Expression of sunflower low-molecular-weight heat-shock proteins during embryogenesis and persistence after germination: localization and possible functional implications

We isolated and sequenced Ha hsp 17.9, a DNA complementary (cDNA) of dry-seed stored mRNA that encodes a low-molecular-weight heat-shock protein (LMW HSP). Sequence analysis identified Ha hsp17.9, and the previously reported Ha hsp17.6, as cDNAs encoding proteins (HSP17.6 and HSP17.9) which belong to different families of cytoplasmic LMW HSPs. Using specific antibodies we observed differential expression of both proteins during zygotic embryogenesis under controlled environment, and a remarkable persistence of these LMW HSPs during germination. Immuno-blot analysis of HSP17.9 proteins in two-dimensional gels revealed that the polypeptides expressed in embryos were indistinguishable from LMW HSPs expressed in vegetative tissues in response to water deficit; but they appeared different from homologeous proteins expressed in response to thermal-stress. Tissue-print immunolocalization experiments showed that HSP17.9 and HSP17.6 were homogeneously distributed in every tissue of desiccation-tolerant dry seeds and young seedlings under non-stress conditions. These results demonstrate developmental regulation of specific, cytoplasmic, plant LMW HSPs, suggesting also their involvement in water-stress tolerance.     

Multiple mechanisms of membrane anchoring of Escherichia coli penicillin-binding proteins

Abstract: The major penicillin-binding proteins (PBPs) of Escherichia coli play vital roles in cell wall biosynthesis and are located in the inner membrane. The high M _r PBPs 1A, 1B, 2 and 3 are essential bifunctional transglycosylases/transpeptidases which are thought to be type II integral inner membrane proteins with their C-terminal enzymatic domains projecting into the periplasm. The low M _r PBP4 is a DD-carboxypeptidase/endopeptidase, whereas PBPs 5 and are DD-carboxypeptidases. All three low M _r , PBPs act in the modification of peptidoglycan to allow expansion of the sacculus and are thought to be periplasmic proteins attached with varying affinities to the inner membrane via C-terminal amphiphilic α-helices. It is possible that the PBPs and other inner membrane proteins form a peptidoglycan synthesizing complex to coordinate their activities.     

Agonist Binding to α2-Adrenoceptors Is Elevated in the Locus Coeruleus from Victims of Suicide

Abstract: The binding of an agonist, p-[¹²⁵I]iodoclonidine, and an antagonist, [³H]yohimbine, to α₂-adrenoceptors was measured autoradiographically in the locus coeruleus from 10 pairs of antidepressant-free victims of suicide and age-matched controls. Agonist binding to α₂-adrenoceptors was significantly greater in the locus coeruleus from victims of suicide compared with control subjects. In contrast, antagonist binding to α₂-adrenoceptors in the locus coeruleus did not differ significantly between control and suicide subjects. HPLC analysis of norepinephrine in tissue sections of the locus coeruleus did not reveal any differences between control subjects and suicide victims, suggesting that differences in agonist binding are not a result of differences in retention of the endogenous agonist norepinephrine in tissue sections. The increase in agonist binding to α₂-adrenoceptors in the locus coeruleus of victims of suicide links an altered expression of the high-affinity state of autoinhibitory α₂-adrenoceptors with suicide.     

A putative catabolite-repressed cell wall protein from the mycoparasitic fungus Trichoderma harzianum

A cDNA clone encoding a putative cell wall protein (Qid3) was isolated from a library prepared from chitin-induced mRNA in cultures of the mycoparasitic fungus Trichoderma harzianum. The predicted 14 kDa protein shows a potential signal peptide, several hydrophobic domains and certain motifs that are structurally similar to proline-rich and glycine-rich plant cell wall proteins. Expression of the qid3 gene is derepressed in the absence of glucose. When introduced in yeast, qid3 expression causes cell division arrest into cytokinesis and cell separation, probably due to its cell wall localization.     

Response of root mRNA population to sulphate shortage in maize seedlings

Roots of ten-days-old seedlings obtained from a maize hybrid grown in complete or in sulphate-deprived medium were used to extract Poly(A)+RNA. The response to sulphate deprivation, which is known to increase the uptake capacity up to ten times, was manifested also by the expression of three mRNA species, as shown by the in vitro translation of the mRNA population. One hour after transfer to complete nutrient medium all three mRNAs were still present.Abbreviations BSA Bovine Serum Albumine - DTT 1,4-Dithio-DL-Threitol - EDTA Ethylenediaminetetraacetic-acid - MES 2-(N-Morpholino) ethane sulfonic acid - SDS Sodium Dodecyl Sulfate - TCA Trichloracetic acid - TRIS Tris(hydroxy-methyl)-aminomethane     

Acclimation of Arabidopsis thaliana to the light environment: Changes in composition of the photosynthetic apparatus

