Variation in relative growth rate and its components in the annual Polygonum aviculare in relation to habitat disturbance and seed size

Polygonum aviculare is an annual weedy species showing extensive genetic variation in seed and leaf size and colonizing various types of man-disturbed habitats. A growth analysis was conducted on 12 genotypes representative of three regimes of disturbance of natural habitat (trampling, weeding, and no disturbance in the course of the growing season), grown under productive conditions in order to test whether relative growth rate (RGR) varies at the intraspecific level and, if so, which growth parameters may explain its variation. RGR showed significant genotypic variation (0.355–0.452 g g^-1 day^-1), positively correlated with specific leaf area (SLA) and leaf mass ratio (LMR) and negatively correlated with unit leaf rate per unit leaf area (ULR_A). Thus, the paramount importance of leaf area ratio (LAR=SLA×LMR) in determining growth rate variation between different herbaceous species is confirmed at the intraspecific level in this species. Genotypes originating from trampled habitats had smaller seeds and smaller leaves than genotypes from habitats subject to other disturbance regimes. Additionally, they showed a lower LAR, not entirely compensated for by a higher ULR_A, which resulted in a positive allometric relationship between seed size and RGR. It is hypothesized that their lower SLA, correlated with a higher leaf dry matter content (possibly a consequence of a higher cell wall content per unit leaf area) and their lower LMR have been co-selected with small leaf size as adaptations promoting resistance to trampling stress. It is suggested that variation in cell size and/or gibberellin content might be the mediators of the correlation found between seed size, leaf size and growth parameters within this species.     

An RNA:DNA-based growth model for young-of-the-year winter flounder Pseudopleuronectes americanus (Walbaum)

A laboratory calibration experiment was conducted to determine the relationship between nucleic acid-based variables and growth rate in young-of-the-year winter flounder Pseudopleuronectes americanus . Three temperatures and three feeding levels were used to produce a variety of growth rates. Nucleic acid analyses were conducted on white muscle tissue using an ultraviolet absorption assay. RNA concentration (μg mg⁻¹ wet tissue mass) and the ratio of RNA:DNA ( R _RD) were positively correlated with a mass-based instantaneous growth coefficient ( G _M) ( r = 0·42 and 0·72, respectively). Fifty-one per cent of the variability in growth rate was explained by the simple linear regression G _M=−0·02615 + 0·00848 R _RD ( P < 0·001). This model can be used to estimate recent growth rates for early juvenile winter flounder (27–52 mm standard length) at temperatures ranging from 11 to 24° C.     

Effect of Growth Rate on the Macromolecular Composition of Prototheca zopfii, a Colorless Alga Which Divides by Multiple Fission

Prototheca zopfii, a eukaryote that divides by multiple fission, was investigated to determine how growth rate controls daughter cell number. The macromolecular composition, cell size, and number of nuclei per cell were determined in cultures during balanced growth in various media. Cellular mass, ribonucleic acid (RNA), deoxyribonucleic acid (DNA), carbohydrate, and nuclear number increased as positive linear functions of growth rate, whereas nuclear ploidy remained constant with a value of 0.098 pg of DNA/nucleus. The ratios of RNA to protein, protein to mass, and carbohydrate to mass were unaffected by growth rate, whereas the ratios of DNA to protein and RNA to DNA could be expressed as curvilinear functions of growth rate, the former negative and the latter positive. The dependency of normalized gene dosage (DNA/protein) on growth rate appeared as a distinguishing feature of multiple fission. Determination of the normalized rates of protein and RNA synthesis revealed that both increase linearly with growth rate. It is concluded that Prototheca zopfii may exist in a number of physiological states which are characterized by a unique size and macromolecular composition and which are dictated by growth rate.     

