Effects of low temperaturestressonexcitation energy partitioning and photoprotection in Zea mays

Analysis of thepartitioning of absorbed light energy within PSII into fractions utilised by PSIIphotochemistry (FPSII), thermally dissipated via DpH- and zeaxanthin-dependent energy quenching (FNPQ) and constitutive non-photochemical energy losses (Ff,D) was performed in control and cold-stressed maize (Zea mays L.) leaves. The estimated energy partitioning of absorbed light to various pathways indicated that the fraction of FPSII was twofold lower, whereastheproportionofthermallydissipatedenergythrough FNPQwasonly30%higher,incold-stressedplantscompared withcontrolplants.Incontrast, Ff,D,thefractionofabsorbedlightenergydissipatedbyadditionalquenchingmechanism(s), was twofold higher in cold-stressed leaves. Thermoluminescence measurements revealed that the changes in energy partitioning were accompanied by narrowing of the temperature gap (DTM) between S2/3QBand S2QAcharge recombinations in cold-stressed leaves to 8 � C compared with 14.4 � C in control maize plants. These observations suggest an increased probability for an alternative non-radiative P680 + QAradical pair recombination pathway for energy dissipation within the reaction centre of PSII in cold-stressed maize plants. This additional quenching mechanism might play an important role in thermal energy dissipation and photoprotection when the capacity for the primary, photochemical (FPSII) and zeaxanthin-dependent non-photochemical quenching (FNPQ) pathways are thermodynamically restricted in maize leaves exposed to cold temperatures.