Numerical analysis of allozyme variation inCucurbita pepo

Cucurbita pepo, represented by cultivated forms of squash, pumpkins, and ornamental gourds, is a morphologically diverse species. Although several classifications of the cultivars have been proposed, none has been fully accepted. In an attempt to clarify the systematics of theC. pepo cultivars, allozyme variation was assayed. Twelve loci representing 6 enzyme systems (GOT, IDH, MDH, PER, PGI, and PGM) were screened. Seven of the loci were polymorphic. Electrophoretic data were collected for 50 accessions representing 14 commercial cultivars and a landrace from Mexico. Statistical analyses of the allozyme data revealed a biochemical basis for characterizing cultivars that agrees with morphology. Principal component analysis and cluster analysis revealed a major subdivision within the species above the level of cultivars. Genetic identities among groups of cultivars were much lower than those usually found among conspecific populations for outcrossing plants, possibly reflecting the influences of populational subdivision, drift, and selection particular toC. pepo.     

Influence of phosphorus and sulfur nutrition on composition ofClitoria ternatea L.

Summary A greenhouse experiment on a silt loam surface soil (Typic Hapludult) was done to investigate effects of P and S on yield, quality aspects and sugar reserves in the tropical forage legumeClitoria ternatea L. Four levels of P and two N treatments (NH₄NO₃ vs symbiotic) were arranged in a factorial design with four replications. After the first cutting two levels of S were imposed on this design.Phosphorus enhanced dry matter yield in the first cutting. Its effect was smaller in the second cutting. Amount of P required to produce maximum plant yield dropped from 200 mg/kg soil (or more) at the first cutting to 50–100 mg/kg at the second. Added S improved growth at suboptimal levels of P. At optimal P and S, symbiotic and +N plants yielded alike.Phosphorus and S fertilization caused several changes in plant composition. Nitrogen concentration was raised by S treatment and lowered by P. Combined addition of P and S lowered plant nitrate content. In symbiotic plants, soluble sugar concentrations were higher than in N-treated plants, and were increased by P and S treatment. In N-treated plants, neither P nor S increased reducing sugar concentration, but they increased total sugar.     

Heterogenous distribution of potassium and phosphorus in Acanthamoeba castellanii

Using x-ray microanalysis technique the distribution of potassium, phosphorus and sulphur was analysed in Acanthamoeba castellanii cells. Distribution of potassium was nonuniform; the high level of the element was observed in the cortex region of these cells. Distribution of phosphorus was shown to be similar to that of potassium, whereas sulphur was rather uniformly distributed.     

Effect of cytokinins on ribosomal RNA gene expression in excised cotyledons of Cucurbita pepo L.

Excised pumpkin (Cucurbita pepo L.) cotyledons were used to investigate the effects of two different types of cytokinins: N⁶-benzyladenine and N₁-(2-chloro-4-pyridyl)-N₂-phenylurea on RNA synthesis in isolated nuclei. Treatment of cotyledons with both cytokinins resulted in a rapid enhancement of nuclear RNA-polymerase-I activity (EC 2.7.7.6). Maximum stimulation of RNA polymerase I, responsible for rRNA synthesis, was observed 4–6 h after the start of cytokinin action. The activity of RNA polymerase II was stimulated much more slowly and to a lesser extent. Uridine 5-monophosphate-uridine analysis of the alkalidigested nascent pre-rRNA chains showed that the stimulation of RNA-polymerase-I activity was the consequence of an increase of the polyribonucleotide-clongation rate. No significant change in the number of transcribing enzyme molecules was defected after hormone treatment (86·10³ RNA-polymerase-I molecules per diploid genome).Indications that de-novo protein synthesis is necessary for cytokinin-mediated RNA-polymerase stimulation were derived from experiments showing inhibition by cycloheximide.Abbreviations BA N⁶-benzyladenine - [PU]-30 N₁-(2-chloro-4-pyridyl)-N₂-phenylurea - UMP undine 5-monophosphate - UTP udine 5-triphosphate     

Polyphenol oxidase in the roots ofCucurbita pepo L.

Z ko?en? tykveCucurbita pepo L., sorta ?Kaba?ky”, byl získán acetonový preparát, který má polyfenoloxydásovou aktivitu v??i pyrogallolu, podstatně men?í v??i pyrokatechinu ?i DOPA. Je kompetitivně inhibován DIECA, dále KCN, není inhibován NaN₃, co? svěd?í pro Cu-enzym polyfenoloxydasového typu. Kvantitativní rozdíly mezi variantami ?NS” a ?-Ca” nebyly zji?těny, kvalitativní rozdíly, dané afinitou v??i substrátu, nejsou pr?kazné.     

