[Evaluation of processing suitability of bread cereals in official responsibility]. / DON- und ZEA-Gehalte in Weizen, Roggen und Gerste: Besondere Ernteermittlung.

In the annual national survey ('Besondere Ernteermittlung') the quality of German cereals was analysed. The samples for this approach were collected from statistically selected fields. One of the analysed parameters was the content of mycotoxins. Thus, it was possible to get an area-wide survey of the content of mycotoxins under natural growing conditions. In 2003 a total number of 974 samples were analysed consisting of wheat, rye and barley samples. A special mode of choosing the wheat samples ensured also a statistically validated result for the federal states of Germany. In the year 2003 the content of the mycotoxins DON and ZEA in wheat and rye samples was lower than in 2002 referred to the median. On the other hand the frequency of detection of DON was not reduced. In barley, which was analysed for the first time in this kind of study, the level of DON was in between the levels of wheat and rye.

Tuber physiology and properties of starch from tubers of transgenic potato plants with altered plastidic adenylate transporter activity.

We showed recently that antisense plants with decreased activity of the plastidic ATP/ADP-transporter protein exhibit drastically reduced levels of starch and a decreased amylose/amylopectin ratio, whereas sense plants with increased activity of the transporter possessed more starch than wild-type plants and an increased amylose/amylopectin ratio. In this paper we investigate the effect of altered plastidic ATP/ADP-transporter protein expression on primary metabolism and granule morphology in more detail. Tuber tissues from antisense and sense plants exhibited substantially increased respiratory activity compared with the wild type. Tubers from antisense plants contained markedly increased levels of free sugars, UDP-Glc, and hexose phosphates, whereas phosphoenolpyruvate, isocitrate, ATP, ADP, AMP, UTP, UDP, and inorganic pyrophosphate levels were slightly decreased. In contrast, tubers from sense plants revealed a slight increase in adenine and uridine nucleotides and in the levels of inorganic pyrophosphate, whereas no significant changes in the levels of soluble sugars and metabolites were observed. Antisense tubers contained 50% reduced levels of ADP-Glc, whereas sense tubers contained up to 2-fold increased levels of this sole precursor for starch biosynthesis. Microscopic examination of starch grain morphology revealed that the size of starch grains from antisense tubers was substantially smaller (50%) compared with the wild type. The large starch grains from sense tubers appeared of a more angular morphology, which differed to the more ellipsoid shape of wild type grains. The results suggest a close interaction between plastidial adenylate transport and starch biosynthesis, indicating that ADP-Glc pyrophosphorylase is ATP-limited in vivo and that changes in ADP-Glc concentration determine starch yield, as well as granule morphology. Possible factors linking starch synthesis and respiration are discussed.

Growth Kinetics, Carbohydrate, and Leaf Phosphate Content of Clover (Trifolium subterraneum L.) after Transfer to a High CO(2) Atmosphere or to High Light and Ambient Air.

Intact air-grown (photosynthetic photon flux density, 400 microeinsteins per square meter per second) clover plants (Trifolium subterraneum L.) were transfered to high CO(2) (4000 microliters CO(2) per liter; photosynthetic photon flux density, 400 microeinsteins per square meter per second) or to high light (340 microliters CO(2) per liter; photosynthetic photon flux density, 800 microeinsteins per square meter per second) to similarly stimulate photosynthetic net CO(2) uptake. The daily increment of net CO(2) uptake declined transiently in high CO(2), but not in high light, below the values in air/standard light. After about 3 days in high CO(2), the daily increment of net CO(2) uptake increased but did not reach the high light values. Nightly CO(2) release increased immediately in high light, whereas there was a 3-day lag phase in high CO(2). During this time, starch accumulated to a high level, and leaf deterioration was observed only in high CO(2). After 12 days, starch was two- to threefold higher in high CO(2) than in high light, whereas sucrose was similar. Leaf carbohydrates were determined during the first and fourth day in high CO(2). Starch increased rapidly throughout the day. Early in the day, sucrose was low and similar in high CO(2) and ambient air (same light). Later, sucrose increased considerably in high CO(2). The findings that (a) much more photosynthetic carbon was partitioned into the leaf starch pool in high CO(2) than in high light, although net CO(2) uptake was similar, and that (b) rapid starch formation occurred in high CO(2) even when leaf sucrose was only slightly elevated suggest that low sink capacity was not the main constraint in high CO(2). It is proposed that carbon partitioning between starch (chloroplast) and sucrose (cytosol) was perturbed by high CO(2) because of the lack of photorespiration. Total phosphate pools were determined in leaves. Concentrations based on fresh weight of orthophosphate, soluble esterified phosphate, and total phosphate markedly declined during 13 days of exposure of the plants to high CO(2) but changed little in high light/ambient air. During this time, the ratio of orthophosphate to soluble esterified phosphate decreased considerably in high CO(2) and increased slightly in high light/ambient air. It appears that phosphate uptake and growth were similarly stimulated by high light, whereas the coordination was weak in high CO(2).

