Research - Plant Vascular Development

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Phloem conduits are essential inter-organ communication systems that enable the plants to respond to environmental and developmental cues. During the last decades, Arabidopsis thaliana seedlings roots have been proved to be an excellent system to study vascular development as their being rather transparent enabled their most inner cell layers to be imaged. Within the root meristem, differentiating protophloem strands can be unequivocally identified when root is stained with propidium iodide and imaged using confocal microscopy due to their enhanced cell wall staining. During protophloem differentiation, nucleus breaks down, cell wall gets thicker and callose deposition takes place in the cell walls of adjacent cells.

Root protophloem differentiation
“Root protophloem differentiation”: Confocal microscopy image of 5-day-old root meristems in the protophloem differentiation region where cell wall thickening, nuclei degradation, and callose deposition can be observed. Yellow asterisks mark protophloem strands.

Remarkably, a tight balance of a lipid compound, phosphatidylinositol-4,5-biphosphate (PIP2) is essential for protophloem differentiation, as shown by the presence of some undifferentiated cells in the protophloem strands of mutants with disturbed levels of PIP2. Additionally, a perturbed progression of protophloem development leads to a reduced meristematic activity associated with a higher density of lateral roots. Thus, elucidating the molecular mechanisms by which PIP2 regulates protophloem differentiation will bring us closer to understand how to shape root architecture.

Root vasculature
“Root vasculature”: Toluidine blue-stained histological cross sections of wild type root (A) and phosphoinositide deficient mutant (B) at the position of differentiated protoxylem. Arrowhead indicated differentiated protophloem (A) and undifferentiated cell at the position of the protophloem (B).
propidium iodide stained root meristems
3-Confocal microscopy images of a propidium iodide stained root meristems of a wild type plant (A) and a phoshpoinoisitide-deficient mutant (B). Discontinuous progression of protophloem strand (marked by arrow heads) leads to a reduced meristem size.
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Fri Jul 21 00:11:00 CEST 2017
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