Effects of Boron on Proton Transport and Membrane Properties of Sunflower (Helianthus annuus L.) Cell Microsomes.

Boron deficiency and toxicity inhibit ATP-dependent H+ pumping and vanadate-sensitive ATPase activity in sunflower roots and cell suspensions. The effects of boron on H+ pumping and on passive H+ conductance, as well as on fluorescence anisotropy in KI-washed microsomes isolated from sunflower (Helianthus annuus L. cv Enano) cell suspensions, have been investigated. Boron deficiency reduced the total and vanadate-sensitive ATPase activities as well as the vanadate-sensitive ATP-dependent H+ pumping without affecting the amount of antigenic ATPase protein as measured by immunoblotting with an Arabidopsis thaliana plasma membrane anti-H+-ATPase polyclonal antibody. Kinetic studies revealed that boron deficiency reduced Vmax of vanadate-sensitive ATPase activity with little change in the apparent Km for Mg2+-ATP. Proton leakage was greater in microsomal vesicles isolated from cells grown without boron and incubated in reaction medium without added boron, and this effect was reversed by addition of boron to the reaction medium. Fluorescence anisotropy indicated that diphenyl hexatriene and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene probes were immobilized to a greater extent in microsomes from cells grown without boron than in those from cells grown with 100 [mu]M H3BO3. The apparent decrease of membrane fluidity in microsomes from cells grown without boron was reversed by the addition of boron to the reaction medium. Taken together these data suggest that inhibition of H+ gradient formation in microsomes from sunflower cells grown in the absence of boron could be due to the combined effects of reduced H+-ATPase activity and increased passive conductance across the membrane, possibly resulting from increased membrane rigidity.

Characterization of proton extrusion in sunflower cell cultures.

Cell suspensions derived from callus root tips of sunflower (Helianthus annuus L., cv. enano) were obtained in order to assess the effects of different chemical and physical agents on cell H+ extrusion. Cell H+ efflux was sensitive to temperature, pH, inhibitors of plasmalemma H(+)-ATPase and Ca2+ and K+ concentrations in the assay medium, as well as to the light intensity at which cells were cultivated. Thus, in the darkness and at 60 mumol/m2/s of illumination, a strong inhibition of H+ extrusion was detected as compared to cells grown at 30 mumol/m2/s. H+ extrusion by cells grown at 30 mumol/m2/s was unaffected by the presence of calcium in the assay medium, while at 60 mumol/m2/s such an activity increased when calcium was removed. These results provide the basis for the use of cell suspensions as an appropriate model to investigate the involvement of membrane-associated processes in plant tolerance mechanisms to different environmental stresses.

Cell wall acyl-lipids, proteins and polysaccharides in mature and germinated olive pollen.

Proteins, acyl-lipids and polysaccharides from cell walls of mature and germinated olive pollen were studied. In general, hemicelluloses are the most abundant polysaccharides, arabinose in mature and glucose in germinated pollen being the main components of these macromolecules. Protein content and its amino acid composition are very similar in walls from mature and germinated pollen, these compounds showing a weak acid character. Free-fatty acids are the most abundant lipid molecules in mature and germinated pollen walls and a decrease in acyl-lipids, especially in polar lipids, as well as a higher unsaturation of their fatty acid components are observed after germination.

Lipid biosynthesis and composition in oil bodies and microsomes of olive fruit.

Both lipid synthesis and composition in oil bodies and microsomes of olive fruit at the first stage of development have been studied. The rate of fatty-acid synthesis in isolated oil bodies was saturated by 4.0 microM [2-14C]-malonyl-CoA. The fatty-acids synthesized of phospholipids and neutral lipids were saturated and monounsaturated. Neutral lipids, galactolipids and, above all, phospholipids were the major acyl-lipid components of microsomal fraction, oleic and palmitic being their principal fatty-acids. When the lipids of microsomes were labelled in vivo with [1-14C]-acetate, phospholipids and neutral lipids exhibited a higher biosynthesis rate relative to the galactolipids. The increase in saturated and monounsaturated fatty-acid synthesis in microsomes, was also accompanied by an important [1-14C]-acetate incorporation into polyunsaturated acids. The data presented here, in conjunction with our previous morphological results, suggest the possibility that olive fruit oil bodies could contain the necessary enzymes for the reserve lipid biosynthesis.