Identification and Characterization of Glycolate Oxidase and Related Enzymes from the Endocyanotic Alga Cyanophora paradoxa and from Pea Leaves.

Glycolate oxidase (GO) has been identified in the endocyanom Cyanophora paradoxa which has peroxisome-like organelles and cyanelles instead of chloroplasts. The enzyme used or formed equimolar amounts of O(2) or H(2)O(2) and glyoxylate, respectively. Aerobically, the enzyme did not reduce the artificial electron acceptor dichlorophenol indophenol. However, after an inhibitor of glycolate dehydrogenase, KCN (2 millimolar), was added to the assay medium, considerable aerobic glycolate:dichlorophenol indophenol reductase activity was detectable. The leaf GO inhibitor 2-hydroxybutynoate (30 micromolar), which binds irreversibly to the flavin moiety of the active site of leaf GO, inhibited Cyanophora GO and pea (Pisum sativum L.) GO to the same extent. This suggests that the active sites of both enzymes are similar. Cyanophora GO and pea GO cannot oxidize d-lactate. In contrast to GO from pea or other organisms, the affinity of Cyanophora GO for l-lactate is very low (K(m) 25 millimolar). Another important difference is that Cyanophora GO produced sigmoidal kinetics with O(2) as varied substrate, whereas pea GO produced normal Michaelis-Menten kinetics. It is concluded that there is considerable inhomogeneity among the glycolate-oxidizing enzymes from Cyanophora, pea, and other organisms. The specific catalase activity in Cyanophora was only one-tenth of that in leaves. NADH-and NADPH-dependent hydroxypyruvate reductase (HPR) and glyoxylate reductase activities were detected in Cyanophora. NADH-HPR was markedly inhibited by hydroxypyruvate above 0.5 millimolar. Variable substrate inhibition was observed with glyoxylate in homogenates from different algal cultures. It is proposed that Cyanophora has multiple forms of HPR and glyoxylate reductase, but no enzyme clearly resembling leaf peroxisomal HPR was identified in these homogenates. Moreover, no serine:glyoxylate aminotransferase activity was detected. These results collectively indicate the possibility that the glycolate metabolism in Cyanophora deviates from that in leaves.

Isolation of Intact Chloroplasts from Dunaliella tertiolecta.

Cells of Dunaliella tertiolecta from the log phase of growth were broken by rapid extrusion at low pressure through a Yeda press and the chloroplasts were isolated by centrifugation through a Percoll gradient. Osmolarity of the growth media, the suspending media, and the Percoll gradient was kept identical to minimize change in chloroplast volume and mitochondrial entrapment. The isolated intact chloroplasts were obtained in a 30 to 50% yield based on chlorophyll and were stable to washing with buffered medium. Isolated chloroplast yield and purity was dependent on cell culture condition; a cycle of 16 hours light and 8 hours dark with continuous high CO(2) was optimum. Isolated chloroplasts were about 90% intact by microscopic examination, ferricyanide-dependent O(2) evolution, and the distribution of four stromal enzymes. Enzymes associated with glycolate metabolism were not in the chloroplast fraction. The isolated chloroplasts with 10 millimolar bicarbonate evolved 24 micromoles of O(2) and fixed 21 micromoles of CO(2) per hour per milligram of chlorophyll, which rates were about one-third of those by whole cells. The inhibition of oxygen evolution by 10 millimolar phosphate was reversed by P-glycerate. Whole chloroplasts were also isolated from cells adapted to low CO(2) in air for 24 hours. On low CO(2) the cells excreted more gelatinous material, which had to be removed with additional washing of the cells, before it was possible to obtain good chloroplast preparations.

