Heterogeneity in apoplastic barrier deposition, respiration and ion accumulation in the roots of diverse barley seedlings
Date
2020
Authors
Ahmad Sohaimi, Muhammad Khairul Hisyam
Editors
Advisors
Wege, Stefanie
Byrt, Caitlin (Australian National University)
Schilling, Rhiannon (South Australian Research and Development Institute (SARDI))
Byrt, Caitlin (Australian National University)
Schilling, Rhiannon (South Australian Research and Development Institute (SARDI))
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Abstract
The formation of both root endodermal and exodermal barriers can contribute to plant tolerance to saline, water and O2-limited environments. Previous studies have suggested that cultivated barley (Hordeum vulgare) does not form an exodermal layer, whereas wild Hordeum grasses can form an inducible exodermal barrier in response to abiotic stress. Here a diverse barley collection was used as a resource for experiments to assess genetic diversity in root apoplastic barriers. Barke and seven wild barley accessions with the greatest diversity in root barrier formation were selected from the collection and the relationships between the formation of barriers and trends in the following properties were assessed: (i) Root and shoot growth, (ii) Na+ and K+ accumulation and (iii) Root O2 consumption, and (iv) Response to phytohormone treatments. The lines with the most substantial exodermal barriers tended to have lower rates of root respiration relative to the other lines, revealing the possibility that the lines differed in their partitioning of energy for cell wall formation relative to other processes. Investigation of the regulation of root barrier formation by phytohormones revealed that treatments with abscisic acid enhanced root suberisation in barley, similar to observations reported previously for Arabidopsis. Treatments with the ethylene precursor 1-Aminocyclopropane-1-carboxylic acid had no effect on barrier formation, differing from trends in Arabidopsis. This indicates that the mechanisms regulating changes in cell wall barriers differ in barley relative to Arabidopsis. A wild barley line, HID138, was identified which had a strong exodermal barrier, and had higher K+ retention relative to commercial Barke, raising the possibility that the exodermal barrier could have had a role in preventing K+ loss from the roots. To further evaluate the relationship between the exodermal barrier and ion accumulation, a subset of progeny lines from the Barke x HID138 NAM population (HEB13s) were phenotyped. The findings did not reveal a strong relationship between the differences in K+ retention and the variation in
exodermal barrier deposition, indicating further research is needed to clarify the role of the
exodermis.
Both cell wall barriers and variation in ion transport mechanisms can contribute to differences
in ion content. To explore potential variation in ion transport mechanisms the transcript
abundance and the sequences of the Na+ transporter HvHKT1;5 were analysed in lines of
interest. This revealed differences in HKT1;5 sequences in the lines. Barke contains a nonfunctional
HvHKT1;5 which codes for a proline at position 189, whereas HvHKT1;5 in the
wild barley lines coded for leucine (L) at position 189. The analysis of transcript abundance
revealed that HvHKT1;5 was not expressed at the early seedling stage, excluding a contribution
of this transporter to the observed differences in tissue ion content at the stage tested.
The diversity in apoplastic barriers in the diverse collection is likely to be a useful resource for
studying the role of these barriers in abiotic stress tolerance.
School/Discipline
School of Agriculture, Food and Wine
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2021
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