The effect of growth and starvation on the lysis of the ruminal cellulolytic bacterium Fibrobacter succinogenes.

Growing cultures of Fibrobacter succinogenes assimilated more ammonia than could be accounted for by cellular protein, RNA, or DNA and released large amounts of nonammonia nitrogen. The difference between net and true growth was most dramatic at low dilution rates, but mathematical derivations indicated that the lysis rate was a growth rate-independent function. The lysis rate was sevenfold greater than the true maintenance rate (0.07 h-1 versus 0.01 h-1). Because slowly growing cells had as much proton motive force and ATP as fast-growing cells, lysis was not a starvation response per se. Stationary-phase cells had a lysis rate that was 10-fold less than that of growing cells. Rapidly growing cells were not susceptible to phenylmethylsulfonyl fluoride, but phenylmethylsulfonyl fluoride increased the lysis rate of the cultures when they reached the stationary phase. This latter result indicated that autolysins of stationary-phase cells were being inactivated by a serine proteinase. When growing cells were treated with the glycolytic inhibitor iodoacetate, the proteinase-dependent transition to the stationary phase was circumvented, and the rate of lysis could be increased by as much as 50-fold.     

Regulation of DNA chain elongation in SV3T3 cells in relation to growth rate.

Regulation of DNA synthesis was investigated in SV40 transformed 3T3 cells exhibiting variable growth rates and residence times in S phase when cultured in the presence of different serum concentrations. Pulse-labeled DNA was chased into large molecular weight material in vivo much more slowly in slowly growing cells than in cells growing at the normal rate. Consistent with this, the joining of short (less than 10 S) chains to form long (greater than 10 S) chains by whole cell lysate system in vitro was greatly impaired in slowly growing cells compared to controls. Thus the lengthening of S phase in SV3T3 cells growing slowly in low serum is reflected in a reduced rate of DNA chain elongation. The presence of cycloheximide during chase in vivo reduced the rate of conversion of pulse-labeled molecules into large molecular weight DNA in both slowly growing and normally growing cells.     

Parallel changes in protein synthesis and messenger RNA content in growing and resting epithelial cells of Xenopus laevis

The regulation of cell growth can be achieved at many levels but ultimately the regulatory factors must alter protein synthesis since growing cells always exhibit an increased rate of protein synthesis compared to resting cells. Some studies using growing and nongrowing mammalian cells have shown that the rate of protein synthesis compared to resting cells. Some studies using growing and nongrowing mammalian cells have shown that the rate of protein synthesis is directly dependent on mRNA content. Other studies have shown that growing and resting cells have similar amounts of mRNA and that protein synthesis is regulated by the proportion of mRNA in polysomes. We have analyzed mRNA content in growing and resting epithelial cells of Xenopus laevis. Quantitation of poly(A)⁺ mRNA by uniform labeling with ³H-uridine and by ³H-poly(U)hybridization demonstrated a direct relationship between mRNA content and the relative rate of protein synthesis in growing and resting cells. Likewise, after serum stimulation of resting cells the increase in mRNA content closely paralleled the increase in protein synthesis. Our results suggest that control of protein synthesis in growing and nongrowing cells is exerted before the translational level.     

Influence of growth rate on protein synthesis and distribution of ribosomes in HeLa cells.

HeLa cells have been grown at different rates in steady-state continuous and semi-continuous culture. Slowly growing cells contain more protein and less RNA than rapidly growing cells, but appear to synthesize protein by less efficient use of the available RNA. The rate of RNA accumulation increases rapidly with increasing growth rate and rapidly growing cells contain more ribosomal subunits, and more and larger polysomes, but have fewer monoribosomes than slowly growing cells.     

The influence of metabolic rate on otolith increment width in Atlantic salmon parr, Salmo salar L.

The influence of metabolic rate on otolith accretion in Atlantic salmon parr was investigated by comparing oxygen consumption rate and increment width in fast and slow growing individuals. Increment width was found to be positively correlated to mean daily oxygen consumption in both fast growing (S1) and slow growing (S2) parr. The results support previous suggestions that a process related to metabolic rate, rather than somatic growth, governs the rate of otolith accretion.     

