Altered resource allocation during seed development in Arabidopsis caused by the abi3 mutation

The regulation of whole-plant resource allocation during seed development in Arabidopsis thaliana was investigated by examining growth rate and partitioning of ¹⁴CO₂ in wild-type plants and those carrying the abi3 mutation. Plants carrying the abi3 mutation partitioned more resources into seed development than the wild type. The extra resources were available as a result of delayed senescence of the cauline leaves in the mutant. After supply of ¹⁴CO₂ at later stages of reproductive development differences in patterns of ¹⁴C distribution between mutant and wild type were consistent with long-term changes in growth and allocation. The role of long-distance signals in the regulation of seed yield in Arabidopsis is discussed.     

Endogenous hormone levels in explants and in embryogenic and non-embryogenic cultures of carrot

Carrot ( Daucus carota L. F1 hybrid Starca) excised hypocotyls were cultured on Murashige and Skoog medium with and without 2,4-dichlorophenoxy acetic acid (2,4-D) to determine the effect of this plant growth regulator on their further development and their endogenous hormone levels. Culture in the absence of 2,4-D stimulated root development at one end of the hypocotyl segments and increased the endogenous levels of free indole-3-acetic acid (IAA), zeatin/zeatin riboside and N ⁶(Δ²-isopentenyl) adenine/ N ⁶(Δ²-isopentenyl) adenosine, as determined by radio-immunoassay. On the other hand, the presence of 2,4-D in the culture medium promoted callus induction and proliferation, together with abscisic acid (ABA) accumulation, in the hypocotyl segments during the first weeks of culture. When the callus segments generated in the hypocotyl sections cultured in the presence of 2,4-D were cultivated further, the development of two callus types was observed, one composed of preglobular and globular embryos and the other translucent, watery and lacking any sign of organisation. The embryos of the first type germinated when callus segments were transferred to regeneration conditions, while no change was observed when the second type was induced to regenerate. Higher levels of free IAA and ABA were obtained in the embryogenic calli when compared to the non-embryogenic, while no differences were observed among callus types in the other hormones evaluated. The possible role of the different plant hormones during induction of somatic embryogenesis is discussed.     

Involvement of epidermal cells in stomata movement: The effect of ABA

ABA affected K⁺ and solute transport between guard cells and epidermal cells as indicated by K⁺ staining and plasmolysis. ABA enhanced K⁺ (⁸⁶Rb) uptake into epidermal cells. To find out whether the ABA enhanced accumulation of K⁺ (⁸⁶Rb) in epidermal cells is active, uptake in the presence of exogenous ATP was studied. These studies hinted that K⁺ (⁸⁶Rb) uptake by epidermal cells is a passive process, while its release is an active one. This was verified by applying iodoacetate, which interferes with energy supply. The epidermal cells thus seem to play a role in stomatal movement.     

Endogenous abscisic acid levels are linked to decreased growth of bush bean plants treated with NaCl

This paper studies the relative importance of endogenous ABA and ion toxicity in the leaf growth inhibition caused by NaCl in salt-adapted and unadapted bush beans. Adaptation to salt-stress was achieved by germination of seeds in 75 m M NaCl, while unadapted plants were germinated in tap water. The adaptation process caused a transitory increase in leaf ABA, Na⁺ and Cl⁻ concentrations, while leaf expansion was inhibited. However, when grown for 8 or 13 days in 75 m M NaCl-containing nutrient solution, primary and first trifoliolate leaves of salt-adapted plants had greater areas than those of unadapted plants. Concentrations of ABA, Na⁺ and Cl⁻ in these leaves were lower in adapted plants, and a strong negative correlation between leaf expansion growth and either leaf Na⁺, Cl⁻ or ABA concentrations could be established. However, in the second trifoliolate leaves only the ABA, but not the Na⁺ or Cl⁻, concentrations were significantly correlated with leaf expansion. Our results suggest that salt-induced inhibition of leaf expansion growth in bush beans is mediated by ABA rather than Na⁺ or Cl⁻ toxicity. Moreover, the increase of ABA, induced by the salt-pretreatment, seems to play an important role in limiting the accumulation of Na⁺ and Cl⁻ in the leaves, leading to adaptation of bush beans to salt-stress.     

