(Too Many) Mathematical Models of Circadian Clocks (?)

Many mathematical models derived from the principles obtained from empirical observations in chronobiology have been proposed and explored. They cover several organisms and phenomena, and utilize quite different formal approaches. These models can be divided into the ones that intend to describe pacemaker core function, such the Goodwin-oscillator family, non-genetic approaches or purely mathematical (i.e., without clear biochemical correlations) models, and the ones that represent events depending on pacemaker activity, i.e., photoperiodic phenomena. We aim to illustrate the diversity of mathematical and methodological approaches to describe circadian systems and related matters.     

Potential Conservation of Circadian Clock Proteins in the phylum Nematoda as Revealed by Bioinformatic Searches

Although several circadian rhythms have been described in C. elegans, its molecular clock remains elusive. In this work we employed a novel bioinformatic approach, applying probabilistic methodologies, to search for circadian clock proteins of several of the best studied circadian model organisms of different taxa (Mus musculus, Drosophila melanogaster, Neurospora crassa, Arabidopsis thaliana and Synechoccocus elongatus) in the proteomes of C. elegans and other members of the phylum Nematoda. With this approach we found that the Nematoda contain proteins most related to the core and accessory proteins of the insect and mammalian clocks, which provide new insights into the nematode clock and the evolution of the circadian system.     

甜瓜幼苗叶片光合变化特性

为探讨甜瓜光响应变化特性与环境因子的关系,选择光响应曲线适宜测定的时段,以甜瓜幼苗为试材,将1 d分为3个时段:10:00-12:00、12:00-15:00和15:00-17:00,每个叶位叶片测定1 d,并采用直角双曲线修正模型拟合光响应曲线,研究不同时段下甜瓜叶片光响应曲线、光响应参数的变化趋势和不同叶位叶片光响应参数特性。结果表明:当环境中光合有效辐射增强,叶面温度(Tl)升高,空气相对湿度(RH)降低;当环境中光合有效辐射减弱,Tl降低,RH升高。10:00-12:00光响应曲线和12:00-15:00的第1-4叶光响应曲线呈双曲线,在强光下趋向饱和状况,12:00-15:00的第5叶光合速率和15:00-17:00光合速率在强光下出现明显的光抑制现象。1 d的不同时段均表现为10:00-12:00最大净光合速率(P_max)和光饱和点(LSP)最高,12:00-17:00降低;12:00-15:00光补偿点(LCP)和暗呼吸速率(R_d)较高,其它两个时段较低,10:00-17:00光补偿点量子效率(φ_c)、气孔导度(G_s)和胞间CO₂浓度(C_i)总体呈降低趋势,气孔限制值(L_s)升高。10:00-15:00相同时段测得的不同叶位叶片光响应参数,以第4-5叶光合性能较好,15:00-17:00以第3叶P_max最高,第5叶次之;10:00-17:00 G_s和C_i以第5叶较低,第1叶较高,L_s以第5叶较高,第1叶较低。RH为影响P_max的主要决策因子,测定时段、叶面饱和蒸汽压亏缺(Vpdl)和Tl为主要限制因子。10:00-12:00适宜进行光响应曲线测定,气孔限制为不同时段光合作用不同的主要因素,非气孔限制为影响不同叶位叶片光合作用的主要因素。     

Estimation of heterozygosity for single-probe multilocus DNA fingerprints

In spite of the increasing application of DNA fingerprinting to natural populations and to the genetic identification of humans, explicit methods for estimation of basic population genetic parameters from DNA fingerprinting data have not been developed. Contributing to this omission is the inability to determine, for multilocus fingerprinting probes, relatively important genetic information, such as the number of loci, the number of alleles, and the distribution of these alleles into specific loci. One of the most useful genetic parameters that could be derived from such data would be the average heterozygosity, which has traditionally been employed to measure the level of genetic variation within populations and to compare genetic variation among different loci. We derive here explicit formulas for both the estimation of average heterozygosity at multiple hypervariable loci and a maximum value for this estimate. These estimates are based upon the DNA restriction-pattern matrices that are typical for fingerprinting studies of humans and natural populations. For several empirical data sets from our laboratory, estimates of average and maximal heterozygosity are shown to be relatively close to each other. Furthermore, variances of these statistics based on simulation studies are relatively small. These observations, as well as consideration of the effect of missing alleles and alternate numbers of loci, suggest that the average heterozygosity can be accurately estimated using phenotypic DNA fingerprint patterns, because this parameter is relatively insensitive to the lack of certain genetic information.      

河西走廊酒泉地区盐碱土未培养放线菌多样性

采用免培养技术对河西走廊酒泉地区的原生盐碱土、次生盐碱土和农田土中的放线菌群落结构及其多样性进行分析.结果表明: 河西走廊酒泉地区原生盐碱土克隆文库分归于19个OTUs,分属于微球菌亚目、丙酸杆菌亚目、棒状杆菌亚目、弗兰克氏菌亚目、假诺卡氏菌亚目和放线菌目未知类群;次生盐碱土克隆文库分归于14个OTUs,分属于微球菌亚目、丙酸杆菌亚目和放线菌目未知类群;农田土克隆文库分归于7个OTUs,分属于微球菌亚目和棒状杆菌亚目;微球菌亚目是3种不同类型土壤中的共有种群,是原生盐碱土和农田土中的优势种群.多样性指数和稀释性曲线分析结果显示,3种不同类型土壤中放线菌种群丰富度为原生盐碱土>次生盐碱土>农田土;原生盐碱土、次生盐碱土的稀释性曲线均未趋于平稳,说明盐碱土中放线菌多样性比实际更加丰富.