A minimal model of light-induced circadian rhythms of nitrate reductase activity in leaves of barley

Observed circadian rhythms of nitrate reductase (NR) (EC 1.6.6.1) activity in leaves of barley ( Hordeum vulgare L. cv. Herta) under continuous light conditions are described by a simple kinetic model. The oscillatory mechanism has been decomposed into the negative and positive feedback loops which are necessary according to present theories of chemical oscillating systems. Our results indicate that the decrease of NR activity in darkness can be considered as a reversible unimolecular conversion of the active form of NR into an inactive form, forming a negative stabilizing feedback loop. The light-induced increase of NR activity is related to a positive destabilizing feedback loop. In our treatment this process is represented as an autocatalytical reaction.     

Analyses of abiotic stress and brassinosteroid-related some genes in barley roots grown under salinity stress and HBR treatments: Expression profiles and phylogeny

We aimed to investigate abiotic stress (WAK, HvPIP1.1, HvPIP1.2, HvPIP1.3, HvPIP1.5, CYCD3, DREB2) and brassinosteroid-related gene (DWARF4) expressions in barley (Hordeum vulgare L. cv. “Hilal”) roots grown under different salt (150 and 250 mM), HBR (0.5 and 1 μM), and salt + HBR applications during 48 and 72 h at dark with their controls. Phylogenetic trees were also constructed to observe relationships among genes found in other plants. The expression of HvPIP1.2 and WAK reduced after salt treatment while HvPIP1.3, DREB2 and DWARF4 expressions increased. HvPIP1.1, HvPIP1.2, HvPIP1.3, HvPIP1.5 and DWARF4 expressions were upregulated under only HBR applications. Salt + HBR treatments increased HvPIP1.1, DREB2 and DWARF4 but decreased HvPIP1.2. Phylogenetic analyses indicated that Oryza sativa L. shared similar sequences with HvPIP1.5. CYCD3 could diverge relatively earlier from cyclin genes during evolution as it segregates in a distinct clade. Sorghum bicolor showed sequence homology with DREB2. Oryza australiensis L. and DWARF4 were found in the same clade. To our knowledge, this is the first detailed report related to salt stress and HBR applications in terms of the expression of different genes in barley, providing a valuable information for molecular breeding improvement of stress-related traits.     

Contrasting phosphate acquisition of mycorrhizal fungi with that of root hairs using the root hairless barley mutant

Comparisons between plant species or cultivars differing in root hair length have indicated a major impact of root hairs on the mycorrhizal dependency of plants with respect to phosphate (P) uptake. The current study aimed to investigate this relationship by comparing directly the mycorrhizal dependency of a spontaneous root hairless mutant, brb , in Hordeum vulgare cv Pallas and its wild type. Both brb and wild type were grown at different soil P levels in association with different mycorrhizal fungi. P uptake of brb and wild type was similar at high P levels, but P uptake by non-mycorrhizal brb plants at low P levels was substantially lower than that of the non-mycorrhizal wild-type plants. However, P uptake of the mutant was much increased by mycorrhizas and with one fungus, the additional P uptake was effectively translated into increased plant growth. Roots of the mutant contained typical colonization structures and a radioactive tracer confirmed P transport by the extraradical mycelium. This is the first direct evaluation of the relative effectiveness of root hairs and mycorrhizas. Mycorrhizas effectively substituted root hairs in P uptake, whereas the additional P was most often used less effectively in promoting plant growth than P provided by root hairs.     

