The formation of dry zones in the sapwood of conifers II. The role of living cells in the release of water

Abstract

Dry zones in conifer wood, characterised by gas filled tracheids, were induced by the injection of dilute solutions of various toxic chemicals followed by incubation at 10 or 20 "G. The development of dry zones did not occur at lower temperatures nor with concentrated solutions and was prevented or retarded in an atmosphere of nitrogen. These results are discussed in relation to the development of dry zones in infections by Fomes annosus and other fungi and in the formation of heartwoocL It is postulated that the gradual death of ray cells alters their metabolism in such a way that gas emboli are evolved in adjacent tracheids; this can occur at sites of infection or at a distance under the influence of transportable or diffusible toxins.

Initial defence responses in sapwood of Eucalyptus nitens(Maiden) following wounding and fungal inoculation

“…Although drying does not seem to be dramatic, the withdrawal of water from vessels following wounding must be sucient to instigate the accumulation of phenols and formation of tyloses (however, elicitation processes by fungi may also prove to induce these factors). Phenol biosynthesis appears to require the presence of oxygen { [8,29] R.B. Pearce, unpublished work} and the accumulation of phenols can be detected in E. nitens from 24 h after wounding.…”

“…the ®rst hours or days) may determine the ability of the tree to restrict the long-term spread of decay resulting from infection [1, 14, 23±25]. Increased oxygen access following wounding has been linked to the production of antimicrobial phenolics [8,29] while changes in vessel osmotic potential can lead to the formation of tyloses [20]. The formation of tyloses and phenolics as defence responses appear ubiquitous among woody plants [23,37].…”

“…gravimetric methods) are used routinely [8,26,29]. However, this method is limited to relatively large wood blocks where immediate water loss upon preparation is reduced in signi®cance.…”

Spatial Patterns in Hyphal Growth and Substrate Exploitation within Norway Spruce Stems Colonized by the Pathogenic White-Rot Fungus Heterobasidion parviporum

“…Like heartwood of Norway spruce formed under normal circumstances without any pathological effects (3), the RZ is also separated from the sapwood by a dry transition zone (30). Infection of conifer sapwood by H. annosum sensu lato is known to induce the formation of dry zones ahead of the expanding colony (5,6), but what triggers the formation and expansion of the RZ remains unknown.…”

Scots pine responses to number and density of inoculation points with Leptographium wingfieldii Morelet, a bark beetle-associated fungus

“…The rate of fungal colonization is slow in the nutrient-rich ray cells and faster in the tracheids. Development of dried, non-conducting zones in the sapwood of conifers was frequently observed in response to fungal invasion [7,8]. They are generally located at the margin of the stained areas and elaborated in response to fungal activity [12,28].…”