Penetrometer resistance,root penetration resistance and root elongation rate in two sandy loam soils

Root penetration resistance and elongation of maize seedling roots were measured directly in undisturbed cores of two sandy loam soils. Root elongation rate was negatively correlated with root penetration resistance, and was reduced to about 50 to 60% of that of unimpeded controls by a resistance of between 0.26 and 0.47 MPa. Resistance to a 30° semiangle, 1 mm diameter penetrometer was between about 4.5 and 7.5 times greater than the measured root penetration resistance. However, resistance to a 5° semiangle, 1 mm diameter probe was approximately the same as the resistnace to root penetration after subtracting the frictional component of resistance. The diameter of roots grown in the undisturbed cores was greater than that of roots grown in loose soil, probably as a direct result of the larger mechanical impedance in the cores.     

Phosphorus availability under alley cropping and mulched and unmulched sole cropping systems in Costa Rica

Phosphorus availability was measured in soils under five cropping systems: alley cropping with Erythrina poeppigiana, alley cropping with Gliricidia sepium, sole cropping with Erythrina poeppigiana mulch applied, sole cropping with Gliricidia sepium mulch applied, sole cropping with no mulch. The following parameters were measured: 1) plant-available soil P assessed by P uptake of maize and bean bioassay plants; 2) phosphate desorbable by anion exchange resin; 3) adsorption of added P into isotopically exchangeable and non-exchangeable pools.In the bioassay, P uptake of beans declined in the order: mulched sole-cropped>unmulched sole-cropped>alley-cropped soils. For maize the relative uptake was: mulched sole-cropped>unmulched sole-cropped = alley-cropped soils. These results suggest trees had not incorporated a significant quantity of P into the system after seven years and, probably, there was a decrease in available soil P due to the sequestration of P in the tree biomass. Potentially resin-desorbable P was higher in alley-cropped and mulched sole-cropped soils than in unmulched sole-cropped soils. The adsorption and desorption of added P into and from exchangeable and non-exchangeable pools did not differ between alley-cropped and unmulched sole-cropped soils.Crop yield and crop N, P and K uptake were all higher in the alley crops than in the unmulched sole crop. The supply of P to the crop under alley cropping seems to be dependent on P cycled and released from the mulch. The P cycle in alley cropping appears to be self-sustaining at least under conditions of moderate P fertiliser input.     

Dietary modulation of α-amylase activity in eight geographical strains of Sitophilus oryzae and Sitophilus zeamais

Rank transformation of specific activity values of -amylase across four strains of Sitophilus oryzae (L.) and four strains of S. zeamais Motschulsky indicates that levels of these predominant enzymes are highest in adults feeding on hulled barley or long-grain brown rice. Intermediate activity levels are found in weevils feeding on yellow corn (maize) and lowest levels are found in wheat-fed weevils. Although extracts prepared from barley contain inhibitory activity against two purified isoamylases from S. oryzae, levels of the naturally-occurring -amylase inhibitors against these two enzymes are about 2.2-fold and 6.1-fold, respectively, more concentrated in wheat. Ingestion of these amylase inhibitors and formation of an inactive enzyme:inhibitor complex with previously secreted amylase may account for the lower activity of amylase in weevils of both species feeding on wheat. Amylase levels across all strains feeding on a given diet are about 2-fold higher in S. oryzae than in S. zeamais. Significant differences in activity levels were also found between strains in both species. Since -amylase is a predominant digestive hydrolase in these species, the degree to which cereal diets affect amylase levels may indicate their suitability as potential hosts.

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Résumé La transformation de rang des valeur d'activité spécifique de l'-amylase de 4 souches de S. oryzae et de 4 souches de S. zeamais montre que les niveaux les plus élevés de ces enzymes prédominantes s'observent chez les adultes nourris d'orge mondé ou de riz brun á grains longs. Des niveaux intermédiaires d'activité ont été obtenus chez les insectes élevés sur maïs jaune, et les niveaux les plus faibles chez ceux élevés sur blé. Bien que les extraits préparés à partir d'orge présentent une activité inhibitrice de deux isoamylases purifiées de S. oryzae, les niveaux des inhibiteurs naturels -amylase de ces deux enzymes sont environ respectivement 2,2 et 6,1 fois plus concentrés dans le blé. L'ingestion de ces inhibiteurs d'amylase et la formation d'un complexe enzyme inactive/inhibiteur avec l'amylase secrétée antérieurement, peut rendre compte de la plus faible activité de l'amylase chez les charançons consommant du blé. Le niveau d'amylase de S. oryzae est 2 fois plus élevé que celui de S. zeamais pour toutes les souches élevées sur un régime donné. Des niveaux d'activité significativement différents ont été trouvés suivant les souches pour chacune des deux espèces. Puisque l'amylase est la principale hydrolase digestive de ces espèces, l'intensité de la modification des teneurs en amylase par la consommation de céréales peut indiquer leur adéquation comme hôtes potentiels.

