Estimation of Tissue Construction Cost from Heat of Combustion and Organic Nitrogen Content

Abstract. We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen content. The method predicts glucose equivalents, the amount of glucose required to provide carbon skeletons and reductant to synthesize a quantity of organic product. Glucose equivalents have previously been calculated from the elemental composition of tissue. We define construction cost as the amount of glucose required to provide carbon skeletons, reductant and ATP for synthesizing the organic compounds in a tissue via standard biochemical pathways. The fraction of the total construction cost of a compound or tissue (excluding costs of transporting compounds) that is reflected in its glucose equivalents is the biosynthetic efficiency ( E _B). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total construction cost can be estimated to ± 6% of the value obtained from biochemical pathway analysis.
Construction costs of leaves of three chaparral species were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differences were probably due to a combination of inaccuracy in the estimated biosynthetic efficiency and technical difficulties with biochemical analysis, one of the older methods of determining construction cost.     

Comparison of chlorophyll fluorescence emission characteristics of wheat leaf tissue and isolated thylakoids as a function of excitation wavelength

Abstract. Chlorophyll fluorescence emission spectra and the kinetics of 685 mm fluorescence emission from wheat leaf tissue and thylakoids isolated from such tissue were examined as a function of excitation wavelength. A considerable enhancement of fluorescence emission above 700 nm relative to that at 685 nm was observed from leaf tissue when it was excited with 550 nm rather than 450 nm radiation. Such excitation wavelength dependent changes in the emission spectrum occurred over an excitation spectral range of 440–660 nm and appeared to be directly related to the total quantity of radiation absorbed at a given excitation wavelength. Experiments with isolated thylakoid preparations demonstrated that changes in the fluorescence emission spectrum of the leaf were attributable to the optical properties of the leaf and were not due to the intrinsic characteristies of the thylakoid photochemical apparatus. This was not the case for the observed excitation wavelength dependent changes in the 685 nm fluorescence induction curve obtained from leaf tissue infiltrated with DCMU. Excitation wavelength dependent changes in the ratio of the variable to maximal fluorescence emission and the shape of the variable fluorescence induction were observed for leaf tissue. Isolated thylakoid studies showed that such changes in the leaf fluorescence kinetics were representative of the way in which the photochemical apparatus in vivo was processing the absorbed radiation at the different excitation wavelengths. The results are considered in the context of the use of fluorescence emission characteristics of leaves as non-destructive probes of the photochemical apparatus in vivo.     

The nitrogen balance of Raphanus sativus X raphanistrum plants. I. Daily nitrogen use under high nitrate supply

Abstract Growth-chamber cultivated Raphanus plants accumulate nitrate during their vegetative growth. After 25 days of growth at a constant supply to the roots of 1 mol m^?3 (NO^?₃) in a balanced nutrient solution, the oldest leaves (eight-leaf stage) accumulated 2.5% NO^?₃-nitrogen (NO₃-N) in their lamina, and almost 5% NO₃-N in their petioles on a dry weight basis. This is equivalent to approximately 190 and 400 mol^?3 m^?3 concentration of NO^?₃ in the lamina and the petiole, respectively, as calculated on a total tissue water content basis. Measurements were made of root NO^?₃ uptake, NO^?₃ fluxes in the xylem, nitrate uptake by the mesophyll cells, and nitrate reduction as measured by an in vivo test. NO^?₃ uptake by roots and mesophyll cells was greater in the light than in the dark. The NO^?₃ concentration in the xylem fluid was constant with leaf age, but showed a distinct daily variation as a result of the independent fluxes of root uptake, transpiration and mesophyll uptake. NO^?₃ was reduced in the leaf at a higher rate in the light than in the dark. The reduction was inhibited at the high concentrations calculated to exist in the mesophyll vacuoles, but reduction continued at a low rate, even when there was no supply from the incubation medium. Sixty-four per cent of the NO^?₃ influx was turned into organic nitrogen, with the remaining NO^?₃ accumulating in both the light and the dark.     

