Visible light-induced oxidation of unsaturated components of cutins: a significant process during the senescence of higher plants

Visible light-induced oxidation of 18-hydroxyoleic acid (a cutin component) was observed in senescent leaves of parsley. The photoproducts thus formed were then detected in different natural samples. 9-Hydroperoxy-18-hydroxyoctadec-10( trans)-enoic and 10-hydroperoxy-18-hydroxyoctadec-8( trans)-enoic acids deriving from type II (i.e. involving 1O 2) photooxidation of 18-hydroxyoleic acid were detected after visible light-induced senescence experiments carried out with Petroselinum sativum and subsequent cutin depolymerisation. These results showed that in senescent plants, where the 1O 2 formation rate exceeds the quenching capacity of the photoprotective system, 1O 2 can migrate outside the chloroplasts and affect the unsaturated components of cutins. Significant amounts of 9,18-dihydroxyoctadec-10( trans)-enoic and 10,18-dihydroxyoctadec-8( trans)-enoic acids resulting from the reduction of these photoproducts of 18-hydroxyoleic acid were also detected in different natural samples. These results well support the significance of the photooxidation of the unsaturated components of higher plant cutins in the natural environment.