Cell suspension cultures of spruce (Picea abies): inactivation of extracellular enzymes by fungal elicitor-induced transient release of hydrogen peroxide (oxidative burst)

Elicitation of suspension culture cells of spruce [Picea abies (L.) Karst] with a fungal cell wall preparation of the spruce pathogenic fungus Rhizosphaera kalkhoffii Bubak induced inactivation of extracellular enzymes. Extracellular peroxidase, -glucosidase and acid phosphatase, secreted by the cells during growth, and also -amylase and pectinase from Aspergillus strains, added to an elicited cell culture, were inactivated. Inactivation is caused by an elicitor-mediated transient release of H₂O₂ from the cells (oxidative burst). H₂O₂ released into the medium was determined with ABTS (2,2'-Azino-bis-(3-ethylbenthiazoline-6-sulfonate)) (formation of blue colour) and with phenol red (destruction of pH indicator). The release started only minutes after beginning of elicitation and its inactivating effect existed for more than 1 day. Release of H₂O₂ is a biphasic process with a first smaller maximum at 1 h, followed by a second larger increase, peaking at 5–6 h and returning to approximately the control levels thereafter. Also H₂O₂ is transiently released in small quantities from cell incubations in the absence of elicitor as a stress response of the cells to manipulations of the cultures. Extracellular enzymes secreted into the medium could also be inactivated by direct addition of exogenous H₂O₂. Catalase prevents inactivation of the secreted extracellular enzymes, however, to a limited extent only because, as a result of contact of cells and medium, catalase becomes inactivated. The ionophores A 23187 and cycloheximide induced release of H₂O₂ and, when present together with elicitor, induction was synergistically increased.     

l-Phenylalanine ammonia-lyase in suspension culture cells of spruce (Picea abies)

The activity of l-phenylalanine ammonia-lyase (PAL) (EC 4.3.1.5) was determined in seedlings, callus cells, cell suspension cultures and in young needles of spruce (Picea abies) (L.) (Karst). PAL activity increased up to 10 fold in response to transferring suspension cultured cells into new cultivation medium. PAL was also induced about 10 fold when callus cells were transferrd into liquid medium. The increase was transient and it required the presence of a carbohydrate.In cell suspension cultures, grown in the dark (white cells), but not in light-grown cultures (green cells), PAL activity was induced up to 30 fold by UV-light.With a cell wall preparation of Rhizosphaera kalkhoffii, a forest pathogenic fungus, used as elicitor, the activity of PAL could be induced more than 10 fold. The degree of induction depended on the elicitor concentration. Induction was prevented by cycloheximide but not by actinomycin D.     

Epigenetic Control of Immunity

Immunity relies on the heterogeneity of immune cells and their ability to respond to pathogen challenges. In the adaptive immune system, lymphocytes display a highly diverse antigen receptor repertoire that matches the vast diversity of pathogens. In the innate immune system, the cell''s heterogeneity and phenotypic plasticity enable flexible responses to changes in tissue homeostasis caused by infection or damage. The immune responses are calibrated by the graded activity of immune cells that can vary from yeast-like proliferation to lifetime dormancy. This article describes key epigenetic processes that contribute to the function of immune cells during health and disease.     

Patterns of early succession on bare peat in a Swiss mire after a bog burst

Questions: How does plant diversity (species richness, species abundance and rate of change) evolve in early succession on bare peat? Does succession converge towards one equilibrium stage or end up in several stages? Is there a regular pattern in succession velocity? Location: A mire in the calcareous Jura Mountains of northwest Switzerland. Method: Twenty‐one 1‐m² permanent plots on bare peat were used to monitor temporal stages over a 21‐year period (1988 to 2008) in a Swiss mire where a slide occurred in 1987. Species diversity and life forms were analysed based on Shannon's equitability index and cover. We used classification and metric ordination techniques to investigate patterns of successional rates and trends. The high temporal resolution of the survey allowed the pattern of succession velocity to be analysed. Results: Species richness increased continuously over the 21 years of succession. The highest cover throughout the study period was the life form sedge. Time trajectories of the 21 plots revealed three alternative pathways towards intermediate equilibrium stages in the first years, still not converging in the later stages. Changes in succession velocity reached a first maximum about 6 years after the slide had occurred and a second maximum 12 years later.