Immunocytochemical Evidence that Secretion of Pectin Occurs During Gel (Gum) and Tylosis Formation in Trees

Abstract

During gel (gum) formation in angiosperm trees, fibrillar material accumulated in protective layers of xylem parenchyma cells before being secreted across half-bordered pit membranes into vessel elements. Immunogold labeling demonstrated that this fibrillar material was mainly composed of partially esterified pectic polysaccharides. The primary wall of expanding tyloses, an extension of the parenchyma protective layer, secreted similar pectic substances to completely block vessel elements. In most studies, these occluding structures were reported to be formed in response to causative factors such as aging processes, injuries, or infections. Current observations support the view that partial to complete embolism, which almost always accompanies these factors, might be the main cause triggering the formation of vessel occlusions. Whereas pectin seems to be the basic component of gels (gums) and of the external layer of tyloses, other substances, such as phenols, were also detected either as a part of these plugs or as accumulations beside them in vessels. Finally, it is proposed that the term 'gel' instead of 'gum' be used in future studies to describe the occluding material secreted by ray and paratracheal parenchyma cells.

Tissue invasion and alteration in eggplant infected with Verticillium dahliae: A light and transmission electron microscopy study

“…As some evidence was obtained that the subtending host wall was much degraded, the detachment of vessel wall components cannot be due to simple mechanical damage resulting from sample manipulation. In comparison, pectinlabelled compounds present in vessel lumina in the wilt-affected plants studied were more often than otherwise found to be released from tyloses or directly secreted by paratracheal cells (Et-Touil et al 2005;Ouellette et al 1999Ouellette et al , 2004dRioux et al 1998). Therefore, gel formation, if any in the present case, would not originate from host wall alteration as mentioned by others (Beckman 1987;Cooper 1998;Vander Molen et al 1977, for example).…”

Histopathology of Fusarium wilt of staghorn sumac (Rhus typhina) caused by Fusarium oxysporum f. sp. callistephi race 3. III. Host cell and tissue reactions

“…These similarities pertain to the thickening and deposition of new wall layers, including gelatinous ones in fibres, and to the deposition of suberin-like layers in tyloses, paratracheal parenchyma cells, and in cells of the medullary sheath and of the barrier zones formed. Labelling of tylosis walls for pectin and cellulose was equivalent to that observed in elms (Rioux et al 1998). The areas containing cells with very opaque content and thickened walls, surrounding groups of vessel elements, also recalled those occurring in elms (American, Siberian, and different clones) and in non-hosts inoculated with the Dutch elm disease (DED) pathogen (Et-Touil et al 2005;Ouellette and Rioux 1992;Rioux and Biggs 1994).…”

“…For localizing pectin compounds, a monoclonal antibody (denoted JIM 5 and kindly provided by Dr. R. Keith, Long Ashton Research Institute, UK) was used as previously described (Rioux et al 1998).…”

Laurel Wilt in Natural and Agricultural Ecosystems: Understanding the Drivers and Scales of Complex Pathosystems

“…The production of gels [125] and tyloses [126] in the xylem are two of the most common attributes of affected woody plants [127][128][129][130][131].…”

“…Tyloses are formed in xylem lumena in response to pathogen infection, embolism, aging, and injury [131]. They are outgrowths from adjacent parenchyma cells, and even though they can prevent desiccation, damage, and infection of adjacent cells [131], they also reduce hydraulic conductivity (water conductance) [132].…”