Photoprotection and photoinactivation of Photosystem II

Light is both necessary for photosynthesis and harmful to the photosynthetic apparatus. This project investigates the photoprotection and photoinactivation of Photosystem II, and recovery from photoinactivation.

Light, as the energy source for photosynthesis, is essential for plant life. During normal photosynthesis, however, there is a small but significant probability of Photosystem (PS) II complexes being damaged by light, leading to a loss of ability to evolve oxygen. This damage arises partly because, in order to split water molecules, it is necessary to generate by the use of light energy strong oxidants, which may inadvertently damage PS II. Upon photodamage, PS II is less fluorescent, and non-uniform damage across a leaf can give a fluorescence image of reasonable resolution. Recovery from photoinactivation of PS II requires new synthesis of the D1 protein in the PS II reaction centre. Under sunny conditions, the entire population of D1 protein is renewed approximately once a day. Given the continual damage to PS II which occurs during normal photosynthesis and which is exacerbated under environmental stress, plants have evolved a number of photoprotective strategies to minimize photoinactivation of PS II. One of these strategies is the inactive-photosystem II mediated quenching of excitation energy, a kind of last-ditch defence mechanism. Research is directed at understanding the mechanisms of photoprotection and photoinactivation of PS II, using biochemical, biophysical and physiological techniques.