Genome Size Variation in Maize Populations Selected for Cold Tolerance

Previous studies have indicated a relationship between genome size and cold tolerance in plants. Many species adapted to growth in cool environments have large genome sizes. These studies are based on interspecific DNA content variation. In this study, the nuclear DNA content of eight maize populations was determined. These populations were obtained from the University of Nebraska and represent populations selected for cold tolerance and their respective unselected original populations. Intraspecific DNA content variation was observed between the selected and unselected populations. Upon assessing the data based solely on cold tolerance, no clear relationship between genome size and cold tolerance was apparent. When both freeze tolerance and cold tolerance were considered, populations which were cold tolerant and exhibited a certain degree of freeze tolerance were observed to have significantly larger genomes relative to the unselected populations. Thus, it appears that the relationship between intraspecific genome size variation and cold tolerance is similar to the relationship between interspecific genome size variation and growth at cooler temperatures in plants.     

Stability of RAPD markers for determining cultivar specific DNA profiles in rye (Secale cereale L.)

Summary Cultivar specific DNA profiles in rye were revealed by polymerase chain reaction (PCR) using randomly amplified polymorphic DNA (RAPD) sequences. Ten base primers were used for the amplification of genomic DNA of rye cultivars by PCR. RAPD analysis was found to be reproducible among samples between PCR runs. When amplification profiles of different rye cultivars were compared using various primers, the overall profiles were cultivar specific. However, not all primers revealed polymorphisms. These primers appear to amplify conserved sequences in all rye cultivars. Intracultivar studies were conducted on two of the cultivars. In the cultivar Imperial, no polymorphisms were observed among ten plants analyzed with five primers. In the cultivar Balboa, polymorphisms were observed among fifty plants with four of the ten primers analyzed. Despite the small amount of intracultivar variability, RAPD analysis has the potential to be a rapid and reliable method of cultivar identification in this outcrossing species.     

Evaluation in Appalachian pasture systems of the 1996 (update 2000) National Research Council model for weaning cattle

This study was conducted to evaluate the accuracy of the National Research Council's (2000) Nutrient Requirements of Beef Cattle computer model when used to predict calf performance during on-farm pasture or dry-lot weaning and backgrounding. Calf performance was measured on 22 farms in 2002 and 8 farms in 2003 that participated in West Virginia Beef Quality Assurance Sale marketing pools. Calves were weaned on pasture (25 farms) or dry-lot (5 farms) and fed supplemental hay, haylage, ground shell corn, soybean hulls, or a commercial concentrate. Concentrates were fed at a rate of 0.0 to 1.5% of BW. The National Research Council (2000) model was used to predict ADG of each group of calves observed on each farm. The model error was measured by calculating residuals (the difference between predicted ADG minus observed ADG). Predicted animal performance was determined using level 1 of the model. Results show that, when using normal on-farm pasture sampling and forage analysis methods, the model error for ADG is high and did not accurately predict the performance of steers or heifers fed high-forage pasture-based diets; the predicted ADG was lower (P < 0.05) than the observed ADG. The estimated intake of low-producing animals was similar to the expected DMI, but for the greater-producing animals it was not. The NRC (2000) beef model may more accurately predict on-farm animal performance in pastured situations if feed analysis values reflect the energy value of the feed, account for selective grazing, and relate empty BW and shrunk BW to NDF.     

Leaf area index response of four obsolete and four modern cotton cultivars to two nitrogen levels

The optimal nitrogen (N) rate for cotton (Gossypium hirsutum L.) production in the late 20th century is greater than it was in the middle of the century (112 versus 27 kg ha^‐1). Part of the reason for this difference is that modern cultivars exhibit a greater harvest index than obsolete cultivars. This greater harvest index helps to allow modern cultivars to utilize greater N rates. However, factors other than harvest index, such as the development of leaf area in response to N, may also play an important role. Therefore, the objective of this study was to characterize leaf area index (LAI) of four obsolete and four modern cultivars at a low and high fertilizer N level. Cotton was grown in the field for two years (1992 and 1993) with two locations each year. The locations were a Beulah fine sandy loam and a Dubbs silt loam. Two preplant fertilizer‐N rates were used, a low (22 kg N ha^‐1) and a high(112 kg N ha^‐1). Leaf area index was determined at three stages in each year (early, mid, and late season). Yield was determined at maturity. Averaged across years, locations, and cultivars, late‐season LAI increased from 2.32 at 22 kg N ha^‐1 to 3.15 at 112 kg N ha^‐1 by late season. In 1992, modern and obsolete cultivars had similar LAI responses to N at early and mid season but by late season, LAI of modern cultivars was greater under high N than the obsolete cultivars (3.53 versus 2.95). Lint yield of the four modern cultivars was 372 kg ha^‐1 greater than the four obsolete cultivars at 112 kg N ha^‐1 and 289 kg lint ha^‐1 greater at 22 kg N ha^‐1 in 1992. The LAI response to N level of the modern cultivars was similar to that of obsolete cultivars in 1993 at all three sampling dates. In 1993, the lint yield of modern cultivars was 238 kg ha^‐1 greater than obsolete cultivars under 112 kg N ha^‐1 and 182 kg lint ha^‐1 at 22 kg N ha^‐1. In summary, our results best support the hypothesis that the higher yield of modern cultivars at high fertilizer N is unrelated to their LAI.     

