Poor aeration in NFT and a means for its improvement

Because water can restrict rapid diffusive exchange of gases we have examined how far the nutrient solution is adequately aerated in NFT systems used for glasshouse tomato production. Measurements were at various places of: the concentrations of dissolved O₂ and dinitrogen oxide (nitrous oxide), the maximum rate of O₂ flow to an O₂-consuming sink (O₂ flux density), and the electrochemical (redox) potential. Whalehide pots containing peat-based or peat-sand based composts used to stand the plants in the NFT solution were found waterlogged and poorly aerated. Dissolved O₂ in solution drawn from the pots rarely exceeded 1-2 mg l^-1. This small amount of O₂ was associated with accumulations of dinitrogen oxide, a gaseous product of anaerobic microbial respiration. Oxygen flux density was also small but redox potentials remained above 300 mV which was too high to favour the formation of Phytotoxins such as Mn(II), Fe(II) or H₂S. Replacing the composts with more open structured inorganic media such as Perlite, Rockwool or Capogro almost completely eliminated the symptoms of poor aeration observed in the composts. On one occasion the O₂ dissolved in the flowing nutrient solution was found to be depleted by c. 50%. Thus the whole system can sometimes be subject to considerable O₂ deficits.     

Determination of Feeder Cell‐Based Cellular Niches Supporting the Colonization and Maintenance of Spermatogonial Stem Cells from Prepubertal Domestic Cat Testes

Recently, isolation and in vitro culture of putative spermatogonial stem cells (SSCs) in the domestic cat have been conducted. However, the cellular niche conditions that facilitate the establishment and long‐term maintenance of feline SSCs (FSSCs) have not been described. Therefore, we investigated the type of feeder cells used to stimulate colony formation and growth of FSSCs among the various factors in the FSSC niche. Spermatogonial stem cells isolated from feline testes were cultured on mitotically inactivated testicular stromal cells (TSCs) derived from cats, dogs and mice, and mouse embryonic fibroblasts (MEFs). The formation and growth of colonies derived from SSCs cultured on each type of feeder cell were identified at passage 0, and the morphology, alkaline phosphatase (AP) activity and expression of SSC‐specific genes in surviving colonies were investigated at passage 4. Among these diverse feeder cells, TSCs from cat showed the greatest colony formation, growth and maintenance of FSSCs, and SSC colonies cultured by passage 4 showed a typical dome‐shaped morphology, AP activity and expression of SSC‐specific genes (NANOG, OCT4, SOX2 and CD9). Accordingly, these results demonstrate that feline TSCs could be used as feeder cells to support the establishment and maintenance of SSCs from domestic cats.     

Partial Masking of the Canine Electroretinogram by Oscillatory Potentials

Recording the electroretinogram (ERG) in dogs has become a standard procedure in clinical ophthalmology. The ERG provides highly objective information about retinal function that is otherwise unobtainable from dogs. However, problems may be encountered in measuring the latencies amplitudes of the a and b waves, depending upon the amplifier bandwidth used to record the potential. Superimposed on the canine ERG are other complex retinal potentials, some of which have higher frequency spectra than those that give rise to a and b waves. Whereas an amplifier bandwidth of 1.0 to 100 Hz or more insures that the slower components of the ERG are recorded, it also allows higher frequency oscillatory potentials (OP) to be recorded on the b wave. The OP cause a notching in the peak of the b wave thus necessitating a decision about how to measure the b wave. Bandwidth characteristics of the ERG and OP are presented and some possible methods for measuring the OP-contaminated ERG are discussed.     

Zinc in wheat grain as affected by nitrogen fertilization and available soil zinc

Greenhouse and field experiments were conducted to determine the influence of nitrogen (N) fertilization and DTPA‐extractable soil zinc (Zn) on Zn concentration in wheat (Triticum aestivum L., cv. Pioneer 2375) grain. Application of zinc sulfate (ZnSO₄) in the range of 0 to 8 mg Zn kg^‐1 increased linearly DTPA‐extractable Zn in an incubated calcareous soil from 0.3 to 5.0 mg kg^‐1. Application of these rates of ZnSO₄ to the same soil under greenhouse conditions increased Zn concentration of wheat grain from 26 to 101 mg kg^‐1. The influence of 134 kg urea‐N ha^‐1 on Zn concentration in wheat grain at eight field sites, with DTPA‐extractable soil Zn levels ranging from 0.3 to 4.9 mg kg^‐1, was studied. Nitrogen fertilizer increased wheat‐grain yields in four of the eight experiments but had little effect on grain‐Zn concentration. Grain‐Zn concentration ranged from 31 to 45 mg kg^‐1 in N‐fertilized plots at the various sites and was related (r=0.74*) to DTPA‐extractable soil Zn.     