Quality of a stress-sensitive Cucurbita pepo L. pollen

The quality of Cucurbita pepo L. pollen was studied using field pollinations and the fluorochromatic-reaction test. The extreme sensitivity of this pollen to dehydration and ageing is demonstrated. Controlled stress applied to mature pollen leads to the development of seedless fruits. Molecular signals seem to be involved in the induction of this parthenocarpy. These results indicate the existence of distinct sequences involved in the completion of the fertilization program of pollen. With pollen altered by stress, the fertilization process may be stopped at different stages of its completion. We bring evidence that Cucurbita pepo plants have developed special adaptations in order to compensate for the poor viability of their pollen.Abbreviation FCR fluorochromatic reaction     

Modelling the influence of bioturbation on the vertical distribution of sedimentary phosphorus in L. Esrom

A multilayer sediment-water exchange model was used to evaluate the importance of bioturbation in the profundal sediments of L. Esrom. The temporal variation of the vertical distribution of sedimentary phosphorus fractions was modelled with an objective function of 1.50. Deviations between measured and simulated values occurred in the spring, where the measured pool of sedimentary phosphorus sharply declined in the surface sediments. The application of a model for the activity ofChironomus anthracinus based on biomass, oxygen consumption and temperature improved the model in the spring period. The downwards transport of easy-degradable surface sediments reduced the average release of sedimentary phosphorus from 12 mg P · m⁻² · day⁻¹ to 11 mg P · M⁻² · day⁻¹. The introduction of a similar model for the other important burrowing species in L. Esrom,Potamothrix hammoniensis, lowered the objective function to 1.37 and increased the average release to 12.5 mg P · m⁻² · day⁻¹. The minor role of bioturbation in sediment processes is discussed.     

Effect of potassium nutrition of rice on rhizosphere redox status

With four soils differing in K supplying power and with four rice cultivars (Oryza sativa L.) differing in K uptake kinetic parameters, the relationship between K fertilizer application and soil redox status in rhizosphere and; the distribution of ferrous iron and other toxic substances on the root surface and in the rhizosphere; and the effect of K supply on uptake of reduced iron by rice plants have been studied.The results show that K application on K-deficient soils reduced the content of active reducing substances and ferrous iron in the soil, raised the soil redox potential in the rhizosphere, increased the Eh value of rice roots and lowered the content of iron in the rice plants. These effects of K varied with different rice cultivars. When no K fertilizer was applied, active reducing substances and ferrous iron in rhizosphere soils were decreased more by the rice cultivars absorbing K strongly (e.g. Shanyou 64) than by cultivars absorbing K weakly (e.g. Zhongguo 91). Therefore, the diminution of the toxic substances by K application in the weakly K-absorbing cultivars was more significant.The observation of a rhizobox separated by a nylon screen showed that appreciably more iron oxides, compared with the control, were deposited at or adjacent to the root surfaces of the rice plant supplied with K fertilizer, fully demonstrating the relationship between K nutrition and the total oxidizing power of rice plants. According to the distribution of active reducing substances and ferrous iron, the oxidizing range of the rice root extended in K application treatment a few centimeters away from the root plane. K application to rice affected the soil redox status in rhizosphere in many ways. The main effect was an increase of the oxidizing power of the rice root. As a result, the value of soil Eh was increased, the contents of active reducing substances and ferrous iron were lowered, as well as the number of oxygen consuming microorganisms.     

Effect of phosphorus,potassium and zinc fertilizers on iron toxicity in wetland rice (Oryza sativa L.)

During the period January–August 1996, an investigation was carried out in La Mata, Cotuí, Dominican Republic with the objective to study the effect of P, K and Zn fertilizers on Fe toxicity in the rice varieties JUMA-57 (sensitive to Fe toxicity), ISA-40 and PSQ-4 (both tolerant to Fe toxicity). The rate of fertilizer application was 22 and 62 kg P ha^–1; 58 and 116 kg K ha^–1; 3 and 7 kg Zn ha^–1 and a constant dose of 140 kg N ha^–1 and 40 kg S ha^–1 on all fertilized plots. The control received no fertilizer. JUMA-57 was the only variety that showed symptoms of Fe toxicity. The observed symptoms showed a yellow to orange colour. Symptoms of Fe toxicity appeared first one week after transplanting (WAT), decreased at the fourth WAT, but returned six WAT and continued until the end of the experiment. Fertilizer application reduced symptom intensity and increased grain yield in all varieties, but only JUMA-57 did not reach the maximum yield typical for that variety. Fertilizer application did not completely overcome the toxicity effect, i.e. in symptom intensity and grain yield. The positive effect of fertilizer application could not be attributed to a specific nutrient. Intensity of symptoms was not related to Fe concentration in the leaves. The average Fe concentration of 108 mg kg^–1 was not high enough to be considered toxic. Symptoms could not be explained through Mn toxicity (average Mn concentration in the leaves was 733 mg kg^–1) nor Zn deficiency (average Zn concentration in the leaves was 20 mg kg^–1). There was a clear relationship, though, between soil DTPA extractable Fe and symptom intensity or grain yield. The toxic effect was observed when the DTPA extractable Fe in the flooded soil was above 200 mg kg^–1. From these results, we concluded that the Fe toxicity resulted from high Fe in the root zone and not from high Fe concentrations in the leaves.     

