Non-invasive methods for determination of cellular growth inPodophyllum hexandrum suspension cultures

Culture conductivity and on-line NADH fluorescence were used to measure cellular growth in plant cell suspension cultures ofPodophyllum hexandrum. An inverse correlation between dry cell weight and medium conductivity was observed during shake flask cultivation. A linear relationship between dry cell weight and culture NADH fluorescence was obtained during the exponential phase of batch cultivation in a bioreactor under the pH stat (pH 6) conditions. It was observed that conductivity measurement were suitable for biomass characterisation under highly dynamic uncontrolled shake flask cultivation conditions. However, if the acid/alkali feeding is done for pH control the conductivity measurement could not be applied. On the other hand the NADH fluorescence measurement allowed online-in situ biomass monitoring of rather heterogenous plant cell suspension cultures in bioreactor even under the most desirable pH stat conditions.     

林木耗水调控机理研究进展

林木的蒸腾耗水量是造林设计与环境水分研究的重要参数。本文就林木耗水的气孔与非气孔调节机制、木质部空穴和栓塞的发生和恢复机理、树体组织水容等方面进行了综述,对它们在树木水分传输过程中的调控作用和意义开展了探讨。目前在蒸腾气孔调节方面,包括,蒸腾午休、夜间蒸腾、气孔振荡和补偿现象等气孔行为的研究工作有待深入。栓塞木质部和空穴化导管恢复的临界条件与重新充注对植物水分运输的重要生理作用要进一步加强。树体组织水容对树木水分传输和耗水的调控机制问题应加以重视。     

Can root electrical capacitance be used to predict root mass in soil?

Background

Electrical capacitance, measured between an electrode inserted at the base of a plant and an electrode in the rooting substrate, is often linearly correlated with root mass. Electrical capacitance has often been used as an assay for root mass, and is conventionally interpreted using an electrical model in which roots behave as cylindrical capacitors wired in parallel. Recent experiments in hydroponics show that this interpretation is incorrect and a new model has been proposed. Here, the new model is tested in solid substrates.

Methods

The capacitances of compost and soil were determined as a function of water content, and the capacitances of cereal plants growing in sand or potting compost in the glasshouse, or in the field, were measured under contrasting irrigation regimes.

Key Results

Capacitances of compost and soil increased with increasing water content. At water contents approaching field capacity, compost and soil had capacitances at least an order of magnitude greater than those of plant tissues. For plants growing in solid substrates, wetting the substrate locally around the stem base was both necessary and sufficient to record maximum capacitance, which was correlated with stem cross-sectional area: capacitance of excised stem tissue equalled that of the plant in wet soil. Capacitance measured between two electrodes could be modelled as an electrical circuit in which component capacitors (plant tissue or rooting substrate) are wired in series.

Conclusions

The results were consistent with the new physical interpretation of plant capacitance. Substrate capacitance and plant capacitance combine according to standard physical laws. For plants growing in wet substrate, the capacitance measured is largely determined by the tissue between the surface of the substrate and the electrode attached to the plant. Whilst the measured capacitance can, in some circumstances, be correlated with root mass, it is not a direct assay of root mass.     

Midday stomatal conductance is more related to stem rather than leaf water status in subtropical deciduous and evergreen broadleaf trees

Midday depressions in stomatal conductance (g_s) and photosynthesis are common in plants. The aim of this study was to understand the hydraulic determinants of midday g_s, the coordination between leaf and stem hydraulics and whether regulation of midday g_s differed between deciduous and evergreen broadleaf tree species in a subtropical cloud forest of Southwest (SW) China. We investigated leaf and stem hydraulics, midday leaf and stem water potentials, as well as midday g_s of co‐occurring deciduous and evergreen tree species. Midday g_s was correlated positively with midday stem water potential across both groups of species, but not with midday leaf water potential. Species with higher stem hydraulic conductivity and greater daily reliance on stem hydraulic capacitance were able to maintain higher stem water potential and higher g_s at midday. Deciduous species exhibited significantly higher stem hydraulic conductivity, greater reliance on stem capacitance, higher stem water potential and g_s at midday than evergreen species. Our results suggest that midday g_s is more associated with midday stem than with leaf water status, and that the functional significance of stomatal regulation in these broadleaf tree species is probably for preventing stem xylem dysfunction.     

基于最大熵原理的浙江毛竹胸径分布及测量不确定度评定

应用最大熵原理构造了测树因子概率分布的统一模型,这样构造的模型具有明确的解析表达式,并能克服常用方法无法解释测树因子服从某种概率分布的真正原因,从而为测树因子统计分布建模提供了一种有效方法.使用1-3阶样本矩、1-4阶样本矩与1-5阶样本矩,用所构建的概率分布统一模型分别对浙江省域毛竹胸径分布分别作了仿真试验,结果表明当采用1-4阶样本矩时,仿真效果最好,而且比通过假设检验的Weibull分布仿真结果理想:(1)图形非常相似,对实测数据都能很好的模拟;(2)最大熵法的离差平方和为0.00018,Weibull分布的为0.00045[1].由于各种系统与非系统的原因,都会影响测量结果的准确性,对所构建的模型作了不确定度评定,表明结果具有很大的可靠性,测量结果的估计:7.85100,测量结果的标准不确定度:1.82710,置信概率:0.96020.     

