The IdiA protein of Synechococcus sp. PCC 7942 functions in protecting the acceptor side of Photosystem II under oxidative stress

Synechococcus sp. strains PCC 7942 and PCC 6301 contain a 35 kDa protein called IdiA (Iron deficiency induced protein A) that is expressed in elevated amounts under Fe deficiency and to a smaller extent also under Mn deficiency. Absence of this protein was shown to mainly damage Photosystem II. To decide whether IdiA has a function in optimizing and/or protecting preferentially either the donor or acceptor side reaction of Photosystem II, a comparative analysis was performed of Synechococcus sp. PCC 7942 wild-type, the IdiA-free mutant, the previously constructed PsbO-free Synechococcus PCC 7942 mutant and a newly constructed Synechococcus PCC 7942 double mutant lacking both PsbO and IdiA. Measurements of the chlorophyll fluorescence and determinations of Photosystem II activity using a variety of electron acceptors gave evidence that IdiA has its main function in protecting the acceptor side of Photosystem II. Especially, the use of dichlorobenzoquinone, preferentially accepting electrons from Q_A, gave a decreased O₂ evolving activity in the IdiA-free mutant. Investigations of the influence of hydrogen peroxide treatment on cells revealed that this treatment caused a significantly higher damage of Photosystem II in the IdiA-free mutant than in wild-type. These results suggest that although the IdiA protein is not absolutely required for Photosystem II activity in Synechococcus PCC 7942, it does play an important role in protecting the acceptor side against oxidative damage. This revised version was published online in June 2006 with corrections to the Cover Date.     

Molecular studies of photobionts of selected lichens from the coastal vegetation of Brazil

A light microscopic and molecular analysis of photobionts in Ramalina and Cladonia from coastal habitats of Brazil is presented. A Bayesian phylogenetic analysis of ITS rDNA sequences suggests a Trebouxia lineage which is preferentially tropical in geographic distribution. This highly diverse clade also includes the morphological similar species Trebouxia higginsiae and galapagensis. Within the predominantly tropical clade of Trebouxia we distinguish several subclades, three of which are represented in our samples of Ramalina species. Since sexuality has not been recognized in coccal lichenised photobionts until recently, we cannot apply a biological species concept, but when compared with the sequence diversity between known species we conclude that several new species need to be described in this clade. The mutually exclusive presence of other Trebouxia lineages in temperate samples of Ramalina suggests an evolution towards higher selectivity in this genus. A strictly tropical lineage is not conspicuous in the photobionts of the genus Asterochloris sampled from Cladonia so far.     

Production of cyanophycin, a suitable source for the biodegradable polymer polyaspartate, in transgenic plants

The production of biodegradable polymers in transgenic plants in order to replace petrochemical compounds is an important challenge for plant biotechnology. Polyaspartate, a biodegradable substitute for polycarboxylates, is the backbone of the cyanobacterial storage material cyanophycin. Cyanophycin, a copolymer of l-aspartic acid and l-arginine, is produced via non-ribosomal polypeptide biosynthesis by the enzyme cyanophycin synthetase. A gene from Thermosynechococcus elongatus BP-1 encoding cyanophycin synthetase has been expressed constitutively in tobacco and potato. The presence of the transgene-encoded messenger RNA (mRNA) correlated with changes in leaf morphology and decelerated growth. Such transgenic plants were found to produce up to 1.1% dry weight of a polymer with cyanophycin-like properties. Aggregated material, able to bind a specific cyanophycin antibody, was detected in the cytoplasm and the nucleus of the transgenic plants.     

Pathways of IAA Production from Tryptophan by Plants and by Their Epiphytic Bacteria: A Comparison

Metabolites of tryptophan were investigated using 2 systems: a bacterial (Peastem homogenates containing the epiphytic bacteria) and a plant system (pea stem sections under sterile conditions). The plant system produces: indolepyruvic acid (IPyA), indoleacetaldehyde (IAAld) indoleacetic acid (IAA), indoleethanol (tryptophol, IAAol), indolecarboxylie acid (ICA), indolecarboxaldehyde (ICAld). Bacteria produce additionally: indoleactic acid (ILA), tryptamine (TNH₂) and the unknown Xb and Yb, but IAAld was not detected. A nonacidic inhibitor extract from pea stems decreases the gain of IAA, IPyA, ILA, Yb. It increases the gain of IAAld, IAAol, TNH₂, Xb, and (only in the bacterial system) ICA and ICAld. Three sites of inhibitor action are suggested, namely the steps Try → IPyA, TNH₂→ IAAld, IAAld → IAA.     

