The frequency of embryogenic pollen grains is not increased by in vitro anther culture in Nicotiana tabacum L.

The numbers of embryogenic (S) grains present in in-situ mature anthers of Nicotiana tabacum L. were compared to the numbers of embryos and plantlets produced in cultured anthers excised at the optimal mitotic stage of development for anther culture. The Feulgen technique of staining embryos caused a considerable loss of grains from cultured anthers but this did not seriously affect the determination of the percentage of embryos present. In no instance did the numbers of embryos produced exceed the maximum number of S grains found, and the distributions of S grain and embryo frequencies in anthers were similar. In rare instances S grains which had undergone the first embryogenic division were observed in situ. The results indicate that all grains capable of embryogenesis are determined during early flower formation and that their number is not increased by in vitro culture.     

Resolution of electron microscope autoradiography. IV. Application to analysis of autoradiographs

The previous publications of this series described the expected grain distributions around model radioactive structures in EM autoradiographs as a function of the specimen resolution. This family of expected distributions was called the "universal curves". In the present study, experiments on 14C-sources were compared, significant differences were found depending on the energy of the isotope. These differences were primarily in the tails of the distributions, and are therefore important in correcting for cross-scatter when analyzing electron microscope autoradiographs. Using the universal curves unique for 125I, 3H, and 14C, we designed three sets of transparent overlays, or "masks", one set for each of these isotopes. The masks can be used by an investigator in a manner similar to that suggested by Blackett and Parry to generate grain distributions in autoradiographs on the basis of any desired hypothesis regarding the levels of radioactivity in different structures. A subsequent comparison between these generated distributions and those obtained from the observed grains in these autoradiographs leads to a determination of the most likely levels of radioactivity in the tissue. A computer (described in an Appendix by Land and Salpeter) can be used to find the "best fit" levels of radioactivity in complex cases. The accuracy of the masks was checked on generated line sources for each of the three isotopes.     

Relevance of physiological efficiency in wheat grain quality and the prospects of improvement

Released and pre-released bread wheat varieties evaluated in national wheat programme of India (503 genotypes) during 2005–14 under different environments were examined for the role of physiological parameters in grain quality. Genotypes with slow plant height growth but faster rate of grain filling enhanced protein content. Plants where growth in height and grain development was slow, grains were hard, provided proportionate vegetative growth phase is longer. Steady grain growth rate benefited gluten strength and gluten quality. Irrespective of total crop duration, longer reproductive phase was an effective indicator of higher flour recovery and test weight. Magnitude and significance of morphological attributes in grain quality was almost similar to that of physiological processes, therefore prospects of utilizing these field traits were examined to enhance grain properties. Early heading and longer grain filling was effective to increase test weight whereas delayed heading and shorter plant height enhanced protein content. Bold grains hampered grain hardness and delayed heading added more bran in the flour. Genotypes with poor grain bearing and quick grain ripening had lower sedimentation value. Instead of protein, it was wet gluten which expressed negative association with yield. To improvise gluten quality, extended reproductive phase but with less grain weight was helpful. Contribution of longer post-anthesis period was observed crucial in flour recovery. These useful simple field expressions can be deployed to uplift quality of wheat grains.     

The Effect on Wheat Grain Growth of the Removal or ABA Treatment of Glumes and Lemmas

When the glumes and lemmas were removed from wheat spikeletsduring the main grain filling period the uptake of sucrose intothe subtended grains was reduced in a few hours, but the abilityto synthesize starch was not affected for several days, by whichtime a marked loss of water content had occurred. When the deglumedears were covered to maintain high humidity, the grains hada weight and water content similar to those from unprotecteddeglumed ears. The application of ABA to the glumes occasionallyhad a small short-term effect on the uptake of sucrose intothe grain, but there were no long-term effects on dry matteraccumulation despite increased glume senescence. When the glume and lemma were removed shortly after anthesisthe subtended grain grew much less than grains from intact florets,with fewer and smaller aleurone cells. The removal of the lemmafrom the third floret of the spikelet had a similar effect onthe third grain, which could be partly reversed by removal ofthe grains in the lower florets. The role of the glumes andlemmas in grain development is discussed in the light of theseresults.     

