Occurrence and Location of Suberin in Wound Reaction Zones in Xylem of 17 Tree Species

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Abstract
The occurrence and location of suberin in xylem tissues following mechanical wounding were determined using phloroglucinol HCl in conjuction with ultraviolet fluorescence microscopy. In all species examined, thin intracellular suberin lamellae were detected in ray and/or axial parenchyma present at the time of wounding and located approximately 0.8-1.2 mm centripetal to the wound surface. Suberized xylem parenchyma was associated with a visibly discolored wound reaction zone in which xylem vessels and fibers were often found plugged with amorphous phloroglucinol-positive material or occluded by tyloses. In Castanea dentata, Hamamelis virginiana, Prunus avium, Quercus rubra, Salix nigra, and Ulmus americana, tyloses were suberized. The location of suberin in xylem ray and axial parenchyma and in vessels corresponds to walls 1, 2, and 3 of the CODIT model sensu Shigo and Marx (26). However, the suberized cells per se did not form continuous "walls." Instead, cell distribution appeared discontinuous, and often suberin was restricted only to occasional cells. The normal distribution of parenchyma in nonwounded tissue precluded formation of distinct, continuous suberized boundaries following wounding. However, in most species, continuous boundaries were formed from conjoined suberized parenchyma cells and vascular elements impregnated or occluded with phloroglycinol-positive materials or tyloses. Other specied studies were: Acer negundo, Acer saccharum, Betula papyrifera, Carya cordiformis, Fraxinus americana, Morus rubra, Ostrya virginiana, Pinus strobus, Prunus persica, Prunus serotina, Tsuga canadensis.