An embryogenic cell line of maize from A188 (Minnesota) contains Mu1-like elements

The maize inbred line A188 is popularly used for the production of embryogenic cell lines. A188, maintained at the University of Minnesota, was found upon molecular analysis to contain 2 to 4 copies of a DNA sequence very similar in structure to transposable Mu1 elements, which have been implicated in Robertson's Mutator system. These Mu1-like elements are in the same chromosomal locations in sibling plants and in A188 cell cultures derived from them. This suggests that the elements are in an inactive state and do not undergo transposition. However, we have observed that they are not modified at the target sites for certain restriction endonucleases. Possible causes for the apparent lack of transposition of these Mu1-like elements in these A188 lines are discussed. Inasmuch as the elements do not transpose, they must be maintained in this line as homozygous Mendelian elements by self-pollination.Journal paper no. J-12269 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011. Project 2707.     

Host Status of Five Weed Species and Their Effects on Pratylenchus zeae Infestation of Maize

The host suitability of five of the most common weed species occurring in maize (Zea mays L.) fields in South Africa to Pratylenchus zeae was tested. Based on the number of nematodes per root unit, mealie crotalaria (Crotalaria sphaerocarpa) was a good host; goose grass (Eleusine indica), common pigweed (Amaranthus hybridus), and thorn apple (Datura stramonium) were moderate hosts; and khaki weed (Tagetes minuta) was a poor host. Only the root residues of khaki weed suppressed the P. zeae infestation of subsequently grown maize. When goose grass, khaki weed, and mealie crotalaria were grown in association with maize in soil infested with P. zeae, goose grass and khaki weed severely suppressed maize root development; this resulted in a low number of nematodes per maize root system and a high number of nematodes per maize root unit. Mealie crotalaria did not restrict maize root growth and did not affect nematode densities per maize root system or maize root unit. Special attention should be given to the control of mealie crotalaria, which is a good host for P. zeae, and goose grass, which, in addition to its ability to compete with maize, is also a suitable host for P. zeae.     

Age Structure and Community Diversity of Nematodes Associated with Maize in Iowa Sandy Soils

Age structure of nematode populations around maize growing in sandy soils in Iowa was studied at soil depths of 0-15and 15-30 cm for 2 years. Numbers of Longidorus breviannulatus were generally greater at 0-15 cm than at 15-30 cm deep until mid to late season. The decline in numbers of females as the season progressed indicates that fecundity slowed and is evidence of only one generation per year. Peak populations of Pratylenchus scribneri and Xiphinema americanum occurred in late August or early September. Adults of Hoplolaimus galeatus were few in the roots but common in the soil, indicating that fertilization occurred mostly in the soil. Numbers of P. scribneri were generally greater at the lower depth, especially late in the season. Community diversity (H'') was less when nematode biomass was used instead of numbers. Numbers of H. galeatus did not decline over the winter. Numbers of L. breviannulatus, P. scribneri, and X. americanum declined significantly over the winter, but not between spring cultivation and planting.     

Effects of UV-C radiation on extension growth, H+-extrusion and transmembrane electric potential in maize coleoptile segments

The effect of 253.7 nm ultraviolet radiation on elongation growth, medium acidification and changes in electric potential difference between vacuole and external medium in cells of maize ( Zea mays L.) coleoptile segments was investigated. It was found that irradiation with 390, 1170, 3900 and 5 850 J m⁻² UV-C (ultraviolet radiation 253.7 nm) inhibited elongation growth, whereas at 195 J m⁻² stimulation of growth was observed. The administration of IAA (10⁻⁵ M ) to the incubation medium of coleoptile segments partially abolished the inhibitory effect of UV-C. The pH of the incubation medium, measured simultaneously with growth, showed that the exposure of the segments to UV-C caused inhibition of H⁺-extrusion (or stimulation of H⁺ uptake). The presence of IAA (10⁻⁵ M ) in the incubation medium promoted (except after 5850 J m⁻² irradiation) H⁺-extrusion to a level comparable with that produced by IAA in non-irradiated segments. In UV-C irradiated segments the potential difference underwent significant alterations. Irradiation of coleoptile segments with 390 J m⁻² caused a transient depolarization, which was fully reversible within 30 min, while at higher doses depolarization was irreversible. The hyperpolarization of the membrane potential (MP) in cells of maize coleoptile induced by IAA was completely nullified by subsequent irradiation with UV-C. It is suggested that UV-C inhibited IAA-induced growth by a mechanism independent of cell wall acidification.     

