Visible light-dependent degradation of long-chain alkenes in killed cells of Emiliania huxleyi and Nannochloropsis salina

Photo- and Free Radical-Mediated Oxidation of Lipid Components During the Senescence of Phototrophic Organisms

“…In contrast, di-, tri-, and tetraenes were strongly photodegraded during irradiation. The visible light-dependent degradation of phytoplanktonic n-alkenes showed apparent second-order kinetics with respect to light exposure and the half-life doses obtained logically decrease with increasing number of double bonds in these compounds (Mouzdahir et al, 2001). …”

“…Though potentially selective, photochemical degradation of alkenones is not fast enough in killed cells of E. huxleyi to induce strong modifications of the 37 K U  ratio before the photodestruction of the photosensitizing substances (Rontani et al, 1997b;Mouzdahir et al, 2001). UVR also appeared to be inefficient to alter the 37 K U  ratio (Christodoulou et al, 2010).…”

“…Visible light-induced photodegradation of these compounds was thus previously investigated in order to determine if photochemical processes could appreciably modify 37 K U  ratios during algal senescence (Rontani et al, 1997b;Mouzdahir et al, 2001;Christodoulou et al, 2010). Though potentially selective, photochemical degradation of alkenones is not fast enough in killed cells of E. huxleyi to induce strong modifications of the 37 K U  ratio before the photodestruction of the photosensitizing substances (Rontani et al, 1997b;Mouzdahir et al, 2001).…”

“…This may explain the difference of photoreactivity observed between the alkenones and fatty acids with the same number of unsaturations. We also previously attributed the poor photoreactivity of alkenones to a localisation of these compounds elsewhere than in cell membranes (Rontani et al, 1997b;Mouzdahir et al, 2001), which could significantly decrease the likelihood of interaction between singlet oxygen and alkenones. Although this hypothesis is well supported by the recent results of Eltgroth et al (2005), who demonstrated that alkenones are mainly localized into cytoplasmic vesicles, the migration of singlet oxygen from phytodetritus to attached heterotrophic bacteria previously observed (Rontani et al, 2003a;Christodoulou et al, 2010) strongly suggests a diffusion of this excited form of oxygen also in these cytoplasmic vesicles.…”

“…The visible light-induced degradation of n-alkenes was previously investigated in killed cells of the Prymnesiophycea E. huxleyi and the Eustigmatophycea Nannochloropsis salina (Mouzdahir et al, 2001).…”