Elevation Vadimezan of CO2 concentration increased the
value of K1/2(Ci) (the half-saturation constant) for photosynthesis, whereas high N supply lowered it. Neither short-term nor long-term CO2 enrichment had inhibitory effects on respiration rate, irrespective of the N supply, under which the algae were grown. Under high-N growth, the Q10 value of respiration was higher in the elevated-CO2-grown algae than the ambient-CO2-grown algae. Either short- or long-term exposure to CO2 enrichment decreased respiration as a proportion of gross photosynthesis (Pg) in low-N-grown H. fusiformis. It was proposed that in a future world of higher atmospheric CO2 concentration and simultaneous coastal eutrophication, the respiratory carbon flux would be more sensitive to changing temperature. “
“This study assessed the implication of oxidative stress in the mortality of cells of Microcystis aeruginosa Kütz. Cultures grown at 25°C were exposed to 32°C, darkness, and hydrogen peroxide (0.5 mM) for 96 h. The cellular abundance, chl a concentration and content, maximum photochemical RAD001 efficiency of PSII (Fv/Fm ratio), intracellular oxidative stress (determined with dihydrorhodamine 123 [DHR]), cell mortality (revealed by SYTOX-labeling of DNA), and activation of caspase 3–like proteins were assessed every 24 h. The presence of DNA degradation in cells of M. aeruginosa was also assessed using
a terminal deoxynucletidyl transferase-mediated dUTP nick end labeling (TUNEL) assay at 96 h. Transferring cultures from 25°C to 32°C was generally beneficial to the cells. The cellular abundance and chl a concentration increased, and the mortality remained low (except for a transient burst at 72 h) as did the oxidative stress. In darkness, cells did
not divide, and the Fv/Fm continuously decreased with time. The slow increase in intracellular oxidative stress Thalidomide coincided with the activation of caspase 3–like proteins and a 15% and 17% increase in mortality and TUNEL-positive cells, respectively. Exposure to hydrogen peroxide had the most detrimental effect on cells as growth ceased and the Fv/Fm declined to near zero in less than 24 h. The 2-fold increase in oxidative stress matched the activation of caspase 3–like proteins and a 40% and 37% increase in mortality and TUNEL-positive cells, respectively. These results demonstrate the implication of oxidative stress in the stress response and mortality of M. aeruginosa. “
“The genus Mallomonas, a common and often abundant member of the planktic community in many freshwater habitats worldwide, consists of 180 species divided into 19 sections and 23 series. Classification of species is based largely on ultrastructural characteristics of the siliceous scales and bristles that collectively form a highly organized covering over the cell.