The membrane geometry of the prolamellar body

Summary When etioplasts are exposed to light, the branched tubular lattice of the prolamellar body becomes the large flat discs of the primary lamellae. We show that in spite of the very different apparent morphology of these two membranous structures, their membranes have similar average curvature and inside-outside surface areas. This implies that the packing or molecular organization of the lipids and proteins can be similar in the two structures, and that consequently the transformation does not require much high energyflip-flop of membrane components from one side to the other. We also discuss the relative physiological stability of the two structures.     

Inhibition of selected plant systems by stereoisomers of chloramphenicol

The stereospecificity of chloramphenicol isomers on the inhibition of several plant systems was investigated. l-Threo, d-erythro, l-erythro and the antibiotic d-threo-chloramphenicol were effective inhibitors of auxin-induced elongation, ¹⁴C-leucine uptake and ¹⁴C-leucine incorporation into the protein fraction of coleoptiles from Avena sativa and Triticum vulgare. The isomers also inhibited Avena coleoptile uptake of ¹⁴C-α-aminoisobutyric acid and the de novo synthesis of α-amylase by aleurone layers from Hordeum vulgare seeds. All four compounds inhibited these processes to about the same extent and over a similar high concentration range (5 × 10⁻⁴ to 5 × 10⁻³ M). Bioassay of extracts from Avena coleoptiles treated with the non-antibiotic isomers revealed no tissue conversion into d-threo-chloramphenicol.     

NaCl-induced amoeboid plastids and mitochondria in meristematic cells of barley roots

The barley (Hordeum vulgare L.) seeds were germinated in the non-saline conditions after 12 h imbibition in 2 % of NaCl solution. The results of treatment were: (l) the membrane system in meristematic cells of root tips developed well; (2) many profiles of endoplasmic reticulum and Golgi bodies appeared; and (3) the quantities of amoeboid plastids and amoeboid mitochondria increased. Thus the inhibitory effects of short-term NaCl stress on plants were reversible, and simultaneously NaCl treatment enhanced the metabolic activities in cells. The amoeboid form may be an adaptive form of plastids or mitochondria to an enhanced metabolic activity.     

Characterisation of progeny from backcrosses of triploid hybrids between Hordeum vulgare L. (2x) and H. bulbosum L (4x) to H. vulgare

Interspecific hybridisations between Hordeum vulgare L. (cultivated barley) and H. bulbosum L. (bulbous barley grass) have been carried out to transfer desirable traits, such as disease resistance, from the wild species into barley. In this paper we report the results of an extensive backcrossing programme of triploid hybrids (H. vulgare 2x x H. bulbosum 4x) to two cultivars of H. vulgare. Progenies were characterised cytologically and by restriction fragment length polymorphism analysis and comprised (1) haploid and diploid H. vulgare plants, (2) hybrids and aneuploids, (3) single and double monosomic substitutions of H. bulbosum chromosomes into H. vulgare and (4) chromosomal rearrangements and recombinants. Five out of the seven possible single monosomic chromosome substitutions have now been identified amongst backcross progeny and will be valuable for directed gene introgression and genome homoeology studies. The presence amongst progeny of 1 plant with an H. vulgare-H. bulbosum translocated chromosome and one recombinant indicates the value of fertile triploid hybrids for interspecific gene introgression.     

Isolation and culture of barley megasporocyte protoplasts

An efficient technique has been developed for the isolation of barley megasporocyte protoplasts at early meiotic prophase. Ovules were dissected out of ovaries under aseptic conditions, subjected to a brief enzymatic digestion, and then transferred to a modified Kao medium with 90 g/l sucrose and 20 mM CaCl₂. A small incision was made with a scalpel through the softened epidermal cell layer of the nucellus and the megasporocyte could then be liberated into the medium by applying gentle pressure on the nucellus. The megasporocyte appeared to be completely devoid of a wall and changed its in situ pyriform shape to completely spherical when extruded into the medium. Four to nine protoplasts could typically be isolated per spike. Protoplasts cultured in medium degenerated after a few days. Viability was dramatically improved if protoplasts were co-cultivated with barley microspores undergoing microspore embryogenesis. More than half of the protoplasts were still alive after 6 days of culture, and in some cases they survived more than 12 days of culture. Fluorescence microscopy of the cultured protoplasts stained with 4,6-diamidino-2-phenylindole (DAPI) or aniline blue revealed that the protoplasts remained uninuclear and reformed their callose wall.     

The influence of genotype and temperature pre-treatment on anther culture response in barley (Hordeum vulgare L.)

