Immunogold labelling of pectic homogalacturonan (HG) epitopes in epidermal cell wall thickenings.
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TEM image of material embedded in LR White and examined unstained in transverse section. Short transverse lines along right-hand edge of images demarcate approximate boundaries between the cuticle (cu) and the cell wall thickening comprised of the primary cell wall (cw) and thickening of Igersheim (ti), the latter two layers intergrade and cannot be distinguished, especially in these unstained sections. (A) Outer tangential cell wall of epidermal cell immunolabelled with LM19 for de-esterified HG. This form of HG is present in most parts of the wall, but absent from the cuticle. (B) Outer tangential cell wall of epidermal cell immunolabelled with LM20 for methyl-esterified HG. This epitope is likewise absent from the cuticle, but mainly confined to the central portion of the wall thickening in this particular section. However, this distribution pattern is very variable and in other sections the methyl-esterified HG may be spread more or less throughout the wall thickening. (C) Enlarged portion of a band of Igersheim immunolabelled with LM20 for methyl-esterified HG. This epitope is abundantly and uniformly present throughout the thickening. This contrasts with de-esterified HG which is very sparsely present in these bands (not illustrated, but confirming pattern depicted in Figure 6A & C above).