Photosynthesis

About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.

Globally Distributed Uncultivated Oceanic N2-Fixing Cyanobacteria Lack Oxygenic Photosystem II

Abstract: Biological nitrogen (N2) fixation is important in controlling biological productivity and carbon flux in the oceans Unicellular N2-fixing cyanobacteria have only recently been discovered and are widely distributed in tropical and subtropical seas Metagenomic analysis of flow cytometry-sorted cells shows that unicellular N2-fixing cyanobacteria in "group A" (UCYN-A) lack genes for the oxygen-evolving photosystem II and for carbon fixation, which has implications for oceanic carbon and nitrogen cycling and raises questions regarding the evolution of photosynthesis and N2 fixation on Earth

Interaction of cadmium with glutathione and photosynthesis in developing leaves and chloroplasts of Phragmites australis (Cav.) Trin. ex Steudel.

Abstract: We investigated how the presence of cadmium (Cd) at the emergence of Phragmites australis Trin. (Cav.) ex Steudel plants from rhizomes interacted with leaf and chloroplast physiological and biochemical processes. About 8.5 nmol Cd mg 1 chlorophyll was found in leaves, and 0.83 nmol Cd mg 1 chlorophyll was found in chloroplasts of plants treated with 50 m Cd. As a result, a 30% loss of chlorophyll was measured concomitantly with a comparable percentage reduction in light-saturated photosynthesis. Rubisco content and activity were lowered by 10% and 60%, respectively. Antioxidant activity was stimulated by Cd treatment and was associated with an increase in the glutathione and pyridine pools, and with a larger pool of reduced glutathione. It is suggested that the glutathione pool and its predominance in the reduced state protected the activity of many key photosynthetic enzymes against the thiophilic binding of Cd. Chloroplast ultrastructure was not significantly altered with 50 m treatment and the efficiency of photosystem II, measured as the fluorescence ratio Fv/Fm, remained high because F0 and Fm were proportionally decreased. In plants treated with 100 m Cd, all effects were exacerbated, but Fv/Fm remained close to that of control leaves and the glutathione and pyridine nucleotides pools were lowered. The results suggest that glutathione exerted a direct important protective role on photosynthesis in the presence of Cd. Most plants respond to cadmium (Cd) present in the root environment: the metal ion is absorbed on cortical cell walls or it is channeled into roots, where it is then subsumed into the closest vacuoles or loaded into the xylem for transport into leaves