The influence of temperature on light enhanced glycoalkaloid synthesis in potato

The influence of temperature on total glycoalkaloid (TGA) synthesis in tubers exposed to light (250 jumol m“² s”² PAR, Photosynthetically Active Radiation) or dark environments for 96 h was examined in three potato cultivars. Following 96 h light or dark the tubers were stored without light at 5°C or 24°C and TGA concentrations monitored over the subsequent 30 and 90 days. Exposure to light and cultivar were found to be major factors influencing TGA concentrations; temperature had no significant effect. TGA content in illuminated tubers of cvs ‘Pentland Hawk’ and ‘Kerrs Pink’ were significantly higher (P < 0.01) compared with tubers placed in the dark. TGA concentrations in cv. ‘Desiree’ increased significantly only following exposure to light at low temperatures (P < 0.05). Removal of tubers from storage at 5°C and immediate illumination at 24°C altered the ratio of glycoalkaloids in cvs ‘Pentland Hawk’ and ‘Kerrs Pink’. Regardless of cultivar and storage temperature TGA concentrations were higher at the end of the storage period compared with initial TGA concentrations. During storage TGA concentrations fluctuated widely and gradual accumulation of glycoalkaloids with time was rarely demonstrated except in cv. ‘Desiree’. Tubers stored at 24°C accumulated higher TGA concentrations than those stored at 5°C in cv. ‘Kerrs Pink’ but not in cvs ‘Pentland Hawk’ and ‘Desiree’. Tubers of cv. ‘Kerrs Pink’ exposed to light prior to storage accumulated glycoalkaloids more rapidly than unexposed tubers during storage at 24°C and occasionally at 5°C. Light enhanced glycoalkaloids are not degraded over time.     

Brent Geese Branta bernicla and Zostera; factors affecting the exploitation of a seasonally declining food resource

Brent Geese Branta bernicla wintering at Lindisfarne, northeastern England, fed almost exclusively on intertidal habitats. Their main food supply was two species of Eelgrass Zostera noltii and Zostera angustifolia. Although abundant when the birds arrived in September, this Zostera was rapidly depleted during the period October-December. Brent Goose food intake rate declined with the decreasing food supply, and the birds responded by extending the time that they spent feeding. When it was no longer possible to extend the time spent feeding (i.e. they were feeding for all of the time that the food supply was available to them), they moved away from the site. The geese fed extensively at night in order to achieve their daily feeding requirements, especially later in the season. Conversion of daily food intake to energetic intake suggested that there may have been an energetic trigger acting: the geese left the site when they were unable to satisfy their basic energy demand. No evidence was found for direct interference competition between Brent Geese and the other grazer in the system, Wigeon Anas penelope: the two species showed no spatial segregation in their feeding areas at the scale investigated nor any temporal avoidance of each other.     

Comparative analysis of tandem repeats from hundreds of species reveals unique insights into centromere evolution

Background

Centromeres are essential for chromosome segregation, yet their DNA sequences evolve rapidly. In most animals and plants that have been studied, centromeres contain megabase-scale arrays of tandem repeats. Despite their importance, very little is known about the degree to which centromere tandem repeats share common properties between different species across different phyla. We used bioinformatic methods to identify high-copy tandem repeats from 282 species using publicly available genomic sequence and our own data.

Results

Our methods are compatible with all current sequencing technologies. Long Pacific Biosciences sequence reads allowed us to find tandem repeat monomers up to 1,419 bp. We assumed that the most abundant tandem repeat is the centromere DNA, which was true for most species whose centromeres have been previously characterized, suggesting this is a general property of genomes. High-copy centromere tandem repeats were found in almost all animal and plant genomes, but repeat monomers were highly variable in sequence composition and length. Furthermore, phylogenetic analysis of sequence homology showed little evidence of sequence conservation beyond approximately 50 million years of divergence. We find that despite an overall lack of sequence conservation, centromere tandem repeats from diverse species showed similar modes of evolution.

Conclusions

While centromere position in most eukaryotes is epigenetically determined, our results indicate that tandem repeats are highly prevalent at centromeres of both animal and plant genomes. This suggests a functional role for such repeats, perhaps in promoting concerted evolution of centromere DNA across chromosomes.     

