Abstract
Radial growth has long been a subject of interest in tree biology research. Recent studies have brought a significant change in the understanding of some basic processes characteristic to the vascular cambium, a meristem that produces secondary vascular tissues (phloem and xylem) in woody plants. A new hypothesis regarding the mechanism of intrusive growth of the cambial initials, which has been ratified by studies of the arrangement of cambial cells, negates the influence of this apical cell growth on the expansion of the cambial circumference. Instead, it suggests that the tip of the elongating cambial initial intrudes between the tangential (periclinal) walls, rather than the radial (anticlinal) walls, of the initial(s) and its(their) derivative(s) lying ahead of the elongating cell tip. The new concept also explains the hitherto obscure mechanism of the cell event called ‘elimination of initials’. This article evaluates these new concepts of the cambial cell dynamics and offers a new interpretation for some curious events occurring in the cambial meristem in relation to the radial growth in woody plants.
Highlights
With an estimated global forest growing stock of 530.5 billion m 3 (Köhl et al 2015), production of wood and bark by the activity of vascular cambium, the lat‐ eral meristem in woody plants, is one of the most important biological processes on1 3 Vol.:(0123456789)A
The circumferential expansion in the storeyed and non-storeyed cambia is believed to occur by different mechanisms, i.e. through longitudinal anticlinal divisions coupled with the symplastic growth of the resultant sister initials in storeyed cam‐ bium, while through oblique anticlinal divisions followed by intrusive growth of the sister initials in the case of non-storeyed cambium (Fahn 1990; Larson 1994; Evert 2006)
Recent studies on the radial growth of arborescent plants have brought out the fol‐ lowing facts related to the cambial cell dynamics: (1) The frequent periclinal divisions of cambial cells contribute adequately to the radial expansion of the symplastically growing cambium tissue by adding new layers of derivatives
Summary
With an estimated global forest growing stock of 530.5 billion m 3 (Köhl et al 2015), production of wood and bark by the activity of vascular cambium, the lat‐ eral meristem in woody plants, is one of the most important biological processes on. The cambium exists in a form of cylinder of multi-layered meristematic cells between xylem and phloem tissues (Fig. 1a–c) It surrounds the central wood core and is itself surrounded by an outer cylinder of bark in the long axis (root and shoot) of woody plants. Studies undertaken on the cambial cell growth during the last two decades (Karc‐ zewska 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 stud‐ ies have elucidated certain characteristic features of the cambium from new angles, suggesting that the mechanical strains in the cambial tissue likely affect the pro‐ cesses involved in the formation of wood and the consequent increase in the cam‐ bial circumference. This article attempts to compare these newly emerging concepts with the traditional knowledge of the cambial dynamics, with special focus on radial growth of wood in stems and roots and the consequent expansion of the cambial circumference
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