The nutritional ecology of larvae of Alsophila pometaria and Anisota senatoria feeding on early- and late-season oak foliage

The larvae of Alsophila pometaria (Harr.), feeding on the young foliage of oak, has a higher relative growth rate (RGR) and relative nitrogen accumulation rate (RNAR) than the larvae of Anisota senatoria (J. E. Smith), feeding on the mature foliage of oak. Although the young oak foliage is more efficiently digested by A. pometaria (higher AD's), it is not more efficiently assimilated and used for growth (no difference in ECI's). Thus, the higher growth rate of A. pometaria is due entirely to a higher consumption rate (RCR and RNCR). Young foliage is significantly higher in nitrogen and water than mature foliage, but phenol and tannin levels are comparable in young and old foliage. A. pometaria consumes the foliage of different oak species at the same rate, independent of nitrogen content, while A. senatoria increases its consumption rate in response to decreased nitrogen levels. As a result, the growth rate of A. pometaria is directly related to leaf nitrogen content, while the growth rate of A. senatoria is independent of leaf nitrogen. The two species of insects have digestive systems that are very similar biochemically, and that are well-designed for effective protein digestion. Tannins and phenols do not influence the nutrional indices of either species. We suggest that the major benefit of spring feeding is the availability of succulent, high-nitrogen foliage, and not the avoidance of high-tannin foliage. The spring feeder appears to have a feeding strategy that favors rapid growth at the expense of efficiency, while the late summer feeder has a strategy that favors efficiency over rate.

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Résumé Alimentées sur feuillage jeune de chêne, les chenilles d'Alsophila pometaria avaient un taux relatif de croissance (RGR) et un taux relatif d'accumulation d'azote (RNAR) plus élevés que les chenilles d'Anisota senatoria alimentées sur feuillage mûr de chêne. Bien que le jeune feuillage soit plus efficacement digéré par A. pometaria (AD plus élevé), il n'est pas assimilé et utilisé pour la croissance avec de meilleurs rendements (les ECI ne sont pas différents). Ainsi le taux de croissance plus élevé d'A. pometaria est dû entièrement à un taux de consommation plus important (RCR et RNCR). Le feuillage jeune est significativement plus riche en azote et en eau que le feuillage mûr, mais les niveaux de phénol et de tanins sont les mêmes. A pometaria consomme les feuilles de différentes espèces de chênes au même taux, indépendamment de la teneur en azote, tandis que A. senatoria accroît sa consommation en réponse à une diminution de la teneur en azote. Il en résulte que le taux de croissance d'A. pometaria dépend directement de la teneur en azote des feuilles, tandis que celui d'A. senatoria en est indépendant. Les systèmes digestifs des deux insectes sont biochimiquement semblables et sont efficaces pour la digestion des protéines. Les tanins et les phénols n'influent pas sur les indices nutritionnels de ces deux espèces. Nous estimons que le principal intérêt de l'alimentation printanière est la disponibilité en feuillage succulent, riche en azote, et non l'absence de feuilles à haute teneur en tanin. L'alimentation printanière semble correspondre à une strategie alimentaire qui favorise la croissance aux dépens de l'efficacité tandis que l'alimentation en fin d'été est une stratégie qui favorise l'efficacité sur la rapidité.

     

Glycine cleavage and generation of one-carbon units in Euglena gracilis

Euglena gracilis Klebs (strain Z) was maintained in division synchronized autotrophic culture, receiving either air (low CO₂) or 5% CO₂ in     

栗树种质资源的多样性及其保存利用

本文在总结板栗(Castanea mollissima Bl.)种质资源调查研究的基础上,论述了以板栗为主的中国栗属植物遗传变异的多样性。并且从生态地理学上分析板栗种内变异的分布,提出了板栗遗传变异沿生态地理梯度变化的规律,为板栗种质资源的利用提供了依据。文中指出,当前正面临着板栗种质流失的严重问题,尤其随着良种的推广,必将带来遗传种质贫乏的后果。为此,提出了有关保存和利用的具体建议。     