华南贵州早奥陶世红花园组的镰箭类牙形刺

本文描述了产自华南贵州下奥陶统红花园组(桐梓红花园标准剖面,沿河甘溪剖面和贵阳黄花冲剖面)的四个镰箭类牙形刺种:Drepanoistodus sp.cf.nowlani,Paltodus sp.cf.P.subaequalis,Paltodus sp.A和Paroisto-dus sp.。D.sp.cf.nowlani为红花园组常见种,但另三种则相对稀少。在红花园组标准剖面,Paltodus sp.cf.P.subaequalis最低出现于该组底部,证实此层位为晚特马豆克期。文中详细图示了产于瑞典下奥陶统的两个带化石种:Paltodus deltifer和Paroistodus proteus,以及瑞典镰箭刺属的三个常见种:Drepanoistodus forceps,D.basiovalis和D.sp.cf.D.suberectus。通过与瑞典材料的详细对比,我们认为华南以前关于P.proteus和P.deltifer两种的记述多有误,须重新厘定。     

Anticancer immunotherapy by CTLA-4 blockade: obligatory contribution of IL-2 receptors and negative prognostic impact of soluble CD25

The cytotoxic T lymphocyte antigen-4 (CTLA-4)-blocking antibody ipilimumab induces immune-mediated long-term control of metastatic melanoma in a fraction of patients. Although ipilimumab undoubtedly exerts its therapeutic effects via immunostimulation, thus far clinically useful, immunologically relevant biomarkers that predict treatment efficiency have been elusive. Here, we show that neutralization of IL-2 or blocking the α and β subunits of the IL-2 receptor (CD25 and CD122, respectively) abolished the antitumor effects and the accompanying improvement of the ratio of intratumoral T effector versus regulatory cells (Tregs), which were otherwise induced by CTLA-4 blockade in preclinical mouse models. CTLA-4 blockade led to the reduction of a suppressive CD4⁺ T cell subset expressing Lag3, ICOS, IL-10 and Egr2 with a concomitant rise in IL-2-producing effector cells that lost FoxP3 expression and accumulated in regressing tumors. While recombinant IL-2 improved the therapeutic efficacy of CTLA-4 blockade, the decoy IL-2 receptor α (IL-2Rα, sCD25) inhibited the anticancer effects of CTLA-4 blockade. In 262 metastatic melanoma patients receiving ipilimumab, baseline serum concentrations of sCD25 represented an independent indicator of overall survival, with high levels predicting resistance to therapy. Altogether, these results unravel a role for IL-2 and IL-2 receptors in the anticancer activity of CTLA-4 blockade. Importantly, our study provides the first immunologically relevant biomarker, namely elevated serum sCD25, that predicts resistance to CTLA-4 blockade in patients with melanoma.     

Activation of hypothalamic RIP‐Cre neurons promotes beiging of WAT via sympathetic nervous system

Activation of brown adipose tissue (BAT) and beige fat by cold increases energy expenditure. Although their activation is known to be differentially regulated in part by hypothalamus, the underlying neural pathways and populations remain poorly characterized. Here, we show that activation of rat‐insulin‐promoter‐Cre (RIP‐Cre) neurons in ventromedial hypothalamus (VMH) preferentially promotes recruitment of beige fat via a selective control of sympathetic nervous system (SNS) outflow to subcutaneous white adipose tissue (sWAT), but has no effect on BAT. Genetic ablation of APPL2 in RIP‐Cre neurons diminishes beiging in sWAT without affecting BAT, leading to cold intolerance and obesity in mice. Such defects are reversed by activation of RIP‐Cre neurons, inactivation of VMH AMPK, or treatment with a β3‐adrenergic receptor agonist. Hypothalamic APPL2 enhances neuronal activation in VMH RIP‐Cre neurons and raphe pallidus, thereby eliciting SNS outflow to sWAT and subsequent beiging. These data suggest that beige fat can be selectively activated by VMH RIP‐Cre neurons, in which the APPL2–AMPK signaling axis is crucial for this defending mechanism to cold and obesity.