Biomedical subjects

Martin J Mueller

Publications and source records attributed to Martin J Mueller.

21 records · Page 2Linked to original sources

PubMed2003

Cyclopentenone isoprostanes induced by reactive oxygen species trigger defense gene activation and phytoalexin accumulation in plants.

Lipid peroxidation may be initiated either by lipoxygenases or by reactive oxygen species (ROS). Enzymatic oxidation of alpha-linolenate can result in the biosynthesis of cyclic oxylipins of the jasmonate type while free-radical-catalyzed oxidation of alpha-linolenate may yield several classes of cyclic oxylipins termed phytoprostanes in vivo. Previously, we have shown that one of these classes, the E1-phytoprostanes (PPE1), occurs ubiquitously in plants. In this work, it is shown that PPE1 are converted to novel cyclopentenone A1- and B1-phytoprostanes (PPA1 and PPB1) in planta. Enhanced formation of PPE1, PPA1, and PPB1 is observed after peroxide stress in tobacco cell cultures as well as after infection of tomato plants with a necrotrophic fungus, Botrytis cinerea. PPA1 and PPB1 display powerful biologic activities including activation of mitogen-activated protein kinase (MAPK) and induction of glutathione-S-transferase (GST), defense genes, and phytoalexins. Data collected so far infer that enhanced phytoprostane formation is a general consequence of oxidative stress in plants. We propose that phytoprostanes are components of an oxidant-injury-sensing, archaic signaling system that serves to induce several plant defense mechanisms.

Arabidopsis↗

PubMed2003

NPR1 modulates cross-talk between salicylate- and jasmonate-dependent defense pathways through a novel function in the cytosol.

Plant defenses against pathogens and insects are regulated differentially by cross-communicating signal transduction pathways in which salicylic acid (SA) and jasmonic acid (JA) play key roles. In this study, we investigated the molecular mechanism of the antagonistic effect of SA on JA signaling. Arabidopsis plants unable to accumulate SA produced 25-fold higher levels of JA and showed enhanced expression of the JA-responsive genes LOX2, PDF1.2, and VSP in response to infection by Pseudomonas syringae pv tomato DC3000, indicating that in wild-type plants, pathogen-induced SA accumulation is associated with the suppression of JA signaling. Analysis of the Arabidopsis mutant npr1, which is impaired in SA signal transduction, revealed that the antagonistic effect of SA on JA signaling requires the regulatory protein NPR1. Nuclear localization of NPR1, which is essential for SA-mediated defense gene expression, is not required for the suppression of JA signaling, indicating that cross-talk between SA and JA is modulated through a novel function of NPR1 in the cytosol.

Arabidopsis Proteins↗

PubMed2002

Purification and partial amino acid sequences of an esterase from tomato.

Screening of 18 suspension plant cell cultures of taxonomically distant species revealed that a methyl jasmonate hydrolysing enzyme activity (0.21-5.67 pkat/mg) occurs in all species so far analysed. The methyl jasmonate hydrolysing esterase was purified from cell cultures of Lycopersicon esculentum using a five-step procedure including anion-exchange chromatography, gel-filtration and chromatography on hydroxylapatite. The esterase was purified 767-fold to give an almost homogenous protein in a yield of 2.2%. The native enzyme exhibited a M(r) of 26 kDa (gel-filtration chromatography), which was similar to the M(r) determined by SDS-PAGE and MALDI-TOF analysis (M(r) of 28547 kDa). Enzyme kinetics revealed a K(m) value of 15 microM and a V(max) value of 7.97 nkat/mg, an pH optimum of 9.0 and a temperature optimum of 40 degrees C. The enzyme also efficiently hydrolyzed methyl esters of abscisic acid, indole-3-acetic acid, and fatty acids. In contrast, methyl esters of salicylic acid, benzoic acid and cinnamic acid were only poor substrates for the enzyme. N-Methylmaleimide, iodacetamide, bestatin and pepstatin (inhibitors of thiol-, metal- and carboxyproteases, respectively) did not inactivate the enzyme while a serine protease inhibitor, phenylmethylsulfonyl fluoride, at a concentration of 5 mM led to irreversible and complete inhibition of enzyme activity. Proteolysis of the pure enzyme with endoproteinase LysC revealed three peptide fragments with 11-14 amino acids. N-Terminal sequencing yielded an additional peptide fragment with 10 amino acids. Sequence alignment of these fragments showed high homologies to certain plant esterases and hydroxynitrile lyases that belong to the alpha/beta hydrolase fold protein superfamily.

Acetates↗