Variation in Photorespiration in Lolium

The rate of photorespiration in several grass species was shownto be highly variable and dependent on the species, genotype,and conditions under which the plants were grown. Photorespiration,measured as oxygen uptake, was negligible in Cenchrus ciliarisand Paspalum dilatatum but significant in Lolium spp. and Festucaarundinacea. There were significant differences in the rateof photorespiration among plants within a Lolium populationof diverse origin and these differences were independent ofthe conditions under which the plants were grown. Among thetemperate grasses there was a significant correlation betweenphotorespiration and the CO₂-compensation concentration andboth parameters were very low in P. dilatatum. Plants grownin day/night temperatures of 15/10 °C compared with 25/20°C had faster rates of dark respiration but slower ratesof light respiration when measured at the same temperature.Photorespiration was faster than dark respiration although differencesin respiration among plants in the light were not shown in thedark.     

Strong Patterns in Homooligomer Tracts Occurrences in Non-Coding and in Potential Regulatory Sites in Eukaryotic Genomes

Abstract

Previous studies of the dinucleotides flanking both the 5′ and 3′ ends of homooligomer tracts have shown that some flanks are consistently preferred over others (1,2). In the first preferred group, the homooligomer tracts are flanked by the same nucleotide and/or the complementary nucleotides, e.g., ATA_n, TTA_n, CCG_n, where n=2–5. Runs flanked by nucleotides with which they cannot base pair are distinctly disfavored. (In this group A/T_n are flanked by C and/or G; G_n/C_n are flanked by A/T, e.g., CGA_n, T_nGG, G., AT). The frequencies of runs flanked by AorT, and G or C (“mixed” group) are as expected. Here we seek the origin of this effect and its relevance to protein-DNA interactions. Surprisingly, within the first group, runs flanked by their complements with a pyrimidine-purine junction (e.g., TTA_n, C_nGG) are greatly preferred. The frequencies of their purine-pyrimidine junction mirror-images is just as expected. This effect, as well as additional ones enumerated below, is seen universally in eukaryotes and in prokaryotes, although it is stronger in the former. Detailed analysis of regulatory regions shows these strong trends, particularly in GC sequences. The potential relationship to DNA conformation and DNA-protein interaction is discussed.     

Peroxisomes in Rice Coleoptiles Grown in Air and in Anoxia

Rice coleoptiles grow under anoxia. When the ultrastructure of anoxic coleoptile cells was examined, it was seen that most organelles maintain their integrity, with the exception of peroxisomes (unspecialized type). The lack of O₂ greatly reduced the number of these organelles and altered the ultrastructure of the remaining ones. To examine the effect of O₂ on peroxisome development in more detail, coleoptiles grown in air were transferred to N₂ and anoxic coleoptiles were transferred to oxygen. Marker enzyme activity was measured in entire coleoptiles as well as in the isolated organelles. As expected, anoxia greatly depressed enzyme activity when imposed from the beginning of the germination process, while it had a lesser effect when imposed for only two days on aerobic seedlings. When coleoptiles were grown constantly under N₂, the density of the organelles was 1.216 g/cm³, while the corresponding aerobic organelles showed a buoyant density of 1.241 g/cm³. When transferred to air the anoxic peroxisomes reached the intermediate density of 1.227 g/cm³. The results confirm the particular sensitivity of rice peroxisomes to O₂ availability.     

