Uptake and distribution of nitrogen in wheat plants supplied with different amounts of nitrogen after stem elongation

The uptake of nitrogen and its distribution between shoots and between organs within shoots in wheat (Triticum aestivum) was studied from the start of stem elongation to 28 days after anthesis in a glasshouse experiment with eight nitrogen levels between 0·1 and 12·8 mequiv./litre. There was no net uptake of nitrogen in plants supplied with 0·8 mequiv./litre or less; with more nitrogen the absorption increased linearly. Twenty to 44% of the total plant nitrogen was absorbed after anthesis, this fraction increasing with nutrient supply. The nitrogen allotted to the main shoot decreased until the onset of anthesis and increased thereafter at the expense of the tillers, except with 12·8 mequiv./litre, where nitrogen percentage in the main shoot decreased also after anthesis. Raising nitrogen supply increased the proportion of plant nitrogen recovered in the tillers. Nitrogen accumulated in the ear after emergence and by the 28th day after anthesis it contained between 52% and 73% of the total plant nitrogen. The ear of the main shoot had a higher proportion of shoot nitrogen than that of the tillers. The fraction of ear nitrogen supplied by retranslocation decreased from almost 100% with 0·8 mequiv. N/litre or less to nil with 12·8 mequiv./litre. Increasing nitrogen application decreased the fraction of total nitrogen allocated to the ear.     

Rapid, sequential changes in surface morphology of PC12 pheochromocytoma cells in response to nerve growth factor

The effect of nerve growth factor (NGF), a substance that promotes the differentiation and maintenance of certain neurons, was studied via scanning electron microscopy utilizing the PC12 clonal NGF-responsive pheochromocytoma cell line. After 2-4 d of exposure to NGF, these cells acquire many of the properties of normal sympathic neurons. However, by phase microscopy, no changes are discernible within the first 12-18 h. Since the primary NGF receptor appears to be a membrane receptor, it seemed likely that some of the initial responses to the factor may be surface related. PC12 cells maintained without NGF are round to ovoid and have numerous microvilli and small blebs. After the addition of NGF, there is a rapidly initiated sequential change in the cell surface. Ruffles appear over the dorsal surface of the cells with 1 min, become prominent by 3 min, and almost disappear by 7 min. Microvilli, conversely, disappear as the dorsal ruffles become prominent. Ruffles are seen at the the periphery of cell at 3 min, are prominent on most of the cells by 7 min and are gone by 15 min. The surface remains smooth from 15 min until 45 min when large blebs appear. The large blebs are present on most cells at 2 h and are gone by 4 h. The surface remains relatively smooth until 6-7 h of NGF treatment, when microvilli reappear as small knobs. These microvilli increase in both number and length to cover the cell surface by 10 h. These changes were not observed with other basic proteins, with α-bungarotoxin (which binds specifically to PC12 membranes), and were not affected by an RNA synthesis inhibitor that blocks initiation of neurite outgrowth. Changes in the cell surface architecture appear to be among the earlist NGF responses yet detected and may represent or reflect primary events in the mechanism of the factor’s action.     

Long- and short-term responses of leaf carbohydrate levels and photosynthesis to decreased sink demand in soybean

Axillary buds and the apical portion of shoots of soybean [Glycine max (L.) Merr. cultivar Turchina] plants were trimmed to investigate long-term regulation of photosynthesis by sink demand at ambient CO₂ and 22 °C. Also, in intact and trimmed shoots, the CO₂ level was increased to 660 μmol mol^?1 and temperature was lowered to 5°C to examine the superimposed short-term responses of photosynthesis to low sink demand. Under growth conditions, trimming the shoots increased leaf photosynthesis and the levels of sucrose, glucose-6-phosphate (G6P) and 3-phosphoglycerate (PGA), as well as the G6P/fructose-6-phosphate (F6P) and sucrose/starch ratios, while it decreased the level of starch and the triose-phosphate (glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, TP)/PGA ratio. Photosynthesis enhancement was accompanied by increased chlorophyll contents and ribulose-l,5-bisphosphate carboxylase oxygenase (Rubisco) activity. Sink removal consistently increased photosynthesis measured under a variety of conditions (growth CO₂ or a short-term change to 660 μmol mol_-1 CO₂; growth temperature or a short-term change to 5 °C), except when low temperature was combined with ambient CO₂; the increase in photosynthesis was higher under short-term elevated CO₂ than at ambient CO₂. In contrast with its effect at ambient CO₂, shoot trimming increased the levels of TP and ribulose-1,5-bisphosphate (RuBP) and the TP/PGA ratio under high-CO₂ conditions.     