Identification of a calmodulin-stimulated (Ca2++ Mg2+)-ATPase in a plasma membrane fraction isolated from maize (Zea mays) leaves

Plasma membranes were isolated from light-grown, 14-day-old maize leaves ( Zea mays L . cv. Golden Cross Bantam) using aqueous two-phase partitioning. The plasma membrane (PM) fraction contained < 0.3% of the total chlorophyll, < 0.2% of the mitochondrial marker enzyme activity, minimal contamination by endomembranes and 34% of the total PM.
A calmodulin-stimulated (Ca2++ Mg2+)-ATPase was identified in the PM-enriched fraction. The Ca2++ calmodulin stimulation was dependent on Mg2+, saturated at ca 25 μM total Ca2+, had a pH maximum at 7.2 and was maximally stimulated by 600 n M bovine brain calmodulin. The stimulation was not greatly affected by the anion present and showed a divalent cation specificity of Ca2+ > Sr+2 ± Mn+2 > Co2+± Cu2+ > Ba2+. The napthalenesulfonamide W7, an antagonist of calmodulin action, completely inhibited the calmodulin stimulation at 175 μM , while the less active analogue W5 was ineffective at this concentration. La3+, an inhibitor of PM Ca2+ transport, showed a 50% inhibition of calmodulin-stimulated ATPase activity at ca 200 μM . Taken as a whole, these data demonstrate the presence of a calmodulinstimulated, (Ca2++ Mg2+)-ATPase on the cytoplasmic surface of the plasma membrane of maize leaf cells.     

The effects of aflatoxin B1 on immature germinating maize (Zea mays) embryos

Immature maize (Zea mays L.) embryos were treated with aflatoxin B₁ concentrations, ranging from 0.1 g ml^–1 to 25 g ml^–1. Below 5 g ml^–1 aflatoxin B₁, root and shoot elongation was not significantly inhibited. Ultrastructurally, root tip cells showed little deterioration, except a possible diffused clearing in mitochondria and plastids. As the toxin concentration was increased above 5 gml^–1, shoot, and particularly root elongation, was progressively inhibited. Associated with this, there was an apparent decrease in the ribosome population. Furthermore, membranes, particularly the vacuolar membrane, became abnormal and vacuolar distension occurred. At 20 and 25 g ml^–1, these effects were exacerbated, and mitochondria and plastid structure was disrupted. At these concentrations, there was evidence of a disruption in lipid metabolism. The results are discussed in the context of known aflatoxin effects on cellular control mechanisms and ultrastructure in animal systems.     

Influence of maize root mucilage on soil aggregate stability

This study was undertaken to determine the effects of root exudates on soil aggregate stability. Root mucilage was collected from two-month old maize plants (Zea mays L.) Mucilage and glucose solutions were added at a rate of 2.45 g C kg⁻¹ dry soil to silty clay and silt loam soils. Amended soils, placed in serum flasks, were incubated for 42 d with a drying-wetting cycle after 21 d. Evolved CO₂ was measured periodically as well as the water-stable aggregates and soluble sugar and polysaccharide content of the soil. In mucilage-amended soils CO₂ evolution started with a lag phase of 2–3 days, which was not observed in glucose-amended soils. There was then a sharp increase in evolved CO₂ up to day 7. During the second incubation period there were only small differences in evolved C between treatments. Incorporation of mucilage in both soils resulted in a spectacular and immediate increase in soil aggregate stability. Thereafter, the percent of water-stable aggregates quickly decreased parallel to microbial degradation. On completion of the incubation, aggregate stability in the silty clay soil was still significantly higher in the presence of mucilage than in the control. This work supports the assumption that freshly released mucilage is able to stick very rapidly to soil particles and may protect the newly formed aggregates against water destruction. On the silty clay, microbial activity contributes to a stabilization of these established organo-mineral bounds.     

Effects of limestone and gypsum application to a Malaysian ultisol on soil solution composition and yields of maize and groundnut

A field experiment was conducted on an Ultisol in Malaysia to assess changes in soil solution composition and their effects on maize and groundnut yields, resulting from limestone and gypsum application. The results showed that soil solution Ca in the lime treatment remained mainly in the zone of incorporation, but in the gypsum treatment some Ca moved into 15–30 cm zone. Al³⁺ and AlSO₄ ⁺ were dominant Al species in the soil solution of nil treatment. Liming decreased Al³⁺ and AlSO₄ ⁺, but increased hydroxy-Al monomer activities. However, gypsum application resulted in an increase of AlSO₄ ⁺ activity and in a decrease of Al³⁺ activity. Relative maize and groundnut yields were negatively correlated with Al³⁺, Al(OH)²⁺ and Al_sum activities. Likewise, relative yields were negatively correlated with Al concentration and the Al concentration ratio and positively correlated with soil solution Mg concentration and Ca/Al ratio.     

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.