Intra‐leaf gradients of photoinhibition induced by different color lights: implications for the dual mechanisms of photoinhibition and for the application of conventional chlorophyll fluorometers

Abstract

Summary• We studied how different color lights cause gradients of photoinhibition within a leaf, to attempt to resolve the controversy of whether photon absorption by chlorophyll or by manganese (Mn) is the primary cause of photoinhibition, as suggested by the excess-energy hypothesis or the two-step hypothesis, respectively.• Lincomycin-treated leaf discs were photoinhibited by white, blue, green or red light. Combining a microfiber fluorometer, a fiber-thinning technique and a micromanipulator enabled us to measure the chlorophyll fluorescence signals within a leaf. Photoinhibition gradients were also compared with results from various conventional fluorometers to estimate their depth of signal detection.• The severity of photoinhibition was in the descending order of blue, red and green light near the adaxial surface, and in the descending order of blue, green and red light in the deeper tissue, which correlated with the chlorophyll and the Mn absorption spectrums, respectively. These results cannot be explained by either hypothesis alone.• These data strongly suggest that both the excess-energy and the two-step mechanisms occur in photoinhibition, and fluorometers with red or blue measuring light give overestimated or underestimated F v ⁄F m values of photoinhibited leaves compared with the whole tissue average, respectively; that is, they measured deeper or shallower leaf tissue, respectively.

Non-intrusive Assessment of Photosystem II and Photosystem I in Whole Coral Tissues

“…The fact that acute heat stress caused remarkable changes in P700 kinetics, the steady-state level of P700 + and the P700 kinetics area suggests that electron flow from PSII has a strong impact on the redox state of P700 + , similarly to the situation in higher plants (Oguchi et al, 2011;Jia et al, 2014). This is corroborated with the observations that the P700 kinetics area completely disappeared in the presence of DCMU (Figure 3) and the steady state P700 + increased, as the linear electron flow from PSII reducing P700 + has completely stopped.…”

Excess Diffuse Light Absorption in Upper Mesophyll Limits CO2 Drawdown and Depresses Photosynthesis

“…8). Instead, we best predicted the sun-grown leaf's light response curve by assuming that f PSII increased linearly from 0.5 at the adaxial surface to 0.85 at the abaxial surface (similar to the observations of Oguchi et al [2011]). The shade-grown leaf predictions, on the other hand, best matched the observed data by assuming a constant f PSII of 0.5 throughout the leaf.…”

Photoinactivation of Photosystem II in wild-type and chlorophyll b-less barley leaves: which mechanism dominates depends on experimental circumstances

“…PS II complexes at shallow depths are more susceptible to photoinactivation of PS II than in deeper tissue (Oguchi et al 2011b). The mutant leaves, with no light-harvesting complex II (LHCII), contained less than half as much Chl per unit leaf area as the wild type (e.g., Leverenz et al 1992).…”