3 – The Primary Cell Walls of Flowering Plants

Inactivation of red beet β-glucan synthase by native and oxidized phenolic compounds

In vitro plant cells, tissues and organ cultures are not fully autotrophic establishing a need for carbohydrates in culture media to maintain the osmotic potential, as well as to serve as energy and carbon sources for developmental processes including shoot proliferation, root induction as well as emission, embryogenesis and organogenesis, which are highly energy demanding developmental processes in plant biology. A variety of carbon sources (both reducing and non-reducing) are used in culture media depending upon genotypes and specific stages of growth. However, sucrose is most widely used as a major transport-sugar in the phloem sap of many plants. In micropropagation systems, morphogenetic potential of plant tissues can greatly be manipulated by varying type and concentration of carbon sources. The present article reviews the past and current findings on carbon sources and their sustainable utilization for in vitro plant tissue culture to achieve better growth rate and development.

Review: role of carbon sources for in vitro plant growth and development

Biosynthesis of glucans occurred in cell-free fractions isolated from onion stem (Allium cepa L.) enriched in either dictyosomes or plasma membranes. beta-1,3- and beta-1, 4-Glucans were synthesized in differing proportions and at different rates as the concentration of uridine diphosphoglucose or the proportion of dictyosomes or plasma membrane varied. At low (1.5 mum) UDP-glucose concentrations synthesis of alkali-insoluble glucan was correlated with abundance of dicytosomes; most of the substrate utilized by plasma membrane was for glycolipid synthesis. At high (1 mm) UDP-glucose concentration, the synthesis of alkali-insoluble glucans correlated with the abundance of plasma membrane. Substrate enhancement of beta-1, 4-glucan synthesis in dictyosome fractions was less than proportional to increases in substrate concentration. In contrast, beta-1, 4-glucan synthesis by plasma membrane was more than proportionately increased. At high substrate concentrations the synthesis of beta-1, 3-glucans predominated in both dictyosome and plasma membrane fractions. The results show that the capacity to synthesize glucans resides in both Golgi apparatus and plasma membranes of onion stem, but that the plasma membrane has the greatest capacity for synthesis of alkali-insoluble glucans at high UDP-glucose concentrations.

β-Glucan Synthetases of Plasma Membrane and Golgi Apparatus from Onion Stem

(1->3)- and (1->4)-[beta]-glucan synthase activities from higher plants have been physically separated by gel electrophoresis in nondenaturing conditions The two glucan synthases show different mobilities in native polyacrylamide gels Further separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a different polypeptide composition in these synthases Three polypeptides (64, 54, and 32 kD) seem to be common to both synthase activities, whereas two polypeptides (78 and 38 kD) are associated only with callose synthase activity Twelve polypeptides (170, 136, 108, 96, 83, 72, 66, 60, 52, 48, 42, and 34 kD) appear to be specifically associated with cellulose synthase activity The successful separation of (1->3)- and (1->-4)-[beta]-glucan synthase activities was based on the manipulation of digitonin concentrations used in the solubilization of membrane proteins At low dipitomin concentrations (005 and 01%), the ratio of the cellulose to callose synthase activity was higher At higher digitonin (05-1%) concentrations, the ratio of the callose to cellulose synthase activity was higher Rosette-like particles with attached product were observed in samples taken from the top of the stacking gel, where only cellulose was synthesized Smaller (nonrosette) particles were found in the running gel, where only callose was synthesized These findings suggest that a higher level of subunit organization is required for in vitro cellulose synthesis in comparison with callose assembly

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Cellulose and Callose Biosynthesis in Higher Plants (I. Solubilization and Separation of (1->3)- and (1->4)-[beta]-Glucan Synthase Activities from Mung Bean)

M. Meryl Smith

Papers

β-Glucan synthesis by cell-free extracts from Lolium multiflorum endosperm

β-GLUCAN SYNTHESIS BY LOLIUM MULTIFLORUM ENDOSPERM PREPARATIONS