Showing papers by "University of Hohenheim published in 1995"

Formation of complexes between polyvinyl pyrrolidones or polyethylene glycols and tannins, and their implication in gas production and true digestibility in in vitro techniques

Abstract: Various tannin-complexing agents have been used to study the potential adverse effects of tannins on rumen metabolism. Using a method based on turbidity formation, the binding of various tannin-complexing agents (polyvinyl polypyrrolidone (PVPP), polyethylene glycol (PEG) of molecular weights 2000 to 35,000, and polyvinyl pyrrolidone (PVP) of molecular weight 10,000, 40,000 and 360,000) to tannins (tannic acid, purified tannins from quebracho (Aspidosperma quebracho) and leaves of trees and shrubs (Acioa barteri, Dichostachys cinerea, Guiera senegalensis, Piliostigma reticulatum)) was investigated at different pH values. The binding of all the tannins with PVPP was highest at pH 3-4 and lowest at pH 7. For all the pH range (3-7) studied, the binding of PEG was higher than that of PVP. For all the tannins except tannic acid, the binding to PVP was the same from pH 4.7 to 7. Similar results were observed for the PEG of molecular weight 6000 or higher for all the tannins except quebracho tannins for which the binding increased as the pH increased from 3 to 7. The binding with PEG 2000 decreased to a greater extent as the pH reached near neutral and for PEG 4000 this decrease was slightly lower. Addition of these tannin-complexing agents to the in vitro gas system resulted in higher gas production from tannin-rich feeds (increase varied from 0 to 135%). The PEG were the most effective followed by PVP and PVPP. The PEG 35,000 was least effective. The efficiency of other PEG was similar. The PEG 6000 was preferred to PEG 2000 or 4000 as its binding to tannins was higher at near neutral pH values. The gas production increased with an increase in the amount of PEG 6000 up to 0.6 g/40 ml rumen-fluid-containing medium containing 0.5 g tannin-rich feed, beyond which no increase was observed. The percentage increase in gas value at 24 h fermentation correlated significantly with tannin values, the highest correlation (r 0.95) being with protein precipitation capacity of tannins. The increase in gas production was associated with higher production of short-chain fatty acids with little change in their molar proportions, suggesting an increase in organic matter digestibility by inclusion of the PEG in tannin-rich feeds. However, apparent and true digestibilities were lower on addition of the PEG, due to the presence of PEG-tannin complexes in the residues. The use of this bioassay (percentage increase in gas production in the presence of PEG 6000) along with other tannin assays would provide a better insight into the nutritional significance of tannins.

Distribution and function of proteoid roots and other root clusters

Abstract: Proteoid roots are bottlebrush-like clusters of rootlets which form along lateral roots. They are characteristic of most species of the Proteaceae, which are mainly distributed in Australia and South Africa. Homologous root clusters are present in species of the Casuarinaceae, Mimosaceae, Fabaceae, Myricaceae and Moraceae. Many similarities exist between these species in relation to morphology and function of root clusters. Many are non-mycorrhizal and are highly efficient in phosphorus (P) acquisition. In these species, proteoid roots and proteoid-like root clusters are abundant when grown on infertile soils. Their formation is predominantly affected by the P status of the plants, being induced at low P levels and repressed at high P levels. Proteoid roots and proteoid-like root clusters play an important role in acquisition of P and other mineral nutrients. Although increase in root surface area may be a contributing factor, in many species these roots excrete large amounts of organic acids and phenolics. The excretion of these compounds in a small soil volume gives rise to extensive nutrient mobilization by acidification, reduction and chelation of sparingly soluble forms of P and micronutrients such as Fe and Mn.

