Substrates regulate the phosphorylation status of nitrate reductase

The effect of substrates on the phosphorylation status of nitrate reductase (NR; EC 1.6.6.1) was studied. The enzyme was obtained from the first leaf of 7-day-old oat (Avena sativa L. cv. Suregrain) plants, grown in the light. When desalted crude extracts were incubated with ATP, NR was strongly phosphorylated, as evidenced by the inhibition of the enzyme's activity in the presence of Mg²⁺. NR sensitivity to Mg²⁺ remained unchanged when 10 mM nitrate was added to crude extracts after ATP. Addition of nitrate before or simultaneously with ATP slightly decreased Mg²⁺ inhibition of NR, which was strongly diminished in the presence of 10 mM NO₃^?+ 100 µM NADH. Incubation with NADH alone did not affect the enzyme's susceptibility to Mg²⁺ inhibition. When ammonium sulfate was added to crude extracts, NR was recovered in a 0-40% saturation fraction (F1). After incubation of F1 with ATP, the sensitivity of the enzyme to Mg²⁺ inhibition remained low, but it strongly increased after mixing F1 with a 45-60% saturation fraction (F2) suggesting that also in oats an additional factor (inactivating protein, IP), which probably binds to phospho-NR, would be required to keep the phosphorylated enzyme inactive in a +Mg²⁺ medium. Addition of 10 mM NO₃^?+ 100 µM NADH together with desalted F2 did not prevent Mg²⁺ inhibition suggesting that NO₃^? did not interfere with IP binding to phospho-NR. Again, incubation of F1 with both substrates during in vitro phosphorylation kept the enzyme active after adding F2, even in the presence of Mg²⁺, After in vitro phosphorylation, NR in crude extract was hardly reactivated when incubated alone or in the presence of 10 mM NO₃^? at 30°C. On the other hand, a strong and very rapid reactivation was found when the extract was incubated with both nitrate and NADH. Microcystine, an inhibitor of types 1 and 2A phosphoprotein phosphatases, inhibited the reactivation of phospho-NR induced by the substrates. The results presented here show that the substrates could prevent NR phosphorylation and induce the enzyme's dephosphorylation, but they were effective only after their binding to the NR protein. Thereby, they seemed to affect the NR protein itself and not the phosphatase- or the kinase-proteins. It has been reported that nitrate binding to the enzyme's active site induces conformational changes in the NR protein. We propose that this conformational change would prevent NR phosphorylation, by converting the enzyme into a form in which the site recognized by the protein kinase is no longer accessible, and, simultaneously, stimulate NR dephophorylation by allowing the specific phosphatases to recognize NR.     

Digestibility of whole-crop barley and oat silages in dairy heifers

This study evaluated the digestibility of whole-crop cereal silage (WCCS) made from oats and six-rowed barley harvested at the heading, early milk and early dough stages, and two-rowed barley harvested at the early milk and early dough stages of maturity. The eight WCCSs were fed to 32 Swedish Red heifers in a changeover design over three periods of 28 days each. The heifers were first fed ad libitum for 17 days and then at 0.95 of ad libitum for 11 days of each period. During the last 5 days all faeces and orts were collected to determine the digestibility of the silages. Only the maturity stage effect was significant for the WCCS organic matter (OM) digestibility and the average OM digestibility was higher at the heading stage (698 g/kg) than at early milk (647 g/kg) and early dough (652 g/kg) stages of maturity. For neutral detergent fibre (NDF) digestibility the crop × maturity stage effect was significant. The NDF digestibility decreased from the heading to the early milk stage for both six-rowed barley (746 to 607 g/kg) and oats (698 to 596 g/kg). There was no further significant decrease in NDF digestibility for six-rowed barley at the early dough stage (577 g/kg), but for two-rowed barley it decreased from the early milk (682 g/kg) to the early dough (573 g/kg) stage, and also for oats the NDF digestibility was lowest at the early dough stage (507 g/kg). The decrease in NDF digestibility during maturation was to a large extent compensated by an increase in starch concentration in the crops. The starch digestibility was lower for six-rowed barley at early dough stage (948 g/kg) than at early milk stage (977 g/kg), and was also lower compared with oats (979 g/kg) at early dough stage. The average crude protein (CP) digestibility was higher at the heading (646 g/kg) and the early milk (642 g/kg) stages than at the early dough stage (599 g/kg), and oats had higher average CP digestibility (650 g/kg) than six-rowed (613 g/kg) and two-rowed (624 g/kg) barley. Delaying the harvest of WCCS from the heading to the early milk and dough stage of maturity will decrease the OM digestibility; as a result there is a decreased NDF digestibility.     

