Abstract
Application of the dintroaniline compound, oryzalin, which inhibits microtubule formation, to the unicellular green alga Penium margaritaceum caused major perturbations to its cell morphology, such as swelling at the wall expansion zone in the central isthmus region. Cell wall structure was also notably altered, including a thinning of the inner cellulosic wall layer and a major disruption of the homogalacturonan (HG)-rich outer wall layer lattice. Polysaccharide microarray analysis indicated that the oryzalin treatment resulted in an increase in HG abundance in treated cells but a decrease in other cell wall components, specifically the pectin rhamnogalacturonan I (RG-I) and arabinogalactan proteins (AGPs). The ring of microtubules that characterizes the cortical area of the cell isthmus zone was significantly disrupted by oryzalin, as was the extensive peripheral network of actin microfilaments. It is proposed that the disruption of the microtubule network altered cellulose production, the main load-bearing component of the cell wall, which in turn affected the incorporation of HG in the two outer wall layers, suggesting coordinated mechanisms of wall polymer deposition.
Highlights
Plant cell walls are composites of polymers that are assembled and organized into intricate structures that surround the protoplast, where they serve multiple roles including defence, turgor resistance and controlled cell growth, water and mineral uptake, and communication (Baskin et al, 2004; Cosgrove, 2005; Sarkar et al, 2009; Keegstra, 2010; Fry, 2011)
Live cells may be labelled with monoclonal antibody (mAb) with specificity for epitopes present in land plant cell wall polymers or carbohydrate-binding module (CBM), and placed back into growth medium where they continue division/expansion and retain the label for 10 d or more, depending on the polymer in question
rhamnogalacturonan I (RG-I) was identified in the cell wall using INRA-RU2 (Fig. 1E) but, unlike JIM5, INRA-RU2 localized in a layer below the outer wall lattice and in a more homogenous labelling that was interrupted by dark puncta
Summary
Plant cell walls are composites of polymers that are assembled and organized into intricate structures that surround the protoplast, where they serve multiple roles including defence, turgor resistance and controlled cell growth, water and mineral uptake, and communication (Baskin et al, 2004; Cosgrove, 2005; Sarkar et al, 2009; Keegstra, 2010; Fry, 2011). Cell wall architecture is highly dynamic, and synthesis, assembly, and any subsequent remodelling require precisely coordinated interactions between the cell endomembrane system, cytoskeletal network, plasma membrane, and multiple cross-talking signal transduction pathways. The nature of these interactions, especially during development and in response to environmental stresses, is poorly understood and only recently has this been the focal point of detailed study. Cellulose microfibrils are generally described as being tethered by xyloglucan and other hemicellulosic (crosslinking glycan) polymers, and these have been proposed to influence microfibril slippage during wall and cell expansion (Popper and Fry, 2005, 2008; Fry, 2011); the nature, extent, and significance of this cross-linking have recently been discussed (Cosgrove and Jarvis, 2012; Park and Cosgrove, 2012). There are doubtless many other interpolymeric associations that are critical for wall architecture and function, but that have yet to be recognized and characterized
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