Suberized tyloses in trees: An ultrastructural and cytochemical study

Abstract

The nature of the wall layers observed in suberized tyloses was studied in Populus basalmifera L., Ulmus americana L. and Quercus rubra L. As the suberin layers were present only in tyloses that had completed their expansion, most of the results concern mature tyloses. The cyto-and immunocytochemical tests were conducted, respectively, with an exoglucanase having a binding affinity for 13(l~4)-D-glucans, the subunits of cellulose, and with two monoclonal antibodies specific for un-esterified and esterified pectic molecules. In the three species, labelling for pectic compounds was intense over the external layer of tyloses but usually more dispersed or nearly absent over the layer corresponding to a primary wall that was, however, intensely labelled for 13(1 ~4)-Dglucans. The outer wall layer, comparable to a middle lamella in mature tyloses, was continuous with similar material that appeared to be secreted by the tylosis. This material was particularly abundant in pit chambers, in void spaces between the tylosis and the vessel wall, particularly at the junction of the vessel and two adjacent cells, and close to the rim of vessel perforation plates. In P. balsamifera, a single suberized layer or occasionally a succession of suberized and cellulose-containing layers was observed internal to the tylosis primary wall. In U. americana, the wall of tylosis was similar to that of P. balsamifera except that, at times, a secondary-wall-like layer was formed and only a single suberized layer was observed. In Q. rubra, the suberized layer was always observed internal to the tylosis secondary wall. Simple pits were also constantly noted in Q. rubra tyloses. The occasional occurrence of a cellulosic layer internally to the suberized layer was observed in the three species. Histochemical tests revealed that lignin was also an important component of the tylosis wall. The tyloses frequently contained phenolic compounds in close association with the suberized layers. The significance of the formation of suberized tyloses in trees is discussed.Abbreviation: TEM = transmission electron microscope

The Parenchyma of Secondary Xylem and Its Critical Role in Tree Defense against Fungal Decay in Relation to the CODIT Model

“…infected with Dutch elm disease ( Ophiostoma novo-ulmi ), localized blockage of vessels is so efficient, owing to production of toxins by the fungus, that vertical transport to the canopy is often blocked, contributing significantly to tree death (Newbanks et al, 1983; Ouellette et al, 2004; Solla et al, 2005). Vascular blockage by gels containing pectins along with suberin arising from parenchyma was found to occur quite rapidly in the secondary xylem of U. americana (American elm) after inoculation of Ophiostoma novo-ulmi (Rioux et al, 1995). The hydraulic redundancy model (Ewers et al, 2007; Schenk et al, 2008) explains how these trade-offs can be affected by the degree of “inter-connectivity” between vessels in plants, where species with an integrated redundancy (high degree of inter-connectedness) create alternate pathways around blockages arising from tyloses or disease.…”

Vascular Occlusions in Grapevines with Pierce’s Disease Make Disease Symptom Development Worse

“…Tyloses are the vascular occlusions in many infected plants, such as oak (Quercus spp.) with oak wilt (Struckmeyer et al, 1958;Blaedow and Juzwik, 2010), American elm (Ulmus americana) with Dutch elm disease (Ouellette and Rioux, 1992;Rioux et al, 1995), and hop (Humulus lupulus) infected with Verticillium spp. (Talboys, 1958).…”

Tyloses and gels associated with cellulose accumulation in vessels are responses of plane tree seedlings (Platanus × acerifolia) to the vascular fungus Ceratocystis fimbriata f. sp platani

“…Bar=1 µm walls. The process by which tyloses arise from vesselassociated parenchyma cells was shown to be associated with the active production of pectic compounds with a fibrillar aspect, resulting in the accumulation of gel within the vessel lumen (Rioux et al 1995(Rioux et al ,1998 and occlusion.…”