Nutritional regulation of degradation of aspartate transcarbamylase and of bulk protein in exponentially growing Bacillus subtilis cells.

The rate of degradation of aspartate transcarbamylase in exponentially growing Bacillus subtilis cells was determined by measurement of enzyme activity after the addition of uridine to repress further enzyme synthesis and by specific immunoprecipitation of the enzyme from cells grown in the presence of [3H]leucine. Aspartate transcarbamylase was degraded with a half-life of about 1.5 h in cells growing on a glucose-salts medium with NH4+ ions as the sole source of nitrogen. Replacement of NH4+ in this medium with a combination of the amino acids aspartate, glutamate, isoleucine, proline, and threonine reduced the degradation rate to an undetectable level. Various other amino acids and amino acid mixtures had smaller effects on the rate of degradation. The carbon source also influenced the degradation rate, but to a smaller extent than the nitrogen source. The effects of these nutritional variables on the rate of bulk protein turnover in growing cells were generally similar to their effects on degradation of aspartate transcarbamylase. Since the degradation of aspartate transcarbamylase has been shown to be 10 to 20 times faster than bulk protein turnover, the results suggest that a substantial portion of protein turnover in growing cells represents regulable, rapid degradation of a number of normal proteins, of which aspartate transcarbamylase is an example.     

Direct measurement of actin polymerization rate constants by electron microscopy of actin filaments nucleated by isolated microvillus cores

We used actin filament bundles isolated from intestinal brush-border microvilli to nucleate the polymerization of pure muscle actin monomers into filaments. Growth rates were determined by electron microscopy by measuring the change in the length of the filaments as a function of time. The linear dependence of the growth rates on the actin monomer concentration provided the rate constants for monomer association and dissociation at the two ends of the growing filament. The rapidly growing ("barbed") end has higher association and dissociation rate constants than the slowly growing ("pointed") end. The values of these rate constants differ in 20 mM KCl compared with 75 mM KCl, 5 mM MgSO4. 2 microM cytochalasin B blocks growth entirely at the barbed end, apparently by reducing both association and dissociation rate constants to near zero, but inhibits growth at the pointed end to only a small extent.     

Phycomyces: distribution of growth velocities in the growing zone

Distribution of growth velocities in the growing zone of stage IVb Phycomyces sporangiophores was measured by photographing the growing zone after dusting it with starch grains. When the entire growing zone is fully dark-adapted to red light and then subjected to a saturating white light stimulus, the entire growing zone increases in growth rate. When the growing zone is partially light-adapted, again the entire growing zone responds when subjected to a saturating white light stimulus but to a lesser degree than the fully dark-adapted sporangiophore. Phototropic mutants of class 1 and class 2 show a distribution of growth in the growing zone similar to wild type sporangiophores both during steady-state growth and during light-stimulated growth.     

中国的城市化及其发展趋势

中国的城市化有３个特点：（１）不匀速,城市数目和城市人口长期增长缓慢,近十年来急剧加快;（２）中小城市发展快,而大城市和特大城市增长慢。（３）特大城市和大城市主要集中于东部沿海地区,中国城市化引起的生态问题有：环境污染,供水紧张,地面沉降等,新中国成立以来,虽然政府采取了多种措施。改善城市环境也收到了一定效果,但目前在从计划经济向市场经济转变的过渡期间城市化高速发帐题仍然十分严重。迫切需要进一步加     

Characteristics of the polar assembly and disassembly of microtubules observed in vitro by darkfield light microscopy

We describe here the continuous observations of the polymerization of individual microtubules in vitro by darkfield microscopy. In homogeneous preparations we verify that polymerization can occur onto both ends of microtubules. The assembly of microtubules is polar, with one end growing at three times the rate of the other. The differential rate of elongation can be used to determine the polarity of growth off cellular nucleating centers. We show that the microtubules grow off the proximal end of ciliary axonemes at a growth rate equal to that of the slow growing end of free microtubules, while growth off the distal end proceeds at the same rate as the fast growing end. Applying this technique to microtubule growth from metaphase chromosomes isolated from HeLa and CHO cells, we demonstrate that chromosomes initiate polymerization with the fast growing end facing away from the chromosome nucleation site. The opposite ends of free microtubules show different sensitivities to microtubule depolymerizing agents such as low temperature, Ca++ or colchicine as measured directly by darkfield microscopy. The differing rates of assembly and disassembly of each end of a microtubule suggest that a difference in polarity of growth off nucleating sites could serve as one basis for regulating the polymerization of different groups of microtubules in the same cell.     

