Germ Layer Interactions in Pattern Formation of Amphibian Mesoderm during Primary Embryonic Induction

Mesodermal differentiation of dorsal marginal zone (DMZ) before and after invagination was analyzed by a series of combination experiments with different kinds of ectoderm.
Lower DMZ of early gastrula didn't show any axial-mesoderm (notochord and somitic mesoderm) but lateral mesoderm (mesenchyme, mesothelium, or blood cells) in combinant with non-competent ventral ectoderm, while combinant with competent ectoderm was found to have well-differentiated axial-mesoderm with deutero-spinocaudal neurals. The axial-mesoderms have origin in the ectoderm. Uninvaginated DMZ of middle gastrula also showed difference in mesodermal differentiation between competent and non-competent ectoderms; axial-mesoderm differentiation was much better in competent than in non-competent. The axial-mesoderm originated from the uninvaginated DMZ. Archenteron roof of late gastrula showed regional difference in mesodermal differentiation in both combinants with competent and non-competent. The present study further demonstrated that there was regionality in promoting effect of induced neurectoderm on axial-mesoderm differentiation of invaginated archenteron roof.
The present experiments suggest that the cranio-caudal and dorso-ventral axis formations of amphibian mesoderm are finally determined by sequential and reciprocal interactions between the mesodermal anlage and the overlying ectoderm. It should be also shown that lower DMZ acts to trigger a series of the sequential interactions during primary embryonic induction.     

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。     

Phylogenetic and phenotypic originality and abundance in a cerrado plant community

The originality of a species is how much that species contributes to the rarity of traits in a community. Here we tested the relation between abundance and both phylogenetic and phenotypic originality. We measured nine traits associated with defence against herbivory, as well as phylogenetic information and abundance for woody plant species in a woodland cerrado in southeastern Brazil. About 90% of the species accounted for about 50% of the phylogenetic and phenotypic originality: most woody species had low originality. Abundance was related to tougher leaves, lower specific leaf area and lower originality based on nutritional quality. Our results suggest that herbivory may reduce the abundance of species with low resistance to herbivory and with different nutritional quality. Nevertheless, abundance was not related to either phylogenetic or phenotypic originality, so extinction of rare species may not endanger overall community function as long as more abundant species are retained. We argue that this is a consequence of the low complementarity of a large number of woody species.     

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.      

胞外三磷酸腺苷对铅胁迫下植物细胞损伤和过氧化氢及其清除酶水平的调节

细胞外三磷酸腺苷（extracellular adenosine-5'-triphosphate）是植物细胞的重要信号分子。以烟草悬浮细胞BY-2（Nicotiana tabacum L.cv.Bright Yellow-2）为材料,探讨了胞外三磷酸腺苷对铅胁迫下细胞损伤、H₂O₂（过氧化氢）含量及H₂O₂清除酶活性的影响。结果显示,随着Pb（NO₃）₂浓度的不断提高（30~400 μmol·L^-1）,细胞外三磷酸腺苷含量呈现出逐渐下降的趋势,但胞内三磷酸腺苷含量及细胞的受损伤程度逐渐增大;同时,H₂O₂含量和过氧化氢酶的活性均有所上升,并在200 μmol·L^-1 Pb（NO₃）₂处理下达到最大值,而过氧化物酶的活性则不断降低。较之Pb（NO₃）₂胁迫下的细胞,对Pb（NO₃）₂胁迫的细胞加入外源三磷酸腺苷使得细胞受损伤程度显著降低,H₂O₂含量减少,过氧化氢酶活性减弱,而过氧化物酶活性增强。实验结果表明,Pb（NO₃）₂胁迫诱导的植物细胞损伤和H₂O₂及其清除酶水平的变化能受到细胞外三磷酸腺苷水平的调节。     

Evolution of the primary and secondary structures of the E1a mRNAs of the adenovirus

In this paper we investigate and compare (evolutionary) patterns in the primary and secondary structure of four homologous E1a mRNAs of the adenovirus. Our main results are as follows: (1) The similarity of the coding regions of the mRNA sequences reflects both similarity in function (i.e., oncogenicity) and evolutionary divergence. (2) The similarity of the leader and the trailer regions reflects host specificity (i.e., human or simian) and must therefore arise from convergence. (3) Minimal energy foldings of the mRNAs show similar secondary structures (in particular around the splice sites). The conservation of pre-mRNA secondary structure shows that mRNAs are subject to selection constraints in addition to those associated with proteins. (4) The conserved secondary (helical) structures consist of nonhomologous subsequences, i.e., shifts have occurred. The observed shifts near the splice sites seem to be the simplest way of dealing with the dual constraints.      