8 – Functions of Mineral Nutrients: Macronutrients

Abstract: Publisher Summary The chapter discusses the more common classification as well as functions of macro- and micronutrients, with typical examples of the various functions of macronutrients. The importance of the reduction and assimilation of nitrate for plant life is similar to that of the reduction and assimilation of carbon dioxide (CO2) in photosynthesis. Nitrate reductase is an enzyme that is regulated by several different modes exerted at different levels—namely, enzyme synthesis, degradation, and reversible inactivation, as well as regulation of effectors and the concentration of substrate. In addition to its function in inducing synthesis of nitrate reductase, nitrate, together with light, might act as a “signal” altering the partitioning of photosynthetic carbon flow in leaves. With an increasing supply of nitrate, the capacity for nitrate reduction in the roots becomes a limiting factor, and an increasing proportion of the total nitrogen is translocated to the shoots in the form of nitrate. The carbon skeletons for these different amino acids are derived mainly from intermediates of photosynthesis, glycolysis, and the tricarboxylic acid cycle. The highest growth rates and plant yields are obtained by a combined supply of both ammonium and nitrate. Depending on the plant species, their development stage, and organ, the nitrogen content required for optimal growth varies between 2% and 5% of the plant dry weight. When the potassium supply is abundant “luxury consumption” of potassium often occurs, which deserves attention for its possible interference with the uptake and physiological availability of magnesium and calcium.

Role of Arbuscular Mycorrhizal Fungi in Uptake of Phosphorus and Nitrogen From Soil

Abstract: Colonization of plant roots by arbuscular mycorrhizal fungi can greatly increase the plant uptake of phosphorus and nitrogen. The most prominent contribution of arbuscular mycorrhizal fungi to plant growth is due to uptake of nutrients by extraradical mycorrhizal hyphae. Quantification of hyphal nutrient uptake has become possible by the use of soil boxes with separated growing zones for roots and hyphae. Many (but not all) tested fungal isolates increased phosphorus and nitrogen uptake of the plant by absorbing phosphate, ammonium, and nitrate from soil. However, compared with the nutrient demand of the plant for growth, the contribution of arbuscular mycorrhizal fungi to plant phosphorus uptake is usually much larger than the contribution to plant nitrogen uptake. The utilization of soil nutrients may depend more on efficient uptake of phosphate, nitrate, and ammonium from the soil solution even at low supply concentrations than on mobilization processes in the hyphosphere. In contrast to ectomy...

In vitro effects of and interactions between tannins and saponins and fate of tannins in the rumen

Abstract: The rate of fermentation of hay was not affected by purified tannins from Quercus incana and Dichostachys cinerea at 0.13 mg ml -1 of the in vitro medium whereas a decrease of 4% in the rate was observed for Acioa barteri tannins at this level. At 0.23 mg and 0.47 mg of tannins per ml, the decrease in rate varied from 4 to 13% and 13 to 20%, respectively. The decrease in in vitro true digestibility of dry matter was 3, 6 and 7% for Q. incana, D. cinerea and A. barteri, respectively, at a tannin concentration of 0.47 mg ml -1 , and 17, 21 and 27%, respectively, at 0.93 mg ml -1 . There was no change in the potential extent of digestion up to 0.47 mg ml -1 for any of the tannins studied. These results suggested that the rate of digestion is affected to a greater extent than the potential extent of digestion or the in vitro true digestibility and that different tannins even at the same level have different degrees of effect. Tannin-saponin interactions were studied using tannic acid (TA), quebracho tannin (QT) and quillaja saponin (S) at different concentrations (0.2, 0.4 and 0.6 mg ml -1 ) alone and in combination with each other. The decrease in the rate of digestion and true digestibility was additive when both the TA and the S were present. Similar results were obtained when TA was replaced by QT except that the effects with QT were more marked as compared to TA at the same concentration. Saponins had little effect on the potential extent of digestion and true digestibility. These tannins also decreased the production of short-chain fatty acid (SCFA) and their molar proportions (acetate decreased whereas propionate increased). Efficiency of microbial protein synthesis, expressed as the ratio of 15 N incorporation per unit of SCFA production, was higher with both S and the tannins studied. A substantial amount (71-93%) of tannins soluble in aqueous acetone was released from leaves of some trees and shrubs on incubation in the in vitro medium for 48 h. The rumen liquor was not capable of degrading oligomeric condensed tannins.

