Studies on the Secretion of Maize Root Cap Slime

Abstract

The distribution of fucose-containing polysaccharides in apical 1-cm sections of corn (Zea mays cv. (3) showed that when the distribution of label appearing in fucose was expressed as a ratio of label in xylose, the ratio was higher in the apical 0.5-mm section of the root. An autoradiographic study by Kirby and Roberts (7) Figure 1. Twentyfive root tips and 1 ml of medium were removed from the incubation flask and washed four times with 1 ml of chilled distilled H20. The medium and washings were combined and filtered through a glass fiber disc. The filtrate was made to 80% (v/v) alcohol and allowed to stand at 4 C overnight. The precipitate (secreted material) was then collected on a glass fiber disc and counted. The final soluble filtrate was reduced to a standard volume and is referred to as the supernatant medium. The washed roots were homogenized in 1 ml of chilled glass-distilled H,O in a glass-Teflon homogenizer at 4 C. The brei was either filtered through a glass fiber disc, and the filter was washed with water or centrifuged at 20,000g for 30 min, then resuspended and recentrifuged. The centrifuged pellet or filter disc is referred to as the insoluble cell wall material. The remaining filtrate was combined with the washings, made to 80% (v/v) alcohol, and allowed to stand at 4 C overnight; it was then filtered through a glass fiber disc. The resulting precipitate is designated the homogenate precipitate, and the filtrate, which was reduced in volume, is referred to as unincorporated uptake (Fig. 1).Root tips and secreted materials were also fractionated chemically as outlined by Ray and Baker (10). After the required incubation time in L-fucose-1-[rH], 100 root tips (5 mm) were ground in a glass-Teflon motorized homogenizer at 4 C with 4 ml of incubation medium. The brei was centrifuged at 20,000g for 30 min. The supernatant was retained and the pellet was resuspended with 1 ml of distilled H20 and recentrifuged. The supernatants were combined and the pellet was retained. The supernatant was made 80% (v/v) alcohol and allowed to stand at 4 C for 24 hr. The precipitate was collected on a glass fiber filter disc and is referred to as the cold water-soluble material. The pellet was extracted with 5 307 www.plantphysiol.org on May 10, 2018 -Published by Downloaded from

Auxin-binding Sites of Maize Coleoptiles Are Localized on Membranes of the Endoplasmic Reticulum

“…Cytochrome oxidase was determined by adding an appropriate aliquot (10-50 ,lI) of particle suspension or gradient fraction to 0.5 ml of 20 ,uM reduced Cyt c in 50 mm tris buffer (pH 7.5), and following optical density at 550 nm with a recording spectrophotometer. NADH:-and NADPH:Cyt c reductases were assayed similarly but the medium contained 20 ,lM oxidized Cyt c, 80 ,mM NADH or NADPH, and 1 mm KCN.…”

Accumulation of Al in Root Mucilage of an Al-Resistant and an Al-Sensitive Cultivar of Wheat

“…Because the root-tip region is the site of the most intense mucilage production (Paul1 and Jones, 1975), immobilization of A1 in this layer could constitute an important mechanism that protects the meristem from A1 injury (Horst et al, 1982) through exclusion of A1 from the cell symplasm (Taylor, 1988(Taylor, , 1991. Chelate ligands present in the mucilage may bind A1 and thereby present a physical or chemical barrier to the inward movement of A1 (Henderson and Ownby, 1991).…”

“…Chelate ligands present in the mucilage may bind A1 and thereby present a physical or chemical barrier to the inward movement of A1 (Henderson and Ownby, 1991). Enhanced exudation of malate (Delhaize et al, 199313;Basu et al, 1994b;Ryan et al, 1995a, 199513) and citric acid (Miyasaka et al, 1991;Pellet et al, 1995) have been reported in Al-resistant cultivars of T. aestivum, Phaseolus vulgaris, and Z. mays. Furthermore, Horst et al (1982) showed that 50% of total A1 in 5-mm root tips of V. unguiculata was bound to mucilage.…”

Metabolic alterations proposed by proteome in rice roots grown under low P and high Al concentration under low pH

“…Plant roots grown under Al stress secrete organic acids and moderate the toxicity of Al ions by chelation [24]. A viscous mucilage, consisting mainly of polysaccharides, is secreted from roots and may act as a barrier to Al toxicity [25,26]. Moderation by organic acids, proteins, and other ligands, accumulation of Al in vacuoles, and activation of Al-tolerant enzymes have been suggested as symplasmic tolerance mechanisms [27].…”