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Scholarly Works (3 results)

  • Article
  • Peer Reviewed
The Proceedings of the International Plant Nutrition Colloquium XVI (2009)

The way calcium (Ca) is stored in plants impacts upon plant, human and animal nutrition. An X-ray microanalysis study of over 40 angiosperm species has highlighted conserved accumulation patterns for Ca across different plant families; Ca is often stored in specific leaf cell-types. For instance, in grass monocots Ca accumulation occurs within vacuoles of epidermal cells whereas in the majority of eudicots Ca is predominantly stored within mesophyll cell vacuoles. To correlate gene expression with Ca accumulation profiles we micropipetted RNA from epidermal and mesophyll cells of the eudicot Arabidopsis thaliana. Cell specific RNA libraries were analysed by microarray and qPCR revealing a number of candidate membrane transporters with greater relative expression in the Ca-rich mesophyll. Knockout mutagenesis of one candidate AtCAX1, a tonoplast-localized Ca2+/H+-antiporter, resulted in no mutant phenotype. When the expression of AtCAX3, a complementing family member was also abolished, this resulted in a reduction in total leaf [Ca] and perturbance of the Ca distribution pattern. The double knockout plant had a 3-fold higher apoplastic [Ca] which correlated with reduced stomatal conductance, photosynthetic rate and consequently growth. Apoplastic [Ca], stomatal conductance and growth rate could be recovered to wild-type levels by reducing [Ca] in the growth medium. We implicate CAX1 and its homologues as major regulators of Ca distribution and apoplastic [Ca] in leaves within and between plant orders. Such information will be helpful for the manipulation of Ca within specific cell types of leafy vegetables as a tool for improving human and animal nutrition.

    Cover page: Calcium Compartmentation in Arabidopsis Mesophyll Cells, A Mechanism to Regulate Apoplastic Calcium, Photosynthetic Rates and Growth, Involves Low-affinity, High-capacity Ca<sup>2+</sup>/H<sup>+</sup> Antiporters
    • Article
    • Peer Reviewed
    The Proceedings of the International Plant Nutrition Colloquium XVI (2009)

    Remobilisation of phosphate (Pi) within a plant is critical for sustaining its growth under external Pi fluctuation and for seed production. The barley transporter, HvPht1;6 has been implicated in Pi remobilisation. However, functional characterisation of HvPht1;6 and other known plant Pi transporters has been limited owing to the lack of a suitable expression system. In this report, we expressed HvPht1;6 in Xenopus laevis oocytes allowing the first detailed characterisation of a plant phosphate transporter. HvPht1;6 increased efflux of Pi near oocyte resting membrane potentials, dependent on external Pi concentration. Inward currents activated by negative membrane potentials were consistent with nH+:HPO42- (n>2) co-transport, and were dependant on Pi concentration gradient and pH. The large inward current (Pi influx) at -150 mV was also observed for other oxyanions including SO42- and NO3-. Inward and outward currents showed linear dependence on the concentration of external HPO42- and membrane potential, suggesting that HvPht1;6 may, in hyperperpolarised phloem cells, load Pi from the apoplast; and in depolarised cells, such as senescing mesophyll cells, unload Pi to the apoplast. The electrophysiological properties of HvPht1;6 are consistent with its suggested role in the remobilisation of Pi in barley plants. Our results demonstrate that using modified bath solution, X. laevis oocytes can be used for studies of electrophysiological properties of plant proton-coupled Pi transporters.

      Cover page: Barley phosphate transporter 1;6 shows broad inorganic anion transport activity when expressed in Xenopus laevis oocytes
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2019)
      Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.
        Cover page: Large expert-curated database for benchmarking document similarity detection in biomedical literature search
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