Levels of protein, RNA, DNA, glycogen and lipid during growth and development of Daphnia magna Straus (Crustacea: Cladocera)

1. Protein, RNA, DNA, glycogen and lipid content were determined in Daphnia magna on days 0, 2, 4, 6, 8 and 21 of growth and development. The composition of D. magna as percentage of reconstituted dry weight was similar to other zooplankton with the exception of DNA content, which was lower than values previously reported.
2. The relative content of protein, RNA, DNA and reconstituted dry weight changed during the 21-day growth period, and these changes were related to growth rate and total growth of D. magna . RNA:protein, RNA: reconstituted dry weight, and protein:RNA : DNA ratios were highly correlated to relative growth rate and total growth as measured by protein content or reconstituted dry weight.
3. Addition of progeny biomass to adult biomass increased correlations between biochemical ratios and absolute growth rate, but had little effect on relationships involving relative growth rate or total growth.
4. The relationship between biomolecule ratios and growth established for D. magna grown under optimal conditions was not successful in predicting growth of D. magna reared under crowded conditions.
5. These data indicate that variation in biochemical ratios among life, stages of D. magna may be used to predict growth of organisms grown under similar conditions, but may not be extended to other situations. It is suggested, however, that variation in biochemical ratios in a particular life stage of a zooplankton species may be related to the productivity for that species.     

Cytophotometric evidence of variation in genome size of desmognathine salamanders

The amount of DNA per haploid genome, the C-value, is often directly correlated with nuclear and cell volume, but inversely correlated with cell replication rate. Also, rates of cellular growth sometimes appear to be correlated with organismal developmental rates and life history patterns. Among vertebrates, salamanders exhibit the greatest variation in genome size. In the present study we have examined interspecific and intraspecific variation in blood cell DNA levels in the genus Desmognathus, which shows greater variation in life history traits than any other salamander genus. Specimens of Desmognathus quadramaculatus, D. monticola, D. ochrophaeus and D. wrighti were collected from nature at two localities in the southern Appalachian Mountains. Estimates of genome size in pg of DNA were obtained from blood smears by DNA-Feulgen cytophotometry, using erythrocyte nuclei of Xenopus laevis as an internal reference standard of 6.35 pg DNA per cell. C-values of Desmognathus are the smallest in the order Caudata. Although significant variation in DNA levels was found among the four species, the differences were small, and do not support previously proposed relationships between C-value and life-history variation.     

Growth hormone modulates the degradative capacity of muscle nucleases but not of cathepsin D in post-weaning mice

We determined whether recombinant human growth hormone (rhGH) administration might modulate the enzyme degradative capacity of the muscle lysosomal system and influence muscle growth. Muscle cathepsin D, acid RNase and DNase II activities are determined in the gastrocnemius muscle of rhGH-treated post-weaning female BALB/c mice. Linear regressions were used to analyze the relationships of each enzyme with their respective substrate. GH induced a depletion-recovery response of muscle growth through a mechanism which is similar to catch-up growth. In these conditions, cathepsin D activity decreased with age in all animals (GH: 40%; saline: 79%), showing a substantial developmental decline that could reflect changes in the rate of protein breakdown. However, the degradative capacity of cathepsin D was paradoxically unmodified in rhGH-mice compared with saline mice (according to the enzyme vs. substrate linear regression slope), in spite of the increase in enzyme activity elicited by GH. This suggests that the muscle protein breakdown is not increased by GH-treatment in post-weaning mice. The enhancement of muscle protein deposition as indicated by the augmented muscle cell size (protein:DNA ratio) of rhGH-mice (increased 178% from 25 to 50 days) vs. saline, can be attributed to a higher muscle K(RNA). In contrast, acid RNase and DNase II activities directly participate in muscle RNA and DNA degradation. Both nucleases were inhibited by GH treatment (a decrease of 48% and 63%, respectively, vs. saline at 50 days). The decrease in RNase activity suggests an inverse relation between the rate of protein synthesis (high) and acid RNase activity (low), leading to spare muscle RNA for synthesizing protein during catch-up growth. Also, low DNase II activity could contribute to inhibiting of muscle DNA degradation, facilitating muscle growth. Thus, GH seems to act as a direct modulator of the degradative capacity of skeletal muscle nucleases but not of cathepsin D, influencing DNA and RNA degradation during the depletion-recovery response to GH of gastrocnemius muscle in female post-weaning mice.     

