The impact of wind and mechanical stress on growth and development of Brachypodium distachyon stems

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Student thesis: Doctoral ThesisDoctor of Philosophy

Original languageEnglish
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Award date2019
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Abstract

The wind is an important abiotic stress from an agronomic and economic point of view. While the response of plants to various abiotic stresses is intensively studied, there is relatively little research on wind stress (WS) and mechanical stress (MS) in plants, especially in the grasses. This study aims to provide information on how wind stress and mechanical stress affect the growth and development of the model grass Brachypodium distachyon. In particular, the study focussed on the consequences of WS and MS on cell wall composition
and architectural features of the stems, as well as phenotypic, molecular and metabolic responses. The study includes a comparison of two genotypes of Brachypodium, Bd21 and ABR6. Phenotypic observation demonstrated a reduction in main stem length and delayed flowering, reduction in seed yield and aboveground biomass for the two genotypes. More detailed analysis, including histology, anatomy, and composition analysis of stem cell walls, showed
differences in response to WS and MS and between both genotypes Bd21 and ABR6. Investigation showed alterations in cell wall thickness of particular stem tissues as well as the organisation of stem tissues. Immunolocalisation using a range of monoclonal antibodies against non-cellulosic cell wall glycans, revealed differences in the labelling pattern obtained with pectin-related antibodies between treatments and genotypes. Mechanical stimulation enhanced pectin methylesterase activity and an increase in lignin content localised mostly in
the cortex and interfascicular tissue. Differences in cell wall monosaccharide content were also observed. Sugar release after enzymatic hydrolysis was significantly reduced after both stress treatments. Furthermore, three-point-bending tests showed differences in the mechanical properties of stems exposed to WS/MS compared with control. In an attempt to provide functional information on the responses to WS and MS molecular and metabolomic analysis were performed. Molecular analysis revealed alterations in cell wall-related, LOX, and PME genes expression in response to WS and MS in both genotypes. Metabolic analysis unravelled pathways involved in response to mechanical stimulation.
The study showed that wind and mechanical stress induce significant architectural changes across multiple scales, from the whole plant to organ, tissue, cellular and molecular level highlighting the complex nature of how plants respond to mechanical stimulation.

Keywords

  • Brachypodium distachyon, cell wall, wind stress, mechanical stress, mechanical stimulation, immuno-localisation, RT-PCR, metabolite profiling