Effects of clipping and soil compaction on growth,morphology and mycorrhizal colonization of Schizachyrium scoparium,a C4 bunchgrass

Summary A factorial design of clipping and compaction was used to study the responses of Schizachyrium scoparium and its mycorrhizal symbionts to these stresses. All treatment combinations significantly reduced the growth and biomass of plants relative to controls. Compaction significantly reduced tillering and crown expansion while clipping increased tillering early in the growing season and reduced it later. Mycorrhizal colonization of roots was highest in the clipped plots and lowest in compacted plots. Spore number was highest in compacted plots and lowest in clipped plots. It appears that spore number may be negatively correlated with root growth since any treatment that reduced plant growth yielded higher spore numbers. The combination of clipping and compaction reduced plant growth the most, but had intermediate effects on mycorrhizal colonization and spore number.     

Cooperation of epidermis and inner tissues in auxin-mediated growth of maize coleoptiles

The function of the epidermis in auxinmediated elongation growth of maize (Zea mays L.) coleoptile segments was investigated. The following results were obtained: i) In the intact organ, there is a strong tissue tension produced by the expanding force of the inner tissues which is balanced by the contracting force of the outer epidermal wall. The compression imposed by the stretched outer epidermal wall upon the inner tissues gives rise to a wall-pressure difference which can be transformed into a water-potential difference between inner tissues and external medium (water) by removal of the outer epidermal wall. ii) Peeled segments fail to respond to auxin with normal growth. The plastic extensibility of the inner-tissue cell walls (measured with a constant-load extensiometer using living segments) is not influenced by auxin (or abscisic acid) in peeled or nonpeeled segments. It is concluded that auxin induces (and abscisic acid inhibits) elongation of the intact segment by increasing (decreasing) the extensibility specifically in the outer epidermal wall. In addition, tissue tension (and therewith the pressure acting on the outer epidermal wall) is maintained at a constant level over several hours of auxin-mediated growth, indicating that the inner cells also contribute actively to organ elongation. However, this contribution does not involve an increase of cell-wall extensibility, but a continuous shifting of the potential extension threshold (i.e., the length to which the inner tissues would extend by water uptake after peeling) ahead of the actual segment length. Thus, steady growth involves the coordinated action of wall loosening in the epidermis and regeneration of tissue tension by the inner tissues. iii) Electron micrographs show the accumulation of striking osmiophilic material (particles of approx. 0.3 m diameter) specifically at the plasma membrane/cell-wall interface of the outer epidermal wall of auxin-treated segments. iv) Peeled segments fail to respond to auxin with proton excretion. This is in contrast to fusicoccin-induced proton excretion and growth which can also be readily demonstrated in the absence of the epidermis. However, peeled and nonpeeled segments show the same sensitivity to protons with regard to the induction of acid-mediated in-vivo elongation and cell-wall extensibility. The observed threshold at pH 4.5–5.0 is too low to be compatible with a second messenger function of protons also in the growth response of the inner tissues. Organ growth is described in terms of a physical model which takes into account tissue tension and extensibility of the outer epidermal wall as the decisive growth parameters. This model states that the wall pressure increment, produced by tissue tension in the outer epidermal wall, rather than the pressure acting on the inner-tissue walls, is the driving force of growth.Abbreviations and symbols E _el, E _pl elastic and plastic in-vitro cell-wall extensibility, respectively - E _tot E _el+E _pl - FC fusicoccin - IAA indole-3-acetic acid - IT inner tissue - ITW inner-tissue walls - OEW outer epidermal wall - osmotic pressure - P wall pressure - water potential     

Rapid immunofluorescent determination of cells in the S phase in pea root meristems: An alternative to autoradiography

Photosystem II (PS II) activity and the localization of ribulose-l,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39) were studied in primary leaves of young maize plants ( Zea mays L. cv. Fronica) by tetra-nitro-blue-tetrazoliumchloride reduction and immunolocalization, respectively. In tissue of 3-day-old plants all chloroplasts were structurally identical. From day 4 they developed into their typical appearance of mesophyll and bundle sheath chloroplasts. First PS II-activity was present in both types of chloroplasts. From day 4 it disappeared in bundle sheath chloroplasts concomitant with the loss of grana. RuBP carboxylase on the other hand was only present in bundle sheath chloroplasts at all stages of development. Thus, the control of the development of the photosystems and the Calvin cycle enzymes seem to differ.     