The effects of elevated atmospheric CO2 on the amount and depth distribution of plant water uptake in a California annual grassland

Soil moisture profiles can affect species composition and ecosystem processes, but the effects of increased concentrations of atmospheric carbon dioxide ([CO₂]) on the vertical distribution of plant water uptake have not been studied. Because plant species composition affects soil moisture profiles, and is likely to shift under elevated [CO₂], it is also important to test whether the indirect effects of [CO₂] on soil water content may depend on species composition. We examined the effects of elevated [CO₂] and species composition on soil moisture profiles in an annual grassland of California. We grew monocultures and a mixture of Avena barbata and Hemizonia congesta– the dominant species of two phenological groups – in microcosms exposed to ambient (～370 μmol mol^?1) and elevated (～700 μmol mol^?1) [CO₂]. Both species increased intrinsic and yield‐based water use efficiency under elevated [CO₂], but soil moisture increased only in communities with A. barbata, the dominant early‐season annual grass. In A. barbata monocultures, the [CO₂] treatment did not affect the depth distribution of soil water loss. In contrast to communities with A. barbata, monocultures of H. congesta, a late‐season annual forb, did not conserve water under elevated [CO₂], reflecting the increased growth of these plants. In late spring, elevated [CO₂] also increased the efficiency of deep roots in H. congesta monocultures. Under ambient [CO₂], roots below 60 cm accounted for 22% of total root biomass and were associated with 9% of total water loss, whereas in elevated [CO₂], 16% of total belowground biomass was associated with 34% of total water loss. Both soil moisture and isotope data showed that H. congesta monocultures grown under elevated [CO₂] began extracting water from deep soils 2 weeks earlier than plants in ambient [CO₂].     

Senescence in oat leaves: Changes in translatable mRNAs

Changes in translatable mRNA populations during the senescence of oat (Avena sativa L. cv. Victory) leaves were examined by analyzing the in vitro translation products of isolated RNA. Total RNA was isolated from oat leaves of 7-day-old seedlings, and also after these leaves were aged for different lengths of time under various conditions. Polypeptides from in vitro translations were separated by two-dimensional gel electrophoresis to estimate any changes in translatable mRNA populations associated with senescence. Corresponding leaf samples were monitored for loss of chlorophyll as a measure of the extent of senescence. The aging of excised leaves in the light for 4 days resulted in the disappearance or substantial quantitative decrease of a number of mRNA species, while only five new translatable mRNA species were produced. Three of these mRNAs were unique to aging of leaves under light. Two of these mRNA species were also produced during the early stages of senescence in attached leaves of seedlings grown under light. The translatable mRNA populations of leaves aged for 4 days either on intact seedlings or detached and kept in the light in the presence of kinetin were very similar. Aging of excised leaves in the dark on water for 24 h resulted in very extensive changes in translatable mRNA populations. Over thirty polypeptides disappeared or were substantially reduced in quantity, while about an equal number appeared de novo or were substantially increased in quantity. Aging of these leaves for an additional 24 or 48 h resulted in only a few additional changes in translatable mRNAs. The presence of kinetin during aging of excised leaves in the dark inhibited few of the numerous changes in mRNAs that occured during the first 24 h, but did inhibit most of the changes that occured after 48 or 72 h of aging in the dark. When leaves were first aged in the dark and then returned to light, most of the initial changes in translatable mRNAs expression were reversed. Such changes in mRNAs thus appear to be light-regulated and not necessarily associated with senescence.     

Impact of Crown Rust (Puccinia coronata f. sp. avenae) on Competitive Interactions between Wild Oats (Avena fatua) and Stipa (Nassella pulchra)

Crown rust of oats (Puccinia coronata f. sp. avenae) was investigated as a biocontrol agent for wild oats (Avena fatua) on San Clemente Island, California. Successful restoration of the native habitats of this island will involve the reduction of wild oats and revegetation with native grasses such as stipa (Nassella pulchra). Determination of the outcome of interference between wild oats and stipa is important in the prediction of the success of the biocontrol agent. An addition series design was used to investigate these interactions, with densities of each species ranging from 0 to 2000 seeds per m². Eight replicates were established, four of which were randomly chosen and infected with the pathogen. After 75 days, plant height, dry weight, and seed production were measured. The data were fit to a hyperbola surface model by use of a nonlinear regression procedure. Results indicate that wild oat is the superior competitor at the seedling stage; however, early rust infection greatly reduces fitness of wild oats, causing an increased fitness for stipa. Simulations with a plant community model constructed from the results of the greenhouse experiment and information in the literature indicated that an equilibrium may be established between wild oat and stipa if high initial seeding rates of stipa are used in revegetation.     

