Organic substances in xylem sap delivered to above-ground organs by the roots.
Squash (Cucurbita maxima) xylem sap, an apoplastic fluid, contains t-zeatin riboside, glutamine, methylglycine, myo-inositol, fructose, oligosaccharides of arabinogalactan, glucan, galacturonan, and pectins (rhamnogalacturonan-I and rhamnogalacturonan-II), as well as various proteins, including arabinogalactan and pathogen-related proteins. These substances are mainly produced in stele (xylem) parenchyma and the pericycle in the root-hair zone where ion transporter genes are expressed. Glycine-rich protein genes (CRGRPs) cloned by antiserum raised against whole xylem sap of cucumber (Cucumis sativus) were abundantly expressed in the parenchyma cells surrounding xylem vessels in the root-hair zone. CRGRP proteins accumulated and immobilized in the lignified walls of metaxylem vessels and perivascular fibers in shoots, suggesting a systemic delivery mechanism of wall materials via xylem sap. A major 30-kDa protein (XSP30) found in cucumber xylem sap was homologous to the B chains of a lectin (ricin) and bound to a nonfucosylated core N-acetylglucosamine dimer of N-linked glycoproteins abundant in leaf parenchyma cells. XSP30 gene expression, abundant in root xylem parenchyma and pericycle, and the level of XSP30 protein fluctuated diurnally under the control of a circadian clock, and the amplitude was up-regulated by gibberellic acid produced in young leaves, suggesting a long-distance control system between organs.
Satoh
Shinobu
S
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan, satohshi@sakura.cc.tsukuba.ac.jp
D002473:Cell Wall / Q000378:metabolism; D009930:Organic Chemicals / Q000378:metabolism*; D035261:Plant Components, Aerial / Q000166:cytology / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D052584:Xylem / Q000737:chemistry / Q000378:metabolism*
D009930:Organic Chemicals; D010940:Plant Proteins