Different sex phenotypes of Cucumis sativus L. and C. melo L. and their endogenous gibberellin activity

Summary Gibberellins were extracted from seeds and green plants of different sex types of the closely related species Cucumis sativus L. (cucumber) and C. melo L. (muskmelon). Both seeds and green plants of monoecious and andromonoecious lines of C. sativus contained significantly higher gibberellin levels at all growth stages tested than did a gynoecious line. Gibberellin activity in the monoecious and andromonoecious C. sativus line reached a maximum at the growth stage corresponding to flower differentiation at cotyledonary and first leaf axils. Vernalization of seeds of gynoecious plants resulted in increased male tendency correlated with increased gibberellin activity. In contrast, monoecious and andromonoecious lines of C. melo were gibberellin deficient relative to hermaphroditic and gynoecious lines.Journal Article No 5534 from the Michigan Agricultural Experiment Station. This work was supported by a grant from the Herman Frasch Foundation.     

Acidification of Nova Scotia Lakes

Although water chemistry of precipitation and lakes in Nova Scotia is dominated by C1 from sea salt, correction for marine influence reveals that the dominant anion in acidified lakes is SO₄. Atmospheric deposition of non-marine SO₄ (SO₄) and NO₃- for the period 1977–1980 at 4 stations in southwest Nova Scotia averaged 47 meq SO₄ ^* m^?2 yr^?1 and 21 meq NI₃-m^?2 yr^?1 compared with 38 and 13 meq, respectively, for the average of 3 stations in the northeastern third of the province. Precipitation pH increased from 4.5 to 4.8 along the same axis. Almost 50% of the SO₄ deposition occurred when storms came from the southwest, indicating low pressure tracks which pass south of major Canadian sources of S. SO₄ ^* deposition in metropolitan Halifax (1982 bulk data) was 87 meq m^?2 yr^?1, due to local emissions of ca. 28 300 tonne S in the area, as well as LRTAP. Concurrent deposition of NO₃-N was 15 meq m^?2 yr^?1 (2.1 kg ha^?1 yr ^?1). Loadings from SO₄ deposition in the Halifax area amount to 42 kg ha^?1 yr^?1 and clearly exceed the federal guideline (M.O.I., 1983) of 20 kg ha^?1 yr^?1. Water chemistry of southwest, northeast, and Halifax area lakes show the same general SOI trends as observed for atmospheric deposition. In addition we find a positive relationship between SOI concentrations in the urban lakes and proximity to the center of the urban area.     

Sediment acid neutralization in softwater lakes

Acid neutralizing capacities (ANC) of sediments from McCloud Lake, Florida and seven other lakes in Wisconsin and Florida were as high as 10 meq 100 g^?1 over the pH range 4.5 to 5.5 in well-mixed batch experiments. Exchange of Ca²⁺ and Mg²⁺ accounted for over 50% of the neutralizing capacity; Al solubilization and sulfate adsorption were unimportant in neutralizing H⁺ additions. ANC was correlated with sediment volatile solids content. Sulfate reduction occurred in microcosms that simulated lake-water interactions and subsurface seepage;in situ pore water profiles and a whole-lake mass balance confirm the occurrence of this process in McCloud Lake. Sediment neutralization is important for lakes that receive most of their water from precipitation and thus are particularly susceptible to acidification.     

Acidification of Nova Scotia lakes I: Response of diatom assemblages in the Halifax area

A comparison is made of diatom remains in surficial lake sediments collected in 1971 and 1980. Changes of similar magnitude towards more acid tolerant assemblages are observed in four lakes studied in detail despite widely differing aquatic environments. No attempt is made to reconstruct past chemistry, the significant point being that at the most fundamental level, local lacustrine biological systems are being stressed to the point of alteration. The pattern of that alteration with emphasis on ‘simplification’ is discussed with the suggestion that rates of acidification may be as important as net changes.     