Dual lifetime referencing enables pH‐control for oxidoreductions in hydrogel‐stabilized biphasic reaction systems

pH‐shifts are a serious challenge in cofactor dependent biocatalytic oxidoreductions. Therefore, a pH control strategy was developed for reaction systems, where the pH value is not directly measurable. Such a reaction system is the biphasic aqueous‐organic reaction system, where the oxidoreduction of hydrophobic substrates in organic solvents is catalysed by hydrogel‐immobilized enzymes, and enzyme‐coupled cofactor regeneration is accomplished via formate dehydrogenase, leading to a pH‐shift. Dual lifetime referencing (DLR), a fluorescence spectroscopic method, was applied for online‐monitoring of the pH‐value within the immobilizates during the reaction, allowing for a controlled dosage of formic acid. It could be shown that by applying trisodium 8‐hydroxypyrene‐1, 3, 6‐trisulfonate as pH indicator and Ru(II) tris(4, 7‐diphenyl‐1, 10‐phenantroline) (Ru[dpp]) as a reference luminophore the control of the pH‐value in a macroscopic gel‐bead‐stabilized aqueous/organic two phase system in a range of pH 6.5 to 8.0 is possible. An experimental proof of concept could maintain a stable pH of 7.5 ± 0.15 during the reaction for at least 105 h. With these results, it could be shown that DLR is a powerful tool for pH‐control within reaction systems with no direct access for conventional pH‐measurement.     

A novel cell-based duplex high-throughput screening assay combining fluorescent Ca measurement with homogeneous time-resolved fluorescence technology

Cell-based assays for G-protein-coupled receptor (GPCR) activation applied in high-throughput screening (HTS) monitor various readouts for second messengers or intracellular effectors. Recently, our understanding of diverging signaling pathways downstream of receptor activation and the capability of small molecules to selectively modulate signaling routes has increased substantially, underlining the importance of selecting appropriate readouts in cellular functional screens. To minimize the rate of false negatives in large-scale screening campaigns, it is crucial to maximize the chance of a ligand being detected, and generally applicable methods for detecting multiple analytes from a single well might serve this purpose. The few assays developed so far based on multiplexed GPCR readouts are limited to only certain applications and usually rely on genetic manipulations hindering screening in native or native-like cellular systems. Here we describe a more generally applicable and HTS-compatible homogeneous assay based on the combination of fluorometric detection of [Ca²⁺] with subsequent homogeneous time-resolved fluorescence (HTRF) cAMP readout in the same well. Besides describing development and validation of the assay, using a cell line recombinantly expressing the human PTH1 receptor screening of a small library is also presented, demonstrating the robustness and HTS compatibility of the novel paradigm.     

Comparison of micrometer‐ and scanning electron microscope‐based measurements of avian eggshell thickness

ABSTRACT The study of avian eggshell structure, including composition, pigmentation, thickness, and strength, has important ecological and economic implications. Previous investigators have used a variety of techniques to derive either direct measures or indirect estimates of eggshell thickness. Assessing the repeatability and method agreement of different techniques is necessary to permit comparison of eggshell thickness values from different studies on various genetic stocks, populations, and species. We recorded and analyzed measurements of eggshell thickness using two methods, micrometers and scanning electron microscopy (SEM), for several Palaeognathae and Neognathae taxa, including nonpasserines and passerines. Applying a tolerance‐interval approach, we found that repeatability of measurements for eggs with thinner shells (<300 μm, all Neognathae taxa) was worse than for eggs with thicker shells (Palaeognathae taxa), but was still statistically and biologically reasonable given that the relative magnitude of intramethod agreements was <11%. Our results support previous predictions that measurements made using a micrometer are comparable to those made using SEM. This finding is particularly important given the relative ease and cost efficiency of the micrometer method. Importantly, these new analyses can be used to validate the use of published data from previous studies of micrometer‐based eggshell thickness for both intra‐ and interspecific comparisons.     

Measurements on ground or sectioned otoliths: possibilities of bias

Back-calculation usually requires measurements of growth marks revealed on otoliths by specific preparations. The standardization of the grinding (or sectioning) plane is necessary, but difficult, especially along the antero-posterior axis. In order to show the importance of the grinding plane, tetracycline labelling of eel otoliths ( Anguilla anguilla L.) has been used. This marking has a calcio-traumatic effect on otoliths, which can be revealed with staining techniques. Unless the grinding plane is incorrect, the tetracycline labelling and the staining of the ground surface are then superposed.