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

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.

EPICORMIC SHOOTS INDUCTION AND ROOTING CUTTINGS OF Calophyllum brasiliense

“…The damage to the region area generates a tumescence just above the girdle ( Figure 2E), result from the onsite accumulation of soluble sugars and starch, along with the cessation of stem growth below the girdle (CHANO et al, 2015), in some cases, resulting the death of the plant (BOND; MIDGLEY, 2003) (Figure 2C and D). It is common the intense deepening of the cut, bypassing the cambium and reaching the xylem, reducing the hydraulic conductivity and the translocation of photoassimilates (GLEASON et al, 2016).…”

Transcriptomic analysis of juvenile wood formation during the growing season in Pinus canariensis

“…ex DC. This is not a common model species for this purpose, although it has noteworthy characteristics: it shows a remarkable healing capacity (recently described in López et al 2015;Chano et al 2015) and produces abundant resinous heartwood, which prevents putrefaction and reaches high market values, due to its aesthetic characteristics and its durability even under outdoor conditions (Climent et al 1998;Taylor et al 2002). A special feature of its secondary xylem, i.e.…”

Xylogenesis in response to severe traumatism in the Canary Island pine (Pinus canariensis C. Sm. ex DC)

“…Traumatic wood usually presents malformed tracheary elements and fibers, with altered lignification patterns, and with a high proportion of parenchymatic cells. Orientation of these elements is also very often distorted (Zajaczkowska 2014a, 2014b, Arbellay et al 2014, Chano et al 2015, probably due to altered hormonal flux, and also to altered mechanical signals, as suggested in Chapter 2 (Chano et al 2015). This disorganized xylem implies an evident disadvantage for water and nutrient transport (Arbellay et al 2014).…”

“…On the contrary, this proliferation from (partially) differentiated cells is not usual in conifers. In these species healing takes place mainly from the remaining vascular cambium in the margins of the wound, as described in Chapter 2 for Pinus canariensis (Chano et al 2015).…”

“…ex DC. This is not a common model species for this purpose, although it has noteworthy characteristics: it shows a remarkable healing capacity (described in Chapter 2, Chano et al 2015, andLópez et al 2015) and produces abundant resinous heartwood, which prevents putrefaction and reaches high market values, due to its aesthetic characteristics and its durability even under outdoor conditions (Climent et al 1998, Taylor et al 2002. A special feature of its secondary xylem, i.e.…”