Seasonal mass balance of major ions in three small watersheds in a maritime environment

Three watersheds (16.4, 544, and 83 ha) at distances of 0.5, 20, and 40 km from the Atlantic coast have been monitored for major ion chemistry of precipitation input and streamflow from May 1977 to November 1978. More than 200 precipitation and stramflow samples were analyzed for Na, K, Ca, Mg, chloride and sulphate, as well as pH, conductivity, alkalinity, and compared to similar studies at Hubbard Brook, New Hampshire, U.S.A., and Kejimkujik National Park, Nova Scotia. Major ion chemistry reflects proximity to Atlantic and Bay of Fundy coastal sources of marine aerosols. Evidence is presented implying biological reduction of H ⁺ and S04 to H₂S during summer months for two consecutive growing seasons. Weighted mean annual pH values of precipitation for the three watersheds in Nova Scotia range from 4.11 to 4.63. More than 50% of the H ⁺ in precipitation is retained in the watersheds (with the exception of the ombrotrophic Fink Cove ecosystem), principally at the expense of basic cations being leached from the watersheds. Acidic deposition of Nova Scotian precipitation is predominantly as sulphuric acid, in contrast to ammonium sulphate, characteristic of continental precipitation.     

Seismic imaging of the downwelling Indian lithosphere beneath central Tibet

A tomographic image of the upper mantle beneath central Tibet from INDEPTH data has revealed a subvertical high-velocity zone from approximately 100- to approximately 400-kilometers depth, located approximately south of the Bangong-Nujiang Suture. We interpret this zone to be downwelling Indian mantle lithosphere. This additional lithosphere would account for the total amount of shortening in the Himalayas and Tibet. A consequence of this downwelling would be a deficit of asthenosphere, which should be balanced by an upwelling counterflow, and thus could explain the presence of warm mantle beneath north-central Tibet.     

Use of transesophageal atrial pacing to provide temporary chronotropic support in a dog undergoing permanent pacemaker implantation

A 14.5-kg, 13-year-old female spayed Cocker spaniel was evaluated because of episodic hind limb weakness. Results of examination were consistent with sick sinus syndrome with intermittent second-degree atrioventricular block. Transesophageal atrial pacing was successful in providing chronotropic support during permanent pacemaker implantation. Transesophageal atrial pacing appears to be a viable option for temporary atrial pacing in dogs with hemodynamically marked bradycardia without significant atrioventricular blockade.     

Amphibian population declines in montane southern Mexico: resurveys of historical localities

Declines of amphibian populations have been well documented in the US, Canada, and Central America, but little is known regarding the status of amphibian populations in Mexico. In 2000, we surveyed 43 transects from 3 upland regions in Guerrero and Oaxaca, Mexico. We found 161 adult amphibians belonging to 39 species, representing only 19-48% of the anuran fauna known from these regions. We found one dead (Eleutherodactylus saltator) and one dying frog (Ptychohyla erythromma) from two different streams near Chilpancingo, Guerrero. Both frogs were infected with Batrachochytridium dendrobatidis, a pathogenic fungus involved in other declines of amphibian populations. We collected 368 tadpoles; 60 (19%) tadpoles from 9 different streams among the three regions were missing mouthparts, which is indicative of infection by chytrid fungus. We report additional data from the state of Chiapas, Mexico, that document declines, disease, and apparent extirpations from that region as well. Overall, we report 31 populations (representing 24 species) that appear to have been extirpated, including populations of as many as 11 endemic species that have been missing for 16-40 years and may be extinct.     

Effect of Dietary Phospholipids on the Choline Requirement ofLitopenaeus vannamei Juveniles

An 8-wk feeding trial was conducted with a 3 ± 4 factorial design for evaluating the nutritional relationship between phospholipids (lecithin at 0, 1.5% or 3% of diet) and choline chloride (0, 1,000, 2,000, or 4,000 mg/kg diet) in juvenile Litopenaeus vannamei . In addition, diets with five graded levels of choline chloride (0, 500, 1,000, 2,000, and 4,000 mg/kg) without supplemental phospholipids or cholesterol were fed for determining the dietary choline requirement. Overall survival was 99% with no difference among the dietary treatments. The choline requirement was estimated to be 871 mg/kg diet without dietary phospholipids. No choline requirement was evident when lecithin was provided at 1.5% and 3% of diet. Shrimp growth significantly increased with incremental dietary phospholipids regardless of choline chloride level. These results indicate that lecithin could effectively provide choline. Conversely, synthesis of phospholipids from choline could not meet the phospholipids requirement of shrimp. Both dietary lecithin and choline chloride supplementation reduced lipid in shrimp muscle. However, only lecithin supplementation increased lipid in hepatopancreas, and dietary choline chloride decreased the level of other phospholipids (except phosphatidylcholine) in shrimp muscle.