XLIV Notes on the chemistry of tartaric and citric acid

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Boron bridging of rhamnogalacturonan-II, monitored by gel electrophoresis, occurs during polysaccharide synthesis and secretion but not post-secretion

The cell-wall pectic domain rhamnogalacturonan-II (RG-II) is cross-linked via borate diester bridges, which influence the expansion, thickness and porosity of the wall. Previously, little was known about the mechanism or subcellular site of this cross-linking. Using polyacrylamide gel electrophoresis (PAGE) to separate monomeric from dimeric (boron-bridged) RG-II, we confirmed that Pb(2+) promotes H(3)BO(3)-dependent dimerisation in vitro. H(3)BO(3) concentrations as high as 50 mm did not prevent cross-linking. For in-vivo experiments, we successfully cultured ‘Paul's Scarlet’ rose (Rosa sp.) cells in boron-free medium: their wall-bound pectin contained monomeric RG-II domains but no detectable dimers. Thus pectins containing RG-II domains can be held in the wall other than via boron bridges. Re-addition of H(3)BO(3) to 3.3 μm triggered a gradual appearance of RG-II dimer over 24 h but without detectable loss of existing monomers, suggesting that only newly synthesised RG-II was amenable to boron bridging. In agreement with this, Rosa cultures whose polysaccharide biosynthetic machinery had been compromised (by carbon starvation, respiratory inhibitors, anaerobiosis, freezing or boiling) lost the ability to generate RG-II dimers. We conclude that RG-II normally becomes boron-bridged during synthesis or secretion but not post-secretion. Supporting this conclusion, exogenous [(3)H]RG-II was neither dimerised in the medium nor cross-linked to existing wall-associated RG-II domains when added to Rosa cultures. In conclusion, in cultured Rosa cells RG-II domains have a brief window of opportunity for boron-bridging intraprotoplasmically or during secretion, but secretion into the apoplast is a point of no return beyond which additional boron-bridging does not readily occur

Glycosylinositol phosphorylceramides from <i>Rosa cell</i> cultures are boron-bridged in the plasma membrane and form complexes with rhamnogalacturonan II

Boron (B) is essential for plant cell-wall structure and membrane functions. Compared with its role in cross-linking the pectic domain rhamnogalacturonan II (RG-II), little information is known about the biological role of B in membranes. Here, we investigated the involvement of glycosylinositol phosphorylceramides (GIPCs), major components of lipid rafts, in the membrane requirement for B. Using thin-layer chromatography and mass spectrometry, we first characterized GIPCs from Rosa cell culture. The major GIPC has one hexose residue, one hexuronic acid residue, inositol phosphate, and a ceramide moiety with a C(18) trihydroxylated mono-unsaturated long-chain base and a C(24) monohydroxylated saturated fatty acid. Disrupting B bridging (by B starvation in vivo or by treatment with cold dilute HCl or with excess borate in vitro) enhanced the GIPCs’ extractability. As RG-II is the main B-binding site in plants, we investigated whether it could form a B-centred complex with GIPCs. Using high-voltage paper electrophoresis, we showed that addition of GIPCs decreased the electrophoretic mobility of radiolabelled RG-II, suggesting formation of a GIPC–B–RG-II complex. Last, using polyacrylamide gel electrophoresis, we showed that added GIPCs facilitate RG-II dimerization in vitro. We conclude that B plays a structural role in the plasma membrane. The disruption of membrane components by high borate may account for the phytotoxicity of excess B. Moreover, the in-vitro formation of a GIPC–B–RG-II complex gives the first molecular explanation of the wall–membrane attachment sites observed in vivo. Finally, our results suggest a role for GIPCs in the RG-II dimerization process

Carbon disulfide. Just toxic or also bioregulatory and/or therapeutic?

The overview presented here has the goal of examining whether carbon disulfide (CS2) may play a role as an endogenously generated bioregulator and/or has therapeutic value. The neuro- and reproductive system toxicity of CS2 has been documented from its long-term use in the viscose rayon industry. CS2 is also used in the production of dithiocarbamates (DTCs), which are potent fungicides and pesticides, thus raising concern that CS2 may be an environmental toxin. However, DTCs also have recognized medicinal use in the treatment of heavy metal poisonings as well as having potency for reducing inflammation. Three known small molecule bioregulators (SMBs) nitric oxide, carbon monoxide, and hydrogen sulfide were initially viewed as environmental toxins. Yet each is now recognized as having intricate, though not fully elucidated, biological functions at concentration regimes far lower than the toxic doses. The literature also implies that the mammalian chemical biology of CS2 has broader implications from inflammatory states to the gut microbiome. On these bases, we suggest that the very nature of CS2 poisoning may be related to interrupting or overwhelming relevant regulatory or signaling process(es), much like other SMBs

The influence of iron supply on toxic effects of manganese, molybdenum and vanadium on soybean, peas and flax