Long-term effects of abscisic acid on K+ transport in young wheat plants of different K+ status

The effects of abscisic acid (ABA) on growth, uptake and translocation of potassium ions, K⁺,Mg²⁺-ATPase activity and transpiration were investigated in young wheat ( Triticum aestivum L. cv. Martonvásári-8) plants grown at different K⁺ supplies. Long-term treatment with ABA (10 μ M ) reduced growth in high-K⁺ plants, but had less effect under low-K⁺ conditions. K⁺(⁸⁶Rb) uptake was inhibited by about 70 and 40% in low- and high-K⁺ plants, respectively. The stimulation by K⁺ of the Mg²⁺-ATPase activity in the root microsomal fraction was lost with ABA treatment. It is suggested that the inhibitory effect of ABA on K⁺ uptake may be related to this effects on the K⁺,Mg²⁺-ATPase. Translocation of K⁺ to the shoot was inhibited in low-K⁺ plants only, and it was not affected in high-K⁺ plants. In parallel to this, ABA treatment reduced transpiration by about 50% in low-K⁺ plants, whereas a much smaller effect was seen in high-K⁺ plants. These observations suggest that the regulation by ABA of the stomatal movements is strongly counteracted by high-K⁺ status.     

Phosphate transport in potato cuttings: Effect of gibberellic acid and abscisic acid

Apical cuttings of Solanum tuberosum L. cv. Sirtema were used al different stages of development to study long-distance transport of phosphate. The effects of two hormones, gibberellic acid (GA₃) and abscisic acid (ABA), on this process were also investigated. Before tuberization, phosphate (³²P) supplied to a single leaf was transported preferentially in the young and growing parts of the plant: apical bud, young leaves and roots. After tuberization, the tuber became the principal site of phosphate accumulation. GA³ treatment (10⁻⁴ M) of the tuber as well as of the leaves led to reduced transport of ³²P into the tuber. By contrast, treatment of the tuber with ABA (10⁻⁴M) did not change the ³²P distribution within the plant, while foliar spray with ABA greatly increased the transport into the tuber. The opposite effects of the two hormones on phosphate accumulation by tubers are discussed with regard to their opposite effects on the tuberization process.     

Denitrifying population dynamic and evolution of nitrogen gas during a composting process

Abstract Little information exists about nitrogen losses through microbial activity during treatment of solid urban waste (SUW) by processes such as composting. In the present study, in addition to evaluating the pattern of nitrogen losses by denitrification at different stages of the process, a comparison between the method of Pochon and Tardieux, and an improved gas chromatographic method for estimating denitrifying populations was undertaken, Though the MPN (Most Probable Number) enumerations were higher using the colorimetric method than the gas chromatographic one, the patterns of the two graphs showing numbers of denitrifiers during composing were the same. The highest numbers were revealed immediately after loading the reactor (10⁷–10⁸/g d.w.), lower numbers of denitrifiers were found in the second sampling corresponding to the thermophilic phase (10³–10⁴/g d.w.). These numbers increased gradually as the waste material stabilized (10th to 123rd day of composting) to again reach values of 10⁷–10⁸/g d.w.     