Virus-induced changes in the subcellular distribution of glutathione precursors in Cucurbita pepo (L.)

Changes in glutathione contents occur in plants during environmental stress situations, such as pathogen attack, as the formation of reactive oxygen species leads to the activation of the antioxidative defence system. As glutathione is synthesized out of its constituents cysteine, glycine, and glutamate the availability of these components will limit glutathione synthesis in plants especially during stress situations and therefore the ability of the plant to fight oxidative stress. To gain a deeper insight into possible limitations of glutathione synthesis during pathogen attack the present investigations were aimed to study how the subcellular distribution of glutathione precursors correlates with the subcellular distribution of glutathione during virus attack in plants. Selective antibodies against cysteine, glutamate, and glycine were used to study the impact of Zucchini yellow mosaic virus (ZYMV) infection on glutathione precursor contents within different cell compartments of cells from Cucurbita pepo (L.) plants with the transmission electron microscope (TEM). Generally, levels of cysteine and glutamate were found to be strongly decreased in most cell compartments of younger and older leaves including glutathione-producing cell compartments such as plastids and the cytosol. The strongest decrease of cysteine was found in plastids (- 54 %) and mitochondria (- 51 %) of younger leaves and in vacuoles (- 37 %) and plastids (- 29 %) of older leaves. The strongest decrease of glutamate in younger leaves occurred in peroxisomes (- 67 %) and nuclei (- 58 %) and in peroxisomes (- 64 %) and plastids (- 52 %) of the older ones. Glycine levels were found to be strongly decreased (- 63 % in mitochondria and - 53 % in plastids) in most cell compartments of older leaves and strongly increased (about 50 % in plastids and peroxisomes) in all cell compartments of the younger ones. These results indicate that low glycine contents in the older leaves were responsible for low levels of glutathione in these organs during ZYMV infection rather than limited amounts of cysteine or glutamate. Glutathione precursors were virtually absent in cell walls and intercellular spaces and play therefore no important role during ZYMV attack in the apoplast. While glutamate was absent in vacuoles, elevated levels of glycine (up to 30 %) and decreased cysteine contents (up to - 37 %) were observed in vacuoles during ZYMV infection. The impact of the present results on the current knowledge about glutathione synthesis and degradation on the cellular level during ZYMV infection are discussed.     

Untersuchungen am Phloemexsudat von Cucurbita pepo L.

Summary Tests for enzymes of gluconeogenesis and of the synthesis and degradation of sucrose and polysaccharides have been carried out in the phloem exudate of Cucurbita pepo. All the enzymes which are necessary for the synthesis of sucrose and polysaccharides from metabolites of the citric acid cycle were found to be present in the exudate, except phosphoenolpyruvate carboxykinase. The polysaccharide synthetase was found to exhibit higher activity with glycogen (which is an unnatural polysaccharide in higher plants) than with starch. In addition, polysaccharide synthetase activity could be increased remarkably with 2 mM glucose-6-phosphate and glycogen as primer. Among the enzymes which catabolize sucrose and polysaccharides (phosphorylase, invertase, sucrose phosphorylase), only sucrose phosphorylase showed activity.     

Beobachtungen zur Vererbung gewisser Testaeigenschaften beiCucurbita pepo L.

Zusammenfassung Beobachtungen an unreifen Samen zeigten, daß die Modifikation des Nebenverholzungsgenes in zwei Richtungen erfolgen kann: erstens kann der zeitliche und zweitens der räumliche Einsatz der Verholzung beeinflußt werden.Die vollreif geernteten Versuche des folgenden Jahres bestätigten das Vorhandensein dieser beiden Faktorengruppen.Zusätzliche Verstärkungen und Verholzungen der hhNN-Testen werden beschrieben.Abschließend wird auf die Art der Modifikatoren näher eingegangen.Der Deutschen Forschungsgemeinschaft, mit deren Unterstützung die Arbeiten in den Jahren 1951 bis 1953 durchgeführt wurden, möchte ich meinen verbindlichsten Dank aussprechen. Weiterhin bin ich Herrn Prof. Dr.Burgeff, der in eben diesen Jahren die Versuche stets mit Interesse verfolgte, zu Dank verpflichtet.Mit 1 Textabbildung.     