The investigations were carried out in nutrient solution with iron as ferric citrate and nitrogen in the form of nitrate. Addition of 2.5 p.p.m. vanadium to plants in which iron chlorosis was already-established, either by a lack of iron or by excess manganese, failed to counteract the condition, and caused toxic symptoms. Reduction of the standard iron supply to ½ or ? accentuated the toxicity of 2?5 or 5 p.p.m. V to soybean and flax, but a similar reduction in phosphorus had no influence. Toxicity to peas, however, was increased when the phosphorus was reduced to 1/10, provided the iron level was high (20 p.p.m. Fe). Raising the iron supply to 20 or 30 p.p.m. Fe counteracted the toxicity of manganese (10 p.p.m.), molybdenum (40 p.p.m.) and vanadium (2.5 p.p.m.), but the result was less marked when these three elements were combined. Iron supplied in successive, small doses proved less efficient in overcoming molybdenum or vanadium, but not manganese excess, than the same amount of iron supplied in fewer and larger quantities. Varying the iron supply had little effect when the concentration of the three elements was low. When increased iron supply had reduced the chlorosis caused by high manganese or vanadium, it also reduced the manganese and vanadium contents of the shoot (p.p.m./d.m.), but the molybdenum content was only lowered by high iron when given in non-toxic concentration (0.1 p.p.m. Mo) combined with excess manganese. The iron content of the shoot (%/d.m.) was scarcely affected by the amount of iron supplied, but was generally reduced by high concentrations of manganese, molybdenum or vanadium. Results regarding the effect of vanadium on the phosphorus content of the shoot were conflicting, and differences occurred only when the iron supply was low. Here the phosphorus content of soybean and peas was generally reduced, while that of flax was increased. Yield data for soybean and flax indicated an interaction between manganese with both molybdenum and vanadium if the iron supply was low, but none between molybdenum and vanadium. The effect of all three metals was additive in respect to iron

Observations on the effect of molybdenum on plants with special reference to the solanaceae

In view of the similarity between certain cytological changes induced by virus disease and treatment with molybdenum, pot-and water-culture experiments were carried out to determine further the effect of this element on plant growth. Sodium molybdate was used throughout. 2 Toxic symptoms were produced with the larger dressings of molybdate, injury being shown at much lower concentrations in solanaceous species than in barley. 3 The shoots of tomato and Solanum nodiflorum turned a golden yellow, and potato tubers a reddish yellow colour when the plants were grown with the larger quantities of molybdate. 4 These colour changes were shown to be due to the presence of yellow globules of a tannin-molybdenum compound which had formed within the tissues. 5 Blue granular accumulations occurred in large numbers in molybdenum-treated plants. Their distribution was confined to tissues that contained anthocyanin pigment, and their composition was apparently of an anthocyanin-molybdenum nature

Some interrelationships between manganese, molybdenum and vanadium in the nutrition of soybean, flax and oats

Soybean and flax were grown in nutrient solutions containing high and low levels of molybdenum and vanadium, in combination with toxic (10?25 p.p.m.) and non-toxic (1 p.p.m.) manganese. Molybdenum (20 and to a less extent 10 p.p.m.) intensified the chlorosis induced by manganese excess, though these concentrations were harmless in the presence of 1 p.p.m. Mn. Vanadium (= 1.0, 5 and 10 p.p.m. Mo) counteracted some of the symptoms of manganese toxicity, but the two higher rates were harmful to growth irrespective of the manganese supply. Toxic concentrations of vanadium at first deepened the green colour of the shoot, though apical iron-deficiency chlorosis was generally induced later. Low molybdenum (0.1 p.p.m.) or equivalent vanadium had no influence on growth or iron nutrition at either level of manganese. Visual differences were corroborated by changes in the nitrogen, phosphorus and iron contents of the plants. There was no evidence of replaceability of molybdenum by vanadium. Oats were grown in nutrient solutions containing various combinations of manganese (nil?400 p.p.m.) and molybdenum (nil?20 p.p.m.). The appearance of manganese-deficiency symptoms was not affected by the quantity of molybdenum provided, and the manganese and molybdenum contents of the leaves were mutually independent of the quantity of each element supplied

The influence of the pH of the nutrient solution and the form of iron supply on the counteraction of iron deficiency in peas, soybean and flax by high concentrations of molybdenum

The prevention of chlorosis in flax by high concentrations of molybdenum in a nutrient solution was associated with a delay in the precipitation of iron from ferric citrate, a slower drift of pH towards alkalinity and an increase in the iron content of the root. These effects were greater with ammonium than with sodium molybdate and occurred with solutions started at pH 4.6 but not at pH 6.6. When FeEDTA was the source of iron, a similar delay in pH drift in the solution and accumulation of iron in the root occurred, but there was no chlorosis or precipitation of iron in the control treatment, so the effect of high molybdenum could not be fully determined. When ferric chloride was used, high molybdenum did not prevent chlorosis nor delay iron precipitation or cause accumulation of iron in the root, though the rate of pH drift resembled that of solutions containing the organic forms of iron. Similar results were obtained with peas and soybeans receiving high molybdenum treatment, but suppression of chlorosis was only temporary. It is suggested that the capacity of molybdenum to offset chlorosis is due to the formation, in acid solution, of a complex with phosphorus which renders iron more available by delaying the formation of ferric phosphate. This seems to occur only when iron is supplied in the organic form