We propose a method to determine growth rates of adult copepods based on their nucleic acid contents. We investigated the suitability of this method on the marine copepod Acartia gruni in a range of food concentrations and temperatures. There was a good linear relationship between growth rate (estimated as egg production) and RNA contents of the adult copepods. The slope of the relationship was dependent on temperature. We also built a multipleregression model to predict egg production rates of A. grani as a function of RNA contents and temperature. This method allows very intensive field sampling and does not require incubations onboard. Samples are preserved frozen and analyzed in the laboratory using a very sensitive fluorometric technique that allows working with small numbers of individuals of the desired species.

A fluorometric technique, based on the combination of RNase and DNase incubation with the use of thiazole orange (RNase/DNase method), was investigated to determine DNA and RNA concentrations in marine plankton. Tests were performed to optimize both RNase and DNase assay conditions. The RNase assay should be conducted at 37° C for 20 min with 0.5 μg·mL−1 of DNase‐free RNase. An incubation at 25° C for 20 min with 10 units ·mL‐1 of RNase‐free DNase were the optimal conditions required for DNA digestion by DNase. The detection limits in terms of minimum biomass for reliable measurements of DNA and RNA were 7.5 and 10 μg of protein · (mL assay)−1, respectively. RNA and DNA concentration were estimated in oligotrophic water samples using the RNase/DNase and other available methods (e.g. a double fluorochrome method). The different techniques provided similar DNA estimations. However, the RNase/DNase method provided the highest sensitivity and a low variability for the estimation of RNA.

Diamine oxidase (DAO, EC 1.4.3.6) activity was examined in relation to polyamine content in Helianthus tuberosus L. during the first synchronous cell cycle induced in vitro by 2,4,-dichloro-phenoxyacetic acid in tuber slices and during the in vivo formation of the tuber. The optimal pH, buffer and dithiothreitol concentrations for the enzyme extraction and assay were determined. When added in the assay mixture, catalase enhanced DAO activity, while polyvinylpyrrolidone had no effect; both aminoguanidine and hydrazine inhibited enzyme activity. The time course of the reaction, based on the recovery of Delta(1)-pyrroline from labeled putrescine in lipophilic solvents, showed that it was linear up to 30 minutes; the K(m) of the enzyme for putrescine was of the order of 10(-4) molar. During the first cell cycle, DAO activity exhibited a peak at 15 hours of activation while putrescine content gave a peak at 12 hours. During tuber formation (from August till October) DAO activity was relatively high during the first phase of growth (cell division), decreased until flowering (end of September-early October), and then newly increased during the cell enlargement phase preceding the entry into dormancy (November). Maximum putrescine content was observed at the end of October. The increase in DAO activity paralleled the accumulation of putrescine. This indicates a direct correlation between the biosynthesis and oxidation of putrescine which, as already demonstrated in animal systems, occur simultaneously in physiological stages of intense metabolism such as cell division or organ formation.