Effect of pre-pubertal growth rate of Sohagi ram lambs on some physiological parameters and sexual behavioral patterns at puberty

Thirty healthy Sohagi ram lambs with an average age of 188.6±7.3 days were used to study the effect of pre-pubertal growth rate on some physiological parameters and sexual behavioral patterns at puberty. Ram lambs were divided into three groups (10 animals per each group) according to the previous growth rate until 6 months of age. Groups were marked as fast, medium and slow growing. Animal groups were housed in closed barns with access to an open area. Results showed that age and weight of ram lambs at puberty were significantly affected (P<0.05) by the pre-pubertal growth rate. Ram lambs in the fast growing group were reached to onset puberty firstly at 272.6 days with body weight (BW) 37.1 kg on average then ram lambs in medium group (284.8 days with BW 32.7 kg), while ram lambs in slow growing group were the last (314.1 days with BW 32.5 kg). Blood‎ testosterone‎ concentration at puberty was not significantly different among growing groups (1.494± 0.03 ng/ml on average, ranged from 1.287 to 1.902 ng/ml). Testes measurements from 6 months of age until puberty show that ram lambs in fast growing group had the highest values of testes length, circumference and volume followed by those in medium and slow growing group. Sexual behavioral observation showed that flehmen and mounting behavior were significantly higher for ram lambs in fast growing group (5.63 and 6.75 number/12h) than slow growing group (4.25 and 5.38 number/12h) while in medium growing group were intermediate (4.88 and 5.88 number/12h). From these findings, could be concluded that age, weight and sexual behavioral patterns of Sohagi ram lambs at puberty were affected by pre-pubertal growth rate, and the breeders should strive to achieve good growth rates for their lambs before puberty which led to improving reproductive performance.     

Errors in the Measurement of Root Pressure and Exudation Volume Flow Rate Caused by Damage during the Transfer of Unsupported Roots between Solutions

Plants of Zea mays were grown with their roots confined to growing tubes, consisting of cylindrical or spherical glass tubes fitted at the bottom with a stopcock. Nutrient solution was circulated past the roots, and when a plant was 21 to 25 days old, the stopcock was closed, the root excised from the plant and connected to an apparatus which measured root pressure and exudation volume flow rate. The stopcock was opened and solution was again circulated through the growing tube without dropping the level of the liquid bathing the root in the process. Measurements of pressure and flow rate were made continuously during a period in which the solution was replaced, first by draining and refilling the tube in situ, and second by replacing the growing tube with a beaker of solution. Both these manipulations caused at least temporary and frequently permanent drops in root pressure and flow rate. Plants were also grown in cylindrical tubes with a support medium of either glass beads or Raschig rings which filled the growing tubes. It is shown that the solution bathing these roots could be repeatedly replaced by draining and refilling with no visible effect on the measurements. It is recommended, therefore, that in future, support be provided for the roots of all experimental plants grown by solution culture.     

Organization and dynamics of growing microtubule plus ends during early mitosis

A stable cell line expressing EB1-green fluorescent protein was used to image growing microtubule plus ends at the G(2)/M transition. By late prophase growing ends no longer extend to the cell periphery and were not uniformly distributed around each centrosome. Growing ends were much more abundant in the area surrounding the nuclear envelope, and microtubules growing around the nucleus were 1.5 fold longer than those growing in the opposite direction. The growth of longer ends toward the nucleus did not result from a localized faster growth rate, because this rate was approximately 11 microm/min in all directions from the centrosome. Rather, microtubule ends growing toward the nucleus seemed stabilized by dynein/dynactin associated with the nuclear envelope. Injection of p50 into late prophase cells removed dynein from the nuclear envelope, reduced the density of growing ends near the nuclear envelope and resulted in a uniform distribution of growing ends from each centrosome. We suggest that the cell cycle-dependent binding of dynein/dynactin to the nuclear envelope locally stabilizes growing microtubules. Both dynein and microtubules would then be in a position to participate in nuclear envelope breakdown, as described in recent studies.     

