[Effects of water and light interaction on reactive oxygen metabolism in ginger leaves]

To explore the relationship between water supply in roots, light intensity on leaves and reactive oxygen metabolism, the effects of various treatments including natural light plus normal watering (T1), 50% shading plus normal watering (T2), natural light plus PEG-6000 simulated drought (T3), 50% shading plus simulated drought (T4) on reactive oxygen level and antioxidant enzyme activity in ginger leaves were studied. The results showed that, 6 days after treatment, the O2* production rate and H2O2 and MDA contents remarkably increased in ginger leaves at midday. Treatment T3 showed the greatest increment, followed by T4, T1 and T2 in order. In addition, the activities of SOD and POD in all treatments and CAT in T3 and T4 noticeably decreased, while CAT in T1 and T2 exhibited a high activity at midday. Throughout the whole treatment, reactive oxygen level and antioxidant enzyme activities of ginger leaves in T1 and T2 remained stable, with a higher activity in T1 than in T2. However, the reactive oxygen level kept increasing in leaves exposed to treatments T3 and T4. Meanwhile, the activities of antioxidant enzymes increased firstly and then decreased. Taken together, this study demonstrated that drought stress, especially drought plus light stress, led to an increased accumulation of reactive oxygen in ginger leaves, while shading was conducive to maintaining high activity of protective enzymes, and therefore to reducing reactive oxygen level and alleviate drought-induced injury.