Proliferation of axial parenchymatic xylem cells is a key step in wound closure of girdled stems in Pinus canariensis.

Víctor Chano,Rosana López,Pilar Pita,Carmen Collada,Álvaro Soto

doi:10.1186/s12870-015-0447-z

Abstract

BackgroundWounds caused by fire, herbivorism, rock impacts, etc. cause the direct loss of photosynthetic, storage and/or vascular tissue. In addition, they may entail other damages, such as desiccation of the exposed internal parts, or become a gateway to infection by fungi and other pathogens. To successfully overcome such injuries, plants must reorganize their meristems or even differentiate new ones, producing new traumatic tissues to cover the wound and restore the vascular connection.ResultsIn this work we analyse the anatomical growth response in conifers after debarking and injuring the vascular cambium, using Pinus canariensis as model species, due to its high wound recovery ability. Conversely to angiosperm woody species, this process is initiated and largely driven by the damaged vascular cambium and not by proliferation in the wound surface. We have detected alterations and switches in the divisions of cambial cells, associated to their position relative to the surface and edges of the wound, resulting in disordered traumatic xylem. We also describe the formation of column-like structures, after girdling, which are in part formed by the proliferation of xylem parenchymatous cells, associated to axial resin ducts.ConclusionsAbundant resinosis on the wound surface, typical of conifers, is an efficient barrier against opportunistic fungi, insects, etc. but it also hinders the healing process directly from the surface. Thus, wound closure must be largely carried out from the wound margins, being a much slower process, which very often remains unconcluded for long years. This work also describes for the first time the proliferation of inner parenchymatous cells to form column-like structures, which accelerates wound closure in girdled P. canariensis. Irregularities in the surface of the healing edge or column-like structures result in the production of disordered vascular tissues, compromising their future functionality, and which must be overcome through the fast restoration of the proper polarity in vascular cambium.

Highlights

Wounds caused by fire, herbivorism, rock impacts, etc. cause the direct loss of photosynthetic, storage and/or vascular tissue
As occurs in most conifers, the first response to wounding in P. canariensis is an abundant resinosis in the wound surface, but the wound closure process takes place mostly from the wound edges
While for young twigs of Picea abies, Thuja orientalis or Metasequoia glyptostroboides just a tenuous lignification can be observed in the injury boundary seven-ten days after wounding [39], a layer of strongly suberized cortical parenchymatous cells is already detectable by that time in P. canariensis

Summary

Introduction

Herbivorism, rock impacts, etc. cause the direct loss of photosynthetic, storage and/or vascular tissue. They may entail other damages, such as desiccation of the exposed internal parts, or become a gateway to infection by fungi and other pathogens To successfully overcome such injuries, plants must reorganize their meristems or even differentiate new ones, producing new traumatic tissues to cover the wound and restore the vascular connection. Throughout their usually long lives, trees can be affected by traumatic injuries caused by different agents, from herbivorism to forest fires, from avalanches in mountain environments to impacts from rocks and other material carried by floods or even from pyroclasts propelled by volcanic eruptions. The contrasting anatomical characteristics of gymnosperm and angiosperm xylem may underlie different healing processes leading to the lower regenerating capability of the former

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