Reactive species and antioxidants. Redox biology is a fundamental theme of aerobic life.

The field of antioxidants and free radicals is often perceived as focusing around the use of antioxidant supplements to prevent human disease. In fact, antioxidants/free radicals permeate the whole of life, creating the field of redox biology. Free radicals are not all bad, nor antioxidants all good. Life is a balance between the two: Antioxidants serve to keep down the levels of free radicals, permitting them to perform useful biological functions without too much damage (Halliwell and Gutteridge, 2006). This is especially true in plants, as the rest of this issue reveals. Yet some damage is inevitable, requiring repair systems to maintain cell viability. The purpose of this article is to take a broad view of the field, and highlight some of the fascinating differences between plants and other organisms.