Root cortical senescence decreases root respiration,nutrient content and radial water and nutrient transport in barley

The functional implications of root cortical senescence (RCS) are poorly understood. We tested the hypotheses that RCS in barley (1) reduces the respiration and nutrient content of root tissue; (2) decreases radial water and nutrient transport; and (3) is accompanied by increased suberization to protect the stele. Genetic variation for RCS exists between modern germplasm and landraces. Nitrogen and phosphorus deficiency increased the rate of RCS. Maximal RCS, defined as the disappearance of the entire root cortex, reduced root nitrogen content by 66%, phosphorus content by 63% and respiration by 87% compared with root segments with no RCS. Roots with maximal RCS had 90, 92 and 84% less radial water, nitrate and phosphorus transport, respectively, compared with segments with no RCS. The onset of RCS coincided with 30% greater aliphatic suberin in the endodermis. These results support the hypothesis that RCS reduces root carbon and nutrient costs and may therefore have adaptive significance for soil resource acquisition. By reducing root respiration and nutrient content, RCS could permit greater root growth, soil resource acquisition and resource allocation to other plant processes. RCS merits investigation as a trait for improving the performance of barley, wheat, triticale and rye under edaphic stress.     

Human intestinal circadian clock: expression of clock genes in colonocytes lining the crypt

Biological clock components have been detected in many epithelial tissues of the digestive tract of mammals (oral mucosa, pancreas, and liver), suggesting the existence of peripheral circadian clocks that may be entrainable by food. Our aim was to investigate the expression of main peripheral clock genes in colonocytes of healthy humans and in human colon carcinoma cell lines. The presence of clock components was investigated in single intact colonic crypts isolated by chelation from the biopsies of 25 patients (free of any sign of colonic lesions) undergoing routine colonoscopy and in cell lines of human colon carcinoma (Caco2 and HT29 clone 19A). Per-1, per-2, and clock mRNA were detected by real-time RT-PCR. The three-dimensional distributions of PER-1, PER-2, CLOCK, and BMAL1 proteins were recorded along colonic crypts by immunofluorescent confocal imaging. We demonstrate the presence of per-1, per-2, and clock mRNA in samples prepared from colonic crypts of 5 patients and in all cell lines. We also demonstrate the presence of two circadian clock proteins, PER-1 and CLOCK, in human colonocytes on crypts isolated from 20 patients (15 patients for PER-1 and 6 for CLOCK) and in colon carcinoma cells. Establishing the presence of clock proteins in human colonic crypts is the first step toward the study of the regulation of the intestinal circadian clock by nutrients and feeding rhythms.     

Apparent transinhibition of peptide uptake in the scutellum of barley grain

The uptake of glycylsarcosine (Gly-Sar) into scutella separated from germinating grains of barley ( Hordeum vulgare L. cv. Himalaya) is inhibited by other peptides; in most cases the inhibition is not purely competitive but of a mixed type (simultaneous increase in the apparent K_m and decrease in V_max) (Sopanen, T. 1979. FEBS Lett. 108: 447–450). The aim of the present experiments was to elucidate the mechanism of the mixed inhibition by studying how peptides already taken up into the cells affect the uptake of Gly-Sar.
When scutella were preincubated in the presence of various peptides, 11 of the 13 peptides tested inhibited the subsequent uptake of Gly-Sar by 10 to 45%. The inhibition, studied in detail with leucylleucine and prolylproline, was due to a decrease in V_max. The two peptides having no effect were glycylglycine and D-alanyl-L-alanine which are the only peptides known to date acting as purely competitive inhibitors when present together with the substrate Gly-Sar.
Preincubation with leucine, proline and alanine was not inhibitory, although preincubation with the corresponding dipeptides was. This result, together with the demonstration of intact leucylleucine in the scutella after preincubation with leucylleucine, indicates that the inhibition was caused by the intact peptides.
The results support the notion that in the mixed type inhibition the increase in the apparent K_m is due to competition for the carrier at the outside of the membrane, while the decrease in V_max is due to peptides taken up and binding to the carrier at the inside of the membrane.     

