Photoinhibition in a C4 plant, Zea mays L.: a minireview

Light and oxygen are both essential to life but can also cause some damage to plant photosynthesis and productivity, particularly excess light in the presence of oxygen. This phenomenon is called photoinhibition, i.e. the photooxidative damage of photosystems due to excess light associated or not with abiotic stresses. To tolerate photoinhibition, the plant needs to be able to avoid or tolerate excess light or to repair the photodamage by maintaining the de novo D1 protein synthesis that is essential for PS II complex activity. When the electron transport of the photosystems is diminished because the use of final electron acceptors, ferredoxin or NADPH(2), via the Calvin cycle is reduced, electrons from water photolysis are captured by O-2 forming ROS, which inhibits protein synthesis, even in C-4 plants. To tolerate excess light or repair photodamage under photoinhibitory conditions, several mechanisms exist to reduce ROS and/or maintain ATP production and use for protein synthesis and growth: the scavenging systems (reducing ROS activity), such as the xanthophyll (thermal dissipation of excitation energy) and ascorbate cycle (associated with the Mehler reaction, in the water-water cycle) or the activity of antioxidants compounds, such as carotenoids; the maintenance of cyclic electron flow (only ATP production); and the photorespiration cycle (consuming reducing equivalents and ATP). Photoinhibition is a phenomenon that occurs in C-3 and C-4 plants, such as corn, under PPFD above 1,000 mu mol m(-2) s(-1), and photooxidative damage seems to be more accentuated in mesophyll chloroplasts than in bundle sheath agranal chloroplasts.