Ozone sensitivity in hybrid poplar correlates with insensitivity to both salicylic acid and jasmonic acid. The role of programmed cell death in lesion formation.

Our earlier studies demonstrated that the ozone-sensitive hybrid poplar clone NE-388 displays an attenuated level of ozone-, wound-, and phytopathogen-induced defense gene expression. To determine if this reduced gene activation involves signal transduction pathways dependent on salicylic acid (SA) and/or jasmonic acid (JA), we compared the responses of NE-388 and an ozone-tolerant clone, NE-245, to these signal molecules. JA levels increased in both clones in response to ozone, but only minimal increases in SA levels were measured for either clone. Treatment with SA and methyl jasmonate induced defense gene expression only in NE-245, indicating that NE-388 is insensitive to these signal molecules. DNA fragmentation, an indicator of programmed cell death (PCD), was detected in NE-245 treated with either ozone or an avirulent phytopathogen, but was not detected in NE-388. We conclude that these clones undergo two distinct mechanisms of ozone-induced lesion formation. In NE-388, lesions appear to be due to toxic cell death resulting from a limited ability to perceive and subsequently activate SA- and/or JA-mediated antioxidant defense responses. In NE-245, SA-dependent PCD precedes lesion formation via a process related to the PCD pathway activated by phytopathogenic bacteria. These results support the hypothesis that ozone triggers a hypersensitive response.

Bacillomycin Lc, a new antibiotic of the iturin group: isolations, structures, and antifungal activities of the congeners.

Bacillomycin Lc, a new antifungal antibiotic of the iturin class, was isolated from a strain of Bacillus subtilis as a set of five congeners. The structure as determined by chemical and spectrometric analyses has been shown to differ from that of bacillomycin L by sequence changes from aspartate-1 to asparagine-1 and from glutamine-5 to glutamate-5. The five congeners differ from each other only in the structure of the aliphatic side chain of the constituent beta-amino acid. The hydrophobicity of the beta-amino acid affects the antifungal activity of the congener, as activity increased in the order of increased congener retention on a reversed-phase HPLC column.

The design, synthesis, and crystallization of an alpha-helical peptide.

Twelve- and sixteen-residue peptides have been designed to form tetrameric alpha-helical bundles. Both peptides are capable of folding into amphiphilic alpha-helices, with leucyl residues along one face and glutamyl and lysyl residues along the opposite face. Four such amphiphilic alpha-helices are capable of forming a noncovalently bonded tetramer. Neighboring helices run in antiparallel directions in the design, so that the complex has 222 symmetry. In the designed tetramer, the leucyl side chains interdigitate in the center in a hydrophobic interaction, and charged side chains are exposed to the solvent. The designed 12-mer (ALPHA-1) has been synthesized, and it forms helical aggregates in aqueous solution as judged by circular dichroic spectroscopy. It has also been crystallized and characterized by x-ray diffraction. The crystal symmetry is compatible with (but does not prove) the design. The design can be extended to a four-alpha-helical bundle formed from a single polypeptide by adding three peptide linkers.