Nuclear conditions in haploid Pelargonium in vivo and in vitro

In the shoot apices of the haploid Pelargonium cultivar Kleine Liebling, all mitoses are haploid (n = 9); however, ca. 20% of the interphase nuclei have DNA contents greater than 2C (up to 4C), indicating a tendency to chromosome endoreduplication in this material. — In internodes in vivo, the few mitoses present are haploid (quite probably, cambium cells); in addition to haploid interphases (1C to 2C DNA contents), endoreduplicated (endopolyploid) nuclei and nuclei in the course of endoreduplication occur with a frequency of ca. 40–50% (DNA contents up to 8C). — When internodes are cultured in vitro, differentiated cells are stimulated to divide, thus forming a population of diploid and tetraploid mitoses in addition to the preexistent meristem (haploid) cell population. In the process of time, diploid and tetraploid mitoses continue to be present in the callus, whilst haploid mitoses may decrease in number and eventually disappear. All mitoses analyzed had euploid chromosome numbers (9, 18 and 36) and their DNA contents were correspondingly 2C, 4C and 8C. Since no extensive chromosome counts were made, aneuploidy in the cultured material cannot be excluded; but, if occurring, it should be rather rare. — Under the experimental conditions used, prolonged culture in vitro leads to the production of nuclei with DNA contents (16C and 32C) greater than those occurring in vivo (8C), due to one and two additional DNA replications respectively beyond the limits attained in vivo. Even in these cultures, however, a population of the meristematic haploid cell line (DNA values 1C to 2C) is still present. — The present results are discussed in their relations with previous works on nuclear conditions in vivo and in vitro and on regeneration processes in cultured tissues in plants.     

A comparison of in vitro with in vivo flowering in Gentian

Young nodal explants of Gentiana triflora Pall. var. axillariflora were cultured in a woody plant medium (WPM) supplemented with B5 vitamins, sucrose (3%) and kinetin (2.0 μM). A novel observation was made in that in vitro flowering occurred following development of the axillary bud of the cultures. A comparison was made between in vitro and in vivo flowers. Although smaller in size, the in vitro flowers were morphologically comparable to the in vivo ones. Flowers from both sources were semi-opened or not opened. The colour of the in vitro flowers was paler than those in vivo. Stigma development was generally poor in both in vitro and in vivo flowers. Pollen viability was over 90% in both types of flowers. About 11% and 34% of pollen from in vitro and in vivo flowers, respectively, germinated on WPM containing 100 g l⁻¹ sucrose solidified with 10 g l⁻¹ agar. Hand pollination of stigma could raise viable seed production in in vivo-flowering plants from 0.3 o/o (i.e. without aided pollination) to 3% but none in in vitro-flowering plants where only seed-like structures, probably unfertilised ovules, were found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fumonisins in Maize in Relation to Climate,Planting Time and Hybrids in Two Agroecological Zones in Zambia

Field experiments in the high rainfall zone (HRZ) and the medium rainfall zone (MRZ) in Zambia were designed to determine the natural occurrence of fumonisins (FB_1–2) in Zambian maize hybrids, accumulation of FB_1–2 resulting from artificial inoculation with Fusarium verticillioides and effects of climate and planting time on FB_1–2 in maize. Combined FB_1–2 concentrations varied from 0 to 13,050 ng/g, with an overall mean of 666 ng/g. Maize from the HRZ had low incidences of FB_1–2-positive samples (mean 41%) which contained FB_1–2 below 500 ng/g. In the MRZ, higher incidences (mean 97%) and concentrations (40% of samples >1,000 ng/g) were recorded in two out of three years. There was no correlation between mean location FB_1–2 concentrations in individual years and precipitation, number of rain days or monthly precipitation. Postponing the planting time with 10 or 20 days did not significantly affect FB_1–2 concentration, but it reduced the yields in some years.     