     

Spring development of a Chlamydomonas population in Lake Nimetön,a small humic forest lake in southern Finland

Biomass development and vertical distribution of a Chlamydomonas population in a small humic forest lake was followed by daily sampling in May-June, 1984. Chlamydomonas dominated the phytoplankton spring bloom, forming 71% of the maximum phytoplankton biomass on 18 May. In early May the outflow rate was high and during the 24 hour period when the maximum rate of surface runoff was recorded (8–9 May), 43% of the Chlamydomonas biomass was flushed out of the lake, which delayed the onset of biomass increase. When surface runoff had slowed down Chlamydomonas biomass started increasing and during wax of the population most cells were < 10 µm in diameter. Population maximum lasted for one day (18 May) and there-after Chlamydomonas biomass decreased towards the end of the study. During wane of the population most cells were > 10 µm in diameter.     

Developmental profiles of three embryo-lethal maize mutants lacking leaf primordia: ptd*-1130, cp*-1418, and bno*-747B

The defective kernel (dek) mutants of maize are altered in both their embryo and endosperm development. Earlier studies have indicated that some of the dek mutants are unable to form shoot apical meristems or leaf primoirda. We have examined three embryo lethal dek mutants of this type, ptd*-1130, cp*-1418, and bno*-747B, to obtain a developmental profile for each. Allelism tests show that these three mutants are not allelic. Embryos were examined in early, mid-, and late kernel development as well as at kernel maturity by dissection and sectioning procedures and also at kernel maturity by scanning electron microscopy. All three mutants lag behind normal embryos in their rate of development. Embryos of ptd*-1130 reached the transition stage by early kernel development and progressed no further but underwent cell enlargement and necrosis during late kernel development. Embryos of cp*-1418 reached an early coleoptilar stage by midkernel development. They subsequently increased in size but did not form any leaf primordia. At kernel maturity, they no longer had a shoot apical meristem but often had a well formed root meristem. They appeared to remain healthy and did not become necrotic. Embryos of bno*747B reached the early coleoptilar stage by early kernel development but progressed no further. By kernel maturity, they had grown into masses of irregularly shaped embryonic tissue that no longer resembled any normal embryo stage but were not necrotic. None of these three mutants responded to attempts to support continued embryo development when cultured, but all three mutants formed callus on N6 and MS media supplemented with 2,4-D. These results indicate that these mutants are all uniformly blocked at specific stages early in embryonic development, have different subsequent developmental fates, and represent three different genes performing unique functions that are essential for embryogenesis.     

Glucose control of sucrose synthase in the maize scutellum

The in vivo amounts of UDPG, UTP, UDP and UMP, metabolites known to influence the activity of sucrose phosphate synthase (SPS) and sucrose synthase (SS), were measured throughout 5 hr incubations of scutellum slices in fructose or water, i.e. under conditions of sucrose synthesis or breakdown. Cytosolic concentrations were estimated assuming that these metabolites were confined to the cytosol. Within the estimated in vivo concentration ranges, UDPG, UTP and UDP had little effect on the in vitro SS activity, but glucose (100 mM) inhibited SS in the synthesis direction by 63–70% and in the breakdown direction by 86–93%. Glucose inhibition of SS was considerably less when saturating levels of substrates were used. Sucrose did not inhibit SS. It is concluded that during germination the glucose produced from starch breakdown in the maize endosperm enters the scutellum and inhibits SS, preventing a futile cycle and limiting SS participation in sucrose synthesis.     

