Chemical, isotopic and enzymatic monitoring of free and enclosed seawater : implications for primary production estimates in incubation bottles

Enclosing seawater samples in incubation bottles had 3 main effects on the phytoplankton: first, a large (5-fold in 12 h) increase of phytoplankton biomass, due to the release of grazing pressure by herbivores, Second, an increase (2-fold in 6 h) in ribulose biphosphate carboxylase specific activity (per unit chlorophyll a), which could be due to a smaller dependence on regenerated production (less heterotrophy on excreted compounds). This was also supported by a tight relationship between phosphoenol pyruvate carboxykinase activity and dissolved ammonium. Finally, the large changes in the carbon isotopic composition of the incubated particulate matter, which were highly dependent on the dissolved inorganic nitrogen concentration, were due mainly to physiological processes such as biochemical fractionation rather than physical processes such as CO2 limitation. For environments with high phytoplankton growth rate and high grazing pressure, a duration of incubation greater than 3 h may significantly change the physiology of the organisms and lead to different estimates of carbon assimilation by autotrophs than bulk water estimates

Carbon and nitrogen dynamics during growth and degradation of phytoplankton under natural surface irradiance

International audienc

Prolonged root hypoxia effects on ethylene biosynthesis and perception in tomato fruit

The effects of root hypoxia on ethylene biosynthesis and perception have been documented in many vegetative organs, but not extensively in fruit. Therefore, in the present study, the effects of root hypoxia on ethylene biosynthesis and perception were investigated in tomato (Solanum lycopersicum L.) fruit at five stages of the maturation phase. Our results showed that root hypoxia does not affect ethylene biosynthesis in fruit, but stimulates its reception from other plant parts, as indicated by the increase in the expression of ethylene receptors ETR1 and 3

Rapid assessment of metabolic activity in marine microalgae : application in ecotoxicological tests and evaluation of water quality

A new method for the assessment of the effects of several contaminants on marine microalgae,Tetraselmis suecica (Kyling) Butcher,Skeletonema costatum (Grev.) Cleve, andProrocentrum lima (Ehrenberg) Dodge was developed in 1990. The method is based on the measurement of cell esterase activity using a fluorimetric stain, fluorescein diacetate (FDA), selected from amongst three stains (FDA, Neutral Red, thiazolyl tetrazolium bromure) for its higher sensitivity. Biochemical (K m,V max) and physiological (growth, specific activity) aspects of the enzymatic activity as revealed by the FDA method are discussed. Different categories of compounds (weed-killers, insecticides, metals) and some water samples from Seine Bay were tested for their toxic effects on microalgae. Experiments were performed on microplates using a fluorimetric microplate reader. The various steps of the experiments and data-processing were controlled by software. Applications of the system to rapid ecotoxicological tests (determination of the IC50, i.e., the concentration at which 50% inhibition of growth occurs) and to the assessment of environment quality by studying the toxic effect of water samples on microalgae are proposed