Mycorrhiza and root hairs in barley enhance acquisition of phosphorus and uranium from phosphate rock but mycorrhiza decreases root to shoot uranium transfer

Some phosphate rocks (PR) contain high concentrations of uranium (U), which are potentially toxic via accumulation in soils and food chains, and plant uptake of U is likely to be influenced by characteristics of roots and associated microorganisms. The relative importance of root hairs and mycorrhiza in U uptake from PR was studied using a root hairless barley (Hordeum vulgare) mutant (Brb) and its wild type (WT). Both plant genotypes were grown in pots with Glomus intraradices BEG 87, or in the absence of mycorrhiza, and three P treatments were included: nil P, 2% (w/w) PR and 50 mg KH(2)PO(4)-P kg(-1) soil. Mycorrhiza markedly increased d. wts and P contents of Brb amended with nil P or PR, but generally depressed d. wts of WT plants, irrespective of P amendments. Mycorrhiza had contrasting effects on U contents in roots and shoots, in particular in Brb where mycorrhiza increased root U concentrations but decreased U translocation from roots to shoots. The experiment supports our understanding of arbuscular mycorrhiza as being multifunctional by not only improving the utilization of PR by the host plant but also by contributing to the phytostabilization of uranium.     

Mild phosphorus stress in barley and a related low-phosphorus-adapted barleygrass: Phosphorus fractions and phosphate absorption in relation to growth

Barleygrass ( Hordeum leporinum ) from Australian low-P (phosphorus) soils and commercial barley ( H. vulgare ) with high fertilizer requirements were grown in solution culture at 3 levels of P supply. The high-P-adapted barley produced more biomass at all levels of P supply and was more responsive to added P in terms of rate of tillering, rate of leaf production, final leaf size, and therefore total shoot weight compared to barleygrass. In both species root: shoot ratio decreased in response to improved tissue P status, even at P levels where total biomass did not respond to P supply. Removal of endosperm reserves of barley reduced total biomass to a greater extent than it altered phosphate absorption rate, thus increasing tissue P status and making plants less responsive to added P. Similarly, barleygrass had a slower growth rate but a comparable P absorption rate to that of barley. Thus barleygrass also accumulated tissue P and was unresponsive to added P. All phosphorus chemical fractions increased in response to improved tissue P status, but to differing extents (inorganic-P > nucleic acid-P > lipid-P > ester-P), suggesting that all P fractions (particularly inorganic P) serve, in part, a storage function. Both barleygrass and barley without endosperm had higher concentrations of all P fractions (particularly inorganic P) than did unaltered barley, but this was due entirely to their higher P status (due to slow growth) rather than to any major difference in P metabolism between species. We conclude that slow growth is more important than interspecific differences in P metabolism, P absorption, or efficiency of P utilization in explaining the success of barleygrass and other low-P-adapted species on infertile soils.     

Interaction of MAGED1 with nuclear receptors affects circadian clock function

The circadian clock has a central role in physiological adaption and anticipation of day/night changes. In a genetic screen for novel regulators of circadian rhythms, we found that mice lacking MAGED1 (Melanoma Antigen Family D1) exhibit a shortened period and altered rest–activity bouts. These circadian phenotypes are proposed to be caused by a direct effect on the core molecular clock network that reduces the robustness of the circadian clock. We provide in vitro and in vivo evidence indicating that MAGED1 binds to RORα to bring about positive and negative effects on core clock genes of Bmal1, Rev‐erbα and E4bp4 expression through the Rev‐Erbα/ROR responsive elements (RORE). Maged1 is a non‐rhythmic gene that, by binding RORα in non‐circadian way, enhances rhythmic input and buffers the circadian system from irrelevant, perturbing stimuli or noise. We have thus identified and defined a novel circadian regulator, Maged1, which is indispensable for the robustness of the circadian clock to better serve the organism.     

Genetic components of root architecture and anatomy adjustments to water-deficit stress in spring barley

Roots perform vital roles for adaptation and productivity under water-deficit stress, even though their specific functions are poorly understood. In this study, the genetic control of the nodal-root architectural and anatomical response to water deficit were investigated among diverse spring barley accessions. Water deficit induced substantial variations in the nodal root traits. The cortical, stele, and total root cross-sectional areas of the main-shoot nodal roots decreased under water deficit, but increased in the tiller nodal roots. Root xylem density and arrested nodal roots increased under water deficit, with the formation of root suberization/lignification and large cortical aerenchyma. Genome-wide association study implicated 11 QTL intervals in the architectural and anatomical nodal root response to water deficit. Among them, three and four QTL intervals had strong effects across seasons and on both root architectural and anatomical traits, respectively. Genome-wide epistasis analysis revealed 44 epistatically interacting SNP loci. Further analyses showed that these QTL intervals contain important candidate genes, including ZIFL2, MATE, and PPIB, whose functions are shown to be related to the root adaptive response to water deprivation in plants. These results give novel insight into the genetic architectures of barley nodal root response to soil water deficit stress in the fields, and thus offer useful resources for root-targeted marker-assisted selection.     