Effect of pH and age of culture on cellular fatty acid composition of Leuconostoc oenos

Z. DRICI-CACHON, J.F. CAVIN AND C. DIVIÈS. 1996. This study is concerned with the fatty acid composition of three strains of Leuconostoc oenos grown at different p^H. The most abundant fatty acids were C18: 1 w ⁹, C19: 0 cy( w ^9,10) and C16:0, followed by C16: 1 w ⁹ and C14: 0. The p^H considerably modified the fatty acid distribution in Lo107 (an acidophilic strain) and Lo8413 (a moderately acidophilic strain). However, moderate changes occurred for LoATCC 23277 (a less acidophilic strain). At p^H 2.9, Lo107 has a remarkably high level of C19: 0 cy-( w ^9,10) and C19:0 cy( w ^11,12). Proportions of C18: 1 and C19:0 cyclo acids varied mainly with the p^H of the medium and also as a function of growth phase. The degree of unsaturation of fatty acids also varied with p^H.     

Determination of pig apolipoprotein B genotype by gene amplification and restriction fragment length polymorphism analysis

Summary
Sequence differences within the pig apoB gene can be used to identify rapidly four of eight known pig apoB alleles, designated LPB ¹- LPB ⁸. We describe the use of gene amplification, followed by endonuclease digestion and agarose gel electrophoresis, to discern size and restriction site differences. LPB ⁵, a common allele associated with reduced low density lipoprotein clearance and hypercholesterolaemia in pigs, is identified by a 283-bp insertion in intron 28. LPB ³ and LPB ⁷ are distinguished by a unique Hind III site; LPB ⁸ shares a unique Hinc II site with LPB ⁵. This method facilitates identification of the apoB genotype of pigs used in lipoprotein research and allows for further investigation into the association of particular apoB alleles with lipoprotein metabolism abnormalities.     

Potentiation of 45Ca Uptake and Acute Toxicity Mediated by the N-Methyl-D-Aspartate Receptor: The Effect of Metal Binding Agents and Transition Metal Ions

Abstract: The activities mediated by the N -methyl-D-aspartate (NMDA) receptor were studied in cultured rat cerebellar granule cells. Micromolar concentrations of the metal binding compounds, EDTA, cysteine, and histidine, as well as serum albumin strongly potentiated receptor activity in the presence of millimolar concentrations of Ca²⁺ and Mg²⁺. The findings indicated that these agents remove an endogenous metal, probably Zn²⁺, which attenuates NMDA receptor-mediated ⁴⁵Ca uptake and toxicity. Several added metal ions were therefore tested at low micromolar concentrations. Zn²⁺ was found to be the most potent inhibitor of NMDA-induced ⁴⁵Ca uptake, followed by Cu²⁺ and Fe²⁺. Co²⁺, Cd²⁺, Fe³⁺, and AI³⁺ had no significant effect, whereas Ni²⁺ potentiated the ⁴⁵Ca uptake but inhibited at much higher concentrations. The potentiating agents that remove the endogenous metal had a particularly dramatic effect in the presence of Mg²⁺, the voltage-dependent suppressor of the NMDA receptor. Mg²⁺ also played an important role in the inhibitory effect of added Zn²⁺. Much lower concentrations of Zn²⁺ were needed to achieve inhibition of NMDA-induced ⁴⁵Ca uptake in the presence of Mg²⁺. Under a variety of conditions, a very good correlation was found between NMDA receptor-mediated ⁴⁵Ca uptake and the magnitude of acute neurotoxicity.     

Interaction between superantigen and T-cell receptor Vβ element determines levels of superantigen-dependent cell-mediated cytotoxicity of CD8+ T cells in induction and effector phases

