Photosynthetic pigment concentration, organization and interconversions in a pale green Syrian landrace of barley (Hordeum vulgare L., Tadmor) adapted to harsh climatic conditions

Tadmor is a Syrian barley landrace that has adapted to semi-arid environments. Its leaves are pale green because of a 30% decrease in the chlorophyll and the carotenoid content of the chloroplasts (leading to a 7·5% decrease in light absorption) compared with barley genotypes that are not adapted to harsh Mediterranean climatic conditions (e.g. Plaisant). This difference in pigment content was attenuated during growth of the plants in strong light, but was strongly amplified when strong light was combined with a high growth temperature. The low pigment content of Tadmor leaves was not associated with significant changes in the pigment distribution between the photosystems or between the reaction centres of the photosystems and their associated chlorophyll antennae. No significant difference in the photosynthetic activity (O₂ production per unit absorbed light) was observed between Tadmor and Plaisant. The conversion of violaxanthin to zeaxanthin in strong light and its reversal in darkness were much faster and operated at a higher capacity in Tadmor leaves compared with Plaisant leaves, resulting in an increased photostability of photosystem II in the former leaves. The accelerated xanthophylls interconversion in the Syrian landrace was associated with, and possibly related to, an increased fluidity of the thylakoid membranes. The lipid peroxide level was lower in Tadmor compared with Plaisant. In contrast, no difference was found in the non-photochemical quenching of chlorophyll fluorescence between the two barley genotypes. The data indicate that the pale green Syrian landrace is equipped to survive excessive irradiance through a passive reduction of the light absorptance of its leaves, which mitigates the heating effects of strong light, and through the active protection of its photochemical apparatus by a rapid xanthophyll cycling.     

Predicted microbial biomass in the rhizosphere of barley in the field

Summary Laboratory data for the loss of root material by barley and field data for the growth of barley plants in Syria and in England have been combined to predict the amount of material lost by barley roots during a season, and to predict the resulting microbial biomass in the rhizosphere. The predicted microbial biomass C in the rhizosphere ranged from 10–34% of the total plant biomass C depending mainly upon the value used for rate of loss of root material. Total loss of root material predicted during a season in England constituted 7.7–25.4 percent of C fixed by photosynthesis. The major assumptions made in these calculations are considered, and the predicted values discussed in relation to reported values for soil microbial biomass, CO₂ fluxes from soil and associative nitrogen fixation.     

The gene for trypsin inhibitor CMe is regulated in trans by the lys 3a locus in the endosperm of barley (Hordeum vulgare L.)

Summary A cDNA encoding trypsin inhibitor CMe from barley endosperm has been cloned and characterized. The longest open reading frame of the cloned cDNA codes for a typical signal peptide of 24 residues followed by a sequence which is identical to the known amino acid sequence of the inhibitor, except for an Ile/Leu substitution at position 59. Southern blot analysis of wheat-barley addition lines has shown that chromosome 3H of barley carries the gene for CMe. This protein is present at less than 2%–3% of the wild-type amount in the mature endosperm of the mutant Risø 1508 with respect to Bomi barley, from which it has been derived, and the corresponding steady state levels of the CMe mRNA are about I%. One or two copies of the CMe gene (synonym Itc1) per haploid genome have been estimated both in the wild type and in the mutant, and DNA restriction patterns are identical in both stocks, so neither a change in copy number nor a major rearrangement of the structural gene account for the markedly decreased expression. The mutation at the lys 3a locus in Risø 1508 has been previously mapped in chromosome 7 (synonym 5H). A single dose of the wild-type allele at this locus (Lys 3a) restores the expression of gene CMe (allele CMe-1) in chromosome 3H to normal levels.     