Effect of phosphorus and zinc nutrition on soybean seed phytic Acid and zinc

The relationships between nutrient P and Zn levels and the phytic acid, P, and Zn concentrations in soybean (Glycine max L. Merr. cv `Williams 79') seed were studied. Phytic acid increased linearly from 4.2 to 19.2 milligrams per gram as nutrient P treatment was varied from 2.0 to 50 milligrams per liter and Zn was held constant at 0.05 milligrams per liter. Leaf P concentration during seed development was found to be closely related to the concentrations of seed P and phytic acid. Leaf and seed Zn concentrations both responded positively to increasing nutrient Zn treatment. The effects of P treatment on plant and seed P and phytic acid were largely independent of the effects of Zn treatment on leaf and seed Zn. Phytic acid to Zn molar ratios ranging from 3.6 to 33.8 were observed.

The effects of nutrient P treatments on the concentrations of phytic acid, seed P, and leaf P were also studied in the P-sensitive (gene np) cultivars `Harosoy' and `Clark' and their respective P-tolerant (gene Np) near-isogenic lines L66-704 and L63-1677. In general, the positive relationships observed among nutrient P, leaf P, seed P, and phytic acid concentrations were similar to those observed in the studies with Williams 79. When fertilized with low or moderate nutrient P (2.5 and 25.0 milligrams P per liter, respectively) no significant differences in any parameter were observed between Harosoy or Clark and their respective P-tolerant isolines. When fertilized with high nutrient P (100 milligrams P per liter), Harosoy seed had a significantly higher concentration of phytic acid (30 milligrams per gram) than did seed of its P-tolerant near-isogenic line L66-704 (24.2 milligrams per gram phytic acid), whereas no significant difference was observed between Clark and its P-tolerant near-isogenic line L63-1677 (22.8 and 21.6 milligrams per gram, respectively). Variation in the phytic acid concentrations in the mature seed of the cultivars and isolines more closely paralleled leaf P concentrations observed during seed development (49 days after flowering), than those observed at the onset of seed development (14 days after flowering). Electrophoresis and ion-exchange chromatography revealed that partially phosphorylated intermediates do not appear when phytic acid accumulation is greatly reduced by limiting the nutrient P or when accumulation is greatly accelerated by excess P.

     

Secondary plasmodesmata formation in the minor-vein phloem of Cucumis melo L. and Cucurbita pepo L.

Numerous branched plasmodesmata (pd) are present between bundle-sheath cells (BSCs) and specialized companion cells known as intermediary cells (ICs) in the minor-vein phloem of melon (Cucumis melo L.) and squash (Cucurbita pepo L.). These pd were found to be secondary, i.e., they form across existing walls. Sink, sink-source transition, and source tissues were sampled from developing and mature leaves. In sink tissue, IC precursors divide to produce the two to four ICs and associated sieve elements which are present by the time of the sink-source transition. Plasmodesmata along the interface between the IC precursor and adjacent BSCs in sink tissue are unbranched and few in number. Before the leaf tissue undergoes the sink-source transition, the number of pd channels (individual branches of pd) becomes more numerous. This increase in number of pd channels occurs at least in part and perhaps entirely by branching, resulting in more channels on the IC-side than on the BSC-side. In melon there is a 12-fold increase in the number of pd channels within the IC-side of the interface and a corresponding 9-fold increase in pd channels within the BSC-side. Thus, secondary pd form by the time of the sink-source transition and may be involved in phloem loading and photoassimilate export. The system described is well-defined and amenable to experimental manipulation: secondary pd form in large numbers, at a particular interface, over a short period of time, and in a highly predictable manner.Abbreviations BSC bundle-sheath cell - DAP days after planting - IC intermediary cell - LPI leaf plastochron index - pd plasmodesmata - PI plastochron interval We thank Edith Haritatos, Rich Medville, Esther Gowan, and Nancy Dussault for expert technical assistance. This research was supported by an NSF/DOE/USDA Cornell Plant Science Center fellowship (G.M.V.), Natural Sciences and Engineering Research Council Grant GP0138401 and Université de Montréal, Fonds internes de recherche (D.U.B.), and NSF grant IBN-9419703 (R.T.).