Lipid biosynthesis, oxidative enzyme activities and cellular changes in growing olive fruit.

Fruit of Olea europea L. was examined by light and electron microscopy to determine whether commencement of lipid accumulation depended upon the fruit achieving structural maturity. Maturation of fruit develops progressively from the smallest changes towards the largest in cellular structures. Important metabolic and structural changes have been observed: oil body formation, changes in the structural and reserve lipid biosynthesis and in the fatty acid of total lipid content, as well as in G6PDH and LOX activities. The labelling of fruit lipids by previously incubating the leaves with (1-14C)-acetate and (1,5-14C)-citrate or by putting the labelled substrates directly on the fruit surface, shows a 14C assimilate derived from acetate greater than that from citrate; the incorporation of the latter is higher in the methanol-water fractions. At the beginning of fruit development the lipid biosynthesis with both substrates is greater in polar lipids; on the contrary, the incorporation of 14C into neutral lipids increases during fruit maturation. Additionally, a maximum of substrate export from leaves to fruit coincides with an increase in the lipoxygenase and, above all, in the glucose-6-phosphate dehydrogenase activities. The transported 14C from leaves begins its activity before the small oil bodies close to the tonoplast can be observed in the fruit, and well before the beginning of maturation. The results suggest that structural development and some other rate controlling metabolic steps can govern the initiation of lipid accumulation in olive fruit.

[Lipid biosynthesis in mitochondria from leaves of olive tree (author's transl)]. / Biosynthèse de lipides dans les mitochondries de la feuille d'olivier.

Phospholipids, neutral lipids and, to a lesser extent, glycolipids are the principal lipid components of mitochondria of young olive tree leaves. These lipids are rich in palmitic and oleic acid content. The in vivo incorporation of 1-14C-acetate into the mitochondrial lipids takes place especially in phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol. The saturated, and especially monounsaturated, acids of these lipids constitute the most actively synthesized fatty acids. In vitro, neutral lipids (mono- and diacylglycerol) and phospholipids (lysophospholipids, phosphatidylglycerol and phosphatidylcholine) incorporate a major percentage of radioactivity and in them the saturated and monounsaturated fatty acids are most actively synthesized.

Isolation and characterization of subcellular organelles from young and mature leaves of olive tree.

Subcellular organelles from young and mature leaves of olive tree have been isolated by differential centrifugation of leaf homogenates, and further purified by sucrose gradient centrifugation. Chlorophyll content was used for detecting chloroplasts after both the differential and density gradient centrifugation; aricase and catalase activities for peroxisomal identification, and the antimycin A sensitive and the antimycin-insensitive NADH-cytochrome C reductase as enzyme markers for mitochondria and microsomes, respectively. Chloroplast and mitochondrial respiration were tested polarographically by measuring the oxygen evolved or consumed, respectively, in the noncyclic electron transport chain of photosynthesis with an electron acceptor, and in the respiratory chain when succinate was used as substrate. No remarkable differences were observed between organelles from young and mature leaves, suggesting that the former can be used as a suitable material to study the lipidic biosynthetic pathways of this plant.

[Influence of b and giberellic acid on the transformation of lipids in glucids during the germination of sunflower seeds (author's transl)]. / Influencia del boro y del ácido giberélico sobre la transformación de lípidos en glúcidos durante la germinación de semillas de girasol.

The transformation of total lipids in carbohydrates and the evolution of the fatty acids, constituents of these lipids, during the germination of sunflower seeds, soaked previously in B and giberellic acid solutions, was studied. An inverse relationship between the total content in fatty acids and sugars of the blank (H20) and AG3 treatments was found. However, in the whole germinative process, the B and B + AG3 treatments changed strongly the carbohydrates metabolism and no significant differences of those constituents was observed. The content in fatty acids in the two last treatments showed a great stability and the percentage of these components remained fixed in all the treatments.