The influence of temperature stress pre-treatment on anther culture response has been examined in eight commercially desirable barley cultivars. Spikes were pre-treated in darkness at 4°C for periods of 0, 7, 14, 21 and 28 days. Overall, the optimum pre-treatment period was 21 days, although there were large genotype by pre-treatment interactions. The most responsive cultivar was Igri, with a mean of 38% anthers responding, and relatively little effect of pre-treatment. The greatest effect of pre-treatment was in cv. Heriot, which had 3% response with no pre-treatment and 52% response from 14 days pre-treatment.     

Purification and characterization of a 60-kDa protein from oat, formerly known as a TCP1-related chaperone

Recently, Mummertet al. [Nature363, 644–648 (1993)] isolated a proposed TCP1-related chaperone. Here we report several findings concerning the protein which they sequenced. Two similar N-terminal sequences were obtained from this abundant 60-kDa protein. Internal sequences were also acquired by protease digestion. Initially it was believed the protein was able to completely inhibit citrate synthase aggregation, but later purifications demonstrated that the 60-kDa polypeptide lacked both chaperone activity and the previously reported kinase activity [Grimmet al., Planta178, 199–206 (1989)]. It is now our belief that this protein is neither a chaperone nor a kinase.     

Genetic analyses of rDNA spacer-length variation in barley

Summary The genetic mechanism controlling the inheritance of single and multiple spacer-length variant (slv) phenotypes in barley was investigated in six F₂ segregating populations. The results indicated that two independently assorting loci, each with co-dominant alleles, govern genetic variability for rDNA in barley regardless of the number of bands expressed by a given phenotype. The following chromosomal locations are proposed: sl variants 1, 4, 5, 6, and 7 on chromosome 7, and sl variants 7, 8, 9, 12, and 13 on chromosome 6; sl variant 7 is thus located on both of the chromosomes.     

Comparative mapping of the barley genome with male and female recombination-derived, doubled haploid populations

Male (anther culture) and female (Hordeum bulbosum) derived, doubled haploid populations were used to map the barley genome and thus determine the different recombination rates occurring during meiosis in the F1 hybrid donor plants. The anther culture-derived (male recombination) population showed an 18% overall increase in recombination rate. This increased recombination rate was observed for every chromosome and most of the chromosome arms. Examination of linkage distances between individual markers revealed eight segments with significantly higher recombination in the anther culture-derived population, and one in the Hordeum bulbosum-derived population. Very strong distortions of single locus segregations were observed in the anther culture-derived population, but map distances were not affected significantly by these distortions. There were 1.047 and 0.912 recombinations per chromosome in the anther culture and Hordeum bulbosum-derived doubled haploid populations, respectively.     

Identification of embryogenic microspores of barley (Hordeum vulgare L.) by individual selection and culture and their potential for transformation by microinjection

Summary In order to identify microspores, suitable for transformation via microinjection of DNA, single microspores of barley (Hordeum vulgare L.) were selected after initial preculture of anthers floating on liquid media and analysed for their development in individual culture in microdroplets of culture medium. Conditions for microculture and plant regeneration from single selected embryogenie microspores were established. The technical feasability of intranuclear microinjection was demonstrated by injecting the fluorescent dye Lucifer Yellow. All essential procedures for a transformation system of barley based on microinjection into microspores have thus been performed successfully. Further efforts to increase efficiencies of culture and microinjection procedures are necessary, however, in order to improve the suitability of this approach towards transformation of barley.Abbreviations MES 2 (N-morpholino) ethanesulfonic acid - PEG polyethylene glycol     

Somatic embryogenesis,plant regeneration and somaclonal variation in barley

In vitro culture of immature embryo and young leaf tissues was carried out with five cultivars of barley, Hordeum vulgare. Two cultivars (Albacete and Porthos) responded poorly from both types of explants, while the three others (Dissa, Golden Promise and Ingrid) produced a high frequency of embryogenic callus from these explants (25–60%). For Dissa and Ingrid, young leaf explants were slightly better than immature embryo explants for embryogenic callus induction, while immature embryo cultures of Golden Promise responded better than young leaf explants. Thus, there appears to be a significant genotype × explant interaction in the initiation of embryogenic callus in barley.Some phenotypic variants were detected among the regenerated plants of Golden Promise and Ingrid, most originating by epigenetic changes. Only in one case was the variant phenotype heritable, probably due to a mutation in the chloroplast DNA. Mitotic alteractions were not detected. Consequently, somaclonal variation did not appear to be a very frequent event in plants regenerated from 1- to 6- month-old cultures of barley.     