Cultivar-related differences in the distribution of cell-wall-bound thionins in compatible and incompatible interactions between barley and powdery mildew

Leaf-specific thionins of barley (Hordeum vulgare L.) have been identified as a novel class of cell-wall proteins toxic to plant-pathogenic fungi and possibly involved in the defence mechanism of plants. The distribution of these polypeptides has been studied in the host-pathogen system of barley and Erisyphe graminis DC.f.sp. hordei Marchal (powdery mildew). Immunogold-labelling of thionins in several barley cultivars indicates that resistance or susceptibility may be attributed to the presence or absence of thionins at the penetration site in walls and papillae of epidermal leaf cells.All of the leaf-specific thionin genes are confined to the distal end of the short arm of chromosome 6 of barley. None of the genes for cultivarspecific resistance to powdery mildew which have previously been mapped on barley chromosomes are found close to this locus.     

A cDNA clone encoding the precursor for a 10.2 kDa photosystem I polypeptide of barley

Two cDNA clones for the barley photosystem I polypeptide which migrates with an apparent molecular mass of 9.5 kDa on SDS-polyacrylamide gels have been isolated using antibodies and an oligonucleotide probe. The determined N-terminal amino acid sequence for the mature polypeptide confirms the identification of the clones. The 644 base-pair sequence of one of the clones contains one large open reading frame coding for a 14 882 Da precursor polypeptide. The molecular mass of the mature polypeptide is 10 193 Da. The hydropathy plot of the polypeptide shows one membrane-spanning region with a predicted -helix secondary structure. The gene for the 9.5 kDa polypeptide has been designated PsaH.     

Huge increase in bacterivores on freshly killed barley roots

Abstract Adding fresh roots to intact soil cores resulted in marked increases in microbial and microfaunal activity at the resource islands. Microbial activity increased in two phases following root addition. Respiratory activity and concentration of respiratory enzyme (dehydrogenase) in soil adhering to the roots was very high during the first three weeks resulting in anaerobic conditions in the soil. After a period of low respiratory activity and enzyme content, these quantities increased from 6 to 20 weeks, but not enough to maintain anaerobic conditions. Numbers of protozoa peaked earlier than the nematodes. Based on yield coefficients of microbes and bacterivores, the increase in bacterivores was in accordance with root-induced respiration activity. In soil adhering to roots, numbers of bacterial grazers (protozoa and nematodes) were up to 80 and 30 times higher, respectively, than in the surrounding soil. This effect is up to 20 times higher than observed around live root systems, which may suggest that the rhizosphere effect on microbivores could for the major part result from the decomposition of dead segments of the root system.     

Efficient production of wheat-barley hybrids and preferential elimination of barley chromosomes

Summary Intergeneric hybridization between four common wheat cultivars, Triticum aestivum L. cultivars Chinese Spring, Norin 12, Norin 61, and Shinchunaga, and cultivated barley, Hordeum vulgare L. cultivars Betzes, Nyugoruden, Harunanijou, and Kinai 5 were carried out in a greenhouse under 15 – 20 °C and long-day (15 h) photoperiod conditions. Two days prior to pollination, a 100 mg/1 2,4-D solution was injected into wheat stems. Among wheat cultivars, Norin 12, Norin 61, and Shinchunaga showed higher crossabilities than that of Chinese Spring, suggesting the presence of crossability gene(s) other than the kr system of Chinese Spring. Variation was also found among the barley cultivars as male parents. Betzes barley showed the highest crossability with wheat. Thus, the cross Norin 12×Betzes showed the highest crossability (8.25%), followed by Norin 61 ×Betzes (6.04%), Shinchunaga×Betzes (5.00%), and Shinchunaga×Kinai 5 (5.00%). The embryos were rescued by culture at 15–20 days after pollination. Seventyfour plants were obtained from 82 embryos. The morphology of the hybrid plants resembled that of wheat parents. Among 60 seedlings observed, 28 had 28 chromosomes, 8 had 21, 23 had aneuploid numbers of chromosomes (22–27), and 1 had 29 chromosomes. About half of the aneuploid hybrids showed mosaicism for chromosome number. By analyzing five isozyme markers of barley chromosomes, the chromosome constitutions of the aneuploid hybrids were determined. Barley chromosomes 1 and 5 were found to be preferentially eliminated in the hybrids, while chromosomes 2 and 4 were eliminated infrequently. The conditions and genetic factors for high crossability and the tendency of barley chromosome elimination are discussed.