Specific superantigens activate different T-cell fractions with distinct TCR Vβ elements in association with MHC class II molecules and also induce SDCC against MHC class II⁺ target cells. In the present study, to determine whether the responsiveness of each CD8⁺ T-cell fraction expressing a different TCR Vβ element is primarily determined by the TCR Vβ, we compared the levels of proliferation and SDCC in Vβ3⁺ and Vβ11⁺ T cells upon stimulation with SEA. Upon stimulation with SEA_wt, the levels of proliferation were higher in Vβ3⁺ T cells than in Vβ11⁺ T cells. The levels of SDCC were also higher for the combination of Vβ3⁺ T cells and SEA_wt than for the combination of Vβ11⁺ T cells and SEA_wt during both the induction phase and the effector phase. In addition, upon stimulation with SEA_m, the levels of proliferation were higher in Vβ11⁺ T cells than in Vβ3⁺ T cells. And then, the levels of SDCC were also higher for the combination of Vβ11⁺ T cells and SEA_m than for the combination of Vβ3⁺ T cells and SEA_m during both the induction phase and the effector phase. These results suggest that the SAG-responsiveness of each CD8⁺ T-cell fraction expressing a different TCR Vβ element is primarily determined by the interaction between the TCR Vβ element and the SAG.     

Heat shock regulation in the ftsH null mutant of Escherichia coli: dissection of stability and activity control mechanisms of σ32in vivo

The heat shock response of Escherichia coli is regulated by the cellular level and the activity of σ³², an alternative sigma factor for heat shock promoters. FtsH, a membrane-bound AAA-type metalloprotease, degrades σ³² and has a central role in the control of the σ³² level. The ftsH null mutant was isolated, and establishment of the Δ ftsH mutant allowed us to investigate control mechanisms of the stability and the activity of σ³² separately in vivo . Loss of the FtsH function caused marked stabilization and consequent accumulation of σ³² (≈20-fold of the wild type), leading to the impaired downregulation of the level of σ³². Surprisingly, however, Δ ftsH cells express heat shock proteins only two- to threefold higher than wild-type cells, and they also show almost normal heat shock response upon temperature upshift. These results indicate the presence of a control mechanism that downregulates the activity of σ³² when it is accumulated. Overproduction of DnaK/J reduces the activity of σ³² in Δ ftsH cells without any detectable changes in the level of σ³², indicating that the DnaK chaperone system is responsible for the activity control of σ³² in vivo . In addition, CbpA, an analogue of DnaJ, was demonstrated to have overlapping functions with DnaJ in both the activity and the stability control of σ³².     

Distribution and metabolism of root-applied cytokinins in Pisum sativum

When N ⁶ [8–¹⁴C] furfuryladenine was applied to the intact root system of Pisum sativum L. cv. Meteor seedlings it was almost completely metabolised to other compounds within 24 h. Of the total activity recovered from the plants 94.5% was retained in the root system itself. ¹⁴C was recovered in a number of ethanol-soluble compounds and in ribonucleic acid, deoxyribonucleic acid and protein fractions of roots, stems, leaves and axillary buds. In rapidly growing axillary buds released from apical dominance by removal of the shoot apex the combined nucleic acid fractions accounted for 63.3% of the total ¹⁴C recovered from these organs. Xylem exudate collected from decapitated plants 0 to 12 h after supplying N ⁵[8–¹⁴C]furfuryladenine to the roots consistently contained a single major ¹⁴C-labelled compound which, in three different solvent systems, had the same Rf values as a major endogenous cytokinin isolated from the xylem of unlabelled plants. The content of N ⁶ [8–¹⁴C] furfuryladenine itself in the xylem exudate was always low and in some experiments it could not be detected.
It is suggested that part of the label from N ⁶ [8- ¹⁴CJfurfuryladenine taken up by the intact root system may have become incorporated in an endogenous cylokinin before export to the shoot.     

Ca2+-dependent in vitro phosphorylation of soluble proteins from germinating wheat (Triticum turgidum) endosperm