Influence of environmental factors on the infectivity of Echinococcus multilocularis eggs.

Abstract: The sensitivity of eggs of Echinococcus multilocularis to environmental and controlled laboratory conditions was tested. Egg material was exposed and the infectivity was subsequently monitored by in vitro activation and by oral infection of the natural host, Microtus arvalis. To study the impact of environmental conditions in an endemic area of south-western Germany, eggs were sealed into bags of nylon mesh and exposed to the natural climate during various seasons. The maximal survival time of eggs was 240 days in an experiment performed in autumn and winter and 78 days in summer. A study of the tenacity of eggs under laboratory conditions revealed a high sensitivity to elevated temperatures and to desiccation. At 45 degrees C and 85-95% relative humidity the infectivity was lost after 3 h as well as after 4 h exposure to 43 degrees C suspended in water. Exposure to 27% relative humidity at 25 degrees C as well as exposure to 15% relative humidity at 43 degrees C resulted in a total loss of infectivity within 48 and 2 h, respectively. Temperatures of 4 degrees C and of -18 degrees C were well tolerated (478 days and 240 days survival, respectively), whereas exposure to -83 degrees C and to -196 degrees C quickly killed off the eggs (within 48 h and 20 h, respectively). Eggs of E. multilocularis were not killed off by exposure to various commercially available disinfectants applied according to the manufacturers' instructions and by exposure for 24 h to low concentrations of ethanol. Irradiation with 40 krad. from a 137Caesium source prevented the development of metacestodes but allowed seroconversion of infected rodents.

Salt tolerance of maize (Zea mays L.): the role of sodium exclusion

Abstract: The influence of NaCl and Na 2 SO 4 on growth of two maize cultivars (Zea mays cv. Pioneer 3906 and cv. Across 8023) differing in Na + uptake was investigated in two greenhouse experiments. Na + treatment with different accompanying anions (Cl - /SO 4 2- ) showed that ion toxicity was caused by Na + . While shoot growth of the two cultivars was markedly affected by salt in comparison to the control during the first 2-3 weeks, there were only slight differences between the cultivars. The shoot Ca 2+ concentration was reduced in both cultivars, and the youngest leaves contained an even lower concentration compared with the rest of the shoot. During this first phase, Across 8023 tended to have higher concentrations of Ca 2+ than Pioneer 3906. The Na + -excluding cultivar Pioneer 3906 showed continuous, although reduced, growth compared with the control, while the Na + concentration in the shoot decreased until flowering. Cultivar Across 8023 accumulated Na + until flowering: the reduction in the growth of stressed plants was greater than that for Pioneer 3906. Leaves of cultivar Across 8023 showed clear toxic symptoms, while those of the more salt-tolerant cultivar Pioneer 3906 did not. It is concluded that Na + exclusion contributes to the salt tolerance of maize.

Genetic diversity in European and Mediterranean faba bean germ plasm revealed by RAPD markers.

Abstract: Broadening of the genetic base and systematic exploitation of heterosis in faba bean requires reliable information on the genetic diversity in the germ plasm. Three groups of faba bean inbred lines were examined by means of RAPDs (random amplified polymorphic DNAs) assays: 13 European small-seeded lines, 6 European large-seeded lines, and 9 Mediterranean lines. Out of 59 primers, 35 were informative and yielded 365 bands, 289 of which were polymorphic with a mean of 8.3 bands per primer. Monomorphic bands were omitted from the analyses and genetic distances (GD) were estimated via the coefficient of Jaccard. The mean GD among the European small-seeded lines was significantly greater than those among the lines of the other two groups. Repeatability of GD estimates was high. Cluster (UPGMA) and principal coordinate analyses identified European small-seeded lines and Mediterranean lines as distinct groups with European large-seeded lines located in between. The results are in harmony with published archaeobotanical findings. We conclude that RAPDs are useful for classification of germ plasm and identification of divergent heterotic groups in faba bean.