Organic free radical levels in seeds and pollen: The effects of hydration and aging

In view of their possible role in oxidative deterioration of seeds and pollen, organic free radicals were measured by electron spin resonance in embryonic axes and cotyledons of soybean [ Glycine max (L.) Merr], embryo and endosperm fractions of corn [ Zea mays L.] and pollen of cattail [ Typha latifolia L.]. A pronounced decline in the radical signal ensued when hydration increased above about 7% (wet weight basis) in both the seed materials and in pollen. Moderate hydration of the soybean axis followed by drying led to a small decrease in organic free radicals compared to untreated material, especially if the desiccation step was performed under nitrogen. In a comparison of soybeans of various ages under normal storage, organic free radical levels in the axis showed little or no increase with age. In marked contrast, over 5 days of accelerated aging at 40°C and near-saturating humidity, organic radical levels approximately doubled in the axis. This pronounced increase in free radical content was not associated with a decrease in the proportion of polyunsaturated fatty acids. The data suggest that hydration of seed and pollen causes a release of free radicals from the trapped state.     

Restriction fragment polymorphisms as probes for plant diversity and their development as tools for applied plant breeding

Summary Maize and tomato cDNA clones have been hybridized in Southern blotting experiments to plant genomic DNA prepared from different lines to detect restriction fragment polymorphisms (RFPs). In maize we have found that a high degree of genetic variability is present, even among domestic inbred lines. Most randomly chosen maize cDNA clones can be used to detect elements of this variability. Similar levels of polymorphism are observed when genomic DNA is digested with any of a number of different restriction enzymes and probed with individual clones. When a clone is hybridized to genomic DNAs prepared from several different maize lines, a number of different alleles are often detected at a single locus. At the same time one clone can often detect more than one independently segregating locus by cross hybridization to related sequences at other loci. As expected these markers are inherited as simple codominant Mendelian alleles from one generation to the next and colinkage of these markers can be demonstrated in the progeny from a heterozygous parent. In similar studies with tomato, remarkably different results were found. Few RFPs were demonstrable among domestic Lycopersicon esculentum lines although a higher level of variability could be detected when comparing esculentum with its wild Lycopersicon relatives. These results are discussed in relation to the applied uses of RFPs in plant breeding as well as the inherent variability of different plant genomes.This work was supported in part by funds from Sandoz Ltd. (Basel, Switzerland) and its subsidiary company, Northrup King Co. (Minneapolis, Minn., U.S.A.) as well as by NSF SBIR grant #BSR-8360870.     

α-Mannosidase-1 mutants of Dictyostelium dkoideum: Early aggregation-essential genes regulate enzyme precursor synthesis, modification, and processing

The lysosomal enzyme alpha-mannosidase-1 is one of the earliest developmentally controlled gene products in Dictyostelium discoideum. Although this enzyme is synthesized throughout the first 20 h of development, it is not required for complete morphogenesis, since structural gene (manA) mutants lacking activity develop normally. We isolated six strains deficient in alpha-mannosidase-1 activity which, unlike structural gene mutants, fail to aggregate. Fruiting revertants of these strains accumulate wild-type levels of alpha-mannosidase-1 activity, suggesting that both the enzymatic and morphological defects are caused by single mutations in nonstructural genes essential for early development. Direct genetic evidence for mutations outside of the structural gene was obtained by complementation analysis. We used alpha-mannosidase-1-specific monoclonal antibodies to analyze the biochemical defects in these mad (alpha-mannosidase-1-deficient) mutants. All mad mutants show a significantly reduced relative rate of enzyme precursor biosynthesis. The mad-404 mutation results in a complete lack of precursor biosynthesis, as well as a lack of functional alpha-mannosidase-1 mRNA. In some cases, however, the enzymatic defect results from improper post-translational modification which affects precursor processing. We conclude that a small number of aggregation-essential genes are involved in regulating the synthesis, modification, and processing of alpha-mannosidase-1 during development.     

Purification and properties of indole 2,3-dioxygenase from maize leaves

An indole 2,3-dioxygenase was purified ca 38-fold from maize leaves. The enzyme had an MW of about 98000, an optimum pH of 5.0 and the energy of activation was 9.1 kcal/mol. The K_max for indole was 1.4 × 10^?4 M. The enzyme was inhibited by diethyldithiocarbamate, salicylaldoxime and sodium dithionite. The inhibition by diethyldithiocarbamate was specifically reversed by Cu²⁺. The dialysed enzyme was stimulated by Cu²⁺. Four atoms of oxygen were utilized in the disappearance of 1 mole of indole. Inhibition of the enzyme by -SH compounds and -SH group inhibitors, and their partial removal by Cu²⁺ only, suggested the involvement of -SH groups in binding of Cu²⁺ at the catalytic site.