An examination of subspecific differences in the merus of the fifth walking leg of the amphipod Gammarus duebeni Lilljeborg

Stock SL Pinkster (1970) erected two subspecies of Gammarus duebeni primarily on the basis of a difference in the relative dimensions of the merus on the fifth walking leg. The diagnostic feature was given as the ratio of merus length/width, with ratio < 2 in G. duebeni duebeni and ratio > 2 in G. duebeni celticus. It is shown here that the ratio varies with the size of the animal, and this particular ratio is therefore not valid as a taxonomic character. Regressions of log merus width on log merus length were made on large samples of G. duebeni assumed to belong to subspecies celticus and duebeni respectively. The regressions were significantly diiferent and were used to predict that the ratio log merus width/log merus length is relatively constant in both subspecies. Diagnostic values for this ratio were 0.71–0.73 in celticus and 0.74–0.77 in duebeni. The ratio was also determined in small samples of G. duebeni from other localities in western Britain. The morphological difference which characterizes celticus and duebeni was not associated with habitat salinity or with previously determined physiological characteristics. It may be an instance of cHnal variation reinforced by geographical isolation. Regressions of merus length against cephalic length suggest that the relative growth rates of the merus may also differ in the two subspecies.     

Biological stoichiometry of growth in Drosophila melanogaster

We examined the relationship between growth rate, C:N:P stoichiometry, and nucleic acid content in Drosophila melanogaster. The "Growth Rate Hypothesis" predicts that N and P contents per unit body mass will be high during ontogenetic stages characterized by rapid growth, reflecting the large requirement for P-rich ribosomal RNA during these periods. The ratio of RNA:DNA also is predicted to change with changes in growth rate. Growth is rapid in early D. melanogaster larvae, slowing considerably just prior to pupation. As predicted, a positive relationship was found between growth rate and N and P content, but not C. Thus, body C:P and N:P ratios declined with increasing growth rate. The relationship between RNA content and growth rate also was positive. Additionally, the fraction of total body P contributed by ribosomal RNA increased with increasing growth rate.     

Muscle cell growth in protein deficient rats following administration of sheep red blood cells.

In order to observe the effects of sheep red blood cells (SRBC) administration on the muscle cell growth in malnourished states, adult male Wistar rats (135 +/- 10 g 10 animals per group) subjected during 30 days to 1% and 10% protein diets, were injected (i.v.) either 15.5 x 10(8) sheep red blood cells or 0.5 ml saline/100 g b.w. after 20 days of experiment. On the 10th day after injection the animals were sacrificed and the gastrocnemius muscle was removed, weighed and homogenized. The supernatant fluids were used to evaluate muscle protein, DNA and RNA rates and acid DNase activity. All parameters were depleted in malnourished rats, indicating a muscle cellular atrophy as well as a decrease in muscle protein synthesis per DNA-unit. Muscle hyperplasia and hypertrophy were found in antigenically stimulated rats fed 10% protein against non-stimulated control. In contrast, muscle growth in protein-deficient rats SRBC-treated was unmodified when compared to non-stimulated malnourished muscle, although RNA functionality seems to be enhanced (RNA/DNA). These data suggest that a redistribution of essential nutrients occurred for muscle growth adaptation rather than for defensive mechanism.     

Allocation of resources in an European cyprinid during maturation period as measured by nucleic acids

Changes in the nucleic acid levels of different tissues during a regular gonadal maturation were used to investigate the sex-related size differences in Iberian barbel, Barbus sclateri. Gonadal DNA concentration was associated with gonadal development in both sexes. There was a decline in DNA when ovaries were ripe. In contrast, the maximum size of the testes was related with highest gonadal DNA concentrations. Gonadal growth was not related with liver RNA : DNA ratios of male, while it was with female ratios. White muscle DNA concentrations indicate that somatic cell volume decreased during gonadal growth in both sexes. This suggests the translocation of several elements toward the gonad. Moreover, during gonadal maturation period adult barbel showed no change in their somatic growth. However, males apparently were in poorer metabolic condition (lower muscle RNA : DNA ratio) than females. Females may have allocated additional energy to self-maintenance rather than to breeding effort and it might influenced the cumulative annual growth. One might reasonably assume that there is a trade-off between investment in current versus future reproductive success in female. This result was not seen in males.     