Aminotransfer from Alanine and Glutamate to Glycine and Serine during Photorespiration in Oat Leaves.

(15)N-Labeled glutamate and alanine were used to examine the photorespiratory nitrogen metabolism in oat (Avena sativa L.) leaf slices. Glutamate and alanine supply amino groups for glycine formation during photorespiration. The nitrogen flux from alanine to glycine was estimated to be 3 times higher than that from glutamate. It is concluded from these results that alanine is a direct and important amino donor for photorespiratory glycine formation in oat leaves. The (15)N labeling of serine was almost as high as that of glycine during the initial period of the labeling experiments. Thereafter, the ratio of (15)N label in serine to (15)N label in glycine declined substantially.

L-Lactate dehydrogenase from leaves of higher plants. Kinetics and regulation of the enzyme from lettuce (Lactuca sativa L).

1. L-Lactate dehydrogenase from lettuce (Lactuca sativa) leaves was purified to electrophoretic homogeneity by affinity chromatography. 2. In addition to its NAD(H)-dependent activity with L-lactate and pyruvate, the enzyme also catalyses the reduction of hydroxypyruvate and glyoxylate. The latter activities are not due to a contamination of the enzyme preparations with hydroxypyruvate reductase. 3. The enzyme shows allosteric properties that are markedly by the pH. 4. ATP is a potent inhibitor of the enzyme. The kinetic data suggest that the inhibition by ATP is competitive with respect to NADH at pH 7.0 and 6.2. The existence of regulatory binding sites for ATP and NADH is discussed. 5. Bivalent metal cations and fructose 6-phosphate relieve the ATP inhibition of the enzyme. 6. A function of leaf L-lactate dehydrogenase is proposed as a component of the systems regulating the cellular pH and/or controlling the concentration of reducing equivalents in the cytoplasm of leaf cells.

L-lactate dehydrogenase from leaves of Capsella bursa-pastoris (L.) Med. : I. Identification and partial characterization.

By ammonium sulfate fractionation and gel filtration an enzyme preparation which catalyzed NAD(+)-dependent L-lactate oxidation (10(-4) kat kg(-1) protein), as well as NADH-dependent pyruvate reduction (10(-3) kat kg(-1) protein), was obtained from leaves of Capsella bursa-pastoris. This lactate dehydrogenase activity was not due to an unspecific activity of either glycolate oxidase, glycolate dehydrogenase, hydroxypyruvate reductase, alcohol dehydrogenase, or a malate oxidizing enzyme. These enzymes could be separated from the protein displaying lactate dehydrogenase activity by gel filtration and electrophoresis and distinguished from it by their known properties. The enzyme under consideration does not oxidize D-lactate, and reduces pyruvate to L-lactate (the configuration of which was determined using highly specific animal L-lactate dehydrogenase). Based on these results the studied Capsella leaf enzyme is classified as L-lactate dehydrogenase (EC 1.1.1.27). It has a Km value of 0.25 mmol l(-1) (pH 7.0, 0.3 mmol l(-1) NADH) for pyruvate and of 13 mmol l(-1) (pH 7.8, 3 mmol l(-1) NAD(+)) for L-lactate. Lactate dehydrogenase activity was also detected in the leaves of several other plants.

Apparent Catalase Synthesis in Sunflower Cotyledons during the Change in Microbody Function: A Mathematical Approach for the Quantitative Evaluation of Density-labeling Data.

Density-labeling with 10 mm K(15)NO(3)/70% (2)H(2)O has been used to investigate catalase synthesis in different developmental stages of sunflower (Helianthus annuus L.) cotyledons. A mathematical approach is introduced for the quantitative evaluation of the density-labeling data. The method allows, in the presence of preexisting enzyme activity, calculation of this synthesized activity (apparent enzyme synthesis) which results from the balance between actual enzyme synthesis and the degradation of newly synthesized enzyme at a given time. During greening of the cotyledons, when the catalase activity declines and the population of leaf peroxisomes is formed, the apparent catalase synthesis is lower than, or at best equal to, that occurring during a developmental stage when the leaf peroxisome population is established and catalase synthesis and degradation of total catalase are in equilibrium. This result suggests a formation, in fatty cotyledons, of the leaf peroxisomes by transformation of the glyoxysomes rather than by de novo synthesis.