Immunocytological Comparison of Native and Wound Periderm Maturation in Potato Tuber

American Journal of Potato Research, Mar/Apr 2004 by Sabba, Robert P, Lulai, Edward C

The monoclonal antibody JIM7 recognizes an epitope present in moderately to highly esterified HG (Knox et al. 1990; Willats et al. 2000). Specifically, JIM7 recognizes epitopes with either three or more methyl-esterified galacturonan residues, or alternating methyl-esterified residues, all with adjacent or flanking un-esterified residues (Clausen et al. 2003). JIM7 labeled both phellem and phelloderm cell walls in both immature and mature native periderm (Figure 3A, B). Taken together with the JIM5 labeling pattern, these data indicate that the suberized phellem cell walls do contain HG, but most of it is methyl-esterified. This conclusion is also consistent with results obtained using totally different chemistries, i.e., the histological data showing that ruthenium red stained phellem cell walls, but only after the walls have been chemically de-esterified prior to staining (Sabba and Lulai 2002). Of particular interest, JIM7 labeled phellogen radial walls very weakly in immature native periderm (Figure 3A). In comparison, labeling of phellogen radial walls was intense in mature native periderm (Figure 3B). These results imply that phellogen cell wall thickening resulting from native periderm maturation is accompanied by increases in both un-esterified and esterified HG. JIM7 labeled wound periderm cell walls very weakly (Figure 3C, D). In particular, JIM7 labeled phellogen cells weakly in both immature and mature wound periderm (Figure 3C, D). This result implies that maturation of wound periderm is not associated with an increase in either esterified or un-esterified HG in phellogen radial walls.

The differences between HG labeling of phellogen walls of native and wound periderm imply that different biochemical processes are involved in the strengthening and thickening of phellogen walls accompanying maturation of the two types of periderm. Careful consideration of the differences in maturation and development of resistance to excoriation between the two types of periderm is recommended before making comparisons between native and wound periderm.

ACKNOWLEDGMENTS

The authors thank J. P. Knox for the generous gift of JIM 5 and JIM 7 antibodies, as well as T. P. Freeman and K. C. Vaughn for invaluable technical advice.

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