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 CssPLA(2)alpha gene expression, whereas inhibition of PLA(2) 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 mu mol 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 CssPLA2 alpha, CssPLA(2)beta, CsPLD alpha and CsPLD gamma, 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.