Discerning the effects of photoinhibition and photoprotection on the rate of oxygen evolution in Arabidopsis leaves

Higher plants possess a set of interconnected processes to regulate light harvesting. Non-photochemical quenching of chlorophyll a fluorescence (NPQ) is the fastest process activated to protect the photosystem (PS) II from the absorption of excess light energy. However, damage of PSII reaction centers (RCIls) is often inevitable, a phenomenon known as photoinhibition. Both NPQand photoinhibition undermine PSII quantum yield (Phi(PSII)). Recently, we devised a fluorescence-based methodology that uses the coefficient of photochemical quenching measured in the dark following illumination (qPd) to assess the intactness of RCIls. This procedure enables to express Phi(PSII) as a function (f) of NPQand qPd, Phi(PSII) = f(NPQqPd), thus allowing to efficiently discern between the effects of protective NPQ and photoinhibition upon the efficiency of electron transport. In this study, we addressed the relationship between qPd and Phi(PSII) measured by photosynthetic oxygen evolution in intact leaves of Arabidopsis. We found a linear correlation between qPd and Phi(PSII) of oxygen evolution (as well as Fv/Fm). This relates to the fact that qPd reflects the onset of photoinhibition. These results further demonstrate the validity of the qPd parameter and underlying theory in quantitatively assessing PSII efficiency solely by using this effective and simple fluorescence technique. (C) 2015 Elsevier B.V. All rights reserved.