Effect of Lateral Root Formation on the Vascular Pattern of Barley Roots

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Abstract
The vascular pattern in the root of barley (Hordeum vulgare L.), characterized by discontinuous xylem, is markedly affected by its branching. The roots become divided into unbranched segments alternating with branched segments with a more complex vascular pattern, formed by two systems differing in origin and age: the primary vascular system derived from the procambium and ontogenetically younger connective vascular system derived from stelar parenchyma.Adjacent to the sites of the lateral root initiation, reprogramming of parent stelar parenchyma for connective vascular elements occurs. The connecting phloem is represented by small sieve elements and companion cells, the connecting xylem is composed of small vessel elements with reticulate or scalariform‐reticulate wall thickenings and simple perforations. Development of the connective vascular system secures continuous lateral and axial vascular connection between lateral root and parent root. The extent of the vascular connection in the parent root increases in an acropetal direction.Hydraulic effects of connective vascular tissue formation and parent root segmentation are discussed.