The effect of protein depletion and repletion on muscle-protein turnover in the chick.

Rates of growth and protein turnover in the breast muscle of young chicks were measured in order to assess the roles of protein synthesis and degradation in the regulation of muscle mass. Rates of protein synthesis were measured in vivo by injecting a massive dose of L-[1-14C]valine, and rates of protein degradation were estimated as the difference between the synthesis rate and the growth rate of muscle protein. In chicks fed on a control diet for up to 7 weeks of age, the fractional rate of synthesis decreased from 1 to 2 weeks of age and then changed insignificantly from 2 to 7 weeks of age, whereas DNA activity was constant for 1 to 7 weeks. When 4-week-old chicks were fed on a protein-free diet for 17 days, the total amount of breast-muscle protein synthesized and degraded per day and the amount of protein synthesized per unit of DNA decreased. Protein was lost owing to a greater decrease in the rate of protein synthesis, as a result of the loss of RNA and a lowered RNA activity. When depleted chicks were re-fed the control diet, rapid growth was achieved by a doubling of the fractional synthesis rate by 2 days. Initially, this was a result of increased RNA activity; by 5 days, the RNA/DNA ratio also increased. There was no evidence of a decrease in the fractional degradation rate during re-feeding. These results indicate that dietary-protein depletion and repletion cause changes in breast-muscle protein mass primarily through changes in the rate of protein synthesis.     

Myofibrillar protein synthesis in myostatin-deficient mice

Either increased protein synthesis or prolonged protein half-life is necessary to support the excessive muscle growth and maintenance of enlarged muscles in myostatin-deficient mice. This issue was addressed by determining in vivo rates of myofibrillar protein synthesis in mice with constitutive myostatin deficiency (Mstn(DeltaE3/DeltaE3)) or normal myostatin expression (Mstn(+/+)) by measuring tracer incorporation after a systemic flooding dose of l-[ring-(2)H(5)]phenylalanine. At 5-6 wk of age, Mstn(DeltaE3/DeltaE3) mice had increased muscle mass (40%), fractional rates of myofibrillar synthesis (14%), and protein synthesis per whole muscle (60%) relative to Mstn(+/+) mice. With maturation, fractional rates of synthesis declined >50% in parallel with decreased DNA and RNA [total, 28S rRNA, and poly(A) RNA] concentrations in muscle. At 6 mo of age, Mstn(DeltaE3/DeltaE3) mice had even greater increases in muscle mass (90%) and myofibrillar synthesis per muscle (85%) relative to Mstn(+/+) mice, but the fractional rate of synthesis was normal. Estimated myofibrillar protein half-life was not affected by myostatin deficiency. Muscle DNA concentrations were reduced in both young and mature Mstn(DeltaE3/DeltaE3) mice, whereas RNA concentrations were normal, so the ratio of RNA to DNA was approximately 30% greater than normal in Mstn(DeltaE3/DeltaE3) mice. Thus the increased protein synthesis and RNA content per muscle in myostatin-deficient mice cannot be explained entirely by an increased number of myonuclei.     

Cytophotometric evidence of variation in genome size of desmognathine salamanders

Summary The amount of DNA per haploid genome, the C-value, is often directly correlated with nuclear and cell volume, but inversely correlated with cell replication rate. Also, rates of cellular growth sometimes appear to be correlated with organismal developmental rates and life history patterns. Among vertebrates, salamanders exhibit the greatest variation in genome size. In the present study we have examined interspecific and intraspecific variation in blood cell DNA levels in the genus Desmognathus, which shows greater variation in life history traits than any other salamander genus. Specimens of Desmognathus quadramaculatus, D. Monticola, D. ochrophaeus and D. wrighti were collected from nature at two localities in the southern Appalachian Mountains. Estimates of genome size in pg of DNA were obtained from blood smears by DNA-Feulgen cytophotometry, using erythrocyte nuclei of Xenopus laevis as an internal reference standard of 6.35 pg DNA per cell. C-values of Desmognathus are the smallest in the order Caudata. Although significant variation in DNA levels was found among the four species, the differences were small, and do not support previously proposed relationships between C-value and life-history variation.     