Variation in Aggressiveness Components in the Hemileia vastatrix Population in Brazil

The Pucciniomycete fungus Hemileia vastatrix causes leaf rust on coffee trees. The pathogen is responsible for considerable yield losses in susceptible coffee cultivars if appropriate management strategies are not implemented. Rapid spread and epidemics of rust fungi are usually associated with the emergence of new races of the pathogen that overcome resistance or with the emergence of more aggressive populations of the pathogen. In Brazil, coffee production is dominated by susceptible cultivars of Coffea arabica and Coffea canephora. We assessed aggressiveness in 46 populations of H. vastatrix from Minas Gerais and Espírito Santo, two of the most important coffee‐producing states in Brazil. We observed a significant difference in the incubation period between the populations from Minas Gerais and Espírito Santo when 183 single‐pustule isolates were inoculated onto Catuaí Vermelho IAC 44, a susceptible C. arabica cultivar. Variation in aggressiveness components was observed between and within localities. Isolates with longer incubation periods also tended to have longer latent periods, although there was only a low correlation between these two aggressiveness components (r² = 0.34, P = 2.2 × 10^?16). Low‐sporulating isolates also had significantly longer incubation and latent periods. The H. vastatrix population from Minas Gerais and Espírito Santo is structured by the formation of groups of individuals with differential level of aggressiveness. Our results indicate that the variation in aggressiveness of the Brazilian H. vastatrix population may be associated with the geographic coffee‐producing areas.     

Climate-driven changes in biomass allocation in pines

Future increases in air temperature resulting from human activities may increase the water vapour pressure deficit (VPD) of the atmosphere. Understanding the responses of trees to spatial variation in VPD can strengthen our ability to predict how trees will respond to temporal changes in this important variable. Using published values, we tested the theoretical prediction that conifers decrease their investment in photosynthetic tissue (leaves) relative to water‐conducting tissue in the stem (sapwood) as VPD increases. The ratio of leaf/sapwood area (A_L/A_S) decreased significantly with increasing VPD in Pinus species but not in Abies, Pseudotsuga, Tsuga and Picea, and the average A_L/A_S was significantly lower for pines than other conifers (pines: 0.17 m² cm^?2; nonpines: 0.44 m² cm^?2). Thus, pines adjusted to increasing aridity by altering above‐ground morphology while nonpine conifers did not. The average water potential causing a 50% loss of hydraulic conductivity was ?3.28 MPa for pines and ?4.52 MPa for nonpine conifers, suggesting that pines are more vulnerable to xylem embolism than other conifers. For Pinus ponderosa the decrease in A_L/A_S with high VPD increases the capacity to provide water to foliage without escalating the risk of xylem embolism. Low A_L/A_S and plasticity in this variable may enhance drought tolerance in pines. However, lower A_L/A_S with increasing VPD and an associated shift in biomass allocation from foliage to stems suggests that pines may expend more photosynthate constructing and supporting structural mass and carry less leaf area as the climate warms.     

Oxygen exchange in leaves in the light

Photosynthetic O₂ production and photorespiratory O₂ uptake were measured using isotopic techniques, in the C₃ species Hirschfeldia incana Lowe., Helianthus annuus L., and Phaseolus vulgaris L. At high CO₂ and normal O₂, O₂ production increased linearly with light intensity. At low O₂ or low CO₂, O₂ production was suppressed, indicating that increased concentrations of both O₂ and CO₂ can stimulate O₂ production. At the CO₂ compensation point, O₂ uptake equaled O₂ production over a wide range of O₂ concentrations. O₂ uptake increased with light intensity and O₂ concentration. At low light intensities, O₂ uptake was suppressed by increased CO₂ concentrations so that O₂ uptake at 1,000 microliters per liter CO₂ was 28 to 35% of the uptake at the CO₂ compensation point. At high light intensities, O₂ uptake was stimulated by low concentrations of CO₂ and suppressed by higher concentrations of CO₂. O₂ uptake at high light intensity and 1000 microliters per liter CO₂ was 75% or more of the rate of O₂ uptake at the compensation point. The response of O₂ uptake to light intensity extrapolated to zero in darkness, suggesting that O₂ uptake via dark respiration may be suppressed in the light. The response of O₂ uptake to O₂ concentration saturated at about 30% O₂ in high light and at a lower O₂ concentration in low light. O₂ uptake was also observed with the C₄ plant Amaranthus edulis; the rate of uptake at the CO₂ compensation point was 20% of that observed at the same light intensity with the C₃ species, and this rate was not influenced by the CO₂ concentration. The results are discussed and interpreted in terms of the ribulose-1,5-bisphosphate oxygenase reaction, the associated metabolism of the photorespiratory pathway, and direct photosynthetic reduction of O₂.     

