treatment increased obviously SOD activity, MDA content and relative electric conductivity and decreased markedly APX activity and ascorbate acid (AsA) content.2. SOD activity in petals was remarkably inhibited by 20 mM DDTC pretreatment, and flower tolerance to water deficit was obviously decreased, which was evidenced by the obvious increase of bent neck rate, the significant decrease of water recovery rate and flower water potential and the dramatic reduction of vase life.Three types of SOD were observed in the petals of control in the earlier stages of flower opening, and there were three FeSOD isoforms, two Cu-ZnSOD isoforms and one MnSOD isoform, respectively. The turn of mobility was Cu-ZnSOD>FeSOD>MnSOD; and bands activity was FeSOD>Cu-ZnSOD>MnSOD. By water deficit stress, three new bands, named FeSOD4-6, were induced and MnSOD disappeared simultaneously. However, the newly induced bands by water deficit stress above were inhibited by DDTC pretreatment.3. Compared with Stress control, pretreatment with 1000 mg/L AsA, a substrate of APX, increased effectively water recovery rate of flowers, extended vase life and improved flower opening process. The pretreatment also enhanced effectively APX activity and AsA content in petals, but decreased relative electric conductivity. As our expectation, pretreatment with 500 mg/L β-aminophenol, a suicide inhibitor of APX, acquired contrary results.4. APX activity in petals of water deficit stressed flowers was effectively regulated by 5 mM AsA and 6 mM β-aminophenol. Compared with Stress control, vase life was extended, flower opening process and water relation was alleviated, MDA content was decreased and SOD activity was increased in flowers in which APX activity was increased. Ideal counterevidence was obtained in flowers in which APX activity was inhibited.5. A cDNA fragment of 569 bp was isolated from petals of cut rose 'Samantha' using degenerated primers, and it was inferred from amino acid sequence analysis that Rh-APXI cloned belonged to cytosolic APX gene family. It was shown by Northern analysis that expression changing patterns of Rh-APXI were almost identical with those of APX activity, suggesting that APX activity was possiblyregulated at transcriptional level.