[Aromatic amino acids in the metabolism of higher plants]

Latitudinal drivers of oyster mortality: deciphering host, pathogen and environmental risk factors

Diseases pose an ongoing threat to aquaculture, fisheries and conservation of marine species, and determination of risk factors of disease is crucial for management. Our objective was to decipher the effects of host, pathogen and environmental factors on disease-induced mortality of Pacific oysters (Crassostrea gigas) across a latitudinal gradient. We deployed young and adult oysters at 13 sites in France and we monitored survival, pathogens and environmental parameters. The young oysters came from either the wild collection or the hatchery while the adults were from the wild only. We then used Cox regression models to investigate the effect of latitude, site, environmental factors and origin on mortality risk and to extrapolate this mortality risk to the distribution limits of the species in Europe. We found that seawater temperature, food level, sea level atmospheric pressure, rainfall and wind speed were associated with mortality risk. Their effect on hatchery oysters was generally higher than on wild animals, probably reflecting that hatchery oysters were free of Ostreid herpesvirus 1 (OsHV-1) whereas those from the wild were asymptomatic carriers. The risk factors involved in young and adult oyster mortalities were different, reflecting distinct diseases. Mortality risk increases from 0 to 90% with decreasing latitude for young hatchery oysters, but not for young wild oysters or adults. Mortality risk was higher in wild oysters than in hatchery ones at latitude > 47.6°N while this was the opposite at lower latitude. Therefore, latitudinal gradient alters disease-induced mortality risk but interacts with the initial health status of the host and the pathogen involved. Practically, we suggest that mortality can be mitigated by using hatchery oysters in north and wild collected oysters in the south.

Evidence for an intra- and extraplastidic pre-chorismate pathway

Pea plants grown under different conditions of cultivation, and eight different plant species with variegated leaves were used to study the intracellular localization of shikimate oxidoreductase (EC 1.1.1.25), the marker enzyme of the pre-chorismate pathway. The two series of experiments indicated an intra-and an extraplastidic compartimentalization of the enzyme, and both enzyme activities are regulated differentially. While the extraplastidic activity is permanently demonstrable, the intraplastidic activity is subject to the plants' developmental state and also depends on both illumination and fertilization.

Intermediates in the metabolism of m-carboxy-substituted aromatic amino acids in plants. Phenylpyruvic acids, mandelic acids, and phenylglyoxylic acids

Tracer experiments with 14C-labelled precursors in Iris times hollandica cv. Wedgwood, Reseda Iutea L. And Keseda Odorata L. have demonstrated that 3-(3-carboxyphenyl) alanine and 3-(3-carboxy-4-hydroxyphenyl) alanine can be derived from the corresponding pyruvic acids, presumably by unspecific transaminations, and that (3-carboxyphenyl) glycine and (3-carboxy-4-hydroxyphenyl) glycine can be derived from the corresponding phenylglyoxylic acids. The glycine derivatives are derived from the alanine derivatives, and the corresponding mandelic acids are intermediates in these transformations. The corresponding phenylacetic acids are incorporated only slightly into the glycine derivatives, indicating that oxidation at the benzylic position in the C6-C3 compounds takes place early in the transformation. The corresponding cinamic acids are not metabolized at all in the plants.