Novel loci and a role for nitric oxide for seed dormancy and preharvest sprouting in barley

Barley is used for food and feed, and brewing. Nondormant seeds are required for malting, but the lack of dormancy can lead to preharvest sprouting (PHS), which is also undesired. Here, we report several new loci that modulate barley seed dormancy and PHS. Using genome‐wide association mapping of 184 spring barley genotypes, we identified four new, highly significant associations on chromosomes 1H, 3H, and 5H previously not associated with barley seed dormancy or PHS. A total of 71 responsible genes were found mostly related to flowering time and hormone signalling. A homolog of the well‐known Arabidopsis Delay of Germination 1 (DOG1) gene was annotated on the barley chromosome 3H. Unexpectedly, DOG1 appears to play only a minor role in barley seed dormancy. However, the gibberellin oxidase gene HvGA20ox1 contributed to dormancy alleviation, and another seven important loci changed significantly during after‐ripening. Furthermore, nitric oxide release correlated negatively with dormancy and shared 27 associations. Origin and growth environment affected seed dormancy and PHS more than did agronomic traits. Days to anthesis and maturity were shorter when seeds were produced under drier conditions, seeds were less dormant, and PHS increased, with a heritability of 0.57–0.80. The results are expected to be useful for crop improvement.     

Map locations of barley Dhn genes determined by gene-specific PCR

We previously identified 11 unique barley Dhn genes and found, using wheat-barley addition lines, that these genes are dispersed on four chromosomes 3H, 4H, 5H, 6H. In the present work, more precise positions of barley Dhn genes were determined using gene-specific PCR and 100 doubled haploid lines developed from a cross of Dicktoo and Morex barley. Dhn10 is located on 3H between saflp106 and ABG4. Dhn6 is at the previously determined position on 4H between SOLPRO and BCD265a. Dhn1 and Dhn2 are at the previously determined position on 5H between mR and saflp172. The Dhn locus previously called Dhn4a on barley 5H or Dhn2.2 on T. monococcum 5A is in fact Dhn9 and maps to a revised position between BCD265b and saflp218. Dhn3, Dhn4, Dhn7 and Dhn5 each map to the same position on chromosome 6H, suggesting that the previously reported separation of Dhn3, Dhn4 and Dhn5 may reflect limitations in the accuracy of Southern blot data. In addition to clarifying the map positions of these important stress-related genes, these results illustrate the advantage of gene-specific probes for the mapping of individual genes in a multi-gene family. Received: 11 August 1999 / Accepted: 16 December 1999     

Osmotic stress in barley regulates expression of a different set of genes than salt stress does

Under high salt conditions, plant growth is severely inhibited due to both osmotic and ionic stresses. In an effort to dissect genes and pathways that respond to changes in osmotic potential under salt stress, the expression patterns were compared of 460 non-redundant salt-responsive genes in barley during the initial phase under osmotic versus salt stress using cDNA microarrays with northern blot and real-time RT-PCR analyses. Out of 52 genes that were differentially expressed under osmotic stress, 11, such as the up-regulated genes for pyrroline-5-carboxylate synthetase, betaine aldehyde dehydrogenase 2, plasma membrane protein 3, and the down-regulated genes for water channel 2, heat shock protein 70, and phospholipase C, were regulated in a virtually identical manner under salt stress. These genes were involved in a wide range of metabolic and signalling pathways suggesting that, during the initial phase under salt stress, several of the cellular responses are mediated by changes in osmotic potential.