Genetic diversity patterns in Curcuma reflect differences in genome size

The relationships between genome size and the systematic and evolutionary patterns in vascular plants are equivocal, although a close relationship between genome size and evolutionary patterns has been previously reported. However, several studies have also revealed the dynamic nature of genome size evolution and its considerable ‘ups’ and ‘downs’. Thus, in this study, the phylogenetic relationships among three previously revealed genome size groups and among species of the highly polyploid genus Curcuma were evaluated using AFLP. Our results suggest two main lineages within Indian Curcuma reflecting evolution of genome size. The first one includes hexaploids and higher polyploids of the previously recognized genome size group I, and the second one includes mainly hexaploids of genome size groups II and III. Within genome size group I, relationships among species seem to be influenced by reticulate evolution and higher polyploids are likely to be of allopolyploid origin. Reproductive systems in Indian Curcuma vary considerably among ploidy levels and these differences considerably affect morphological and genetic variation. In general, clonally reproducing species are expected to exhibit low genotypic diversity, but, at the same time, species of allopolyploid origin are expected to maintain higher levels of heterozygosity compared with their progenitors. We investigated intra‐populational genetic variability in Curcuma spp. to evaluate whether mode of reproduction or ploidy represent the main factor influencing the degree of genetic diversity. We found that hexaploid species exhibited significantly higher genetic diversity than higher polyploids (9x, 15x). Our results suggest that this genetic diversity pattern is largely influenced by the mode of reproduction, as higher polyploids reproduce exclusively vegetatively, whereas hexaploids reproduce mainly sexually. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 165 , 388–401.     

Nitric oxide promotes MPK6‐mediated caspase‐3‐like activation in cadmium‐induced Arabidopsis thaliana programmed cell death

Nitric oxide (NO), a vital cell‐signalling molecule, has been reported to regulate toxic metal responses in plants. This work investigated the effects of NO and the relationship between NO and mitogen‐activated protein kinase (MAPK) in Arabidopsis (Arabidopsis thaliana) programmed cell death (PCD) induced by cadmium (Cd²⁺) exposure. With fluorescence resonance energy transfer (FRET) analysis, caspase‐3‐like protease activation was detected after Cd²⁺ treatment. This was further confirmed with a caspase‐3 substrate assay. Cd²⁺‐induced caspase‐3‐like activity was inhibited in the presence of the NO‐specific scavenger 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (cPTIO), suggesting that NO mediated caspase‐3‐like protease activation under Cd²⁺ stress conditions. Pretreatment with cPTIO effectively inhibited Cd²⁺‐induced MAPK activation, indicating that NO also affected the MAPK pathway. Interestingly, Cd²⁺‐induced caspase‐3‐like activity was significantly suppressed in the mpk6 mutant, suggesting that MPK6 was required for caspase‐3‐like protease activation. To our knowledge, this is the first demonstration that NO promotes Cd²⁺‐induced Arabidopsis PCD by promoting MPK6‐mediated caspase‐3‐like activation.     

栲树种群的年龄结构及其生长特征

为了了解栲树的更新方式和更新动态,研究了栲树的生长特征和种群年龄结构.结果表明：栲树种群的年龄结构呈“间歇型”,经历了两个死亡高峰,并存在一个长达30年的断层;栲树的生长受光照的影响,具有很强的可塑性;由于林下光照弱且在垂直空间上不存在差异,栲树生长5～8年后进入生长的第1个抑制期,其年高生长速度可小于0.1 m,并可维持10年;栲树生长的第1个抑制期的起始时间对应着种群第1个死亡高峰期的结束时间,而其结束时间对应着种群第2个死亡高峰期的起始时间,表明栲树生长特征是影响其种群年龄结构的关键因素.