Estimation of growth yield and maintenance coefficient of plant cell suspensions

Methodology is presented for the determination of growth yield (Y(g)) and maintenance coefficient (m) for carbon utilization of plant cells grown in suspension culture. Estimation of Y(g) and m requires measurements of specific growth rate (micro) and specific rate of substrate uptake (q) at different growth limiting substrate concentrations. Batch culture of tobacco cells did not permit evaluation of Y(g) and m because micro is constant and maximal during most of the growth cycle. In batch culture, the period of declining specific growth rate is extremely brief because of the rapid transition from logarithmic growth to stationary phase. This occurs because the K(m) for growth is relatively small compared to the initial sucrose concentration. Thus, when the substrate level reaches the K(m), the large mass of cells rapidly depletes the remaining substrate. In contrast, semicontinuous culture facilitates the determination of Y(g) and m because various steady-state growth rates can be achieved. Mathematical expressions were developed to determine the effective values of micro and q over the semicontinuous replacement interval. The validity of this approach was verified by conducting simulations using experimentally determined parameters.     

Effects of potassium levels over the range occurring in host plants on the growth of an insect herbivore (Manduca sexta)

Third instar tobacco hornworms (Manduca sexta L.: Sphingidae) on low dietary potassium had a lower relative growth rate than individuals on diets with potassium concentrations reflecting those in host-plants, due to decreased consumption rate, lower efficiencies of conversion of ingested and digested food (ECI and ECD), and a prolonged growth/feeding phase. Furthermore, these larvae, when placed on a diet with a moderate potassium concentration through the fourth stadium, ended up being smaller due to lower ECI and less biomass gained, and had a prolonged growth phase, which suggest an irreversible cost of the previous low potassium diet. Third instar hornworms on high potassium diets had lower ECI and ECD, and they had a prolonged growth phase. These individuals, when placed on a moderate potassium diet in the fourth stadium, gained less biomass, than those previously offered hostplant-like-potassium diets. Body potassium concentrations (% dw) at the end of the third stadium were similar among treatment groups. With increasing potassium concentrations in the diet, utilization efficiencies of potassium decreased and potassium concentrations in the frass increased. Correspondingly, water content (% fw) of the newly-molted fourth instar larvae declined with increasing potassium, indicating a passive loss of water during potassium excretion. Low and high dietary potassium reduced survivorship of third instar larvae; fourth instar caterpillars previously fed the low potassium diet also had poor survivorship. We conclude that, within the normal range of potassium concentrations in the hostplants, caterpillar performance is largely unaffected by potassium concentration, but that potassium-poor and potassium-rich diets, such as those hornworms may sometimes experience, can reduce growth and survivorship.     

Hexokinase Levels in Discrete Regions of Rat Brain: Evaluation by Quantitative Immuno fluoresence Using Interactive Laser Cytometry and Comparison with Basal Rates of Glucose Utilization

Relative levels of hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) have been determined in 16 discrete regions of adult rat brain by a quantitative immunofluorescence method. The distribution of immunofluorescence in brain sections was determined by interactive laser cytometry and related to hexokinase content by comparison with standard sections containing known amounts of the enzyme. In many of these regions, referred to here as group I regions, hexokinase content was correlated with previously reported basal rates of glucose utilization. However, several regions (group II regions) in which hexokinase content exceeded that expected from basal rates of glucose utilization were also detected. Compared with the corresponding regions from albino rat brain, higher hexokinase levels were found in the dorsal and ventral lateral geniculate (group I regions) of pigmented Norway rats, a result reflecting previously reported increased glucose utilization by these regions in pigmented rats. There was no difference in hexokinase levels in the superior colliculus, a group II structure, from albino and pigmented rats, a finding implying that a reported increase in rate of glucose utilization in the superior colliculus of pigmented rats is effected without an increase in hexokinase content. It is suggested that group II regions may be adapted to sustain increases in rates of glucose utilization that are, relative to basal rates, considerably greater than those experienced by group I regions.     

