ABSTRACT
The cellulose-enriched tertiary cell walls present in many plant fibers have specific composition, architecture, machinery of formation, and function. To better understand the mechanisms underlying their mode of action and to reveal the peculiarities of fibers from different plant species, it is necessary to more deeply characterize the major components. Next to overwhelming cellulose, rhamnogalacturonan I (RG-I) is considered to be the key polymer of the tertiary cell wall; however, it has been isolated and biochemically characterized in very few plant species. Here, we add RG-I to the list from the phloem fibers of the Phaseolus vulgaris stem that was isolated and analyzed by nuclear magnetic resonance (NMR), dynamic light scattering, and immunolabeling, both within tissue and as an isolated polymer. Additionally, fibers with tertiary cell walls from nine species of dicotyledonous plants from the orders Malphigiales, Fabales, and Rosales were labeled with RG-I-related antibodies to check the presence of the polymer and compare the in situ presentation of its backbone and side chains. The obtained results confirm that RG-I is an obligatory polymer of the tertiary cell wall. However, there are differences in the structure of this polymer from various plant sources, and these peculiarities may be taxonomically related.
Subject(s)
Galactans , Pectins , Galactans/chemistry , Pectins/chemistry , Plants , Cellulose , Cell Wall/chemistryABSTRACT
OBJECTIVE: To describe a case of emphysematous hepatitis which is a rare clinical entity, characterized by a fatal, rapidly progressive infection of the liver with a radiological appearance simulating emphysematous pyelonephritis and to help provide more data about the causative organisms and precipitating factors of this pathology. DATA SOURCES AND SYNTHESIS: Relevant literature was reviewed and, to the best of our knowledge, there is limited data regarding the pathogenesis, causative organisms, and management of this condition. CONCLUSION: Emphysematous hepatitis is a rapidly progressive infection that can be fatal in the absence of appropriate therapeutic intervention. Initial clinical manifestations are usually subtle and thus high clinical suspicion is required for early diagnosis and management of this condition to help decrease the mortality rates.
ABSTRACT
Contractile cell walls are found in various plant organs and tissues such as tendrils, contractile roots, and tension wood. The tension-generating mechanism is not known but is thought to involve special cell wall architecture. We previously postulated that tension could result from the entrapment of certain matrix polymers within cellulose microfibrils. As reported here, this hypothesis was corroborated by sequential extraction and analysis of cell wall polymers that are retained by cellulose microfibrils in tension wood and normal wood of hybrid aspen (Populus tremula × Populus tremuloides). ß-(1â4)-Galactan and type II arabinogalactan were the main large matrix polymers retained by cellulose microfibrils that were specifically found in tension wood. Xyloglucan was detected mostly in oligomeric form in the alkali-labile fraction and was enriched in tension wood. ß-(1â4)-Galactan and rhamnogalacturonan I backbone epitopes were localized in the gelatinous cell wall layer. Type II arabinogalactans retained by cellulose microfibrils had a higher content of (methyl)glucuronic acid and galactose in tension wood than in normal wood. Thus, ß-(1â4)-galactan and a specialized form of type II arabinogalactan are trapped by cellulose microfibrils specifically in tension wood and, thus, are the main candidate polymers for the generation of tensional stresses by the entrapment mechanism. We also found high ß-galactosidase activity accompanying tension wood differentiation and propose a testable hypothesis that such activity might regulate galactan entrapment and, thus, mechanical properties of cell walls in tension wood.
