LIGHT FROM DIFFERENT WAVELENGTHS AFFECTS EXPRESSION OF GENES ENCODING PHOSPHOLIPASES A₂ AND D IN PEEL FROM MANDARINS AT DIFFERENT MATURATION STAGES DURING POSTHARVEST STORAGE

Previous studies showed that blue light reduced fungal colonization by Penicillium digitatum in mature tangerines and activated CssPLA₂α gene expression, whereas inhibition of PLA₂ enzymatic activity allowed infection to progress. Red light, an inhibitor of PLD, promoted infection as well. These data strongly suggested i) involvement of lipid-derived signals on citrus fruit immunity against postharvest pathogens and ii) activation of lipid signalling by light. In this work we explored the potential of LED-light treatments to manipulate lipid signal production in tangerines. We selected two different maturation stages: mature-green and full mature fruit. Fruit were maintained for 3 days in chambers equipped with LEDs emitting from 600-780 nm (red/far red), 580-670 nm (red), 470-620 nm (green) and 410-540 nm (blue) wavelengths, and 40 μmol m^-2 s^-1 of intensity before inoculation with a suspension of Penicillium digitatum spores and then stored for 6 days in the same conditions to follow infection development. The expression of CssPLA₂αα, CssPLA₂β, CsPLD α and CsPLDγ, was studied by quantitative real time PCR. Our results show that blue and green light reduced fungal growth in the fruit surface more effectively in mature-green than in full mature fruit whereas red light treatment promoted decay irrespective of the maturation stage. Gene expression was differentially affected by light, showing a complex regulation.