A 40000 g supernatant fraction from extracts of germinating wheat ( Triticum turgidum Desf. cv. Edmore) endosperm contains protein kinase activity that phosphorylates several endogenous proteins. In vitro incorporation of radiolabel from [³²P]-ATP into phosphoproteins was maximal in the presence of 1 m M CaCl₂ and 5 m M MgCl₂Ca²⁺ at micromolar concentrations greatly stimulated the phosphorylation of 49 and 47 kDa polypeptides and also inhibited the phosphorylation of a few specific polypeptides. The phosphorylation of the 49 and 47 kDa polypeptides was present at 2 days after seed germination and was maximal at 8 days. Quantitative protein changes were also detected during the seed germination, but differences could not be correlated with changes in protein phosphorylation. Phosphoamino acid analysis by two dimensional thin-layer electrophoresis showed that the Ca²⁺-dependent protein kinase phosphorylates a serine residue of the 47 kDa polypeptide. Ca²⁺-dependent protein kinase phosphorylates a serine residue of the 47 KDa polypeptide. Ca²⁺ dependent protein phosphorylktion was inhibited by phenothiazine-derived drugs. Addition of S-adenosylmethionine to the in vitro phosphorylation reaction specifically inhibited the Ca²⁺-dependent protein phosphorylation.     

Internode length in Pisum. Estimation of GA1 levels in genotypes Le, le and led

The levels of GA₁, 3-epiGA₁ and GA₈ in genotypes Le, le and le^d of Pisum sativum L. were determined by gas chromatography-selected ion monitoring (GC-SIM) after feeds of [³H, ¹³C]-GA₂₀ to each genotype. The levels of endogenous and [¹³C]-labelled metabolites were determined by reverse isotope dilution with unlabelled GA₁, 3-epiGA₁ and GA₈. The results demonstrate a quantitative relationship between the level of GA₁ and the extent of elongation both on a per plant and a per g fresh weight basis. These results are consistent with previous findings in peas and other species possessing a predominant early 13-hydroxylation pathway for GA biosynthesis.
The levels of 3-epiGA₁ also decreased in the genotypic sequence Le, le, le^d although not as rapidly as for the level of GA₁. This may suggest that the alleles at the le locus also influence the formation of 3-epiGA₁.     

Cationic and Anionic Requirements for the Binding of 2β-Carbomethoxy-3β-(4-Fluorophenyl)[3H]tropane to the Dopamine Uptake Carrier

Abstract: The present study reports the ion dependency of 2β-carbomethoxy-3β-(4-fluorophenyl)[³H]tropane ([³H]- CFT) binding to the dopamine transporter in the rat striaturn. The results indicate that [³H]CFT binding to synaptosomal P₂ membranes requires low concentrations of Na⁺ (peak binding between 20 and 50 m M Na⁺), is stimulated by phosphate anion or l^-, but is unaffected or only slightly affected by F^-, Cl^-, Br^-, NO₃^-, or SO₄^2-, Concentrations of Na⁺ of >50 m M become inhibitory except in the presence of l^-, which shifts peak binding levels toward higher Na⁺ concentrations and also elevates the peak binding level. K⁺ strongly decreased [³H]CFT binding with a shallow inhibition curve, and Na⁺ could not overcome this effect. Saturation analysis of [³H]CFT binding revealed a single binding site changing its affinity for CFT depending on the concentration of sodium phosphate buffer (6, 10, 30, 50, 130, or 200 m M ; 1 mM plus 49 mM NaCIversus 10 m M plus 40 m M NaCI; or 1 mM plus 129 m M Nal versus 10 m M plus 120 m M Nal). No differences were observed in the density of CFT binding sites between any of the conditions examined.     

Effects of salinity and replacement of K+ by Na+ on lipid composition in two sugar beet inbred lines