Growth responses of tropical forage plant species to vesicular-arbuscular mycorrhizae

Summary Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency.     

Effects of heavy metals on growth and ultrastructure ofChara vulgaris

Summary The toxicity of some heavy metals to the common macrophytic freshwater algaChara vulgaris was studied under laboratory conditions. For experiments, apical tips of algae containing two internodes were cultivated for fourteen days in the presence of various concentrations of cadmium, mercury or lead (as triethyl lead or lead nitrate). Fifty percent growth inhibition occurred with concentrations of 8.5×10^–8 M (9.5 ppb) cadmium, 7.5×10^–7M (150ppb) mercury, 1.6×10^–6 M (330ppb) organic lead or 4× 10^–5 M (8000 ppb) inorganic lead. Sublethal concentrations of these metals caused alterations in the fine structure of internodal cells which turned out to be at least partly metal-specific or in the case of lead, the effects depended on whether the lead was ionic or organically bound. Cadmium and inorganic lead induced disorders of cell wall microfibrils which resulted in local wall protuberances. Mercury affected the chloroplasts which mostly showed considerably increased grana stacks. In addition, mercury caused a dilation of the endoplasmic reticulum and of the mitochondrial tubuli. Organic lead damaged the membrane system of chloroplasts; sheet- or tubule-like thylakoids were disarranged and showed whorl-like structures. At higher concentrations of organic lead, tubular invaginations of the plasmalemma (charasomes) disappeared. The fine structure of nuclei was not altered by any of the metals.     

Growth and body composition changes in mice selected for high post-weaning weight gain on two levels of feeding

Summary Two lines of mice were selected for high post-weaning weight gain (3 to 6 weeks) adjusted for 3 week weight. One line (F) was grown on freely available food and the other (S) on a feeding scale set at the same level for all mice. Food intake of the S line averaged 80% of the F line. The realised heritabilities after 6 generations of selection were 0.38±0.06 and 0.33±0.07 for the F and S lines, respectively. In generation 7, mice from the F and S lines and from an unselected control line (C) were compared on both free and set levels of feeding from 3 weeks to 9 weeks of age. Measurements taken were growth rate, appetite, food conversion efficiency (weight gain/food intake) and body composition (fat, protein, ash, water). The F and S lines grew more rapidly and efficiently than the C line on both levels of feeding, each line performing best on the level of feeding on which it was selected. The average genetic correlation between growth rates of the same line on the two feeding levels was 0.54±0.10. The F line grew 19% faster and was 9% more efficient than the S line on free feeding but the S line grew 15% faster and was 15% more efficient than the F line on set feeding. Relative to the C line, food intake per day on free feeding was 4% higher in the F line and 6% lower in the S line. There was no difference between the lines in food intake/g body weight. The rate of deposition of all body components increased in both selection lines. In the F, S and C lines respectively, efficiencies of gains in body components (10²x gain/food) were 1.79, 1.31 and 1.06 for fat, 1.53, 1.63 and 1.22 for protein and 5.88, 6.45 and 4.98 for protein + water. Apparently energy lost as heat was reduced in both the F and S lines. The partitioning of energy retained was altered in favour of more fat in the F line and more protein in the S line.     