8 – Functions of Mineral Nutrients: Macronutrients

Abstract: The chapter summarizes the role of micronutrients followed by their deficiencies and toxicities. The section on iron covers chloroplast development and photosynthesis, localization and binding state of iron, and root responses to iron deficiency and iron toxicity. The section on manganese covers manganese-containing enzymes, manganese-dependent or activated enzymes, photosynthesis and oxygen (O2) evolution, proteins, carbohydrates, lipids, and cell division. Copper covers copper proteins, carbohydrates, lipid and nitrogen metabolism, lignification, pollen formation, and fertilization. The section on zinc covers zinc-containing enzymes, zinc-activated enzymes, protein synthesis, carbohydrate metabolism, tryptophan and indoleacetic acid synthesis, membrane integrity, zinc-binding forms, and bioavailability. Nickel covers nickel-containing enzymes, role of nickel in nitrogen metabolism, and nickel content in plants. The enzymes covered under molybdenum are nitrate reductase, nitrogenase, xanthine oxidase/dehydrogenase, and sulfite reductase. The section also documents gross metabolic changes of molybdenum. Boron covers boron complexes with organic structures, root elongation and nucleic acid metabolism, cell wall synthesis, phenol metabolism, auxin (IAA) and tissue differentiation, membrane function, pollen germination and pollen tube growth, carbohydrate, and protein metabolism. The section on chlorine discusses photosynthetic O2 evolution, tonoplast proton-pumping ATPase, stomatal regulation, chlorine supply and plant growth, and chlorine supply and osmoregulation. The chapter also includes a summary on the mechanism of (heavy) metal tolerance in higher plants and the various mechanisms into which they can be grouped.

The formation of biogenic amines by fermentation organisms

Abstract: A total of 523 strains representing 35 species related to food fermentation organisms of practical importance were investigated for their potential for formation of biogenic amines (BA). The investigation was performed with resting cells in phosphate buffer (pH 5.5) and the formation of the following BAs was followed: putrescine, cadaverine, histamine, tyramine and 2-phenylethylamine. No potential was observed in species of lactococcus, Leuconostoc, Pediococcus, Streptococcus and several Lactobacillus spp., such as L. Pentosus and L. sake. A remarkable potential to form BA was observed in strains of carnobacteria, Lactobacillus buchneri, L. curvatus, L. reuteri, Staphylococcus carnosus and, to a lesser extent, in L. alimentarius, L. brevis, L. bavaricus, L. delbrueckii ssp. lactis, Micrococcus spp. and S. piscifermentans. In well known species with a practical function in the fermentation of dairy products, wine or cabbage a potential was observed for few strains only. In view of their role as starters in food fermentation, or their potential use in protective cultures and as probiotics, BA formation by the organisms has to be taken into consideration by selecting appropriate strains.

Assessing non-specificity of resistance in wheat to head blight caused by inoculation with European strains of Fusarium culmorum, F. graminearum and F. nivale using a multiplicative model for interaction.

Abstract: To determine whether resistance to Fusarium head blight in winter wheat is horizontal and non-species specific, 25 genotypes from five European countries were tested at six locations across Europe in the years 1990, 1991, and 1992. The five genotypes from each country had to cover the range from resistant to susceptible. The locations involved were Wageningen, Vienna, Rennes, Hohenheim, Oberer Lindenhof, and Szeged. In total, 17 local strains of Fusarium culmorum, F. graminearum, and F. nivale were used for experimental inoculation. One strain, F. culmorum IPO 39-01, was used at all locations. Best linear unbiased predictions (BLUPs) for the head blight ratings of the genotypes were formed within each particular location for each combination of year and strain. The BLUPs over all locations were collected in a genotype-by environment table in which the genotypic dimension consisted of the 25 genotypes, while the environmental dimension was made up of 59 year-by-strain-by-location combinations. A multiplicative model was fitted to the genotype by-environment interaction in this table. The inverses of the variances of the genotype-by-environment BLUPs were used as weights. Interactions between genotypes and environments were written as sums of products between genotypic scores and environmental scores. After correction for year-by-location influence very little variation in environmental scores could be ascribed to differences between strains. This provided the basis for the conclusion that the resistance to Fusarium head blight in winter wheat was of the horizontal and non-species specific type. There was no indication for any geographical pattern in virulence genes. Any reasonable aggressive strain, a F. culmorum strain for the cool climates and a F. graminearum strain for the warmer humid areas, should be satisfactory for screening purposes.