Hydroxycinnamic acid amides in fertile and cytoplasmic male sterile lines of maize

Hydroxycinnamic acid (HCA) amides in fertile and cytoplasmic male sterile lines of maize were determined in reproductive organs, developing grains and cobs. HCA amides occurred in large amounts in the anthers of fertile plants (line F7N) and were absent from the anthers of cytoplasmic male sterile lines (lines F7T and F7C). Restoration of fertility was associated with the production of these compounds (line FC31). Considerable variations were observed in the concentrations of HCA amides at different stages of growth and grain maturation. Changes of HCA amides in the grains which were to produce sterile plants followed a pattern similar to that obtained with the grains which were to produce fertile plants. Accumulation of HCA amides was substantially higher in fertile lines whatever their genotype (F7N, FC31 and F7T x FC31) than in sterile lines. Marked changes occurred in the HCA amide content of embryo and endosperm during grain development. Many changes in HCA amides were observed in cobs during development and maturation, but no substantial differences could be observed between fertile and sterile lines.     

An improved procedure for background correction in autoradiography

In the event of weak autoradiographic labelling, the proportion of truly labelled cells or structures can be calculated from the frequency distributions of grains per area or cell structure for i = 0, 1,..., n grains using the results obtained for an experimental group after the application of a radioactively labelled substance and those obtained for a control group without radioactivity. The principle of this computer-aided method is also applicable when the grain counts are related to varying areas in histological sections.     

Grain size,sucrose level and starch accumulation in developing rice grain

Five rices (Oryza sativa L.) differing in final grain size were studied at the midmilky stage to determine if any factor could be identified which might limit rate of starch accumulation. Only UDP glucose pyrophosphorylase activity increased with increasing grain size. Detached rice panicles incubated in liquid medium containing 1% sucrose and 0.1% glutamine, in addition to minerals and vitamins, produced grains similar to those on intact plants. Sucrose level (0–1.5%) in the medium determined the extent of dry matter and starch accumulation and influenced physiological development of the ripening grains. Chemical and enzymic composition of the grain were similar to previously reported levels in grains of intact panicles analysed at regular intervals after anthesis. Addition of 3-P glycerate or K⁺ to the medium did not improve dry matter accumulation in the developing grain.     

Hormonal changes in the grains of rice subjected to water stress during grain filling

Lodging-resistant rice (Oryza sativa) cultivars usually show slow grain filling when nitrogen is applied in large amounts. This study investigated the possibility that a hormonal change may mediate the effect of water deficit that enhances whole plant senescence and speeds up grain filling. Two rice cultivars showing high lodging resistance and slow grain filling were field grown and applied with either normal or high amount nitrogen (HN) at heading. Well-watered and water-stressed (WS) treatments were imposed 9 days post anthesis to maturity. Results showed that WS increased partitioning of fixed (14)CO(2) into grains, accelerated the grain filling rate but shortened the grain filling period, whereas the HN did the opposite way. Cytokinin (zeatin + zeatin riboside) and indole-3-acetic acid contents in the grains transiently increased at early filling stage and WS treatments hastened their declines at the late grain filling stage. Gibberellins (GAs; GA(1) + GA(4)) in the grains were also high at early grain filling but HN enhanced, whereas WS substantially reduced, its accumulation. Opposite to GAs, abscisic acid (ABA) in the grains was low at early grain filling but WS remarkably enhanced its accumulation. The peak values of ABA were significantly correlated with the maximum grain filling rates (r = 0.92**, P < 0.01) and the partitioning of fixed (14)C into grains (r = 0.95**, P < 0.01). Exogenously applied ABA on pot-grown HN rice showed similar results as those by WS. Results suggest that an altered hormonal balance in rice grains by water stress during grain filling, especially a decrease in GAs and an increase in ABA, enhances the remobilization of prestored carbon to the grains and accelerates the grain filling rate.     

Are There Laws of Genome Evolution?