Differential chemical allocation and plant adaptation: A Py-MS Study of 24 species differing in relative growth rate

The chemical composition of leaves of 24 wild species differing in potential relative growth rate (RGR) was analysed by pyrolysis-mass spectrometry. The variation in RGR significantly correlated with differences in chemical composition: slow-growing species were richer in glucan-based polysaccharides and in C16:0 fatty acid, whereas fast growing ones contained more protein (other than those incorporated in cell walls) and chlorophyll, sterols and diglycerides. Other, apparently significant correlations, e.g. for pentose-based hemicellulose and for guaiacyl lignin appeared solely based on a group separation between mono- and dicotyledonous species.Considering the eleven monocotyledonous and thirteen dicotyledonous species separately, correlations were found in addition to the previously mentioned general ones. Within the group of the monocotyledons the low-RGR species were significantly enriched in pentose-based hemicellulose, ferulic acid and (hydroxy)proline-rich cell wall protein and nearly significant in guaiacyl and syringyl lignin, fast-growing species contained more potassium. Within the group of the dicotyledons slow-growing species were enriched in triterpenes and aliphatic wax esters.In general, the monocotyledons contained more cell wall material such as pentose-based hemicellulose, ferulic acid, glucans (including cellulose) and guaiacyl-lignin, and also more aliphatic wax esters, than the dicotyledons. The dicotyledons, on the other hand, contained somewhat more protein than the grasses.Per unit weight of cell wall, the amount of (hydroxy)proline- rich protein in low-RGR species was comparatively low. A higher investment of cell wall proteins to explain the low rate of photosynthesis per unit of leaf nitrogen of slow-growing species as suggested by Lambers and Poorter (1992), therefore, seems unlikely.Abbreviations HPRP (hydroxy)proline-rich protein(s) - LAR leaf area ratio - LWR leaf weight ratio - MVA multivariate analysis - NAR net assimilation rate - PC principal component - PNUE photosynthetic nitrogen use efficiency - PyGCMS pyrolysis-gas chromatography-mass spectrometry - PyMS pyrolysis mass spectrometry - RGR relative growth rate - SLA specific leaf area - SLM specific leaf mass     

Chromatin-bound DNA-dependent RNA polymerase in developing pea cotyledons

Summary The pattern of cotyledon development in three varieties of Pisum sativum has been defined in terms of cell number, DNA and RNA content and chromatin, bound RNA polymerase activity. Variation was observed in the relative periods of growth by cell division and cell expansion between the three varieties. The mean DNA content per cotyledon cell during growth by cell expansion increased to approximately 50C in one variety, 30C in the second variety and 15C in the third variety. The pattern of chromatin-bound RNA polymerase activity during development suggested that some of the DNA above the 2C level may contribute to RNA synthesis in two of the three varieties studied. In the third variety the RNA polymerase activity decreases throughout the phase of increase in DNA per cell. The chromatin-bound RNA polymerase activity per cell was correlated with the rate of RNA increase per cell.     

Estimating the Growth Rate of Slowly Growing Marine Bacteria from RNA Content

In past studies of enteric bacteria such as Escherichia coli, various measures of cellular RNA content have been shown to be strongly correlated with growth rate. We examined this correlation for four marine bacterial isolates. Isolates were grown in chemostats at four or five dilution rates, yielding growth rates that spanned the range typically determined for marine bacterial communities in nature (μ = 0.01 to 0.25 h^-1). All measures of RNA content (RNA cell^-1, RNA:biovolume ratio, RNA:DNA ratio, RNA:DNA:biovolume ratio) were significantly different among isolates. Normalizing RNA content to cell volume substantially reduced, but did not eliminate, these differences. On average, the correlation between μ and the RNA:DNA ratio accounted for 94% of variance when isolates were considered individually. For data pooled across isolates (analogous to an average measurement for a community), the ratio of RNA:DNA μm^-3 (cell volume) accounted for nearly half of variance in μ (r² = 0.47). The maximum RNA:DNA ratio for each isolate was extrapolated from regressions. The regression of (RNA:DNA)/(RNA:DNA)_max on μ was highly significant (r² = 0.76 for data pooled across four isolates) and virtually identical for three of the four isolates, perhaps reflecting an underlying common relationship between RNA content and growth rate. The dissimilar isolate was the only one derived from sediment. Cellular RNA content is likely to be a useful predictor of growth rate for slowly growing marine bacteria but in practice may be most successful when applied at the level of individual species.     