Degradation of condensed tannins by rumen microbes exposed to quebracho tannins (QT) in rumen simulation technique (RUSITEC) and effects of QT on fermentative processes in the RUSITEC

Abstract: In an earlier study it was observed that the rumen microbes from cattle which had never consumed tannin-containing diets do not have enzymes for degrading condensed tannins. In this study, rumen microbes were exposed to small amounts of quebracho tannins for 8 days using a rumen simulation technique (RUSITEC). The levels maintained in the RUSITEC were 0.1, 0.2 and 0.4 mg of the spray-dried quebracho powder (SDQT) per ml of the medium. After 8 days of tannin exposure, the liquor containing 'exposed/adapted' microbes from RUSITEC was incubated for 40 h without and with purified tannins of quebracho and Dichostachys cinerea leaves in in vitro gas method. There was no degradation of condensed tannins. The enzymes for degradation of condensed tannins were not induced in rumen microbes by exposure to different concentrations of tannins for 8 days in the RUSITEC. In the RUSITEC, SDQT significantly reduced the number of total protozoa, entodiniomorphs and holotrichs; effect was higher on holotrichs. There was no significant change in the levels of short chain fatty acid but the molar proportion of propionate was significantly higher and of butyrate significantly lower at 0.4 mg SDQT ml -1 . Significantly lower levels of ammonia in the medium was also observed on injection of tannins. Microbial mass production, calculated using 15 N incorporation, was similar at 0.1 and 0.2 mg SDQT ml -1 but significantly lower (13%) at 0.4 mg SDQT ml -1 . The dry matter digestibility of the feed (80% hay and 20% barley) was not significantly affected by SDQT.

15 – The Soil–Root Interface (Rhizosphere) in Relation to Mineral Nutrition

Abstract: The chapter explains how in the past decade much progress has been made to gain a better understanding of rhizosphere processes. As used for calcium and magnesium, a similar technique can be used to measure the accumulation of ions in the rhizosphere. Marked differences in redox potential in the rhizosphere occur between plants grown in aerated soils and those grown in submerged soils. The first part of the chapter describes the sources of nitrogen supply and rhizosphere pH, the nutritional status of plants and rhizosphere pH, and the redox potential and reducing processes. The section on rhizodeposition and root exudates covers rhizodeposition and root exudates separately and elaborates the actual process taking place in each case. Mucilage may have a diversity of biological functions, including protection of root apical zones from desiccation, lubrication of the root as it moves through the soil, ion uptake (facilitation or restriction), interaction with soil particles and improving the soil–root contact, especially in dry soil, and causing aggregation of soil in the rhizosphere. The main constituents of the low-molecular-weight root exudates are sugars, organic acids, amino acids, and phenolics. Noninfecting rhizosphere microorganisms cover root colonization and phytohormone precursors. Mycorrhizas have also been explained in detail. Mycorrhizal colonization per se, and any marked change in vesicular-arbuscular mycorrhiza (VAM) root colonization of field-grown plants have implications on soil testing and on simulation models for plant-available mineral nutrients, and phosphorus in particular.

Effects of a vesicular-arbuscular mycorrhizal fungus and other soil microorganisms on growth, mineral nutrient acquisition and root exudation of soil-grown maize plants

Abstract: Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-μm nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterle soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shoot∶root ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, threeto sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots.

