In order to determine the role of alginate-derived oligosaccharides (ADO) in drought stress resistance of tomato (Ly-copersicon esculentum Miller) seedlings, the leaves were exposed to different concentrations of ADO (0.05%, 0.10%, 0.20%, 0.30% and 0.50%) after drought stress was simulated by exposing the roots to 0.6 molL-1 PEG-6000 solution for 6 h. Changes in biomass, electrolyte leakage and malondialdehyde (MDA), free proline, total soluble sugars (TSS) and abscisic acid (ABA), the enzyme activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and phenylalanine ammonia-lyase (PAL) were measured to investigate the effects of ADO treatment. The results showed that the treatment with an ADO concentration of 0.20% exhibited the highest performance of drought stress resistance in the tomato seedlings by decreasing the electrolyte leakage and the concentration of MDA, increasing the contents of free proline, TSS and ABA, and increasing the activities of CAT, SOD, POD and PAL after treatment with ADO. It is suggested that changes in electrolyte leakage, MDA, osmotic solutes, ABA, anti-oxidative enzyme and PAL activities were responsible for the increased drought stress resistance in tomato seedlings. To our best knowledge, this is the first report of the effect of ADO treatment on enhancing the drought stress resistance of tomato seedlings.
LIU RuizhiJIANG XiaoluGUAN HuashiLI XiaoxiaDU YishuaiWANG PengMOU Haijin
Bacteriophages infected different serotypes of Klebsiella were isolated from sewage. Among them, a heatstable polysaccharide depolymerase enzyme which could degrade bacterial exopolysaccharide effectively was prepared from the phage infecting Klebsiella K13. Treatment at 60℃ for 30 min could inactivate most of the K13 phage, with the titration decreasing from 6.4×10^8 PFU/mL to 1.6×10^6 PFU/mL. However, no obvious loss of phage enzyme activity was found after this treatment. The optimum hydrolytic temperature of phage enzyme was 60℃, with an activity 57 % higher than that at 30℃. The addition of phage enzyme could result in a rapid decrease of viscosity of exopolysaccharide （EPS） solution within minutes, indicating that K13 phage polysaccharide depolymerase acts as a kind of endo-glycanohydrolase. HPLC and reducing sugar analysis showed that the hydrolysis of EPS approached approximately the maxi-mum at 4h when the final concentration of phage was 6.0 x los PFU/mL. The results showed that K/eb-siella K13 phage depolymerase enzyme could be used as a good tool for the preparation of EPS oligosac- charide.
