Genotype and phenotype associations with drought tolerance in barley tested in North Africa

A review is presented of genetic strategies deployed in a 3-yr project on drought tolerance in barley. Data were collected on genetic, physiological and agronomic traits in non-irrigated and irrigated field trials in Egypt, Morocco and Tunisia. A wide range of barley germplasm (developed from African and European cultivars, adapted landraces and wild barleys) was tested, and positive traits were found in each gene pool. The contrasting environments of the three North African countries had major effects on plant/genotype performance. Genetic effects were also detected, as were genotype × environment interactions. A range of strategies were deployed to investigate the physiology and genetics of quantitative traits associated with field performance. Quantitative trait locus (QTL) analysis was performed using backcross lines, recombinant inbred lines and doubled haploid mapping populations. A detailed genetic map was generated in the Tadmor × (ER/Apm) recombinant inbred lines, an important mapping population specifically developed by ICARDA (Centre for Agricultural Research in Dry Areas) and CIMMYT (International Maize and Wheat Improvement Center) to study drought. Quantitative trait loci (QTLs) for grain yield and other important morphological and physiological traits were also identified in a population of doubled haploids derived from F2BCj plants from a cross between a cultivar and a wild barley accession. Significantly, the wild parental line was found to contribute a number of positive alleles for yield. Effects of major developmental genes could explain many of the responses observed. QTLs were found to cluster around major genes controlling flowering time (sghI), plant stature (sdwI and arie.GP) and ear type (vrsl), and it is highly likely that the associations represent pleiotropic effects. Some QTLs were associated with candidate genes such as dehydrins and rubisco activase. One of the most significant results was the identification and generation of material that out performed the best local standards in the three participating North African countries; the selected lines have now entered local breeding programmes. The strategies adopted provided information on physiological traits, genotypes and genetic markers that could be used for marker-assisted selection. Target QTLs and their associated genetic markers may be deployed in marker assisted selection programmes to match crop phenology to the field environment.     

Experimental tendon repair: glycosaminoglycan arrangement in newly synthesized collagen fibers.

Changes in the macromolecular orientation and metachromasy of glycosaminoglycans (GAG) in newly synthesized and assembled collagen fibers in rat Achilles tendon after tendon excision were investigated in toluidine blue (TB)-stained preparations, based in the selective absorption of polarized light (= linear dichroism, LD) and of absorption of unpolarized light in situ. Extrinsic LD was observed microspectrophotometrically from the early phases of tendon repair onwards, although the absorption peaks in both parallel and perpendicular directions with respect to the plane of polarized light and the long axis of the collagen fibers occurred at the same wavelength, and thus differed from the pattern situation in normal adult controls. Compared to normal adult tendons, the pattern of LD in newly synthesized and assembled fibers was still not fully attained 110 days after surgical tendon removal. This incomplete recovery possibly reflected the influence of aging during the repair process. There was no correlation between LD and metachromasy. The highest absorption values for metachromatic staining occurred on the 7th day after tendon removal, at a time when LD was not intense. Treatment with hyaluronidase showed that the LD in the early stages of tendon repair was mostly due to hyaluronate whereas the LD in the later stages was due to chondroitin sulfates. The changes in LD during Achilles tendon repair were attributed to gradual modifications in the composition and macromolecular orientation of GAGs relative to the long axis of the collagen fibers.     

Solid-phase Synthesis and Cellular Localization of a C- and/or N-terminal Labelled Peptide

We report the solid-phase synthesis by the Fmoc strategy of a peptide containing a cysteamide group at its C-terminus. This peptide was subject to further modifications including the linkage of fluorophores, namely lucifer yellow and coumarin respectively, at the C- and/or N-terminals. After incubation with living cultured cells these two probes were localized and it is concluded that the post-synthesis modifications can strongly modify the localization of the peptide.     

A Short-Term Decrease in Nitrogenase Activity (C2H2 Reduction) Is Induced by Exposure of Soybean Shoots to Their CO2 Compensation Point

Photosynthesis and nitrogenase acetylene-reducing activity (ARA) were measured in soybeans (Glycine max [L.] Merr.) in which the shoots were exposed for 48 h to 60 [mu]L L-1 CO2, a value corresponding to their CO2 compensation point. Six hours after the beginning of the light period at low CO2, the ARA started to decrease, reaching a rate of 50% of the control rate in 14 to 24 h and 20% of the control rate in 34 to 38 h after the beginning of the CO2 treatment. At these times, there was no net photosynthesis, and the transpiration rate was 20% lower than that in the control plants. An increase in the partial pressure of O2 around the nodules alleviated this inhibition of ARA. The maximal ARA achieved at 40 kPaO2 was 3 times higher than that at 20 kPa O2 and similar to the maximal ARA of the control plants. It was argued that the decrease in ARA of soybean exposed to the CO2 compensation point was due to a decrease in the nodule's permeability to O2 diffusion.