We have developed a rapid procedure for isolating a fraction enriched in plasma membrane from DunalielIa salUna using an aqueous two-phase system (dextran/polyethylene glycol, 6.7%/ 6.7%). An enriched plasma membrane fraction, free of chloroplast and mitochondrial contamination, could be obtained in 2.5 hours. Plasma membrane proteins, which accounted for approximately 1% of the total membrane protein, contained a number of unique proteins compared with the other cell fractions, as shown by gel electrophoresis. The lipids of the plasma membrane fraction from 1.7 molar NaCI-grown cells were extracted and characterized. Phosphafidylethanolamine and phosphatidylcholine were the two most prevalent phospholipids, at 20.6% and 6.0% of the total lipid, respectively. In addition, inositol phospholipids were a significant component of the D. salina plasma membrane fraction.Phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate accounted for 5.2% and 1.5% of the plasma membrane phospholipid, respectively. Diacylglyceryltrimethylhomoserine accounted for 7.9% of the plasma membrane total lipid. Free sterols were the major component of the plasma membrane fraction, at 55% of the total lipid, and consisted of ergosterol and 7-dehydroporiferasterol. Sterol peroxides were not present in the plasma membrane fraction. The lipid composition of enriched plasma membrane fractions from cells grown at 0.85 molar NaCI and 3.4 molar NaCI were compared with those grown at 1.7 molar NaCI. The concentration of diacylglyceryltrimethylhomoserine and the degree of plasma membrane fatty acid saturation increased in 3.4 molar plasma membranes. The relative concentration of sterols in the plasma membrane fraction was similar in all three NaCI concentrations tested.
We tested predictions of the hypothesis that pectin methylesterase in the root cap plays a role in cell wall solubilization leading to separation of root border cells from the root tip. Root cap pectin methylesterase activity was detected only in species that release large numbers of border cells daily. In pea (Pisum safivum) root caps, enzyme activity is correlated with border cell separation during development: 6-fold more activity occurs during border cell separation than after cell separation is complete. Higher levels of enzyme activity are restored by experimental induction of border cell separation. A corresponding increase in transcription of a gene encoding root cap pectin methylesterase precedes the increase in enzyme activity. A dramatic increase in the level of soluble, deesterified pectin in the root tip also is correlated with pectin methylesterase activity during border cell development. This increase in acidic, de-esterified pectin during development occurs in parallel with a decrease in cell wall/apoplastic pH of cells in the periphery of the root cap.Plants of many species produce thousands of healthy somatic cells, which separate physically from the tip of the root and are released into the extemal environment (Knudson, 1919). We refer to these cells as root "border" cells to emphasize that under natural conditions populations of the cells constitute a physical and biological interface between the root surface and the soil environment (Hawes, 1990). Root border cells constitute a uniquely differentiated "tissue" whose proposed function is to protect the growing root tip by regulating the balance of beneficial and pathogenic microorganisms in the rhizosphere (Hawes, 1990). This hypothesis is based on observations of genotype-specific and cell-specific effects of border cells on microbial behavior, development, and ability to form stable associations with roots (Sherwood, 1987; reviewed by Hawes and Brigham, 1992; Hawes et al., 1993).Plants regulate border cell release during development and in response to environmental cues (Hawes and Lin, 1990). When roots are grown in agar, where the separation of border cells can be monitored easily, an individual root may continually release border cells, which ensheath the root from crown to the tip, or it may release cells only intermittently (Hawes and Brigham, 1992). Such differences have no obvious effect on growth rate or on ability of roots to penetrate semisolid media. However, the presence or absence of so ' This work was supported by a grant to M.C.H. from the U.S.* Corresponding author; fax 1-602-621-9290. Department of Energy, Division of Energy Biosciences.739 much organic matter, let alone living cells, is likely to have a significant effect on the physical and biological properties of the rhizosphere.Plant genes controlling border cell separation are not known, but bacterial genes encoding hydrolytic enzymes have been shown to cause plant cell separation by degrading pectic compounds in the cell wall (Collmer and Keen, 1986; Koutojansky, 1...
Root border cells were isolated from alfalfa seedlings, and incubated in culture medium with growth regulators. Alfalfa seedlings yielded 1500-+ 100 cells per root, and initial viability of the cells was 95 -+ 5%. Multiple cell divisions occurred in the border cells within two weeks. Cell clusters transferred to solidified medium containing growth regulators developed into rapidly growing, friable callus. When transferred to growth regulator-free medium, some of the calluses generated normal roots.
The unicellular, wall-less alga DunalielIa salina has been shown to contain an array of proteins modified by the covalent attachment of fatty acids. Myristic acid (14:0) (2,8). Palmitate, generally found in ester linkage (7, 14), appears to be attached almost exclusively to membrane proteins while 14:0, commonly bound in amide linkage, is present in both membrane bound and soluble proteins. It is known that protein acylation can occur either co-or post-translationally (13,19), but the physiological significance of the process remains unclear.Studies ofviral, mammalian and, recently, lower eukaryotic systems, such as Tetrahymena (17) have formed the basis of currently available information on acylated proteins. The first and, to our knowledge, the only characterization of acylated protein from a plant is found in the work of Mattoo and Edelman (9), who reported the palmitoylation of the chloroplast 32-kD herbicide-binding protein of Spirodela oligor-
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.