The phylogenetic position of Rhopalura ophiocomae (Orthonectida) based on 18S ribosomal DNA sequence analysis

The Orthonectida is a small, poorly known phylum of parasites of marine invertebrates. Their phylogenetic placement is obscure; they have been considered to be multicellular protozoans, primitive animals at a "mesozoan" grade of organization, or secondarily simplified flatworm- like organisms. The best known species in the phylum, Rhopalura ophiocomae, was collected on San Juan Island, Wash. and a complete 18S rDNA sequence was obtained. Using the models of minimum evolution and parsimony, phylogenetic analyses were undertaken and the results lend support to the following hypotheses about orthonectids: (1) orthonectids are more closely aligned with triploblastic metazoan taxa than with the protist or diploblastic metazoan taxa considered in this analysis; (2) orthonectids are not derived members of the phylum Platyhelminthes; and (3) orthonectids and rhombozoans are not each other's closest relatives, thus casting further doubt on the validity of the phylum Mesozoa previously used to encompass both groups.      

Structural and functional features of the leaves of Ranunculus trichophyllus Chaix., a freshwater submerged macrophophyte

AZA, 5-Acetamido-1,3,4-thiadiazole-2-sulphonamide
CA, carbonic anhydrase
DIC, dissolved inorganic carbon
Hepes, A-(2-hydroxyethyl)-1 piperazine-ethane sulfonic acid
IC, inorganic carbon
PAR, photosynthetic active radiation
PATAg, periodic acid-thiosemicarbazide-silver proteinate
Tris, tris (hydroxymethyl)-aminomethane

The structural and physiological strategies developed by the leaves of the freshwater macrophyte Ranunculus trichophyllus to adapt to submersed life were studied. Photosynthesis is carried out mainly by the epidermis cells of the numerous segments into which the leaf is finely dissected. In these cells, containing most of the chloroplasts, a peculiar organization of the wall has been identified by cytochemical tests. A thin compact outer region covers the cell surface and splits up forming large lacunae between adjacent cells. Below it, a thick and loose inner region rich in hydrophilic pectic acids occurs, which grows in along the cell sides giving rise to wide transfer areas. In this latter cell wall region, in which the cell/environment contact and exchanges are amplified, the systems for inorganic carbon supply to photosynthetic cells operate. The leaves of R. trichophyllus can rely on environmental CO₂ and HCO₃^– as sources of inorganic carbon for photosynthesis. A mechanism for bicarbonate utilization seems to involve its conversion to CO₂ by an apoplastic carbonic anhydrase, whose activity gains importance as the availability of environmental CO₂ decreases. Interestingly, it has been demonstrated that in this species CO₂ can also be obtained from HCO₃^– by a photodependent increase in plasmamembrane H⁺-ATPase activity in the transfer areas of the epidermis cells. This is the first time that such a mechanism has been noted in a nonpolar leaf of a submerged macrophyte.     