Selecting zinc-efficient cereal genotypes for soils of low zinc status

Deficiencies of zinc are well known in all cereals and cereal-growing countries. From physiological evidence reported elsewhere, it would appear that a critical level for zinc is required in the soil before roots will either grow into it or function effectively; it is likely the requirement is frequently not met in deep sandy, infertile profiles widespread in southern Australia. Because fertilizing subsoils is impractical, this paper presents arguments for breeding cereal varieties with root systems better able to mobilise zinc from soil sources of low availability. Other agronomic arguments are presented in support of breeding for zinc efficiency.Significant genetic variation for this character is described for wheat, barley and oats. Linkage to other efficiency traits (e.g., manganese) is poor suggesting independent mechanisms and genetic control not linked to gross root system geometry. Zinc efficiency traits for sandy and clayey soils appear to be genetically different. Zinc-efficient genotypes absorb more zinc from deficient soils, produce more dry matter and more grain yield but do not necessarily have the highest zinc concentrations in tissue or grain. Although high grain zinc concentration also appears to be under genetic control, it is not tightly linked to agronomic zinc efficiency traits and may have to be selected for independently. High grain zinc is considered a desirable quality factor which not only contributes to the seedling vigour of the next generation but could increase the nutritional value of the grain in areas where a high dependence on grains for food may result in zinc deficiency in humans.     

Embryology of barley. IV. Ultrastructure of the antipodal cells of Hordeum vulgare L. cv. Bomi before and after fertilization of the egg cell

The antipodal cells have been the stepchildren in most investigations of the female gametophyte. In Hordeum vulgare cv. Bomi, three antipodal cells are originally developed chalazally but because of differential growth of the embryo sac they soon become laterally situated and their number increases to 35–50 cells and the shape, size and structure of the cells change in the time before as well as after fertilization. The cells persist until about 60–70 h after pollination. At that time, the embryo consists of about 12–15 cells and a cellularization of the nuclear endosperm has started peripherally. The size of nuclei, and especially nucleoli, in the antipodal cells increases tremendously in the investigated period and the amounts of organelles also change. The walls of antipodals are diversified depending on which cells they are separating, and wall invaginations are developed especially between antipodal cells and surrounding nucellar cells in the placental region. The mitochondria appear in various shapes in section view, very often as cups or dumbbells with a rim in the ends containing cristae and a thin cristae-free base. These bases are sometimes stretched out as thin parts and at last a simple parting occurs. Binary fissions of the plastids happen especially in the hours before and just after egg fertilization. ER is extraordinarily well developed in the whole period of investigation and many ribosomes are attached to the membranes. Dictyosomes form numerous vesicles, especially in the antipodals near the nucellar cells in the placental region. These ultrastructural details support the opinion that antipodal cells may play an important role in the embryo sac and are able to be responsible for the supply of nutrition for the whole gametophyte and take part in the supply of nutrition during embryo formation.     

Geographic distribution of alleles at the Ga2 locus for segregation distortion in barley

Summary A distorted segregation of esterase alleles at the complex loci, Est1, Est2 and Est4, was found in an F₂ population. This distortion is typical for cross combinations between the Ga2Ga2 and ga2ga2 genotypes responsible for segregation distortion, since the Ga2 locus is linked with the complex loci encoding the esterase isozymes. The segregation of esterase isozyme patterns in F₂ populations between 473 varieties of barley and a tester of ga2ga2 genotype was examined, and the genotypes inducing segregation distortion were detected. Varieties with a ga2ga2 genotype are widely distributed throughout the world, whereas Ga2Ga2 varieties are found only in eastern and southern regions of Asia, from Japan to North India, with a low frequency. In varieties collected from these regions, some associations were detected between alleles at the Ga2 locus and esterase isozyme patterns. Additionally, most of the Ga2 barley varieties are naked and possess a BtBtbt2bt2 genotype for a non-brittle rachis.     

Nitrite-driven anaerobic ATP synthesis in barley and rice root mitochondria

Mitochondria isolated from the roots of barley (Hordeum vulgare L.) and rice (Oryza sativa L.) seedlings were capable of oxidizing external NADH and NADPH anaerobically in the presence of nitrite. The reaction was linked to ATP synthesis and nitric oxide (NO) was a measurable product. The rates of NADH and NADPH oxidation were in the range of 12–16 nmol min⁻¹ mg⁻¹ protein for both species. The anaerobic ATP synthesis rate was 7–9 nmol min⁻¹ mg⁻¹ protein for barley and 15–17 nmol min⁻¹ mg⁻¹ protein for rice. The rates are of the same order of magnitude as glycolytic ATP production during anoxia and about 3–5% of the aerobic mitochondrial ATP synthesis rate. NADH/NADPH oxidation and ATP synthesis were sensitive to the mitochondrial inhibitors myxothiazol, oligomycin, diphenyleneiodonium and insensitive to rotenone and antimycin A. The uncoupler FCCP completely eliminated ATP production. Succinate was also capable of driving ATP synthesis. We conclude that plant mitochondria, under anaerobic conditions, have a capacity to use nitrite as an electron acceptor to oxidize cytosolic NADH/NADPH and generate ATP.