Modelling for rearrangement of fusiform initials during radial growth of the vascular cambium in Pinus sylvestris L.

Abstract

In contrast to common belief, recent studies have confirmed that intrusive growth of fusiform cambial initials has a significant role in the rearrangement of the initials, but does not contribute to the cambial circumference increment. We observed a rapid rearrangement of cambial initials on a long series of transverse sections of the vascular cambium and the wood of a 50-year-old pine (Pinus sylvestris L.) tree. A comparison of cell arrangement in consecutive sections, as well as a critical analysis of tangential reconstructions, has confirmed that changes in cell locations in a group of cells on the tangential surface caused no change in the total tangential width of the whole group. Models illustrating changes in locations of the initials have been proposed, assuming that intrusive growth, which makes the growing initials intrude between the neighbouring initials and their immediate derivatives, is localized on the longitudinal edges of cells. We infer that intrusive growth of the cambial initials in P. sylvestris is not involved in the cambial circumference increment, but plays a significant role in the rearrangement of the initials, probably allowing for a relaxation of shearing strains generated during radial growth. The relationship of intrusive growth with the elimination of initials has been discussed with reference to the frequency of anticlinal divisions. It has been proposed that the occurrence of anticlinal divisions in excess over the actual requirement for increase in the cambial circumference could be due to internal shearing strains.

How Do Trees Grow in Girth? Controversy on the Role of Cellular Events in the Vascular Cambium

“…It has also eliminated one ray initial and partially eliminated three others. Similar examples has been presented in numerous studies (Kojs et al 2004b;Jura et al 2006;Włoch et al 2013;Wilczek et al 2011a).…”

“…Recent reports have shown a non-participation of intrusive growth in the circumferential increment (Kojs et al 2004a, b;Jura et al 2006;Włoch et al 2009Włoch et al , 2013Wilczek et al 2011a). In such a situation, symplastic growth that follows the anticlinal division is the only alternative that may provide a common and uniform mechanism for the increase in cambial circumference, both in the storeyed and nonstoreyed cambia.…”

“…The layer of initials is not in fact a perfect layer due to the non-parallelism of its component cells (Włoch 1981), but is a significant demarcation plane between xylem and phloem from developmental point of view. This has also been described as 'the initial surface' (Włoch and Połap 1994;Włoch et al 2013).…”

“…Studies undertaken on the cambial cell growth during the last two decades (Karczewska et al 2009 ; Kojs 2012 ; Kojs et al 2004a , b ; Jura et al 2006 ; Włoch et al 2009 , 2013 ; Wilczek et al 2011a , 2018 ; Miodek et al 2021 ) have led to a new hypothesis on the mechanism of intrusive growth of the cambial initials. These studies have elucidated certain characteristic features of the cambium from new angles, suggesting that the mechanical strains in the cambial tissue likely affect the processes involved in the formation of wood and the consequent increase in the cambial circumference.…”

Revisiting the anatomy of the monocot cambium, a novel meristem

“…Unlike its derivatives which will eventually leave the meristem and differentiate into permanent tissues, the initial cells will remain within the cambium. Taking into account the analysis of cell events (periclinal divisions, Cheadle (1937) b Simpson (1975) c Rudall (1991) d Jura-Morawiec et al (2015) e Larson (1994) f Bailey (1923) g Kojs et al (2004b) h Jura et al (2006) i Włoch et al (2013) periclinal divisions e,f,g,h,i , anticlinal divisions e,f,g,h,i , symplastic growth e,g,h,i , intrusive growth/elimination e,g,h,i Cells rearrangement absent present e,g,h,i…”