Calcium at the Cell Wall-Cytoplast Interface

Attention is given to the role of Ca2+ at the interface between the cell wall and the cytoplast, especially as seen in pollen tubes. While the cytoplasm directs the synthesis and deposition of the wall, it is less well appreciated that the wall exerts considerable self control and influences activities of the cytoplasm. Ca2+ participates as a crucial factor in this two way communication. In the cytoplasm, a [Ca2+] above 0.1 μM, regulates myriad processes, including secretion of cell wall components. In the cell wall Ca2+, at 10 μM to 10 mM, binds negative charges on pectins and imparts structural rigidity to the wall. The plasma membrane occupies a pivotal position between these two compartments, where selective channels regulate influx of Ca2+, and specific carriers pump the ion back into the wall. In addition we draw attention to different factors, which either respond to the wall or are present in the wall, and usually generate elevated [Ca2+] in the cytoplasm. These factors include: (i) stretch activated channels; (ii) calmodulin; (iii) annexins; (iv) wall associated kinases; (v) oligogalacturonides; and (vi) extracellular adenosine 5-triphosphate. Together they provide evidence for a rich and multifaceted system of communication between the cytoplast and cell wall, with Ca2+ as a carrier of information.     

Genetic Identification of Western Mediterranean Sturgeons and its Implication for Conservation

To date, the only native sturgeon species in Western Europe was believed to be Acipenser sturio. However, this species is currently restricted to the Gironde River (Southern France), and it poses serious difficulties for rearing in captivity and for using in recovery programme. Furthermore, it has been questioned whether A. sturio is in fact the only species within the rivers of Western Europe, as A. naccarii, a species previously considered endemic of the Adriatic region, has been reported from the Iberian Peninsula in recent years. Here, we have used forensic techniques to obtain DNA from several museum specimens of sturgeons caught in the Spanish Guadalquivir River and in other European rivers. We analysed DNA sequences from these specimens for five genetic markers (three nuclear and two mitochondrial regions), which were subsequently compared with sequences obtained from A. sturioand A. naccarii. Our study demonstrates that A. naccarii coexists withA. sturio, from the Adriatic Sea to the Iberian Peninsula, a finding that could be taken into account in future sturgeon recovery programmes in Western Europe.     

Construction of a linkage map of the Rennell Island Tall coconut type (Cocos nucifera L.) and QTL analysis for yield characters.

AFLP and SSR DNA markers were used to construct a linkage map in the coconut (Cocos nucifera L.; 2n = 32) type Rennell Island Tall (RIT). A total of 227 markers were arranged into 16 linkage groups. The total genome length corresponded to 1971 cM for the RIT map, with 5-23 markers per linkage group. QTL analysis for yield characters in two consecutive sampling periods identified nine loci. Three and two QTLs were detected for number of bunches and one and three QTLs for number of nuts. The correlation of trait values between characters and evaluation periods is partially reflected in identical QTLs. The QTLs represent characters that are important in coconut breeding. The cosegregation of markers with these QTLs provides an opportunity for marker-assisted selection in coconut breeding programmes.     

Mutations which alter the elbow region of tRNA2Gly reduce T4 gene 60 translational bypassing efficiency.

Translating ribosomes bypass a 50 nucleotide coding gap in bacteriophage T4 gene 60 mRNA between codons 46 and 47 in order to synthesize the full-length protein. Bypassing of the coding gap requires peptidyl-tRNA2Gly detachment from a GGA codon (codon 46) followed by re-pairing at a matching GGA codon just before codon 47. Using negative selection, based on the sacB gene from Bacillus subtilis, Escherichia coli mutants were isolated which reduce bypassing efficiency. All of the mutations are in the gene for tRNA2Gly. Most of the mutations disrupt the hydrogen bonding interactions between the D- and T-loops (G18*psi55 and G19*C56) which stabilize the elbow region in nearly all tRNAs. The lone mutation not in the elbow region destabilizes the anticodon stem at position 40. Previously described Salmonella typhimurium mutants of tRNA2Gly, which reduce the stability of the T-loop, were also tested and found to decrease bypassing efficiency. Each tRNA2Gly mutant is functional in translation (tRNA2Gly is essential), but has a decoding efficiency 10- to 20-fold lower than wild-type. This suggests that rigidity of the elbow region and the anticodon stem is critical for both codon-anticodon stability and bypassing.     

Are dipyridamole (sensitive) calcium channels present in esophageal smooth muscle?

Calcium (Ca²⁺) entry from the extra-cellular space into the cytoplasm through voltage-dependent Ca²⁺ channels, specifically dipyridamole (DHP) sensitive ones (L-type), control a variety of biological processes, including excitation-contraction coupling in vascular and GI muscle cells. It has also been proposed that these channels may control esophageal contractility. However, DHP-sensitive Ca²⁺ channels in esophagus have not been well characterized biochemically. Thus, it is not known if these channels are similar in number or affinity to those in vascular or neural tissues — organs for which clinical use of calcium channel blockers has been successful. Thus, the purpose of this study was to identify and characterize DHP-sensitive calcium channels in esophagus and compare them to vascular, neural, and other GI tissues. Methods — We carried out in vitro receptor binding assays on lower esophageal muscle homogenates, gastric and intestinal and colonic homogenates, and aortic muscle homogenates from ca; and on brain homogenates from rat. We used a radio-labeled dihydropyridine derivative [³H]nitrendipine, to label these sites and co-administration of unlabeled nimodipine to define specific binding. Results — As expected, ligand binding to L-type Ca²⁺ channels in aortic vascular smooth muscle and brain was readily detectable: brain, Bmax = 252 fmol/mg protein, Kd = 0.88 nM; aorta, Bmax = 326 fmol/mg protein, Kd = 0.84 nM. For esophagus (Bmax = 97; Kd = 0.73) and for other GI tissues, using the same assay conditions, we detected a smaller signal, suggesting that L-type Ca²⁺ channels are present in lower quantities. Conclusion — L-type Ca²⁺ channel are present in esophagus and in other GI muscles, their affinity is similar, but their density is relatively sparse. These findings are consistent with the relatively limited success that has been experienced clinically in the use of calcium channel blockers for treatment of esophageal dysmotility.