Chromosomal mapping of tRNA genes from Dictyostelium discoideum

Summary Different wild-type isolates of Dictyostelium discoideum exhibit extensive polymorphism in the length of restriction fragments carrying tRNA genes. These size differences were used to study the organisation of two tRNA gene families which encode a tRNA^Val(GUU) and a tRNA^Val(GUA) gene. The method used involved a combination of classitics. The tRNA genes were mapped to specific linkage groups (chromosomes) by correlating the presence of polymorphic DNA bands that hybridized with the tRNA gene probes with the presence of genetic markers for those linkage groups. These analyses established that both of the tRNA gene families are dispersed among sites on several of the chromosomes. Information of nine tRNA^Val(GUU) genes from the wild-type isolate NC4 was obtained: three map to linkage group I (C, E, F,), two map to linkage group II (D, I), one maps to linkage group IV (G), one, which corresponds to the cloned gene, maps to either linkage group III or VI (B), and two map to one of linkage groups III, VI or VIII (A, H). Six tRNA^Val(GUA) genes from the NC4 isolate were mapped; one to linkage group I (D), two to linkage group III, VI or VII (B, C) and three to linkage group VII or III (A, E, F).     

Attachment of (1→6)-linked malto-oligosaccharide side-chains to amylose and cellulose via 1,2-orthoesters

Comb-like molecules having oligomeric side-chains were prepared by condensation of peracetylated 1,2-(ethyl orthoacetate) derivatives of maltose, maltotetraose, and maltohexaose with 2,3-di-O-phenylcarbamoyl derivatives of amylose and cellulose. The distance between the maltose, maltotetraose, and maltohexaose branch-points introduced into amylose was 3–4, 10, and ～ 17 d-glucose residues, respectively, and only slightly greater for cellulose. Thus, the branch frequency is considerably higher than that obtained previously by using the Bredereck and Helferich reactions. After saponification of the modified polysaccharides, the side chains of d.p. 4 and 6 attached to position 6 in the d-glucose residues of amylose and cellulose were easily extended by enzymic synthesis with potato phosphorylase.     

Effects of thermal stress on tumor antigenicity and recognition by immune effector cells

The primary rationale for the application of clinical hyperthermia in the therapy of cancer is based on the direct cytotoxic effect of heat and the radio-chemosensitization of tumor cells. More recently, additional attention is given to the observation that heat and heat-shock proteins can activate the host’s immune system. The expression of heat-shock genes and proteins provides an adaptive mechanism for stress tolerance, allowing cells to survive non-physiologic conditions. However, the same adaptive mechanism can ultimately favor malignant transformation by interfering with pathways that regulate cell growth and apoptosis. Cytoprotection and thermotolerance raised the concern that heat-treated tumor cells might also be resistant to attack by immune effector mechanisms. Many studies, including those from our group, address this concern and document that heat-exposure, although transiently modulating sensitivity to CTL, do not hinder CTL attack. Moreover, there are promising reports of heat-related upregulation of NK-activating ligands, rendering those tumors which have lost MHC class I molecules target for NK cell attack. Heat-induced cytoprotection, therefore, does not necessarily extend protection from cytotoxic immune mechanisms. When interpreting the effects of heat, it is important to keep in mind that thermal effects on cell physiology are strongly dependent on the thermal dose, which is a function of the magnitude of change in temperature and the duration of heat exposure. The thermal dose required to induce cell death in vitro strongly varies from cell type to cell type and depends on microenvironmental factors (Dewey 1994). Therefore, to dissect the immunological behaviour of a given tumor and its micro-environment at different thermal doses, it is essential to characterize the thermosensitivity of every single tumor type and assess the proportion of cells surviving a given heat treatment. In this review, we summarize the pleiotropic effects that heat exposure has on tumor cells. In particular, we focus on the effects of heat on the antigen presentation of tumor cells and their susceptibility to immune effector mechanisms. We emphasize that the response to thermal stress is not a one-time point event, but rather a time period starting with the heat exposure and extending over several days of recovery. In addition, the response of tumor cells and their susceptibility to immune effector cells is strongly dependent on the model system, on the magnitude and duration of the thermal stress and on the time of recovery after heat exposure. Consideration of these aspects might help to explain some of the conflicting results that are reported in the field of thermal stress response. This article forms part of the Symposium in Writing "Thermal stress-related modulation of tumor cell physiology and immune responses", edited by Elfriede Noessner.