Chilling damage to photosynthesis in young zea mays: II. Photochemical function of thylakoids in vivo

Leaves of Zea mays L. cv. LG11 were chilled for 6 h at 5 °C in a high photon flux density. On return to 20 °C, the leaves showed a 45% decrease in the apparent quantum yield of photosynthetic oxygen evolution. The effects of this chill-treatment on the chlorophyll fluorescence induction kinetics of the leaves indicated a 20-25% decrease in the primary photochemical quantum yield of photosystem II. The fluorescence emission spectra of these leaves demonstrated a marked modification in the distribution of excitation energy within the photochemical apparatus of the thylakoid membranes, such that photosystem I was excessively favoured with respect to photosystem II. These chill-induced changes would result in an enhancement of cyclic over non-cyclic electron transport and account for a decrease in the apparent quantum yield of photosynthetic oxygen evolution.