Interspecific size and number variation in pollen grains and seeds

An interspecific correlation between pollen grain size and seed size is demonstrated by means of the phylogenetic regression, which allows for phylogenetic bias. The correlation was not explained by plant size, mass of DNA per cell, style length or breeding system, although the first three of these factors all correlated with both pollen size and seed size. Two interpretations, involving pollen competition and flower size, are discussed. There is also an interspecific correlation between pollen grain number per flower and ovule number per flower. Some consequences of these correlations for the interpretation of pollen-ovule ratios and sex allocation strategies are considered.     

Coordination of macromolecular synthesis in the slime mould Physarum polycephalum.

Microplasmodia of P. polycephalum were grown either in batch culture, in both complex and defined media to give a 3-4 fold variation in growth rate, or in a chemostate. The protein/DNA ratio of batch cultures was almost invariant, whilst the RNA/DNA ratio increased as a non-linear function of growth rate. The amount of ribosomal RNA, expressed as a fraction of total RNA, showed little variation and this was also true for the proportion of ribosomes found in polyribosomes. Calculation of the rate of protein synthesis per ribosome shows that this parameter increases by approximately 50% over the range of growth rates studied, although it should be emphasized that the effect of protein turnover has not yet been taken into account. Enrichment of batch cultures growing in a defined medium produced an increase in the rate of RNA synthesis. Data obtained with chemostat cultures differed in several respects from those described above for batch cultures, especially at low growth rates, and are discussed in relation to the early stages of differentiation of microplasmodia to spherules.     

Reducing plasma HIV RNA improves muscle amino acid metabolism

We reported (Yarasheski KE, Zachwieja JJ, Gischler J, Crowley J, Horgan MM, and Powderly WG. Am J Physiol Endocrinol Metab 275: E577-E583, 1998) that AIDS muscle wasting was associated with an inappropriately low rate of muscle protein synthesis and an elevated glutamine rate of appearance (Ra Gln). We hypothesized that high plasma HIV RNA caused dysregulation of muscle amino acid metabolism. We determined whether a reduction in HIV RNA (> or =1 log) increased muscle protein synthesis rate and reduced R(a) Gln and muscle proteasome activity in 10 men and 1 woman (22-57 yr, 60-108 kg, 17-33 kg muscle) with advanced HIV (CD4 = 0-311 cells/microl; HIV RNA = 10-375 x 10(3) copies/ml). We utilized stable isotope tracer methodologies ([13C]Leu and [15N]Gln) to measure the fractional rate of mixed muscle protein synthesis and plasma Ra Gln in these subjects before and 4 mo after initiating their first or a salvage antiretroviral therapy regimen. After treatment, median CD4 increased (98 vs. 139 cells/microl, P = 0.009) and median HIV RNA was reduced (155,828 vs. 100 copies/ml, P = 0.003). Mixed muscle protein synthesis rate increased (0.062 +/- 0.005 vs. 0.078 +/- 0.006%/h, P = 0.01), Ra Gln decreased (387 +/- 33 vs. 323 +/- 15 micromol.kg fat-free mass(-1).h(-1), P = 0.04), and muscle proteasome chymotrypsin-like catalytic activity was reduced 14% (P = 0.03). Muscle mass was only modestly increased (1 kg, P = not significant). We estimated that, for each 10,000 copies/ml reduction in HIV RNA, approximately 3 g of additional muscle protein are synthesized per day. These findings suggest that reducing HIV RNA increases muscle protein synthesis and reduces muscle proteolysis, but muscle protein synthesis relative to whole body protein synthesis rate is not restored to normal, so muscle mass is not substantially increased.