Stem cell signaling in immunity and development.

Stem cells in the shoot apical meristem (SAM) of plants are the self-renewable reservoir for leaf, stem, and flower organogenesis. Stem-cell fate and population size are subject to regulation by complex intrinsic signals and environmental cues to ensure balanced plant development, survival, and longevity. Peptides secreted from the shoot stem cells have pivotal roles in controlling cell identity, proliferation, and differentiation through multiple receptor kinase complexes. The best-characterized in vivo and in vitro peptide ligands are the 12-amino acid (aa) and the arabinosylated 13-aa CLAVATA3 peptides (CLV3p) that are perceived by multiple receptors with partially overlapping and distinct expression patterns and functions in the SAM. The primary molecular and cellular signaling mechanisms after the occurrence of ligand-receptor interaction remain elusive. Integrated analyses provide novel evidence for differential peptide-receptor signaling in the dynamic regulation of stem-cell homeostasis and fitness. Surprisingly, the 12-aa CLV3p can trigger immune signaling and limit pathogen invasion via the flagellin receptor kinase FLS2, suggesting a previously unrecognized molecular mechanism underlying enhanced immunity in the SAM area. Because pattern recognition receptor signaling in immune responses also profoundly intercepts plant development, peptide-receptor kinase signaling in immunity and development may share a common evolutionary origin.

Carcinogens in rubber production in the Soviet Union.

In a preliminary phase of a broad research project on cancer among workers in a rubber footwear plant in Moscow, exposure to several known or potential carcinogens was assessed. There were high dust contents bearing both toxic substances and carcinogens. The highest concentrations of benzo[a]pyrene (500-14,400 micrograms) were found on the soot used as a filler, and the maximum N-dimethylnitrosamine (DMNA) level was measured in thiram (150-23,868 micrograms.kg-1). Air samples from the vulcanization process and the pressing of rubber goods showed BaP levels of up to 1.43 micrograms.m-3. In the work area where polyvinyl chloride was used, the mean vinyl chloride concentration was 0.21 (SE 0.06) mg.m-3. The mean value of the acrylonitrile concentrations in the workroom area was 0.19 (SE 0.07) mg.m-3. Very high levels of DMNA and N-diethylnitrosamine were measured in the preparatory shop in the winter.