Genetic Diversity in Monilinia laxa Populations in Peach Orchards in Spain

One‐hundred and forty‐four random amplified polymorphic DNA markers, of which 59 were polymorphic and 85 monomorphic, were used to assess the genetic diversity and to study the structure of Monilinia laxa populations in Spain. Twenty‐one isolates collected from several orchards (subpopulations), in various years and in various hosts, were used. The analysis of population structure revealed that genetic diversity within orchards (H_S) accounted for 97% of the total genetic diversity (H_T), while genetic diversity among the orchards represented only 3%. The relative magnitude of gene differentiation between subpopulations (G_ST) and the estimate of the number of migrants per generation (N_m) averaged 0.032 and 15.1 respectively. The results obtained in dendrograms were in accordance with the gene diversity analysis. Grouping of isolates in the dendrogram was independent of whether they came from the same or different orchards. There was no relationship between clustering among isolates from distinct years and hosts. The relative importance of several evolutionary forces in populations of M. laxa is discussed, together with implications for the management of brown rot.     

Thyroxine in Early Strobilation in Aurelia aurita

Radiochromatographic studies of ¹³¹I-treated Aurelia polypsrevealed synthesis of three compounds tentatively identifiedas monoiodotyrosine (MIT), diiodotyrosine (DIT), and thyroxine(T₄). One compound, MIT, is found within 8 hr after ¹³¹I administration,before the detection of DIT or T₄ which appear within 24 hr.T₄ is not usually detected after 48 hr although MIT and DITwere found up to the segmentation period. None of the compoundswere detected in ephyrae treated with ¹³¹I for 24 hr. Administration of low dosages of the goitrogens, thiourea,,propylthiouracil, and potassium thiocyanate, in conjunctionwith iodide, prevented strobilation induction. Radiochromatographyof jellyfish given the goitrogens and ¹³¹I revealed a reduceduptake of iodide and an impairment of the synthesis of the iodinatedcompounds. Jellyfish use thyroxine directly for strobilatioa inductionas demonstrated by ¹³¹I - labeled T₄ administration. The T₄was detected in the polyps up to the 48-hr period of strobilationduring which time some of the T₄ was excreted into the medium,as was some ¹³¹I. The fact that T₄, synthesis has thus far been found only instrobilating forms of Aurelia suggests that T₄ is involved primarilywith the differentiation of new structures which occurs duringstrobilation.     

Improvement in in?vitro fertilization outcome following in?vivo synchronization of oocyte maturation in mice

Synchronization of oocyte maturation in vitro has been shown to produce higher in vitro fertilization (IVF) rates than those observed in oocytes matured in vitro without synchronization. However, the increased IVF rates never exceeded those observed in oocytes matured in vivo without synchronization. This study was therefore designed to define the effect of in vivo synchronization of oocyte maturation on IVF rates. Mice were superovulated and orally treated with 7.5 mg cilostazol (CLZ), a phosphodiesterase 3A (PDE3A) inhibitor, to induce ovulation of immature oocytes at different stages depending on frequency and time of administration of CLZ. Mice treated with CLZ ovulated germinal vesicle (GV) or metaphase I (MI) oocytes that underwent maturation in vitro or in vivo (i.e. in the oviduct) followed by IVF. Superovulated control mice ovulated mature oocytes that underwent IVF directly upon collection. Ovulated MI oocytes matured in vitro or in vivo had similar maturation rates but significantly higher IVF rates, 2–4 cell embryos, than those observed in control oocytes. Ovulated GV oocytes matured in vitro showed similar maturation rates but significantly higher IVF rates than those observed in control oocytes. However, ovulated GV oocytes matured in vivo had significantly lower IVF rates than those noted in control oocytes. It is concluded that CLZ is able to synchronize oocyte maturation and improve IVF rates in superovulated mice. CLZ may be capable of showing similar effects in humans, especially since temporal arrest of human oocyte maturation with other PDE3A inhibitors in vitro was found to improve oocyte competence level. The capability of a clinically approved PDE3A inhibitor to improve oocyte fertilization rates in mice at doses extrapolated from human therapeutic doses suggests the potential scenario of the inclusion of CLZ in superovulation programs. This may improve IVF outcomes in infertile patients.     

