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Abstract: We determined the temporal and spatial localization of the phytoalexin avenanthramide A, and its biosynthetic enzyme, hydroxycinnamoyl-CoA:hydroxyanthranilate N-hydroxy-cinnamoyltransferase (AsHHT) in oat leaves infected with the crown rust fungus. Accumulation of avenanthramide A and AsHHT was first observed predominantly in hypersensitive response (HR) cells at 36 h post inoculation (hpi), and later in adjacent cells at 48 hpi. At 120 hpi, avenanthramide A was detected in a wider area of infected tissues, but AsHHT-positive signals were only observed in the HR and adjacent cells, suggesting that avenanthramide A was synthesized around the HR cells, and then transported to other parts of the infected tissues in a center-to-periphery manner. [Copyright &y& Elsevier]

The article discusses a study which investigated the induction of cell death, chlorosis, and reactive oxygen species (ROS) generation by Mag-toxin obtained from Pyricularia oryzae. It states that the toxin induced chlorosis on segments of oat leaf incubated in the light. It says that the ROS generation cellular localization induced by the treatment of the toxin was correlated with mitochondria's location. It notes that induction of cell death and ROS generation by the toxin was light-dependent.

Transcriptional activity of the retrotransposon OARE-1 was monitored in oat leaves infected with pathogenic fungi. The transcription of OARE-1 was upregulated in both incompatible and compatible interactions between an oat cultivar and Magnaporthe grisea isolates but more extensively in the compatible. OARE-1 was also strongly activated in a Pc2/vb-carrying oat line inoculated with Helminthosporium victoriae. The upregulation in the Pc2/Vb-carrying oat line was reproduced by treatment with victorin C, the major compound of the host-specific toxin produced by the fungus. These results suggest that OARE-1 is responsive to various signals or stresses associated with compatibility and incompatibility. [ABSTRACT FROM AUTHOR]

Transcriptionally active Ty1-copia LTR-retrotransposons were found in oat using RT-PCR for amplifying the reverse transcriptase domain. Sequence analysis of the RT-PCR clones suggested that oat LTR-retrotransposons consist of at least seven groups, which were tentatively designated as Oatrt1 to Oatrt7. A full length copy of Oatrt1 was isolated from an oat genomic library, and was designated OARE-1. OARE-1 was 8,665 bp long and a member of the BARE-1 subgroup. The oat genome carried it in multiple copies (at least 10,000 copies / a hexaploid genome). The expression of OARE-1 was intensively induced by wounding, UV light, jasmonic acid and salicylic acid, and its pattern was very similar to that of the PAL (phenylalanin ammonia lyase) gene. Furthermore, OARE-1 was highly activated by infection with an incompatible race of the crown rust fungus, Puccinia coronata. These results suggest that OARE-1 is highly sensitive to various abiotic and biotic stimuli leading to plant defense responses. [ABSTRACT FROM PUBLISHER]

SummaryHistological and cytological evidence of where and when apoptotic cells occur in Pc-2/Vb oat cells treated with victorin was obtained by observing DNA strand breaks at both light (LM) and electron microscope (EM) levels using TUNEL techniques. DNA from leaf segments that had been floated on victorin solution with the abaxial epidermis removed showed typical ladders on agarose gels. Nuclear chromatin condensation, followed by cell collapse, started in the mesophyll cells closest to the victorin solution. LM-TUNEL was positive in the non-collapsed cells but not in the collapsed cells in the treated leaves. However, the EM-TUNEL assay was positive in the nuclei of the non-collapsed as well as the collapsed cells where nuclear fragments dispersed into the cytoplasm, and the immunogold density was much higher than that in the cells killed by a high concentration of H2O2, suggesting that the victorin-treated collapsed cells are in the last stage of apoptotic cell death. The immunogold labelling in the victorin-treated non-collapsed cells was restricted to condensed heterochromatin, indicating that chromatin condensation is associated with DNA cleavage. Pharmacological studies indicated that proteases and nucleases may play a role in the apoptotic response. However, the EM-TUNEL assay indicated that EGTA co-incubated with victorin blocked DNA cleavage, but failed to prevent chromatin condensation. Moreover, protein kinases were involved in chromatin condensation, but did not affect DNA digestion, suggesting that chromatin condensation and DNA cleavage are differentially regulated in the death process in oats. [ABSTRACT FROM AUTHOR]