DISTRIBUTION OF PHENOLIC COMPOUNDS, PECTINS AND HEMICELLULOSES IN MATURE PIT MEMBRANES AND ITS VARIATION BETWEEN PIT TYPES IN ENGLISH OAK XYLEM (QUERCUS ROBUR)

Although there is considerable information on the chemistry of bordered intervessel pit membranes, little is known on the pit membrane chemistry of other pit types in hardwoods. This study investigated distribution of phenolic compounds, pectins and hemicelluloses in different mature pit membranes of English oak xylem using transmission electron microscopy coupled with cytochemistry and immunocytochemistry. Mature bordered intertracheid (vasicentric)- and tracheid-vessel pits showed presence of xyloglucan and heteromannan (hemicelluloses) epitopes across the pit membrane (except for the annulus regions) with differences in amounts of epitopes between earlywood (EW) and latewood (LW). In contrast, pectin epitopes were detected only in the annulus regions of pit membranes. Unlike bordered pits, half-bordered (tracheary-parenchyma pits) and simple (parenchyma pits) pit membranes were rich in pectin epitopes but lacked heteromannan epitopes, indicating difference in pit membrane chemistry between pit types. Distribution of phenolic compounds also differed between pit types and between EW and LW. LW also showed great variations in distribution of phenolic compounds between vessels. Together, this study demonstrates that there are great variations in pit membrane chemistry between pit types and between EW and LW in English oak xylem.

The Distribution of un-esterified and Methyl-Esterified Pectic Polysaccharides in Pinus Radiata

A cationic dye which binds acidic polymers such as pectin and monoclonal antibodies, directed against un-esterified and methyl-esterified (JIM5) and only methyl-esterified (JIM7) pectin epitopes, were used, in conjunction with light microscopy, confocal microscopy and immunogold electron microscopy, to study the spatial distribution of pectin in the xylem tissue of Pinus radiata D. Don. Histochemistry demonstrated that pectin was located in the compound middle lamella (CML) of the maturing tracheid cell wall, in addition to the pit membranes and the CML of the ray cell walls. Immunogold labeling showed differential distribution of the pectin epitopes within the CML of the maturing cell walls. Moreover, in the xylem, the JIM5 and JIM7 epitopes were found to be restricted to distinct tissues. Neither epitope occurred in the secondary walls of the xylem cells. These patterns of epitope expression were not maintained in the mature cell. These results represent the first demonstration of restricted spatial patterns of distribution of these epitopes in the xylem tissue of radiata pine and are consistent with results from other coniferous gymnosperms.