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RESEARCH PRODUCT

Rays hamper intrusive growth of vessel elements

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description

Key message In some circumstances vessel elements, both broad and narrow, enlarge only symplastically in tangential direction. Rays play a special role in regulating intrusive enlargement of vessel elements. Abstract The aim of this study was to analyse relations occurring between vessel elements and surrounding cells, i.e. susceptibility to separation of walls of cells occurring in the vicinity of vessel elements, with regard to their type—cells of the axial/radial system. On the basis of separation/lack of separation of cell walls, and thus change in cell contacts/lack of change in cell contacts, we have estimated the contribution of particular types of growth—intrusive and symplastic—in the formation of vessel elements in: Acer pseudoplatanus, Betula pendula, Catalpa bignonioides, Quercus robur and Robinia pseudoacacia. Striking differences in susceptibility to separation of periclinal walls of axial and ray system cells were noticed. Periclinal walls of axial system cells were easily separated, even in cells which were not directly adjacent to vessel elements. Continuity of ray cells was maintained even in cases when the vessel element enlarged directly between two rays. It seems that the direct vicinity of ray increases the contribution, as well as the range of symplastic growth in a tangential direction during vessel element formation. Growth of a vessel element in a tangential direction has been described as intrusive so far. A vessel element seems to enlarge only symplastically, when derived from a mother cell located directly between two rays. Observed differences in susceptibility to separation of cell walls indicate the important role of rays in regulating intrusive expansion of vessel elements.