镇江北固山湿地虉草季节生长动态研究

在虉草(Phalaris arundinacea)整个生长季中,定期测量其株长、鞘高、叶龄及生物量等生长指标,分析和研究虉草的季节生长动态。结果显示:虉草各指标的季节生长动态基本一致,皆呈“S”型曲线,且均以三次方程拟合效果最佳。绝对生长速率和相对生长速率基本同步,呈单峰型曲线,但在负增长出现的时间上稍有差异。各生长指标累积绝对、相对生长速率的季节动态也呈“S”型曲线,同样三次方程拟合效果最佳。     

Interrelation Between Growth Rate of Individual Potato (Solanum tuberosum L.) Tubers and Their Cell Number

In potato plants fast and slow growing tubers develop on thesame plant. A hypothetical causality between tuber growth rateand tuber cell number was investigated by determining the tubercell number with the aid of an automatic counting procedure.Our data show a close correlation between tuber size and cellnumber over the whole range of tuber volumes considered (3–28cm³). If the influence of tuber size on cell number is eliminatedby means of a partial correlation analysis, the cell numberof the entire tuber is not significantly correlated with itsgrowth rate. An exclusive consideration of the smaller cells(10–30 µm) in the apical tuber region, where thecell division rate in potato tubers is highest, reveals a loosebut significant partial correlation to tuber growth rate (r= 0.383, P < 0.05). The growth rate of the slow growing tubers of any potato plantmay be enhanced by removing the fast growing tubers. In thefirst few days this enhanced growth rate is not due to a stimulationof cell division rate, but rather due to cell expansion. Potato, Solanum tuberosum L., tuber growth rate, tuber cell number     

Effects of water stress on leaf growth in tall fescue, Italian ryegrass and their hybrid: rheological properties of expansion zones of leaves, measured on growing and killed tissue

In Expt 1, plants of tall fescue (Festuca arundinacea Schreb.), Italian ryegrass (Lolium multiflorum Lam.) and their F1 hybrid were grown in soil-based compost in a controlled environment, and subjected to full or partial irrigation for 20 d. In Expt 2, plants of the parent species were grown in nutrient solution in the same environment and subjected to osmotic stress (0.76 MPa) for 2 d. In both experiments, distribution of growth in the leaf growing zone (at the base of the growing leaf) was determined, and elastic and plastic compliances were measured on methanol-killed samples of growing zone and of mature lamina using an extensiometer. In Expt 2 plastic compliance coefficient of extension, extensibility, and hydraulic conductance were calculated from changes in leaf extension rate occasioned by imposing linear stress. 'Plastic and elastic compliances of growing zones were 10-20 times greater than those of mature laminae. In both species, drought reduced (a) leaf extension rate, (b) the length of the growing zone, the height of maximum growth, (d) the plastic compliance of whole bases (Expt 1), and (e) hydraulic conductance. The elastic compliance of whole leaf bases was unaffected by drought, but when expressed per unit length of growing zone was increased by drought. Killing with methanol reduced the plastic compliance of leaf bases in control plants, but not in droughted plants.F. arundinacea differed from L. multiflorum in having (a) a lower leaf extension rate (although drought reduced extension by the same proportion in both species), (b) a longer growing zone in droughted plants in Expt 2, a lower elastic and plastic compliance of whole killed leaf bases and laminae, (d) slightly higher plastic compliance in attached growing leaves, and (e) lower plastic compliance per unit length of growing zone in attached leaves. The hybrid was generally intermediate between the parents. the results are discussed in relation to methodology and to crop improvement.Key words: Extensibility, extension coefficient, hydraulic conductance, elastic compliance, plastic compliance, leaf growth, leaf extension rate.      