Effects of tenotomy of the tensor tympani muscle on the acoustic reflex in dogs

The acoustic reflex (AR) was recorded from 12 healthy mixed-breed dogs. Latency and amplitude were measured from ipsilateral and contralateral AR at stimulus frequencies of 1 and 2 kHz and intensities of 70 to 110 dB sound pressure level for ipsilateral AR and 70 to 120 dB hearing level for contralateral AR. Mean latencies for ipsilateral and contralateral AR were between 33.46 and 206.10 ms and between 45.26 and 180.89 ms, respectively, and amplitudes were between 0.14 and 1.79 cm3 and between 0.31 and 1.86 cm3 of air, respectively. Stimulus frequencies and intensities had significant effects (P less than 0.05) on ipsilateral and contralateral AR latencies and amplitudes. Ipsilateral and contralateral AR decays were determined by measuring compliance change during a 10-s pure-tone stimulation at frequencies of 1 and 2 kHz at an intensity of 10 dB above AR threshold. Reflex decays for 1 kHz and 2 kHz frequencies averaged 5.74% and 9.71%, respectively, for ipsilateral AR and 5.08% and 5.40%, respectively, for contralateral AR. Bilateral tympanograms and brain stem auditory-evoked responses were performed on each dog. Mean normal static compliance of the middle ear, as determined by tympanometry, was 0.15 cm3. Unilateral tenotomy of the tensor tympani muscle was done on 6 of the 12 dogs, and each of the preceding procedures were repeated within 1 week after surgical operation. Transection of the tensor tympani tendon did not alter (P greater than 0.05) the latencies or amplitudes of 1 kHz- or 2 kHz-evoked contralateral AR, the latency or amplitude of 1 kHz-evoked ipsilateral AR, or the amplitude of 2 kHz-evoked ipsilateral AR. However, the latency of 2 kHz-evoked ipsilateral AR was significantly (P less than 0.05) increased. Reflex decay increased significantly (P less than or equal to 0.001) for the contralateral reflex elicited by the 2 kHz stimulus. Neither compliance of the middle ear system nor amplitude and latency of the brain stem auditory-evoked response were affected (P greater than 0.05) by tenotomy. Since tenotomy eliminates participation of the tensor tympani in the AR, these data indicate that contraction of this muscle is not primarily responsible for the compliance changes recorded during an acoustic reflex in dogs.     

Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.     

Pathogenicity to alder of Phytophthora species from riparian ecosystems in western Oregon

Described as one of the most destructive pathogens of agricultural crops and forest trees, Phytophthora is a genus of microorganisms containing over 100 known species. Phytophthora alni has caused collar and root disease in alders throughout Europe, and a subspecies has recently been isolated in North America. Reports of canopy dieback in red alder, Alnus rubra, prompted a survey of their overall health and to determine whether P. alni was present in western Oregon riparian ecosystems. Over 1100 Phytophthora isolates were recovered, representing 20 species and 2 taxa. Phytophthora‐type cankers were observed in many trees, and their incidence was positively correlated with canopy dieback. High levels of mortality for red alder were not observed, which suggests these Phytophthora species are not aggressive pathogens. To test this hypothesis, three stem wound inoculations and one root dip were conducted on red alder seedlings using 13 Phytophthora species recovered from the riparian survey. Ten of the 13 Phytophthora species produced significant lesions in at least one pathogenicity test. Phytophthora siskiyouensis produced the largest lesions on red alder from the two stem wound inoculation tests conducted under summer conditions, while P. taxon Pgchlamydo caused the largest lesions during the winter stem wound inoculation test. Phytophthora gonapodyides, P. taxon Pgchlamydo and P. siskiyouensis have previously been found associated with necrotic alder roots and bole cankers in the field, and with the pathogenicity results reported here, we have established these species as causes of Phytophthora root disease and Phytophthora bole canker of alder in Oregon. While none of the Phytophthora species were especially aggressive towards red alder in the pathogenicity tests, they did cause localized disease symptoms. By weakening the root systems or boles of alders, the Phytophthoras could be leaving alders more susceptible to other insects and pathogens.     

Nitrate leaching in an Atlantic Coastal Plain soil amended with poultry manure or urea-ammonium nitrate: Influence of thiosulfate

Nitrate leaching, which can lead to groundwater contamination, is a common occurrence, especially in sandy, well drained soils. Nitrogen from poultry manure (PM) and ammonium fertilizers has been shown to undergo rapid nitrification upon addition to soils, making it highly susceptible to nitrate leaching. Any management technique that could delay nitrification and thereby reduce nitrate leaching would be desirable. Ammonium thiosulfate has been shown to be an effective nitrification inhibitor in laboratory studies and may be useful in reducing nitrate leaching. Soil columns, 75 cm long and inner diameter 19.6 cm, were packed with a reconstituted profile of a Rumford loamy sand and amended with urea-ammonium nitrate (UAN) or PM. Corn was grown in the columns to create a dynamic soil/plant system. Columns were placed in a greenhouse and were leached periodically for a period of 10 weeks with deionized water in amounts intended to simulate early spring and summer rainfall patterns in the Atlantic Coastal Plain. Column leachates, as well as plant and soil samples were collected and analyzed for NO₃-N and NH₄-N. Nitrate-N leaching was largely dependent upon the amount of water moving through the system. Ammonium thiosulfate did not significantly decrease NO₃-N leaching or increase plant N uptake when used in combination with UAN or PM. Comparable amounts of NO₃-N leaching were observed for the UAN and the PM treated column. Additionally, large amounts of NO₃-N leaching were observed with the control columns, suggesting that residual soil N from previous crops can contribute significantly to NO₃-N leaching and may deserve further investigation.     

Effects of bacterial lipopolysachharide on peripheral leukocytes in the American alligator (Alligator mississippiensis)

Alligators were injected intraperitoneally with four different doses (10, 1.0, 0.1, and 0.01 mg/kg body weight) of a mixture of bacterial lipopolysaccharides (LPS) derived from three different types of bacteria (Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae). Injection of the alligators with the LPS mixture resulted in a dose- and time-dependent increase in total peripheral leukocytes Lymphocytes increased at days 3 and 4 post-injection, and decreased back to baseline levels at day 7 for all doses. Alligators that were not treated, and those injected with pyrogen-free saline, did not exhibit statistically significant changes in total leukocytes during the course of the study. Injection of alligators with 0.5 mg LPS/kg body weight derived from one of three bacterial species revealed that the leukocyte increases observed were not statistically different for all three types of LPS. The animals displayed the same increases in total counts and the levels of all circulating leukocyte types were not different between animals treated with a combination of LPS from all three bacterial species.