Acacia saligna as a fodder tree for desert livestock and the interaction of its tannins with fibre fractions

Abstract: Acacia saligna was examined as potential fodder for sheep (27.4 kg) and goats (14.8 kg) raised in arid and semi-arid areas. This leguminous tree remains green all year and can be grown in deserts using only runoff water. Phyllodes collected in March had a crude protein content of 12.5% dry matter (DM) and high tannin content (tannins as tannic acid equivalent to 11.3% and condensed tannins as leucocyanidin equivalent to 8.3% DM). DM intake was low, amounting to 0.80% and 1.05% body mass daily for sheep and goats, respectively. Sheep lost 227 g day -1 and goats 196 g day -1 while on this diet. Dry matter, organic matter and energy digestibilities were low in both species but were higher for goats than for sheep, and negative digestibilities were measured for acid detergent fibre (ADF) and acid detergent lignin (ADL). Metabolisable energy intake for goats was 121.9 kJ kg -0.75 day -1 and for sheep was 8.6 kJ kg -0.75 day -1 . Apparent N digestibility was 17.5% and 0.9% for goats and sheep, respectively, and both species were in negative N balance of 0.25-0.30 g kg -0.75 day -1 . Total water intake and output were higher in sheep than in goats. Extractable tannins were virtually absent in faeces in both species, however, output of condensed tannins and protein in the ADF and ADL fractions were substantially higher. This showed the presence of tannin-protein complexes in these fractions which explained the negative digestibilities of ADF and ADL. It was concluded that Acacia saligna could not be used as a sole dietary source for small ruminants because of low intake and negative nitrogen balance. This was due mainly to the high tannin content. However, the tree might have a potential as a supplementary fodder due to its high crude protein content

CO2-balance for the cultivation and combustion of Miscanthus

Abstract: Miscanthus ‘Giganteus’ is a perennial C4-grass from East Asia. The biomass yield-potential of Miscanthus has been investigated in Germany since 1987. The combustion of biomass offers a possibility for lowering emissions of the greenhouse gas CO2. The CO2 which is set free during combustion has previously been fixed by the plants. The study analyses the demand for energy and the CO2-emissions which are involved in the production of Miscanthus, beginning with propagating the plants to transporting the biomass to the power station. Energy demand and CO2-emissions are compared with those of the provision and combustion of hard coal. The energy content of Miscanthus biomass harvested from one hectare, about 20 t of dry matter, corresponds to the energy content of 12 t hard coal. For each gigajoule of hard coal, 96.6 kg CO2 are emitted during provision and combustion. By combusting Miscanthus instead of hard coal 90% of CO2-emissions can be saved.

Dual inoculation with Aspergillus fumigatus and Glomus mosseae enhances biomass production and nutrient uptake in wheat (Triticum aestivum L.) supplied with organic phosphorus as Na-phytate

Abstract: In a pot experiment, wheat was grown for 50 days in two heat-sterilized low-phosphorus (P) soils supplied with organic P as Na-phytate. Seed inoculation with the phosphatase-producing fungus (PPF) Aspergillus fumigatus or soil inoculation with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae increased shoot and root dry weight and root length, phosphatase activity in the rhizosphere and shoot concentrations of P and to a lesser extent of K and Mg. As a rule, the greatest effects on those parameters were most in the combined inoculation treatment (PPF + VAM). Shoot concentrations of Cu and Zn were only enhanced by VAM, not by PPF. At harvest, depletion of organic P in the rhizosphere soil increased in the order of: sterilized soil < PPF < VAM < PPF + VAM which corresponded with the enhanced P concentrations in the plants. The results demonstrate that organic P in form of Na-Phytate is efficiently used by VAM and that use of organic P can be increased by simultaneous inoculation with phosphatase-producing fungi.