Seasonal variation in photosynthesis in six woody species with different leaf phenology in a valley savanna in southwestern China

During 2003–2005, we examined the effect of seasonal drought on water status, gas exchange, δ¹³C, chlorophyll fluorescence and spectral reflectance in six woody species in a valley savanna near the Yuanjiang River (the upper Red River) in southwestern China. Three different phenological types of these woody species were compared, i.e., an evergreen species, Cyclobalanopsis helferiana, two winter-deciduous (WD) species, Buchanania latifolia and Symplocos racemosa, and three drought-deciduous (DD) species, Terminthia paniculata, Wendlandia tinctoria and Woodfordia fruticosa. We aimed to test the following three hypotheses: (1) the evergreen and WD species employ a drought avoidance strategy, whereas DD species employ a drought tolerance strategy; (2) the evergreen and WD species have a more economical water use strategy than the DD species and (3) the evergreen and WD species have a stronger photoprotection capacity through thermal dissipation than the DD species. At the end of a prolonged drought, the predawn leaf water potential (Ψ_pd) in C. helferiana and S. racemosa dropped to ca. −0.8 MPa, whereas the Ψ_pd in B. latifolia remained close to zero and DD species were leafless. In the rainy seasons, maximal photosynthetic rates of the evergreen (18.4 μmol m⁻² s⁻¹) and W. fruticosa (18.0 μmol m⁻² s⁻¹) were higher than those of the other four species (12.2−13.8 μmol m⁻² s⁻¹). The evergreen and WD species responded to drought by closing stomata and thus maintained a constant relative water content (RWC), which is a typical drought avoidance strategy; however, it is at the expense of carbon gain. DD species maintained a high photosynthetic capacity with a decrease in both stomatal conductance and RWC until the driest period, and then shifted from the drought tolerance strategy to the avoidance mechanism by shoot dieback. There was no significant difference in the means of δ¹³C across the phenological groups. The evergreen and WD species had stronger heat dissipation than the DD species in dry seasons. All species increased leaf spectral reflectance, probably because of degradation of chlorophyll as indicated by the leaf reflectance index, which should reduce light harvesting. All species showed a strong increase in the ratio of red to green spectral reflectance of leaves during dry seasons, indicating the accumulation of anthocyanin, which may contribute to screening sunlight and scavenging reactive oxygen species. Different responses to drought of savanna woody species with different leaf phenologies may facilitate the partitioning of resource use and hence their co-existence.     

Acetylcholinesterase levels in Angiostrongylus cantonensis in relation to the immune response in rats

Beaver J. P. and Dobson C. 1978. Acetylcholinesterase levels in Angiostrongylus cantonensis in relation to the immune response in rats. International Journal for Parasitology8: 9–13. Angiostrongylus cantonensis larvae and adult nematodes synthesize three acetylcholinesterase (AChE) isozymes. The K_m of this isozyme complex changes with the development and migrations of the parasite in the rat host. The levels of parasite AChE changed as the development of A. cantonensis progressed; increasing quantities of AChE were found in young adult A. cantonensis from the brain of rats. After migration to the pulmonary arteries, the quantity of AChE in the parasite was reduced and continued to decline in the aging parasite. Anti-A. cantonensis antibody inhibited parasite AChE activity; this inhibition of the parasite AChE activity changed at stages during development of the parasite which suggested variation in parasite AChE isozyme levels. Haemagglutinating anti-A. cantonensis antibody appeared in the serum of infected rats when the parasites commenced to lay eggs and increased in titre thereafter until 103 days after infection.     