The Use of Stomatal Chloroplast Number for Rapid Determination of Ploidy Level in Maize

The usefulness of using the chloroplast number in epidermal guard cells as an indirect ploidy indicator was evaluated on seed-grown and tissue culture-derived maize plants. For seed-grown plants, two maize genotypes (B89 and R75) which had both diploid and tetraploid seeds available were used as experimental materials. The ploidy levels of seed-grown plants were confirmed by flow cytometric analysis of nuclear suspensions from these plants. For regenerated plants, haploid and diploid levels were examined and the ploidy levels of these plants were determined by chromosome counts of cells from root tips. A positive relationship between the chloroplast number and ploidy level was observed for both seed-grown and regenerated plants. The stomatal guard cells of tetraploid plants had nearly double the number of chloroplasts as the diploid plants. Similar results were found from the regenerated plants. The differences in the mean chloroplast number between diploid and tetraploid seed-grown plants and between haploid and diploid regenerated plants were highly significant. The results of this study demonstrate that counting chloroplasts in guard cells can be an efficient means of screening a large number of plants for ploidy levels. In addition, this study suggests the possibilities of using this method for detecting contaminated seed lots by different ploidy seed and for distinguishing plants of different genotypes.     

Effects of conditioning and maximal incremental exercise on oxygen consumption in sheep

To assess the suitability of sheep for exercise studies, the effect of incremental exercise and conditioning on oxygen consumption (VO2) was studied. Six sheep were adapted to a treadmill and subsequently trained 8 weeks. The sheep were then studied, in random order, using 3 incremental exercise protocols (EX-1, EX-2, and EX-3). The protocols were chosen to approximate high (EX-1), moderate (EX-2), and low (EX-3) intensity exercise by varying treadmill speed and incline. The sheep were then conditioned for an additional 12 weeks and retested on the EX-2 protocol. During exercise, VO2, gas exchange ratio (R), and rectal temperatures (Tb) were recorded. All 3 protocols resulted in significant increases in VO2, R, and Tb (P less than 0.05). Maximum VO2 for EX-1, 49.9 +/- 5.0 ml/min/kg of body weight, was significantly greater than maximum VO2 for EX-2 and EX-3, 37.8 +/- 6.5 and 42.3 +/- 6.0 ml/min/kg, respectively (P less than 0.05), whereas maximum R and maximum Tb were similar. After the additional 12-week conditioning, time on the treadmill increased 40% from 9.58 +/- 0.87 to 13.4 +/- 0.44 minutes, and maximum VO2 increased 27% to 48.1 +/- 9.1 ml/min/kg. These data indicated that maximum VO2 varied with intensity of the exercise, 12 weeks of maximal exercise conditioning was sufficient to produce a measurable training effect (ie, increase endurance and maximum oxygen consumption) and sheep are suitable for maximal exercise studies where VO2 measurements are desired.     

A Randomized Clinical Trial Evaluating Metabolism of Colostral and Plasma Derived Immunoglobulin G in Jersey Bull Calves

Background

Intravenous plasma administration has been recommended in healthy or sick calves with failure of passive immunity.

Hypothesis

IV administered plasma‐derived immunoglobulin G (IgG) undergoes increased catabolism as reflected by a rapid decrease in serum IgG concentration with an increase in fecal IgG concentrations within 48 h.

Animals

Thirty newborn Jersey calves. Fifteen were fed colostrum (CL group) and 15 were given bovine plasma IV (PL group).

Materials and Methods

Randomized clinical trial. Calves in the CL group were fed 3 L of colostrum once, by oroesophageal tubing. Calves in the PL group were given plasma IV at a dosage of 34 mL/kg. Serum and fecal samples were collected at 0 h, 6 h, 12 h, 48 h, 5 d, and 7 d. Serum and fecal IgG concentrations were determined by radial immunodiffusion.

Results

Calves in the CL group maintained serum IgG concentrations consistent with adequate transfer of immunity (≥1,000 mg/dL) throughout the study period. Calves in the PL group achieved median IgG concentrations of ≥1,000 mg/dL at 6 h but the concentrations were <1,000 mg/dL by 12 h. Calves in the PL group were 5 times more likely to experience mortality compared to the CL group (hazard ratio = 5.01). Fecal IgG concentrations were not different between the 2 groups during the first 48 h (P > .05).

Conclusions and Clinical Importance

Catabolism of plasma derived IgG occurs rapidly during the first 12 h after transfusion. Fecal excretion did not explain the fate of the plasma derived IgG.     

Nuclear DNA analysis of maize seedlings treated with the triazole fungicide,triticonazole

Maize kernels were treated with the fungicide triticonazole (RP-727), belonging to the triazole family. The nuclear DNA content was analyzed in various maize plant organs by using flow cytometry. Two fluorochromes with different DNA binding mechanisms were used for probing nuclear DNA and chromatin structure. Results indicated nuclear alterations with the use of triticonazole and the alterations observed were different in the various tissues analyzed. Active meristematic plant organs, such as root tip, did not show any significant change in nuclear DNA, but chromatin structure was altered with increasing concentrations of fungicide. Stem and mesocotyl showed both DNA and chromatin condensation changes with triticonazole concentration, but the trends observed in these two plant organs were opposite. The magnitude of the alterations was minute in the different plant organs studied. These alterations do not appear to be deleterious for normal plant development.