Abstract
We studied how different color lights cause gradients of photoinhibition within a leaf, to help settle the controversy whether photon absorption by Chl or Mn is the primary cause of photoinhibition, suggested by the Excessenergy- or the Mn-hypothesis, respectively.
Lincomycin treated leaf discs were photoinhibited. A combination of a microfiber fluorometer, a fiber thinning technique and a micromanipulator enabled us to measure the Chl fluorescence signals within a leaf. Photoinhibition gradients were also compared with results of various conventional fluorometers.
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 is correlated with the Chl and Mn absorption spectrum, respectively. These results cannot be explained by either hypothesis alone.
These data suggest that both the Excessenergy- and the Mn-mechanisms occur in photoinhibition, and fluorometers with red or blue measuring light give overestimated or underestimated Fv/Fm values of photoinhibited leaves, respectively; they measured deeper or shallower leaf tissue, respectively.
