Tyloses and Gums: A Review of Structure, Function and Occurrence of Vessel Occlusions

Abstract

Vessel occlusion through tyloses or gums is a natural phenomenon occurring with aging and heartwood formation, and in sapwood in response to vessel embolism. These types of vessel occlusion play a crucial role to limit the spread of pathogens and wood decay organisms, also as part of compartmentalization after wounding. In the sapwood, they can be considered to be an effective stress response.Here we review the literature on tyloses and gums in hardwoods, starting with the detailed 19th century account on tyloses by Hermine von Reichenbach. The structural diversity of tyloses (from thin-walled to sclerotic) and gum deposits is highlighted and illustrated. Our understanding of the development of vessel occlusions through vessel contact cells of the ray and axial parenchyma has greatly increased over the last decades, also thanks to ultrastructural and immunocytological studies. We critically discuss the postulated relationships between vessel-to-ray parenchyma pit size and vessel size and the incidence of either tyloses or gums and review the occurrence of these types of vessel occlusions in extant and fossil dicots. All factors identified in the literature as stimuli for vessel occlusion probably act through vessel embolism as a single direct trigger. Attempts in the literature to relate vessel occlusion with mechanisms of vessel refilling and embolism repair are controversial and invite more experimental research.

Bordered pits in xylem of vesselless angiosperms and their possible misinterpretation as perforation plates

“…The multiple functions of the amorphous layer in vessel‐bearing angiosperms include (Spicer ) tylosis formation (Foster ; Chafe ; De Micco et al . ), protection of parenchyma cells against oscillations in hydrostatic‐pressure from neighbouring vessels (Van Bel & Van der Schoot ), regulating the ability of exhibiting deep supercooling (Wisniewski & Davis ) and preserving apoplastic continuity around the protoplast of a lignified cell (Barnett et al . ).…”

Hydraulic Anatomy and Function of Trees—Basics and Critical Developments

“…Themes scale along arrows from cells that make up xylem and other transport tissues to aspects related to landscape ecology. Small 'satellites' contain key words that will be addressed in the text of each of the five themes wider conduit = tyloses) [21,22]. The result of aging processes throughout the tree canopy and associated progressive conduit occlusion leads to a radial profile featuring high rates of water transport in the outer xylem and low or no water transport in the inner xylem, and has been documented for both gymnosperm and angiosperm trees [23][24][25][26].…”

Defense Responses in Aspen with Altered Pectin Methylesterase Activity Reveal the Hormonal Inducers of Tyloses

“…They are ingrowths of parenchyma cells into the lumens of adjacent tracheary elements, whereas gels and/or gums, depending on plant species, are secreted by the parenchyma cells (Rioux et al, 1998). Tyloses have been reported in many groups of vascular plants, including angiosperms (Chattaway, 1949;Gottwald, 1972;Saitoh et al, 1993), conifers (Chrysler, 1908;Peters, 1974;Dute et al, 1999; Feng et al, 2013), progymnosperms (Scheckler andGaltier, 2003), and ferns (De Micco et al, 2016).In aspen (Populus tremula 3 tremuloides), tyloses are formed by ray contact cells (Chafe, 1974). These cells first synthesize secondary wall layers that lignify, together with the walls of adjacent vessel elements (Murakami et al, 1999), then they deposit a tertiary wall layer, called the protective layer, over the secondary wall layer.…”