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 peroxidase activity. The specific activity of other enzymes involved in the ascorbate/glutathione cycle, such as dehydroascorbate reductase and glutathione reductase, and of glutathione peroxidase were modified, resulting in cultured protoplasts with quantitative differences in antioxidant capacity compared to leaves. The hypothesis presented here suggests that the new scavenging system is related to differences in the compartment-specific accumulation of active oxygen species following protoplast isolation.