Preinfection cell wall formation in roots and developing nodules ofAlnus rubra Bong

Summary The establishment of actinorhizal root nodules involves penetration of host cell walls and intracellular colonization by the nitrogen-fixing endosymbiont,Frankia (Actinomycetales). In the early stages of the infection process inAlnus, unusual cell walls with undulate profiles were observed in root tip meristematic derivatives, and in early (preinfection) derivatives of the nodule lobe meristem, inFrankia-inoculated plants. The irregular cell walls attached obliquely to preexisting walls, but were not discontinuous. Serial sections revealed that the unusual walls divided two daughter cells. Microtubules in bundled arrays were abundant near the undulate walls, and radiated in several planes. In the root tips, the anomalous cell walls were observed within one day of inoculation withFrankia.     

A spectrofluorimetric investigation of calf thymus DNA modified by BP diolepoxide and 1-pyrenyloxirane

7β,8α-Dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BP diolepoxide, $\text{1}$) and 1-pyrenyloxirane ($\text{2}$) bind chemically to calf thymus DNA. The fluorescence efficiency of pyrenyl groups in mutagen modified DNA varies appreciably with its conformation and decreases in the order: pyrenees, modified denatured DNA and modified native DNA. A particularly interesting observation is that the fluorescence efficiency of mutagen modified DNA intensifies substantially upon denaturation. Our results suggest that the pyrenyl groups in mutagen modified DNA are intercalated between the base pairs of DNA. Since both $\text{1}$ and $\text{2}$ are powerful frame-shifting mutagens for S. typhimurium TA-98, the intercalative covalent binding of these compounds to DNA may provide a molecular basis for their mutagenic activity.     

Exocrine pancreas under experimental conditions

Summary After the application of parachlorophenylalanine (pCPA), an amino acid analogue, paracrystalline inclusions are observed in the exocrine pancreas of the rat. The formation of the paracrystalline structures varies according to the dose and the time of examination. Although the first alterations can be seen in the Golgi apparatus and the condensing vacuoles, the main localization of these structures is within the cisternae of the RER. At the same time as degenerative changes occur in the cells, involving autophagic and heterophagic processes, regneration also takes place. With the freeze-fracturing method, the paracrystalline inclusions are interpreted as lamellae or plates of probably altered secretory proteins in extremely extended RER-cisternae. The fracture surfaces of the paracrystals show a periodicity of about 80 Å running diagonally to the main axis of the paracrystalline structures, which are mainly oriented from the basal parts of the exocrine pancreatic cells to the cell apices.The mechanism of paracrystalline formation is discussed on the basis of the morphologic results. It could be shown that after pCPA administration the amylase content is decreased concomittantly with degranulation. pCPA seems not to be incorporated into secretory proteins; high intracellular concentrations, however, are required to induce the formation of the paracrystalline structures. This morphological study is the basis for other studies dealing with secretion and intracellular transport in the pancreatic acinar cell under experimental conditions.We are very grateful to Mrs. B. Brühl, Mrs. I. Stenull and cand. med. P. Zahn for technical assistence. We also gratefully acknowledge Prof. Dr. R. Taugner for the help with freeze-fracturing     

Cost modelling of Pseudomonas fluorescens and Pseudomonas chlororaphis as biocontrol for competitive exclusion of Salmonella enterica on tomatoes

Published research on process-based models for biocontrol of foodborne pathogens on produce is limited. The aim of this research was to develop cost model estimates for competitive exclusion (CE) process using Pseudomonas fluorescens and Pseudomonas chlororaphis (non-plant pathogenic and non-human pathogen) as biocontrol against Salmonella enterica on tomatoes. Cost estimates were based on material inputs, equipment, facilities, and projected processing conditions of post-harvest packaging of tomatoes. The microbiological data for inactivation of S. enterica was based on published papers. The small-scale processing facility was assumed to have a processing capacity of 2000 kg of tomatoes/hour for 16 h per day, operational 6 days a week, and for 3-months /year. The large-scale facility was assumed to have a processing capacity of 100,000 kg of tomatoes/hour. Estimated initial capital investment costs for small and large-scale models (production facility) were US$391,000 and US$2.1 million. Application of CE for biocontrol of S. enterica on tomatoes was estimated at US$0.0058–0.073/kg of tomatoes during commercial processing operations. This exceeds chlorine wash technology estimated at US$0.00046/kg and is competitive with gaseous chlorine dioxide at US$0.02–0.21/kg. For high-value produce, CE may complement existing technologies increase food safety, reduce storage loses, and extend shelf life of produce.