9 – Functions of Mineral Nutrients: Micronutrients

Abstract: Publisher Summary The chapter summarizes the role of micronutrients followed by their deficiencies and toxicities. The section on iron covers chloroplast development and photosynthesis, localization and binding state of iron, and root responses to iron deficiency and iron toxicity. The section on manganese covers manganese-containing enzymes, manganese-dependent or activated enzymes, photosynthesis and oxygen (O2) evolution, proteins, carbohydrates, lipids, and cell division. Copper covers copper proteins, carbohydrates, lipid and nitrogen metabolism, lignification, pollen formation, and fertilization. The section on zinc covers zinc-containing enzymes, zinc-activated enzymes, protein synthesis, carbohydrate metabolism, tryptophan and indoleacetic acid synthesis, membrane integrity, zinc-binding forms, and bioavailability. Nickel covers nickel-containing enzymes, role of nickel in nitrogen metabolism, and nickel content in plants. The enzymes covered under molybdenum are nitrate reductase, nitrogenase, xanthine oxidase/dehydrogenase, and sulfite reductase. The section also documents gross metabolic changes of molybdenum. Boron covers boron complexes with organic structures, root elongation and nucleic acid metabolism, cell wall synthesis, phenol metabolism, auxin (IAA) and tissue differentiation, membrane function, pollen germination and pollen tube growth, carbohydrate, and protein metabolism. The section on chlorine discusses photosynthetic O2 evolution, tonoplast proton-pumping ATPase, stomatal regulation, chlorine supply and plant growth, and chlorine supply and osmoregulation. The chapter also includes a summary on the mechanism of (heavy) metal tolerance in higher plants and the various mechanisms into which they can be grouped.

Primary Metabolism in Plant Defense (Regulation of a Bean Malic Enzyme Gene Promoter in Transgenic Tobacco by Developmental and Environmental Cues).

Abstract: NADP-dependent malic enzyme (NADP-ME, EC 1.1.1.40) catalyzes the oxidative decarboxylation of malate to pyruvate, producing CO2 and NADPH. We have examined regulatory properties of a 2.8-kb promoter-leader fragment of a bean (Phaseolus vulgaris L.) NADP-ME gene (PvME1) predicted to encode a cytosolic form of the enzyme by expression analysis of promoter-[beta]-glucuronidase fusions in transgenic tobacco plants. The PvME1 promoter directed strong expression in stems, which was confined to vascular and pith tissues, and was also active in floral and reproductive tissues. Wounding caused a marked induction of promoter activity, which was further strongly enhanced upon application of stimuli related to pathogen defense. Glutathione (reduced form) was the strongest inducer, but oxidized glutathione, fungal elicitor, cellulase, catalase, ascorbic acid, and NADPH were additional potent promoter-stimulating agents. Responsiveness to reduced glutathione was also shown at the level of PvME1 mRNA accumulation in bean plants. The putative contributions of NADP-ME gene expression to the plant defense response and possible mechanisms of defense gene regulation by conditions of oxidative stress as well as by H2O2 and antioxidant levels are discussed.

Epistasis in an Elite Maize Hybrid and Choice of Generation for Inbred Line Development

Abstract: Second cycle breeding, utilizing backcross and F 2 generations, has become the predominant type of line development program in the U.S. maize (Zea mays L.) industry. Epistasis and linkage have been identified as possible limits to progress from selection in F 2 and backcross populations. Objectives of this study were to determine the importance of epistasis in an elite maize hybrid and to determine the appropriate generation for initiation of inbred line development. Six generations of progeny were developed from B73 and B84: the two parental generations, P1 (B73) and P2 (B84); the F 2 generation [(B73 x B84) F 2 ]; the BCP 1 generation [(B73 x B84) x B73]; the BCP 2 generation [(B73 x B84) x B84); and the F 2 -Syn 8 generation (the F 2 generation random mated for eight generations). Testcross progeny were produced by crossing random S 0 plants from each of the six generations onto the inbred tester Mo17. One-hundred progeny of F 2 x Mo17 and F 2 -Syn 8 x Mo17 and 50 progeny of BCP 1 x Mo17 and BCP 2 x Mo17, as well as the parental testcrosses, were harvested. The experiment was evaluated at four locations in 1990 and three locations in 1991. Epistatic effects were significant for grain yield and grain moisture, and accounted for 21 and 18% of the variation among generation means, respectively. The genetic variance and heritability for grain yield ranked F 2 -Syn 8 > F 2 > BCP 1 > BCP 2 , but differences among generations were not significant. The predicted gains for each generation ranked in agreement with the heritability. Under low selection intensities (a = 20%), the predicted mean (usefulness) ranked the generations BCP 2 > F 2 > F 2 -Syn 8 > BCP 1 . Under high selection intensity (a = 1%), usefulness ranked the generations F 2 > F 2 -Syn 8 > BCP 2 > BCP 1 . The choice between F 2 and backcrosses as source populations is primarily a function of selection intensity. Our results suggest little to no advantage of random mating the F 2 before initiating selection and inbreeding.