Research in quantitative evolutionary genomics and systems biology led to the discovery of several universal regularities connecting genomic and molecular phenomic variables. These universals include the log-normal distribution of the evolutionary rates of orthologous genes; the power law-like distributions of paralogous family size and node degree in various biological networks; the negative correlation between a gene's sequence evolution rate and expression level; and differential scaling of functional classes of genes with genome size. The universals of genome evolution can be accounted for by simple mathematical models similar to those used in statistical physics, such as the birth-death-innovation model. These models do not explicitly incorporate selection; therefore, the observed universal regularities do not appear to be shaped by selection but rather are emergent properties of gene ensembles. Although a complete physical theory of evolutionary biology is inconceivable, the universals of genome evolution might qualify as "laws of evolutionary genomics" in the same sense "law" is understood in modern physics.     

To split behaviour into bouts, log-transform the intervals

Analysis of behaviour that is displayed in bouts depends crucially on quantitative estimates of bout criteria, that is, the lengths of the shortest intervals between bouts. Current methods estimate bout criteria by modelling the log-transformed (cumulative) frequency distributions of intervals between events. For analysis of feeding behaviour, these models will not result in biologically meaningful quantitative estimates (Tolkamp et al. 1998, Journal of Theoretical Biology194, 235-250). We proposed a method that models the frequency distribution of log-transformed interval lengths instead. Applying this method to a single data set showed that the log-transformed lengths of intervals between feeding events were distributed as two Gaussians. Here we test this model using a data set of 35 171 intervals between feeding that was obtained during an experiment with 38 cows in three dietary treatment groups. No meaningful bout criterion could be obtained for some individuals, which casts doubt on the general validity of the proposed model. Addition of a third log-normal improved the fit of the model and we hypothesized that this third population represents intervals including drinking. In a second experiment, we found the measurements to be consistent with this hypothesis. We obtained meaningful meal criteria for all individuals by fitting either a double, or a triple, log-normal model to the frequency distributions of the lengths of intervals between feeding. These log-normal models appear to be not only more biologically meaningful than log (cumulative) frequency models but also far more flexible. Copyright 1999 The Association for the Study of Animal Behaviour.     

Peroxidase and amylase activity in developing grains of triticale,wheat and rye

Changes in the activities of peroxidase and amylase were measured during the development of grain of triticale, wheat and rye. Peroxidase and amylase activities were found to be higher in Triticale-1 which possesses highly shrivelled grains. A direct relationship between the degree to which the grain is shrivelled and the activity of peroxidase and enzymes was observed. During grain development, peroxidase and amylase activity per grain increased in Triticale-1, while it decreased in wheat, rye and well filled triticale grains.     

Species abundance distributions and richness estimations in fungal metagenomics--lessons learned from community ecology

Results of diversity and community ecology studies strongly depend on sampling depth. Completely surveyed communities follow log-normal distribution, whereas power law functions best describe incompletely censused communities. It is arguable whether the statistics behind those theories can be applied to voluminous next generation sequencing data in microbiology by treating individual DNA sequences as counts of molecular taxonomic units (MOTUs). This study addresses the suitability of species abundance models in three groups of plant-associated fungal communities - phyllosphere, ectomycorrhizal and arbuscular mycorrhizal fungi. We tested the impact of differential treatment of molecular singletons on observed and estimated species richness and species abundance distribution models. The arbuscular mycorrhizal community of 48 MOTUs was exhaustively sampled and followed log-normal distribution. The ectomycorrhizal (153 MOTUs) and phyllosphere (327 MOTUs) communities significantly differed from log-normal distribution. The fungal phyllosphere community in particular was clearly undersampled. This undersampling bias resulted in strong sensitivity to the exclusion of molecular singletons and other rare MOTUs that may represent technical artefacts. The analysis of abundant (core) and rare (satellite) MOTUs clearly identified two species abundance distributions in the phyllosphere data - a log-normal model for the core group and a log-series model for the satellite group. The prominent log-series distribution of satellite phyllosphere fungi highlighted the ecological significance of an infrequent fungal component in the phyllosphere community.     