The effects of NaCl and replacement of K⁺ by Na⁺ on the lipid composition of the two sugar beet inbred lines FIA and ADA were studied (a) with increasing additions of NaCl to the basal medium, and (b) with increasing replacement of K⁺ by Na⁺ at the same total concentration as in the basal medium. Direct relations were noted between NaCl concentration of the nutrient solution and the phospholipid concentration in the roots of FIA, the genotype characterized by a low K⁺/Na⁺ ratio, as well as between NaCl in the medium and the phospholipid concentration in the shoots of ADA, the genotype with a high K ⁺/Na ⁺ ratio. The sulfolipid level in the roots of FIA was maintained at higher NaCl concentrations, while it was decreased in ADA. The glycolipid concentration in the shoots of ADA and the degree of unsaturation of the fatty acids of the total lipid fraction were decreased by salinity, indicating reduced biosynthesis of chloroplast glycolipids and/or accelerated oxidation of these lipids in the presence of NaCl.
In the Na⁺ for K⁺ replacement experiment a low content of K⁺ in the medium resulted in decreased levels of total lipids, phospholipids and sulfolipid in the roots of both genotypes, which did not relate to root growth. K⁺-leakage from the roots at low K⁺-level in the medium may be reduced by the increase in saturation of the lipids. In the shoots of ADA increased levels of total lipids, phospholipids and Sulfolipid were noted at a low K⁺-concentration of the nutrient solution.     

Abscisic acid levels in seeds of the gibberellin-deficient mutant lh-2 of pea (Pisum sativum)

The lh-2 mutation in garden pea ( Pisum sativum L.) blocks an early step in the gibberellin (GA) biosynthesis pathway, the three-step oxidation of ent -kaurene to ent -kaurenoic acid. As a result, only low levels of GAs, including the bioactive GA₁, are found in shoots and seeds of lh-2 plants. Mutant plants are dwarf in stature, and show increased seed abortion and decreased seed weight, compared with seeds of the tall wild-type (WT) progenitor (cv. Torsdag). The aberrant seed development of lh-2 plants is associated with reduced levels of GA₁ and GA₃, and with an accumulation of abscisic acid (ABA) in young seeds (pre-contact point). This ABA accumulation is typically 3- to 4-fold, and can be up to 6-fold, compared with control plants. To investigate whether the accumulation of ABA is partly responsible for causing the observed seed abortion in lh-2 plants, we constructed a double mutant between the lh-2 allele and wil . The wil mutation blocks ABA biosynthesis, and reduces ABA levels in young seeds by 10-fold. Introduction of the wil mutation reduces the endogenous ABA levels in young lh-2 seeds, but fails to rescue the seeds from abortion. This indicates that the effects of lh-2 on seed development are not mediated through increased ABA levels, and is consistent with previous evidence that GAs are the controlling factor underlying the lh-2 seed phenotype in pea.     

A 10-kDa acyl-CoA-binding protein (ACBP) from Brassica napus enhances acyl exchange between acyl-CoA and phosphatidylcholine

The gene encoding a 10-kDa acyl-CoA-binding protein (ACBP) from Brassica napus was over-expressed in developing seeds of Arabidopsis thaliana . Biochemical analysis of T₂ and T₃ A. thaliana seeds revealed a significant increase in polyunsaturated fatty acids (FAs) (18:2 ^{cis Δ9,12} and 18:3 ^{cis Δ9,12,15}) at the expense of very long monounsaturated FA (20:1 ^{cis Δ11}) and saturated FAs. In vitro assays demonstrated that recombinant B. napus ACBP (rBnACBP) strongly increases the formation of phosphatidylcholine (PC) in the absence of added lysophosphatidylcholine in microsomes from ΔYOR175c yeast expressing A. thaliana lysophosphatidylcholine acyltransferase ( AthLPCAT ) cDNA or in microsomes from microspore-derived cell suspension cultures of B. napus L. cv. Jet Neuf. rBnACBP or bovine serum albumin (BSA) were also shown to be crucial for AthLPCAT to catalyse the transfer of acyl group from PC into acyl-CoA in vitro . These data suggest that the cytosolic 10-kDa ACBP has an effect on the equilibrium between metabolically active acyl pools (acyl-CoA and phospholipid pools) involved in FA modifications and triacylglycerol bioassembly in plants. Over-expression of ACBP during seed development may represent a useful biotechnological approach for altering the FA composition of seed oil.