Photoinhibition of Photosystem I: Its Physiological Significance in the Chilling Sensitivity of Plants

Photoinhibition was defined originally as the decrease in photosynthetic activity that occurs upon excess illumination. The site of photoinhibition has generally been considered to be located in PSII. However, a novel type of photoinhibition has recently been characterized in chillingsensitive plants. This photoinhibition occurs under relatively weak illumination at chilling temperatures and the main site of damage is in PSI. The photoinhibition of PSI is initiated by the inactivation of the acceptor side, with the subsequent destruction of the reaction center and the degradation of the product of the psaB gene, which is one of the two major subunit polypeptides of the PSI reaction center complex. Chilling and oxidative stress (the presence of reactive species of oxygen) are characteristic requirements for the photoinhibition of PSI in vivo.