Intrusive growth of initials does not affect cambial circumference in Robinia pseudoacacia

Abstract

This study aimed to test the hypothesis whether intrusive growth of initial cells is related to the increase in circumference of Robinia pseudoacacia vascular cambium—both qualitatively and quantitatively. The mode of intrusive growth of cambial initial cells was also studied. Samples collected from tree trunks were examined using series of semi-thin transverse sections. Anatomical reconstructions of radial and tangential planes of analysed fragments of cambial tissue were made. Observations and measurements have shown that the intrusive growth of R. pseudoacacia initial cells does not contribute to an increase in tangential dimension of observed tissue fragments where cell rearrangement occurs. Moreover, initially separated tangential walls of cells (between which cambial initial cell elongates intrusively) are transformed into obliquely oriented walls. These results stand in accordance with a statement that only symplastic growth of initials, not intrusive growth, is responsible for the increase in circumference in all woody plants with the continuous cambial cylinder. Moreover, we managed to capture the moment of transition of initial status from one cell to another for the first time. This phenomenon may be explained on the basis of the system of mechanical stresses operating not only in the secondary meristematic tissue but also in a whole plant organism.

Contribution of intrusive and symplastic growths in wood fibre tip development

“…5). Microspaces are regarded as spots of separation of walls of neighbouring cells (Kojs 2012(Kojs , 2013Miodek et al 2021aMiodek et al , 2022, most probably accompanied by loosening of middle lamellae.…”

“…Approximated location of initial surface of the vascular cambium is marked by white, dashed line tangential direction intrusive growth of vessel elements also occurs intrusively between tangential walls of axial system cells (Wilczek et al 2011;Hejnowicz 2012;Gizińska et al 2021). Location of intrusive growth of initial cells between tangential walls of initial cells and their closest derivatives was shown qualitatively (Włoch et al 2001(Włoch et al , 2002(Włoch et al , 2009(Włoch et al , 2013Kojs et al 2004a,b;Jura et al 2006;Karczewska et al 2009;Miodek et al 2021b;Wilczek-Ponce et al 2021), and in the recent time also quantitatively (Miodek et al 2022). Thus, intrusive growth between tangential cell walls appears as a common element of cambial initials, VEMCs, and FMCs functioning.…”

“…66 cm at breast height was selected from a tree stand located in Silesian Botanical Garden in the temperate climate zone, southern Poland (50°17'N, 18°82'E, 330 m above sea level). Black locust was chosen for this study because of the storied structure of its vascular cambium, which is also reflected in deposited layers of the secondary xylem (Miodek et al 2022). This means that fibre bodies are located at the same level (Wilczek et al 2018).…”

“…Tissues were rinsed three times in phosphate buffer (4 °C) and dehydrated (5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, and 90% ethanol solution, pure ethanol, ethanol and propylene oxide solution [1:1], pure propylene oxide). Next, material was embedded in epon resin, which was polymerised in 35 °C, 45 °C and 60 °C (for 24 h at each temperature), cut with Tesla ultramicrotome (semi-thin transverse sections were obtained), stained with PAS (Periodic Acid, Schiff) and toluidine blue, and mounted in Euparal (Karczewska et al 2009;Miczajka et al 2014;Miodek et al 2022). Sections were examined under Olympus BX41 microscope (bright field).…”