Selection for components related to body composition in mice: correlated responses

Summary Correlated responses were estimated in each of two replicate lines of mice selected within full-sib families for high (HF) or low (LF) 12-week epididymal fat pad weight as a percentage of body weight (epididymal fat pad percentage), or high (HL) or low (LL) 12-week hind carcass weight as a percentage of body weight (hind carcass percentage). Two replicate control lines (RC) were maintained. Correlated traits were measured in each of the 10 generations of selection. Realized (r_{G R}) and offspring-sire genetic correlations generally were in agreement. In HF and LF, 3–6 week postweaning gain (r_{G R} = 0.36±0.04) and feed intake (r_{G R} = 0.50±0.13) had positive correlated responses, but feed efficiency and feed intake/metabolic body size did not change. Positive correlated responses were found for subcutaneous fat pad percentage, body weight-adjusted subcutaneous fat pad weight and fat percentage in the hind carcass (r_{G R}'s were 1.04±0.13, 0.93±0.13 and 0.90±0.08). In the hind carcass, fat-free dry (protein + ash) percentage showed a small negative correlated response, and fat-free dry weight did not change. In HL and LL, the correlated responses for the above traits were generally opposite to those observed in HF and LF. Litter size, percentage of infertile matings, and preweaning mortality showed no consistent correlated responses in any of the lines, but an index of fitness combining the three traits showed a decrease in all four selection treatments.Paper no. 11057 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticisms of similar ones not mentioned     

Relationships between growth at the sutures of the rabbit calvarium

The present study was designed to elucidate the relationships between growth increments at the cranial vault sutures in rabbits. Thirteen male New Zealand white rabbits were followed regularly from age 31 to 142 days using a roentgen stereophotogrammetric system. Spherical tantalum markers were implanted into the nasal, frontal, and parietal bones, and implant stability was checked at each stereo examination. Problems with instability were encountered only in the nasal bones. Registered growth rates conformed to our previous investigations. High correlations were observed between the following areas; the coronal suture to the frontonasal suture, the first principal component of the neurocranial suture group to the frontonasal suture, and the principal component of the craniofacial suture group to the coronal suture. Remaining relationships demonstrated dispersion to various extents. The findings indicate that there seems to exist a basic mutual dependence between neural and facial skeletal growth, as well as complex covariations between the various sutures of the rabbit calvarium.     

Short and plump physique of Mexican-American children

Mexican-American children are shorter but relatively heavier than non-Hispanic whites and blacks. The objectives of this paper are to assess the extent to which this "short and plump" physique occurs in data collected in two national surveys (HANES I and II); to determine variations by age, sex, and socioeconomic status; and to investigate the anthropometric characteristics that may account for the overweight. Three groups, defined on the basis of reported ancestry and observed race, are studied: Mexican-Americans (MEXAME), non-Hispanic Whites, (EURAME), and blacks (BLACK). Short stature was clearly associated with the poverty index (PI) in all three groups. MEXAMEs with a PI greater than 1.6 were similar in stature to EURAMEs at the same income level at ages 1-11 years but not at 12-17 years. On the other hand, MEXAMEs were shorter than BLACKs at all ages and income levels. The body mass index (kg/cm2) and poverty were unrelated. With respect to the anthropometric characteristics examined that are related to the body mass index, MEXAMEs and EURAMEs were similar in sitting height as a proportion of total height, arm muscle and fat areas, and triceps skinfold but different in the following ways: MEXAMEs had narrower elbow but broader bitrochanteric breadths and larger chest circumferences and subscapular skinfolds. Greater upper body dimensions and fatfolds seem to best describe the physique of MEXAMEs. However, in multiple regressions, these anthropometric characteristics failed to account fully for the greater relative weight of MEXAMEs as compared to EURAMEs.     

Standards of arm muscle by stature for the assessment of nutritional status of children

This study is based on a sample of 9,134 children ranging in age from 2 to 17 years from which the excessively lean and fat children by skinfold thickness were excluded. This sample was derived from the combined data sets of the first and second National Health and Nutrition Examination Surveys (NHANES I and II) of 1971-1974 and 1976-1980. Means and percentiles of upper arm muscle area were calculated for 3 cm increments in stature from 84 to 184 cm for boys and from 84 to 176 cm for girls. Based on means, Z-score units, and percentile ranges of upper arm muscle area by stature, five operational categories of nutritional status have been established. It is recommended that these standards and this classification system be used to supplement current standards of weight for age and weight for height in order to obtain a more complete assessment of body composition and nutritional status.