Fall Exposure of Beech Saplings (Fagus sylvatica L.) to Ozone and Simulated Acidic Mist: Effects on Gas Exchange and Leachability.

Two yr old beech saplings (Fagus sylvatica L.) were exposed under an early autumn climate to four levels of O3 (10, 40, 75, and 110 nL L-1 O3) with or without preceding simulated acidic mist (pH 3.5). As a first response in gas exchange to O3, stomatal conductance was transiently increased followed by a decline in net photosynthesis. Thus, regarding exposure effects on stomatal behavior, both O3 and acidic mist increased the pollutant flux into the leaf interior. The subsequent impairment of cell permeability consisted of dose-dependent increases in efflux rates of dichlorofluorescein, indicating greater membrane permeabilities. While the efflux rates of Mg and Ca correlated with those of the fluorescent dye, the leachability of K was increased only at the highest O3 levels. Changes in compartmentation of K, Ca, Mg, and S was derived from selective cell wall extraction; thereafter, the exposure to O3 and acidic mist resulted in increased extracellular fractions of these elements

Lipopeptide secondary metabolites from the phytopathogenic bacterium Pseudomonas syringae.

Over the past twenty years or so, significant advances have been made in the study of the secondary metabolism of the widespread phytopathogenic Gram-negative bacterium Pseudomonas syringae. Interdisciplinary approach, which required the expertise of plant pathologists, chemists, biochemists and molecular biologists, led to the discovery of a new family of bioactive peptide secondary metabolites. The determination of their structures was pivotal for the investigations on their biosynthetic pathways, their relevance in the development of plant disease, and for the understanding of the molecular bases of their biological activities in plant, microbial and animal cells. In particular, the antibiotic activities of some of these compounds appear very interesting in the perspective of their utilization both in medicine and in agriculture. The goal of this chapter is to summarize the present knowledge in various areas of research on P. syringae peptide metabolites