Galactolipid synthesis in chromoplasts in vitro

Isolated chromoplasts from Narcissus pseudonarcissus flowers contain: a fatty acid synthesizing system; acyl-CoA synthetase (EC 6.2.1.3); glycero-phosphate acyltransferase (EC 2.3.1.15); acylglycero-phosphate acyltransferase; phosphatidate phosphatase (EC 3.1.3.4); diacylglycerol galactosyltransferase (EC 2.4.1.46); and diacylgalactosylglycerol galactosyltransferase, i.e. all enzymatic activities necessary for the synthesis of diacylgalactosylglycerol and diacylgalabiosylglycerol from acetate, HCO _- ³ , sn-glycerol 3-phosphate, and UDP-d-galactose. Diacylgalactosylglycerol and diacylgalabiosylglycerol, however, are synthesized from these precursors to only a very low extent in an in vitro system. This is attributed to a specificity of diacylglycerol galactosyltransferase for highly unsaturated diacylglycerols. Specificities of acyltransferase reactions were also found.     

Further Studies of Electro-Osmosis in Nitella in Relation to Pores in Membranes

By measuring the number of water molecules per ion which weremoved electro-osmotically through cells of Nitella translucensand N. flexilis it has been shown that a significant differenceexisted between samples of these species in 1965. In each speciesthe electro-osmotic efficiency was greater with Na⁺ than withK⁺⁺. Also 10^-4 to 10^-5 M IAA tended to decrease electro-osmoticefficiencies while IAA, after 30 min. treatment, produced asignificant increase in water flow into the treated end of aliving cell. Calculations based on this work suggest that about10⁸–10⁹ pore sites per cm² exist on the surface membranesfor Na⁺ or K⁺ ion transport.     

Reversible conjugation of gibberellins in situ in maize

Gibberellins [³H]GA₄ (1.33 Curies per millimole) and [³H]GA₂₀ (2.36 Curies per millimole) were injected into the shanks of maize (Zea mays L.) cobs during rapid grain filling and mature seeds were subsequently harvested. Extracts of mature, dry seeds from 1980 feeds yielded only 20 to 30% of the ³H radioactivity in acidic, ethyl acetate-soluble form, and this was principally associated with the precursor, with lesser amounts of the major metabolite, [³H]GA₁ (putative identification based on sequential SiO₂ partition, and gradient-eluted reverse-phase C₁₈ high performance liquid chromatography [HPLC]). Most of the radioactivity in the dry seeds was associated with compounds having partition characteristics of, and co-chromatographing on, sequential SiO₂ partition and reverse-phase HPLC with glucosyl conjugates of the precursors (GA₄ or GA₂₀) and their probable major metabolite (GA₁). The majority of conjugate associated with the precursor GA₄ eluted coincidental with GA₄ glucoside. Subsequent acid or enzymic hydrolysis (β-glucosidase or cellulase) yielded the free GAs, putative identification being based on isocratic HPLC of each ³H-labeled conjugate → hydrolysis → isocratic HPLC of the ³H-labeled hydrolysate. Upon imbibition of the seeds, radioactivity associated with the conjugate fraction decreased; concomitantly, statistically significant increases in levels of free [³H]GA-like compounds were observed. Although the specific ratios of GA-like and GA-glucosyl conjugate-like substances varied substantially across years, hybrids, and even, in different plants from the same hybrid, this `reversible conjugation' (i.e. apparent conjugation during seed maturation followed by release of the GA moiety during germination), was reproducible for [³H]GA₂₀ in seed from two maize hybrids produced over 2 years.