Abstract
The composition, integrity, and architecture of the macromolecular matrix of cell walls, collectively referred to as cell wall ultrastructure, exhibits variation across species and organs and among cell types within organs. Indirect approaches have suggested that modifications to cell wall ultrastructure occur in response to abiotic stress; however, modifications have not been directly observed. Glycome profiling was used to study cell wall ultrastructure by examining variation in composition and extractability of non-cellulosic glycans in cell walls of stem wood, roots, and needles of loblolly pine saplings exposed to high and low soil moisture. Soil moisture influenced physiological processes and the overall composition and extractability of cell wall components differed as a function of soil moisture treatments. The strongest response of cell wall ultrastructure to soil moisture was increased extractability of pectic backbone epitopes in the low soil moisture treatment. The higher abundance of these pectic backbone epitopes in the oxalate extract indicate that the loosening of cell wall pectic components could be associated with the release of pectic signals as a stress response. The increased extractability of pectic backbone epitopes in response to low soil moisture availability was more pronounced in stem wood than in roots or needles. Additional responses to low soil moisture availability were observed in lignin-associated carbohydrates released in chlorite extracts of stem wood, including an increased abundance of pectic arabinogalactan epitopes. Overall, these results indicate that cell walls of loblolly pine organs undergo changes in their ultrastructural composition and extractability as a response to soil moisture availability and that cell walls of the stem wood are more responsive to low soil moisture availability compared to cell walls of roots and needles. To our knowledge, this is the first direct evidence, delineated by glycomic analyses, that abiotic stress affects cell wall ultrastructure. This study is also unique in that glycome profiling of pine needles has never before been reported.
Highlights
The cell wall is the main determinant of form, structure, and mechanical strength of plant cells and influences cell function (Cosgrove, 1997)
Growth parameters were consistently lower in the low compared to the high soil moisture treatment (Figure 1), indicating that the treatments induced a cumulative effect on development
Our results indicate that loblolly pine organs modify cell wall ultrastructure in response to moisture stress and that cell walls of stem wood respond more strongly than cell walls of roots or needles
Summary
The cell wall is the main determinant of form, structure, and mechanical strength of plant cells and influences cell function (Cosgrove, 1997). Changes to cell wall structure and composition may occur sporadically as a plant experiences various abiotic or biotic stresses (Tenhaken, 2015). Recent investigations have explored differences in protein expression in cell walls of stressed and control plants through proteomic profiling (Dani et al, 2005; Zhu et al, 2007; Kong et al, 2010). These approaches have provided some insight into the response of plant cell walls to abiotic stress, they do not provide direct information about cell wall ultrastructure. Glycome profiling offers a powerful and novel way to investigate modifications to cell wall ultrastructure in response to abiotic stress by directly examining changes in the composition, integrity, and architecture of cell walls
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