In an elite cross of maize a major quantitative trait locus controls one-fourth of the genetic variation for grain yield.

Abstract: Quantitative trait loci (QTLs) for grain yield, dry matter content and test weight were identified in an F2 segregating population derived from a single cross between two elite maize lines (B73 and A7) and testcrossed to two genetically divergent in breds. Most of the QTLs inferred were consistent across locations, indicating that the expression of the genes influencing the traits under investigation was largely independent of the environment. By using two different tester lines we found that QTLs exhibited by one tester may not necessarily be detected with the second one. Only loci with larger effects were consistent across testers, suggesting that interaction with tester alleles may contribute to the identification of QTLs in a specific fashion. Analysis across both testers revealed four significant QTLs for grain yield that explained more than 35% of the phenotypic variation and showed an overall phenotypic effect of more than 2t/ha. The major QTL for grain yield, located in the proximity of the Nucleolus Organiser Region, accounted for 24.5% of the phenotypic variation for grain yield and showed an average effect of allele substitution of approximately 1 t/ha. Marker-assisted introgression of the superior A7 allele at this locus in the B73 genetic background will not differ from qualitative trait introgression and will eventually lead to new lines having superior testcross performance.

The usefulness of macrophyte monitoring-systems, exemplified on eutrophication and acidification of running waters

Abstract: Summary Apart from other biological methods, the mapping of submerged macrophytes is an important instrument for longterm monitoring of the quality of running waters. This type of monitoring is particulary suitable to lotie systems with lower dynamic discharge patterns resulting in a wide diversity of macrophytes. Submerged macrophytes react equally to processes of eutrophication and oligotrophication (acidification of waters) caused by man. Their high ability to persist, compared to other groups of organisms, allows for a highly integrative bioindication statement. The overall statement and high local precision achieved with a mapping of macrophytes comply with the increasingly important assessment of the integrity of the ecological system of running waters.

Adaptation of Plants to Adverse Chemical Soil Conditions

Abstract: The chapter provides an outline on the adaptation of plants to adverse chemical soil conditions. Selection and breeding programs designed to improve the adaptation of crop plants to saline soils have to consider the various mechanisms responsible for salt tolerance and sensitivity. Crop plants of the includer type have a much greater potential for better adaptation coupled with sufficient productivity when grown in highly saline soils. Includers of both sodium and chlorine rely on a strict compartmentation of salts within individual leaf cells and on their capacity to maintain a high potassium/sodium ratio in growing tissue. Salt deposition in nonphotosynthetic tissue or excretion to the leaf surface or both these processes are also important for adaptation. In addition to using existing genetic variability within crop species for breeding, it seems promising to introduce important traits of salt tolerance into crop species from their wild relations through interspecific hybridization, as, for example in tomato and wheat. However, in these approaches it is often not sufficiently appreciated that these traits in wild plants are favorable mainly for survival under natural conditions. Furthermore, for crop production in dry saline soils, high water use efficiency (WUE) is of key importance, and the already existing wheat and barley cultivars have a higher WUE and total biomass production on saline soils than most of the salt-tolerant wild species including C4 halophytes.