Effects of fire frequency and season on resprouting of woody plants in southeastern US pine-grassland communities

Past studies suggest that rates of woody plant resprouting following a “topkilling” disturbance relate to timing of disturbance because of temporal patterns of below-ground carbohydrate storage. Accordingly, we hypothesized that fire-return interval (1 or 2 years) and season of burn (late dormant or early growing season) would influence the change in resprout growth rate from one fire-free interval to the next (Δ growth rate) for broadleaf woody plants in a pine-grassland in Georgia, USA. Resprout growth rate during one fire-free interval strongly predicted growth rate during the following fire-free interval, presumably reflecting root biomass. Length of fire-free interval did not have a significant effect on mean Δ growth rate. Plants burned in the late dormant season (February–March) had a greater positive Δ growth rate than those burned in the early growing season (April–June), consistent with the presumption that root carbohydrates are depleted and thus limiting during spring growth. Plants with resprout growth rates above a certain level had zero or negative Δ growth rates, indicating an equilibrium of maximum resprout size under a given fire-return interval. This equilibrium, as well as relatively reduced resprout growth rate following growing season fires, provide insight into how historic lightning-initiated fires in the early growing season limited woody plant dominance and maintained the herb-dominated structure of pine-grassland communities. Results also indicate tradeoffs between applying prescribed fire at 1- versus 2-year intervals and in the dormant versus growing seasons with the goal of limiting woody vegetation.     

A whole-plant analysis of the dynamics of expansion of individual leaves of two sunflower hybrids

Common features in the time-course of expansion of leaves which considerably differed in final area, due to phytomer position, growing conditions and genotype, were identified. Leaf development consisted of two phases of exponential growth, followed by a third phase of continuous decrease of the relative expansion rate. The rate and the duration of the first exponential phase were common to all phytomers, growing conditions and genotypes. Leaves differed in the rate and the duration of the second exponential phase. The decrease of the relative expansion rate during the third phase depended on neither genotype nor growing conditions. It was phytomer-dependent and was deduced from the rate of the second phase via a parameter common to all cases studied. Differences in final leaf area among growing conditions were linked to different expansion rates during the second exponential phase. The duration of the phases at any given phytomer position was the same for the two hybrids in different growing conditions. The dates of developmental events (initiation, end of the two exponential phases, full expansion), and the rate of the second exponential phase, were related to phytomer position, defining a strict pattern of leaf development at the whole plant level. Using this framework simplified the analysis of the response of leaf expansion to genotype and environment.     

Effects of developmental and growth history on metamorphosis in the gray treefrog, Hyla versicolor (Amphibia, Anura)

In ecological models, the timing of amphibian metamorphosis is dependent upon rate of larval growth, e.g., tadpoles that experience a decrease in growth rate can initiate metamorphosis early. Recent authors have suggested that this plasticity may be lost at some point during the larval period. We tested this hypothesis by exposing groups of tadpoles of the gray treefrog, Hyla versicolor, to different growth schedules. In endocrine models, metamorphosis is dependent on thyroxine levels and thyroxine is antagonized by prolactin (amphibian larval growth hormone), consistent with the idea that a rapidly growing tadpole can delay metamorphosis. Thus, we also manipulated the rate of development by supplementing or maintaining natural thyroxine levels for half of the tadpoles in each growth treatment. All tadpoles that received thyroxine supplements metamorphosed at the same time regardless of growth history. They also metamorphosed earlier than tadpoles not treated with thyroxine. Tadpoles not given thyroxine supplements metamorphosed at different times: those growing rapidly during day 15-34 metamorphosed earlier than tadpoles growing slowly. Growth rate before day 15 and after day 34 had no effect on metamorphic timing. The difference in larval period between these rapidly growing tadpoles and their sisters given thyroxine treatments was less than the same comparison for tadpoles that grew slowly during the same period. This apparent prolactin/thyroxine antagonism did not exist after day 34. These results are consistent with the hypothesis of a loss of plasticity in metamorphic timing.