Acclimation to changes in the light environment was investigated in Arabidopsis thaliana (L.) Heynh. cv. Landsberg erecta. Plants grown under four light regimes showed differences in their development, morphology, photosynthetic performance and in the composition of the photosynthetic apparatus. Plants grown under high light showed higher maximum rates of oxygen evolution and lower levels of light-harvesting complexes than their low light-grown counterparts; plants transferred to low light showed rapid changes in maximum photosynthetic rate and chlorophyll-a/b ratio as they became acclimated to the new environment. In contrast, plants grown under lights of differing spectral quality showed significant differences in the ratio of photosystem II to photosystem I. These changes are consistent with a model in which photosynthetic metabolism provides signals which regulate the composition of the thylakoid membrane.Abbreviations Aac1 gene encoding actin - Chl chlorophyll - F far-red-enriched light (R:FR = 0.72) - FR far-red light - H high light (400 mol · m^–2 · s^–1) - L low light (100 ml · m^–2 · s^–1) - LHCII light-harvesting complex of PSII - Lhcb genes encoding the proteins of LHCII - R red light - Rbcs genes encoding the small subunit of Rubisco - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - W white light (R:FR = 1.40) This work was supported by Natural Environment Research Council Grant No. GR3/7571A. We would like to thank H. Smith (Botany Department, University of Leicester) and E. Murchie (University of Sheffield) for helpful discussions.     

Protein expression of a self-compatible allele from Lycopersicon peruvianum: introgression and behavior in a self-incompatible background

Lycopersicon peruvianum (wild tomato) is a gametophytic self-incompatible (SI) species. One natural population has been shown to harbor a self-compatible (SC) allele. A stylar protein associated with the self-compatibility allele has been elucidated using SDS-PAGE. The temporal and spatial expression of this protein is presented and compared with protein expression of two SI alleles. Hybrids containing the SC and SI alleles were used in a backcrossing program to introgress the SC allele into SI backgrounds in six independent lines. Controlled pollinations and SDS-PAGE were used to identify and select classes of progeny. After four backcross generations (approximately 97% recovery of the SI backgrounds) the SC allele still confers self-fertility in lines that contain this allele, providing evidence that the mutation to SC occurred at the S-locus and that the associated protein is likely responsible.     

Protein synthesis in tobacco pollen tubes: preferential synthesis of cell-wall 69-kDa and 66-kDa glycoproteins

One- and two-dimensional electrophoresis of Nicotiana tabacum pollen and pollen tube proteins confirmed that a new protein is preferentially synthesized during pollen germination and tube growth and becomes the most abundant protein in pollen tubes. Analysis of proteins extracted with sodium dodecyl sulfate (SDS) from different pollen tube fractions showed that it is the most abundant non-covalently bound wall protein, characterized by molecular mass of 69 kDa, pI between 7.9 and 8.2, and glycosylation with glucose and/or mannose. Amino acid analysis revealed relative abundance of serine, glutamic acid and glycine, but did not show the presence of hydroxyproline. According to all these characteristics, it cannot be classified as an extensin-like protein. Another prominent wall-bound glycoprotein has a molecular mass of 66 kDa and the same pI as the 69 kDa glycoprotein. These two glycoproteins are similar also in ConA binding, rate of synthesis, and rapid incorporation into pollen tube walls. Their synthesis is strongly reduced by tunicamycin and this inhibition results in the occurrence of new polypeptides in the range of 57–61 kDa. Tunicamycin also inhibited pollen tube growth. At 10 ng ml^-1 and 50 ng ml^-1 the inhibitor reduced pollen tube mass after 24 h of culture by 30% and 85%, respectively. This indicates that tobacco pollen presents a system highly sensitive to tunicamycin and that cotranslational N-linked glycosylation on the rough endoplasmic reticulum is required for 66 and 69 kDa glycoprotein formation and for pollen tube growth. Although other proteins appear during pollen germination and tube growth, the new proteins occur at low levels and seem to originate through modifications of preexisting polypeptides. In contrast to 69 and 66 kDa proteins, most proteins detected by [¹⁴C]amino acid incorporation and fluorography of gels were not revealed by Coomassie blue staining.     

Expression of the major tyrosyl phosphoprotein of 54 KDa in the integument of the medflyCeratitis capitata

Expression of a 54 kDa tyrosyl phosphorylated protein in epidermal cells during the third instar larval stage was followed. It was demonstrated that the 54 kDa protein moiety and its phosphorylated counterpart follow the same developmental profile. The system seems to be regulated only at the onset of the second moult, by an initial signal which regulates both the synthesis and phosphorylation of a 54 kDa protein. The continuous presence this protein in epidermal cells during the third instar stage, as well as during apolysis and histolysis, suggests that it might participate in cell activities taking place during this developmental period. However, the 54 kDa protein could no be involved in specific epidermal cell activities such as histolysis, melanization and sclerotization, since these activities occur only at specific times during the third instar stage.