Light energy dissipation in Quercus ilex resprouts after fire

Holm oak (Quercus ilex) plants that have resprouted after fire have higher photosynthetic capacity than control plants in intact vegetation. In this s tudy, branches detached from forest plants were fed with dithiothreitol (DT T) in the laboratory to inhibit zeaxanthin production and thus reduce the d issipation of light energy as heat. This allowed us to test the hypothesis that plants with greater photosynthetic capacity, and therefore greater pho tochemical sink strength, would suffer a lower reduction in photochemical e fficiency under stressful conditions. Greater rates of photochemistry in re sprouts, which exhibited increased photosynthesis (A), leaf conductance (g) , quantum yield of PSII (Delta F/F-m') and photochemical quenching (q(P)), were related to lower non-radiative dissipation of excess energy as indicat ed by 1 - (F-v'/F-m'). However, the fraction of energy remaining of that us ed in photochemistry or dissipated thermally in the PSII antennae was simil ar in resprouts and controls and was not affected by DTT, especially under high irradiance conditions. Zeaxanthin involvement in PSII protection opera ted in resprouts and controls since DTT induced the same kind of response ( NPQ decrease) but was lower in resprouts. These chlorophyll fluorescence re sults suggest the participation of some additional mechanism for energy dis sipation. Light capture characteristics of the photosynthetic apparatus did not differ between resprouts and controls, and leaf age did not play a det ermining role in the differences observed.