Characterization of an abscisic acid carrier in suspension-cultured barley cells

The uptake of [³H]-abscisic acid in barley (Hordeum vulgareL. cv. Heartland) cell cultures was found to be mediated throughboth non-saturable and saturable components. The kinetic parametersof the saturable component, determined at pH 4.5 and 21 °C,showed a K_m for natural or (+ )-ABA of 1.3±0.7µMand an apparent V_mex of 7.0 ± 2.8 nmol g^–1 cellsh^–1. The carrier showed a strong preference for the naturalenantiomer of ABA as compared to the unnatural one. Other substancestested, e.g. amino acids, organic acids, and other growth regulators,did not appear to interfere with the carrier-mediated uptakeof ABA. At low external concentrations of ABA (below 2.0 µM),the saturable component was greater than the diffusion component.Similarly, between pH 4.0 and 6.0, the saturable uptake wasresponsible for more than 50% of the total uptake. The carriermay be important in vivo for mediating uptake when endogenouslevels of ABA are low (c. 1 µM). The carrier specificity was evident in inhibition experimentsdone with ABA analogues. Our data showed that the carrier couldaccommodate small modifications in the ABA structure. Four analogueswere able to compete efficiently with ( + )-ABA for the bindingsite of the carrier. Three of these competitors were of the(+)-series. Only one ( –)-analogue, (–)-ABA, wasable to inhibit markedly the saturable uptake of ( + )-ABA.The induction of the ABA-respons-ive gene WCS120 (Houde et al.,1992) presented stricter requirements for the ABA molecule thanthe carrier, although with a similar preference for the ( +)-analogues. Besides ( + )-ABA itself, only two of the analoguestested, both ( + )-series, were able to induce the WCS120 geneafter a 24 h incubation period. The absence of correlation betweenthe activity of the analogues as ABA inhibitors in the carriersystem, and their capacity to induce the WCS120 gene tend tosuggest that the carrier is not directly involved in the signaltransduction pathway leading to the induction of this specificgene. Key words: Abscisic acid, barley, gene induction, Hordeum vulgare, uptake carrier     

Cloning of Multiple Forms of Goldfish Vimentin: Differential Expression in CNS

Abstract: In efforts to determine the primary structure of intermediate filament proteins in the goldfish visual pathway, we isolated clones from a retinal λgt11 cDNA expression library that represent goldfish vimentin. We show that there are at least two forms of goldfish vimentin, designated as vimentin α and vimentin β. RNase protection assays indicate that vimentin α mRNA is expressed in low amounts in retina, optic nerve, and brain and in higher amounts in spinal cord. In contrast, vimentin β mRNA is expressed in low amounts in retina, optic nerve, brain, and spinal cord and in very high amounts in eye lens. Immunohistochemical studies show that in the optic nerve, vimentin α is mainly restricted to blood vessels, meninges, and septa. Light staining is observed with this antibody in an astrocytic glial pattern throughout the optic nerve. Two-dimensional gel analysis shows that all of these goldfish vimentins are low abundant components of optic nerve cytoskeletal preparations.     

Nuclear-encoded subunits of human cytochrome c oxidase: SstI restriction fragment length polymorphism

A DNA polymorphism of the nuclear-encoded subunit Va of the human cytochrome c oxidase (COX), a mitochondrial respiratory enzyme, is reported. No polymorphism was detected in genes for the subunits IV and Vb of the same enzyme.     