Size-number trade-offs and pollen production by Papilionaceous legumes

The intra- and interspecific relations between the size and number of pollen grains were examined for 21 species of papilionaceous legumes to test for the trade-off expected from the subdivision of limited resources. We observed a tradeoff between pollen grain diameter and the number of grains produced per flower within 17 of the 21 species examined. For 12 of these species, the observed partial regression coefficient for In (pollen grain diameter) equaled -3, as expected. The remaining five species exhibited more negative partial regression coefficients than expected. Relations between pollen grain size and number that are more negative than expected may result from a decelerating relation between pollen grain size and the resource investment per grain. Flower production significantly influenced pollen production for only eight species so that pollen production seems to be determined primarily on a per flower basis. Interspecifically, pollen size also varied inversely with pollen number for the 21 species even after the effect of phylogenetic relatedness was removed. Pollen size varies relatively little compared to the number of pollen grains produced per flower and therefore may be the primary target of natural selection. The presence of a trade-off in pollen production probably constrains the evolutionary options by which flowering plants can maximize male success.     

Autoradiographic Studies of Intracellular Calcium in Frog Skeletal Muscle

Autoradiographs consisting of a 1000 A thick tissue section and a 1400 A thick emulsion film have been prepared from frog toe muscles labeled with Ca⁴⁵. The muscles had been fixed with an oxalate-containing osmium solution at rest at room temperature, at rest at 4°C, during relaxation following K⁺ depolarization or after prolonged depolarization. From 6 to 39 per cent of K⁺ contracture tension was produced during fixation. The grains in the autoradiographs were always concentrated in the center 0.2 to 0.3 µ of the I band and the region of the overlapping of the thick and thin filaments. The greater the tension produced during fixation, the greater was the concentration in the A band and the smaller the concentration in the I band. Autoradiographs of two muscles fixed by freeze-substitution resembled those of muscles which produced little tension during osmium fixation. Muscles which shortened during fixation produced fewer grains. In the narrow (<2.0 µ) sarcomeres of the shortened muscles, grain density decreased with decreasing sarcomere width. A theoretical analysis of the significance of these grain distributions is proposed and discussed.     

An improved procedure for background correction in autoradiography

Summary In the event of weak autoradiographic labelling, the proportion of truly labelled cells or structures can be calculated from the frequency distributions of grains per area or cell structure fori=0, 1,...,n grains using the results obtained for an experimental group after the application of a radioactively labelled substance and those obtained for a control group without radioactivity. The principle of this computer-aided method is also applicable when the grain counts are related to varying areas in histological sections.Dedicated to Professor Dr. T.H.Schiebler on the occasion of his 65th birthday     

Synthesis of CDP-diacylglycerol by rat liver rough microsomes as visualized by electron microscopic autoradiography: relationship to GTP-stimulated membrane fusion

Using detergent-free conditions of incubation for the analysis of liponucleotide synthesis, we compared GTP-dependent formation of CDP-diacylglycerol (CDP-DG) and membrane fusion in RNA-depleted rough microsomes from rat liver. After incubation of stripped rough microsomes (SRM) in the presence of GTP and [5-3H]-CTP, radioactivity was recovered in lipid extracts and identified by thin-layer chromatography as a single spot which co-migrated with CDP-DG. The nucleotide requirement for CDP-DG synthesis and that for membrane fusion were observed to be identical. We next carried out an electron microscopic autoradiographic analysis on incubated membranes to determine the site of incorporation of [5-3H]-CTP. Silver grains were observed directly over the unilamellar membranes of natural vesicles. In confirmation of the biochemical data, quantitation of silver grain density indicated more grains over membranes incubated in the presence of GTP than over those incubated in the absence of this nucleotide. For membranes incubated in the presence of GTP, the grain density was similar over fused and unfused membranes in the same preparation. When SRM were incubated with the enzyme co-factors required for synthesis of phosphatidylinositol, a GTP-independent membrane fusion was observed by both transmission and freeze-fracture electron microscopy. Together with the biochemical and autoradiographic data, this suggests that phospholipid metabolism may be activated by GTP and lead to the fusion of RER membrane.     

