Pectic epitopes are differentially distributed in the cell walls of potato (Solanum tuberosum) tubers

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Abstract
Six monoclonal antibodies (mAbs) were used to map the distribution of pectic epitopes in the cell walls of potato (Solanum tuberosum L. cvs Kardal and Karnico) tuber tissue in both light and electron microscopes. Unesterified (mAb JIM 5 epitope) and methyl‐esterified (mAb JIM 7 epitope) pectins were abundant and equally distributed in all parenchymal and vascular cell walls. Homogalacturonans (HGAs) involved in Ca2+‐cross‐linking (mAb 2F4 epitope) were localised to the middle lamella and abundant at cell corners. The tuber cortex was densely labelled, but parenchymal cell walls in the perimedullary region contained few epitopes of calcium pectate except at corners and pit fields. In contrast, pectic side‐chains were not detectable in the middle lamella of all parenchymal cell walls, except in the cortex where mAb LM6 (arabinan epitope) labelled the entire wall. The galactan epitope (mAb LM5) was localised to a zone very close to the plasmalemma in cortical cell walls and was also less abundant at pit fields and in vascular cell walls. MAb CCRC‐M2 (rhamnogalacturonan I epitope) did not cross‐react. Our results show that the cell walls of potato tubers are not homogeneous structures and that the pectic composition of the walls is spatially regulated.