Comparison of Rates of Local Cerebral Glucose Utilization Determined with Deoxy[l-14C]glucose and Deoxy[6-14C]glucose

The activity of the pentose phosphate shunt pathway in brain is thought to be linked to neurotransmitter metabolism, glutathione reduction, and synthetic pathways requiring NADPH. There is currently no method available to assess flux of glucose through the pentose phosphate pathway in localized regions of the brain of conscious animals in vivo. Because metabolites of deoxy[1-14C]glucose are lost from brain when the experimental period of the deoxy[14C]glucose method exceeds 45 min, the possibility was considered that the loss reflected activity of this shunt pathway and that this hexose might be used to assay regional pentose phosphate shunt pathway activity in brain. Decarboxylation of deoxy[1-14C]glucose by brain extracts was detected in vitro, and small quantities of 14C were recovered in the 6-phosphodeoxygluconate fraction when deoxy[14C]glucose metabolites were isolated from freeze-blown brains and separated by HPLC. Local rates of glucose utilization determined with deoxy[1-14C]glucose and deoxy[6-14C]glucose were, however, similar in 20 brain structures at 45, 60, 90, and 120 min after the pulse, indicating that the rate of loss of 14CO2 from deoxy[1-14C]glucose-6-phosphate in normal adult rat brain is too low to permit assay pentose phosphate shunt activity in vivo. Further metabolism of deoxy[1-14]glucose-6-phosphate via this pathway does not interfere during routine use of the deoxyglucose method or explain the progressive decrease in calculated metabolic rate when the experimental period exceeds 45 min.     

Utilization of the tricarboxylic acid cycle, a reactor design criterion for the microaerobic production of 2,3-butanediol

A new parameter, the relative utilization of tricarboxylic acid (TCA) cycle beta, is introduced to quantitatively account for the involvement of fermentation pathways and TCA cycle in the utilization of oxygen under oxygen-limiting (microaerobic) conditions. With the facultative anaerobe Enterobacter aerogenes, which produces 2,3-butanediol, a method is proposed to calculate beta from measurement of metabolites and exhaust gas. In continuous culture beta was found to be small under oxygen limitation, indicating that the fermentation pathways were preferred over the TCA cycle and oxygen was almost entirely consumed through oxidation of reduced nicotinamide adenine dinucleotide (NADH(2)) released by fermentation under these conditions. The increase of beta at high oxygen supply revealed a saturation of oxygen utilization through fermentation pathways. It could be concluded that, for the optimal performance of a microaerobic culture, oxygen uptake rate must be kept at such a level that as much NADH(2) as possible from fermentation pathways is oxidized by oxygen, and at the same time the utilization of TCA cycle is kept at a minimum. As the dynamics of the microaerobic culture can be fast, a significant effect of reactor hydrodynamics, i.e., mixing, on the overall performance can be expected. This was confirmed experimentally, and the parameter beta proved to be a useful reactor design criterium for the microaerobic cultivation. (c) 1992 John Wiley & Sons, Inc.     

Chloroplast movements in leaves: Influence on chlorophyll fluorescence and measurements of light-induced absorbance changes related to ΔpH and zeaxanthin formation

Light-induced chloroplast movements were found to cause changes in chlorophyll fluorescence emission, closely matching those in leaf absorptance, both in terms of the kinetics and the maximum extent of the changes observed in different species. The results demonstrate that chloroplast movements can have a significant effect on the efficiency of light utilization in photosynthesis. They further show that chloroplast movements need to be taken into account in measurements of fluorescence quenching and especially in measurements of light-induced optical changes used to monitor zeaxanthin formation and pH associated light scattering in leaves. Means of minimizing and of adjusting for the influences of chloroplast movements in such measurements are discussed.Abbreviations F fluorescence emission - PFD photon flux density - R reflectance - T transmittance - absorptance C.I.W.-D.P.B. Publication No. 1116.     

小黑杨花粉植株H_1株系间变异及其选择利用的研究

小黑杨(Populus xiaohei T.S.Hwang ex C.Wang et Tung)花药离体培养获得单倍体植株,经14年的生长观察,发现花粉植株间表现出明显分离。选出19个株系进行田间比较试验,统计分析,结果发现材积生长差异显著。可从中选出优良株系加以利用,并提出杨树单倍体育种程序。