Lifestyle modifications to prevent and control hypertension. 2. Recommendations on obesity and weight loss. Canadian Hypertension Society,Canadian Coalition for High Blood Pressure Prevention and Control,Laboratory Centre for Disease Control at Health Canada,Heart and Stroke Foundation of Canada

OBJECTIVE: To provide updated, evidence-based recommendations concerning the effects of weight loss and maintenance of healthy weight on the prevention and control of hypertension in otherwise healthy adults (except pregnant women). OPTIONS: The main options are to attain and maintain a healthy body weight (body mass index [BMI] 20-25 kg/m2) or not to do so. For those at risk for hypertension, weight loss and maintenance of healthy weight may prevent the condition. For those who have hypertension, weight loss and maintenance of healthy weight may reduce or obviate the need for antihypertensive medications. OUTCOMES: The health outcome considered was change in blood pressure. Because of insufficient evidence, no economic outcomes were considered. EVIDENCE: A MEDLINE search was conducted for the years 1992-1996 with the terms hypertension and obesity in combination and antihypertensive therapy and obesity in combination. Other relevant evidence was obtained from the reference lists of the articles identified, from the personal files of the authors and through contacts with experts. The articles were reviewed, classified according to study design and graded according to level of evidence. VALUES: A high value was placed on the avoidance of cardiovascular morbidity and premature death caused by untreated hypertension. BENEFITS, HARMS AND COSTS: Weight loss and the maintenance of healthy body weight reduces the blood pressure of both hypertensive and normotensive people. The indirect benefits of a health body weight are well known. The negative effects of weight loss are primarily the frustrations associated with attaining and maintaining a healthy weight. The costs associated with weight loss programs were not measured in the studies reviewed. RECOMMENDATIONS: (1) It is recommended that health care professionals determine weight (in kilograms), height (in metres) and BMI for all adults. (2) To reduce blood pressure in the population at large, it is recommended that Canadians attain and maintain a healthy BMI (20-25). (3) All overweight hypertensive patients (BMI greater than 25) should be advised to reduce their weight. VALIDATION: These recommendations are similar to those of the World Hypertension League, the National High Blood Pressure Education Program Working Group on Primary Prevention of Hypertension, the Canadian Hypertension Society and the Canadian Coalition for High Blood Pressure Prevention and Control. They have not been clinically tested. SPONSORS: The Canadian Hypertension Society, the Canadian Coalition for High Blood Pressure Prevention and Control, the Laboratory Centre for Disease Control at Health Canada, and the Heart and Stroke Foundation of Canada.     

Pregnancy success of lactating Holstein cows after a single administration of a sustained-release formulation of recombinant bovine somatotropin

Background

Results regarding the use of bovine somatotropin for enhancing fertility in dairy cattle are variable. Here, the hypothesis was tested that a single injection of a sustained-release preparation of bovine somatotropin (bST) during the preovulatory period would improve pregnancy success of lactating dairy cows at first service.

Results

The first experiment was conducted in a temperate region of Mexico. Cows inseminated following natural estrus or timed artificial insemination were given a single injection of bST or a placebo injection at insemination (n = 100 cows per group). There was no significant difference between bST and control groups in the proportion of inseminated cows diagnosed pregnant (29 vs 31% pregnant). The second experiment was performed during heat stress in Florida. Cows were subjected to an ovulation synchronization regimen for first insemination. Cows treated with bST received a single injection at 3 days before insemination. Controls received no additional treatment. As expected, bST did not increase vaginal temperature. Treatment with bST did not significantly increase the proportion of inseminated cows diagnosed pregnant although it was numerically greater for the bST group (24.2% vs 17.8%, 124–132 cows per group). There was a tendency (p = 0.10) for a smaller percent of control cows to have high plasma progesterone concentrations (≥ 1 ng/ml) at Day 7 after insemination than for bST-treated cows (72.6 vs 81.1%). When only cows that were successfully synchronized were considered, the magnitude of the absolute difference in the percentage of inseminated cows that were diagnosed pregnant between bST and control cows was reduced (24.8 vs 22.4% pregnant for bST and control).

Conclusion

Results failed to indicate a beneficial effect of bST treatment on fertility of lactating dairy cows.