Subunits polypeptide composition of Rubisco in Avena species

Abstract

Rubisco was extracted and purified from leaves of nineteen Avena species. The holoenzyme shows the already known “slow” and “fast” forms after native electrophoresis. The electrophoresis in denaturing conditions revealed a unique polypeptide for the large subunit and two types of polypeptides for the small subunit. The addition of leupeptin, a thiol proteinase inhibitor, during purification of the holoenzyme, reduced microheterogeneity within both subunit types. Subunit composition of the enzyme appears to be a taxonomic tool for distinguishing three species: A. clauda Dur., A. eriantha Dur. and A. canariensis Baum. Rajh. et Baum.     

Oviposition site selection on oats: the effect of plant architecture,plant and leaf age,tissue toughness,and hardness on cereal leaf beetle,Oulema melanopus

In sequentially planted oat stands, the cereal leaf beetle (CLB), Oulema melanopus (L.) (Coleoptera: Chrysomelidae: Lemini), is found in greater numbers, and lays more eggs, on later planted (younger) oats (Avena sativa L.) (Poaceae). Plant characteristics that could explain this ovipositional preference were examined in a series of experiments. Cage and open field whole plant preference tests confirmed the attraction of ovipositing females to younger oats. A cage effect illustrated the role of plant architecture (plant height) in CLB host selection. Two multiple‐choice and one no‐choice excised leaf experiments determined that characteristics of individual leaves associated with leaf insertion level (leaf number from base to apex) and age influence ovipositional site selection. Leaves of higher insertion level have higher nitrogen content, but fewer eggs are laid on those leaves. Two experiments examining the interaction between total leaf nitrogen and leaf insertion level showed that only leaf insertion level affected oviposition choice. Published literature suggests variation in secondary plant compounds cannot explain O. melanopus ovipositional preference among leaves. Grass leaves of higher insertion level have more extensively developed cells associated with tissue toughness and hardness. The data and supporting literature suggest tissue toughness and hardness are deterring oviposition on oat leaves of higher insertion level. However, newly eclosed larvae are able to feed on leaves usually avoided as oviposition sites. The explanation for this result may be a lack of correlation between host suitability and ovipositional preference.     

Collection ofAvena Macrostachya Bal. Ex Coss. et Dur. (Poaceae) germplasm in algeria

Avena macrostachya Bal. ex Coss. et Dur. is narrowly endemic to two mountain chains in northeastern Algeria, the Aures and the Djurdjura, where it is found at high altitudes. It is taxonomically isolated within the genus, showing a number of primitive features, including perennial habit. There is interest in the possibility of gene exchange with cultivated oats, particularly as regards tolerance of low temperatures, but the availability of germplasm was limited to material from one site. The first systematic attempt to collect germplasm of the species throughout its range was made recently, during which observations were also made on its ecology and conservation status.Avena macrostachya seems to require open conditions above about 1300–1400 m in the Mediterranean region of Algeria. For the first time, germplasm was collected in the Aures, an area where the species seems to be rare and decreasing.     

Incidence of crown rust and virulence of puccinia coronata cda. f.sp. avenae eriks. and the effectiveness of pc genes for resistance in europe,middle east and north africa: Inzidenz von kronenrost und virulenz von puccinia coronata cda. f.sp. avenae eriks. und die wirksamkeit von pc-genen für resistenz in europa,nahost und nordafrika

Crown rust on oat incited by Puccinia coronata Cda f.sp. avenae is a wide-spread disease in Europe, Middle East (Israel) and North Africa (Morocco). High natural levels of the disease were recorded in Austria, Bulgaria, Czech Republic, Estonia, Israel, Italy, Poland, Russia and the former Yugoslavia. The severity of the disease in the European and Mediterranean Oat Disease Nursery (EMODN) between 1995 and 1999 showed that it occurred at damaging levels in a number of countries. Considerable differences in a disease resistance index (DRI) to crown rust among 67 oat lines in the period 1995?–?2000 were found. The values of the DRI ranged from18 (KR 8122) to over 290 (Pc 59, Pc 68). Detailed studies of the virulence combinations of P.coronata f.sp. avenae in Europe, Middle East and North Africa were carried out between 1995?–?2001. There were considerable differences in the average number of virulence among countries. Virulence to Pc 39 and 68 was found for the first time and is a significant finding. Nevertheless the major genes Pc 68, Pc 39, Pc 50-2, Pc Pc 59, Pc 60, Pc 61 proved to be highly effective.