Activities of key enzymes in sucrose-to-starch conversion in wheat grains subjected to water deficit during grain filling

This study tested the hypothesis that a controlled water deficit during grain filling of wheat (Triticum aestivum) could accelerate grain-filling rate through regulating the key enzymes involved in Suc-to-starch pathway in the grains. Two high lodging-resistant wheat cultivars were field grown. Well-watered and water-deficit (WD) treatments were imposed from 9 DPA until maturity. The WD promoted the reallocation of prefixed 14C from the stems to grains, shortened the grain-filling period, and increased grain-filling rate or starch accumulation rate (SAR) in the grains. Activities of Suc synthase (SuSase), soluble starch synthase (SSS), and starch branching enzyme (SBE) in the grains were substantially enhanced by WD and positively correlated with the SAR. ADP Glc pyrophosphorylase activity was also enhanced in WD grains initially and correlated with SAR with a smaller coefficient. Activities of granule-bound starch synthase and soluble and insoluble acid invertase in the grains were less affected by WD. Abscisic acid (ABA) content in the grains was remarkably enhanced by WD and very significantly correlated with activities of SuSase, SSS, and SBE. Application of ABA on well-watered plants showed similar results as those by WD. Spraying with fluridone, an ABA synthesis inhibitor, had the opposite effect. The results suggest that increased grain-filling rate is mainly attributed to the enhanced sink activity by regulating key enzymes involved in Suc-to-starch conversion, especially SuSase, SSS, and SBE, in wheat grains when subjected to a mild water deficit during grain filling, and ABA plays a vital role in the regulation of this process.     

Effects of awns on the photosynthesis and yield of wheat, Triticum aestivum

Two pairs of awned and awnless near-isogenic lines of winter wheat were used in a field study in which canopy enclosure apparatus and carbon-14 dosing were employed to assess the contribution of the awns to photosynthesis and grain yield. Awns contributed an average of 12-2% to canopy gross photosynthesis but did not increase the net photosynthesis of the complete canopy. The presence of awns decreased photosynthesis in the remaining ear structures and in the flag and penultimate leaf laminae. Seven days after dosing during the phase of rapid grain filling, 80% of the carbon recovered was located in the grains. The awns intercepted 9% of the incident visible radiation when fully green, and senesced at similar rates as the ears and flag leaves. In a second experiment the effect of awns on grain yield and its components was investigated in crosses segregating for height and presence of awns. Awns did not increase grain yields in either experiment. It appears that for British conditions in the absence of severe drought there is little advantage to be gained at present by breeding awned varieties of wheat.     

长白山不同演替阶段针阔混交林群落物种多度分布格局

为解释长白山温带森林群落构建和物种多度格局的形成过程, 该文以不同演替阶段的针阔混交林监测样地数据为基础, 采用中性理论模型、生物统计模型(对数正态分布模型)和生态位模型(Zifp模型、分割线段模型、生态位优先模型)拟合森林群落物种多度分布, 并用χ ²检验、Kolmogorov-Smirnov (K-S)检验和赤池信息准则(AIC)选择最佳拟合模型。结果显示: 中性模型能很好地预测长白山温带森林不同演替阶段植物群落的物种多度分布。在10 m × 10 m尺度上, 5种模型均可被χ ²检验和K-S检验接受, 但中性模型拟合效果不如对数正态分布模型、Zifp模型、分割线段模型和生态位优先模型, 表明小尺度上中性过程和生态位过程均能解释群落物种多度分布, 但生态位过程的解释能力相对较大。而在中大尺度上(30 m × 30 m、60 m × 60 m和90 m × 90 m), 中性模型为最优拟合模型, 并且随着研究尺度增加, 生态位模型和生物统计模型逐渐被χ ²检验拒绝, 表明中性过程在长白山针阔混交林群落物种多度分布格局形成中的作用随着研究尺度增加而逐渐增大。该文证实了中性过程在长白山温带针阔混交林群落结构形成中具有重要作用, 但未否认生态位机制在群落构建中的贡献。因此, 温带森林群落构建过程中中性理论和生态位理论并非相互矛盾, 而是相互融合的。在研究森林群落物种多度分布时, 应重视取样尺度和演替阶段的影响, 并采用多种模型进行拟合。