Specific features of the ascorbate/glutathione cycle in cultured protoplasts

Protoplasts: isolated from Nicotiana ln tabacum ( L.) leaves were cultured for 6 days in liquid medium and some features of their antioxidant capacity were investigated. Ascorbate exported into the culture medium was oxidized non-enzymically, whereas important modifications of the enzymic scavenging activity were detected inside protoplasts. A new pool of isoenzymes, most of them with cytoplasmic characteristics, ensures the increased ascorbate p eroxidase activity. The specific activity of other enzymes involved in the ascorbate/glutathione cycle, such as dehydroascorbate reductase and glutath ione reductase, and of glutathione peroxidase were modified, resulting in c ultured protoplasts with quantitative differences in antioxidant capacity c ompared to leaves. The hypothesis presented here suggests that the new scav enging system is related to differences in the compartment-specific accumul ation of active oxygen species following protoplast isolation.