Carotenoids in photosynthesis: Protection of D1 degradation in the light

Abstract

Photosynthesis has been determined with mutants of Anacystis which form different amounts of carotenoids. With these cultures a highly significant correlation between photosynthetic oxygen evolution and the amounts of synthesized carotenoids was observed. In addition, the influence of carotenoids on light-dependent degradation of thylakoid proteins was investigated with Scenedesmus cultures grown in darkness in the presence of norflurazon, an inhibitor of carotenoid biosynthesis. Pre-illumination of cells resulted in decrease of photosynthetic activity accompanied by loss of the D1 protein. This effect is dependent on the length of illumination, and the light intensity, and increased when carotenoid content was lowered during previous growth of the norflurazon-treated cultures.

Radicals and Radical Pairs in Photosynthesis

“…When RC of PS I1 are exposed to light irradiation in the presence of exogenous electron acceptors, a condition that leads to P&;30 formation a biphasic bleaching of the two P-carotenes has been observed and attributed to photooxidation of these molecules by ET to P& (338,339). Strong effects of the presence of carotenoids on the protection of the DI protein against photoinhibition, reported by Sandmann et al (340), seem to support this view. Clearcut evidence of carotenoid radicals in PS I1 has not been reported by EPR.…”

Secondary ketocarotenoid astaxanthin biosynthesis in algae: a multifunctional response to stress

“…This mutant harbors a C-T point mutation in the pds gene, leading to the replacement of the leucine residue by a phenylalanine one in position 516. As this mutation confers a higher specific enzyme activity whereas the replacement by an arginine residue reduces this activity, Sandmann et al (1993) and Liu et al (2010) concluded that the leucine residue at the position 516 plays a decisive role in PQ binding. In the E17 mutant, the pds gene expression is not up-regulated while those of bkt and chy-b are enhanced (Lu et al 2010), probably to cope with the higher amount of intermediates produced.…”

Changes in the cyanobacterial photosynthetic apparatus during acclimation to macronutrient deprivation

“…Furthermore, many components of the photosynthetic apparatus, including Chl and certain electron carriers, can generate toxic oxygen species if they are unable to transfer their excitation energy or high potential electrons to stable molecules in an efficient manner (Krinsky 1979;Siefermann-Harms 1987;Salin 1988), as would likely be the case in nutrient-deprived cells (Demmig-Adams 1990;Demmig-Adams and Adams 1992). Decreasing the level of Chl and functional PS II in nutrientdeprived cells would result in reduced generation of these toxic species (Salin 1988;Young 1991;Sandmann et al 1993). While excitation of PS I could also result in the generation of toxic oxygen species, the hazards of maintaining an active PS I in nutrientdeprived cells would probably be minimal since there would be reduced electron flow into PS I from PS II, and some potential to shunt excess electrons from PS I into the respiratory electron transport chain.…”