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  • Blackwell Science Ltd
  • PANGAEA
  • Public Library of Science (PLoS)
  • 2020-2022
  • 1995-1999  (3)
  • 1
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Treatment with supplementary UV-B resulted in decreases in transcripts of the photosynthetic genes Lhcb and psbA and concomitant increase in transcripts of two pathogen-related genes, PR-1 and PDF1·2, in Arabidopsis thaliana. UV-B exposure caused increases in jasmonic acid (JA) levels and ethylene production. UV-B treatment of jar1 and etr1-1 mutants, which are insensitive to JA and ethylene, respectively, showed that the increase in PR-1 transcripts was dependent on ethylene and PDF1·2 transcripts on both JA and ethylene. In contrast, the down-regulation of photosynthetic transcripts was independent of both compounds. Previous studies have indicated a role for reactive oxygen species (ROS) in the UV-B-induced down-regulation of the photosynthetic genes and up-regulation of PR-1 genes. Here we have shown that ROS are also required for the UV-B-induced up-regulation of PDF1·2 genes. The results indicate that the effects of UV-B on the three sets of genes are mediated through three distinct signal transduction pathways which are similar, but not identical, to pathways initiated in response to pathogen infection. In addition, the increased sensitivity of both jar1 and etr1-1 mutants to UV-B radiation, as compared with wild-type plants, indicated that intact JA and ethylene signal pathways are required for defence against UV-B damage.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Supplementary UV-B was shown to lead to a decrease in transcripts encoding the photosynthetic genes Lhcb and psbA and a concomitant increase in transcripts encoding three acid-type pathogenesis-related proteins, PR-1, PR-2 and PR-5, in Arabidopsis thaliana. UV-B radiation has been reported to lead to the generation of reactive oxygen species (ROS). Here we report that ROS are required for UV-B-induced down-regulation of the photosynthetic genes and up-regulation of PR genes, as the addition of antioxidants before UV-B treatment resulted in a marked reduction in the effect of UV-B on both sets of genes. Rises in ROS are frequently accompanied by increases in salicylic acid (SA) accumulation. UV-B treatment of transgenic NahG Arabidopsis plants, which are unable to accumulate SA, showed that the increase in PR transcripts, but not the decrease in photosynthetic transcripts, was dependent on the increase in SA. In addition, a 3 d exposure to UV-B radiation resulted in a 7-fold increase in SA levels. Oxidant treatment of NahG plants indicated that ROS could not up-regulate PR genes in the absence of SA accumulation; however, the down-regulation of photosynthetic transcripts was unchanged from that in wild-type plants. The results indicate that the effects of UV-B on the two sets of genes are mediated through two distinct signal tranduction pathways. One pathway is ROS-dependent but SA-independent and mediates the down-regulation of photosynthetic genes. The other is SA- and ROS-dependent and mediates the up-regulation of the acidic-type PR genes.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Experiments were conducted to examine the processes leading up to the infection of Lolium temulentum by crown rust (Puccinia coronata), stem rust (P. graminis) and brown rust (P. loliina), and the effects of temperature on these processes and sporulation. Uredia of all three rusts were produced freely if the adaxial leaf surface was inoculated, but did not form following inoculation of the abaxial surface. Light and scanning electron microscopy revealed abnormal growth of germlings on the abaxial surface which had amorphous sheet-like epicuticular waxes and very few stomata. On the adaxial leaf surface germ tubes of all the rusts orientated at right angles to the long axis of the leaf. However, the directional growth of germ tubes was often disrupted when they contacted the surface of bulliform cells at the base of leaf grooves. For P. loliina the optimum temperatures for urediospore germination and sub-stomatal vesicle formation were 12–16°C, and 8–20°C for appressorium formation. The optimum temperatures, for the same stages of fungal development, for P. coronata and P. graminis were higher. Urediospore production of P. loliina was higher at 10°C than at 25°C, but was similar at both temperatures for P. coronata.
    Type of Medium: Electronic Resource
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