Chaetomella acutiseta produces chaetomellic acids A and B which are reversible inhibitors of farnesyl-protien transferase

Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella. Correspondence to: R. B. Lingham     

Interaction of the FAFB-containing subunit with the Photosystem 1 core heterodimer

The structure of the predicted amino acid sequence in the F_X domain of Photosystem 1 was studied by molecular modeling and a working hypothesis was developed for the functional interaction of PsaC with the core heterodimer. We propose that the intervening sequences between homologous cysteines in the F_X cluster form two flexible loops and participate in the binding of PsaC, and that the arginine residues in the two surface-exposed loops may promote the interaction between the P₇₀₀–F_X core and the subunit. The model was tested experimentally; chemical modification of arginine residues in the P₇₀₀–F_X core using phenylglyoxal prevented reconstitution of the core with PsaC and PsaD after insertion of FeS clusters in vitro. Treatment of the P₇₀₀–F_X core with trypsin also prevented reconstitution of terminal electron transfer to F_AF_B, although neither treatments affected the electron transfer to F_X as judged by flash kinetic spectrophotometry. Electron transfer in the P₇₀₀–F_AF_B complex was not impaired by either phenylglyoxal or trypsin treatment indicating that the small subunit(s) protect the arginine residues that become chemically modified or cleaved. The data are consistent with the working model and point to additional experiments designed to identify the specific residues involved in the interaction between the P₇₀₀–F_X core and PsaC.Abbreviations PG- phenylglyoxal - PS 1- Photosystem 1     

EcoRI restriction fragment length polymorphism in human glycogen synthase gene

Two alleles of 10.1 and 8.1 kb of the human glycogen synthase gene have been revealed with the restriction enzyme EcoRI.     

Influence of ovule perforation,plant growth regulators,andl-glutamine on in vitro growth of immature peach embryos

Summary Ovule perforation technique and media components (plant growth regulators andl-glutamine) were tested on in vitro growth of immature (<3 mm) embryos of “Springcrest” and “Earligrande” peaches. Ovule perforation was 2 to 4 times more effective in promoting embryo growth than leaving ovules intact.l-Glutamine (400 mg·liter⁻¹) promoted an increase in growth but could not be used with indole-acetic acid plus kinetin because an antagonistic effect on embryo growth occurred. The use of these exogenous plant growth regulators did not increase embryo growth over in vivo growth.     

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM treeClusia hilariana

Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO₂ fixation rates of 28 mol m^-2 s^-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (q_N) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO₂ fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (q_A) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of q_A throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (F_v/F_m) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in F_v/F_m, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition.     

7B2 Is a Specific Intracellular Binding Protein of the Prohormone Convertase PC2

Abstract: Biosynthetic pulse-chase analyses have previously demonstrated that the prohormone convertase PC2 is first synthesized as a precursor pro-PC2 and that zymogen activation to PC2 occurs following the slow exit of pro-PC2 from the endoplasmic reticulum (ER) and its concentration within the trans-Golgi network (TGN). The endocrine and neural protein 7B2 is first synthesized as a nonglycosylated precursor (pro-7B2), which is cleaved within the TGN by a furin-like ubiquitous convertase at the RRKRR¹⁵⁵S site to generate 7B2. In this report, we demonstrate that within the ER, pro-7B2 binds pro-PC2 but not any of the other convertases furin, PC1, PACE4, or PC5. This specific binding is Ca²⁺ dependent and does not require an N-glycosylated pro-PC2. Mutagenesis of the RRKRRS sequence demonstrated that the intact hexapeptide is critical for this binding, because the latter was abolished by mutations of the RR¹⁵² and greatly diminished by mutations of either the R¹⁵¹ or S¹⁵⁶ residues of pro-7B2. Once the complex is formed in the ER, it is then transported to the TGN where furin or a furin-like convertase cleaves both precursors, even when present as a complex. We also provide evidence that following zymogen cleavage, 7B2 remains bound to PC2, suggesting the presence of at least one other Ca²⁺-dependent binding site within the 7B2 sequence. Coexpression of 7B2 and PC2, although resulting in an elevation of the level of pro-PC2, did not eliminate the processing of pro-PC2 to PC2. Accordingly, cellular coexpression of 7B2 together with PC2 and proopiomelanocortin only marginally diminished the ability of PC2 to cleave proopiomelanocortin into β-endorphin in constitutive cells and had no effect in regulated cells. These results suggest that in vivo pro-7B2 is a specific PC2-binding protein that only transiently inhibits the processing of pro-PC2 until it reaches the TGN.