The Effects Of Exogenous H₂O₂ And AsA On Hyperhydricity And The Characteristics Of Endogenous Reactive Oxygen Species Metabolism Of The Garlic Plantlet In Vitro

Garlic (Allium sativum L.) is an important edible and medicinal plant grown worldwide. Virus-free and rapid propagation is an efficient means in purification and rejuvenation during the production of garlic. But the existence of hyperhydricity in garlic tissue culture is a major problem; therefore the study of hyperhydricity was of great theoretic significance and application value. Previous research showed that there are oxidative stress at different degree in hyperhydricity during in vitro culture, the O2·-generation rate and H2O2 level were significantly higher than that of the normal shoots, the function of protective enzymes of hyperhydric shoots was abnormal and the hyperhydric shoots were stressed and destroyed by oxygen free radicals more heavily than normal shoots, which revealed that hyperhydricity is closely connected with reactivated oxygen species metabolism.In order to clarify the mechanism of garlic hyperhydricity induced by reactive oxygen species and provide theoretical basis for control the hyperhydricity, in this experiment, using the garlic variety'Ershuizao'as test materials, the effects of hyperhydricity and reactive oxygen species metabolism under exogenous H2O2 stress and the occurrence and location of endogenous reactive oxygen species and the effects of hyperhydricity and reactive oxygen species metabolism of the garlic plantlet in vitro under exogenous H2O2 stress, exogenous 'H2O2+AsA' treatment and normal culture conditions were studied. The main results are as follows:1. Exogenous H2O2 influenced the normal growth of plantlet and 2.0 mmol·L-1 H2O2 stress significantly enhanced the hyperhydricity of the garlic plantlet in vitro. The activity of SOD, POD, CAT and APX increased at first and then decreased, the MDA levels and the rate of elect rolyte leakage was increased under oxidative stress during the culture. The result indicated that the oxygen free radicals can induce the occurrence of hyperhydricity and the lipid peroxidation may be one of the induction factors of hyperhydricity.2. The histochemical localization of O2·- and H2O2 demonstrated that endogenous reactive oxygen species accumulated mainly in leaves and pesudostem under different treatments. Cytochemical staining showed that H2O2 accumulation was observed mostly in cell walls and intercellular space nearby chloroplast. The studies preliminarily confirmed that exogenous H2O2 stress enhanced the production of endogenous O2·- and H2O2 of the garlic plantlet in vitro effectively and application of exogenous AsA significantly decreased the accumulation of reactive oxygen species induced by H2O2 stress.3. The results showed that application of exogenous AsA increased the activity of protective enzymes and the contents of antioxidant substances, and decreased the level of lipid peroxidation and the accumulation of reactive oxygen species of the garlic plantlet in vitro under exogenous H2O2 stress,. There was certain alleviate effects of exogenous AsA on the damage of reactive oxygen species induced by H2O2 stress of the the garlic plantlet in vitro, thereby reduce the hyperhydricity plantlet rates significantly.