Geographic variation in seed dormancy among populations of Echinochloa crus-galli

In 1991–1993, we investigated the incidence of seed dormancy in 25 local populations of barnyard grass, Echinochloa crus-galli (L.) P.Beauv., in the western Czech Republic. The percentage of germination after 4 months afterripening of dry seeds at 25°C varied between 0.0 and 83.6%. Although there were significant annual differences in the percentage of germination at some localities, typical proportions of dormant seeds persisted over 3 years at field sites where the seed bank was not disturbed. One-way ANOVA (using data from 14 cultivated or abandoned fields) revealed that 73.0% of variance in seed dormancy incidence could be attributed to the effect of locality (P<0.001). Incidence of dormancy was not correlated with mother plant stature (dry above-ground biomass, number of tillers, maximal stem height) nor seed mass. There was a significant correlation (r ²=0.403, P<0.005) between dormancy incidence at natural localities in 1991 and in F₁ offspring sown at experimental grounds at Praha-Ruzyn in 1992. The results indicate that heredity is important in maintaining local variation in seed dormancy, probably favoured by the self-pollinating reproduction of barnyard grass.     

稗草DNA的快速提取研究

优化了稗草DNA的提取条件,水浴时间为60min,无水乙醇用量为0.60ml,细胞提取液用量为6．0ml,饱和NaAc溶液用量为1.0ml,酚／氯仿／异戊醇溶液、氯仿／异戊醇溶液和异丙醇与样液体积比别为0．60、1．0和0．60。从稗草种子提取时,产率为430μg／g。琼脂糖凝胶电泳证实,所提稗草DNA无断裂降解。     

拟南芥突变体种子休眠与萌发的研究进展

种子的休眠和萌发是一个复杂的过程,至今尚未能清楚阐明其调控机制。目前已从拟南芥突变体中鉴定了一些与种子萌发和休眠相关的基因,有助于阐明种子休眠和萌发的分子机制。本文综述了拟南芥突变体种子休眠与萌发方面的研究进展。赤霉素是促进种子萌发的主要因素之一,RGL、SPY、GCR、SLY和GAR等基因的表达参与赤霉素对种子萌发的调控。脱落酸与种子休眠有关,ABI1、ABI2、ABI3、ABI4、ABI5、FUS3、LEC、MARD和CIPK等基因参与了脱落酸的调控过程。对3类乙烯反应的突变体（ein、etr和ctr）以及油菜素内酯突变体（det和bri）的研究表明乙烯和油菜素内酯是通过拮抗脱落酸而促进种子萌发的。光对种子萌发的调节,是通过具有Ser／Thr蛋白激酶活性的光敏色素PhyA、PhyB、PhyC、PhyD和PhyE,以磷酸化／去磷酸化方式调节其它与萌发相关基因的表达。含氮化合物对种子萌发的促进,可能是以一种依赖一氧化氮的方式解除种子休眠。     

Characterization of alternating-temperature regimes that remove seed dormancy in seeds of Brachiaria humidicola (Rendle) Schweickerdt

Abstract Seeds of Brachiaria humidicola were subjected, on a thermogradienl plate, to a wide range of alternating-temperature cycles (24 h) and constant temperatures with intermittent exposure to diffuse laboratory light, in the presence and absence of 10 mol m^?3 KNO_V The optimum regime for maximum percentage germination was alternating temperatures of 35°C for 4hd^?1 and 13°C for 20 hd^?1. Almost no germination occurred at any constant temperature. Thermoperiods in which the warmer temperature was applied for the longer part of the 24 h cycle were much less stimulatory; in the presence of KNO₃, however, the germination under such regimes was much improved, although there was little effect on seeds experiencing near-optimum alternating-temperature regimes. This investigation is the first step in identifying which of 10 attributes of alternating temperatures are stimulatory, in order to predict the efficacy of different temperature regimes and to identify the stimulatory characteristics that must ultimately be explained by cellular physiology. The work shows that amplitude, thermoperiod and mean temperature must all be incorporated in a quantitative model.     

Molecular organization of the mating type (Mat) locus of Exserohilum monoceras (Setosphaeria monoceras), a bioherbicide agent for Echinochloa weeds

Mating-type genes were cloned and sequenced in the heterothallic phytopathogenic fungus Exserohilum monoceras, a candidate bioherbicide for the control of Echinochloa weeds in rice fields. Using PCR-based methods, we determined both idiomorphs and flanking regions of these genes. The structural organization of the E. monoceras Mat locus was similar to that of other heterothallic ascomycetes. The MAT1-1-1 gene was 1191 bp and encoded a predicted protein of 379 amino acids with an α box domain. The MAT1-2-1 gene was 1093 bp and encoded a predicted protein of 345 amino acids with a high mobility group box domain. Expression of both MAT genes was detected under vegetative and invasive growth conditions. MAT-specific primers were developed to assess the mating-type frequency of E. monoceras field isolates. Both mating types were observed in Japanese field isolates. Analysis of mating types and sexual hybridization of E. monoceras could provide useful approaches for the conventional genetic manipulation of this fungus to produce a more efficient bioherbicide.     

种子休眠机理研究概述

种子休眠是植物本身适应环境和延续生存的一种特性,是种子植物进化的一种稳定对策。野生植物特别是原产温带的植物,其种子大多有深而长的休眠期。关于种子休眠的概念有多种,这些概念引出了许多学说、假说和模型。种壳障碍、胚形态发育不完全和生理后熟以及种子中含有化学抑制剂等,都可导致种子休眠。根据不同的分类标准可将种子分成不同类型,一般将种子分为强迫休眠和机体休眠;机体休眠又可分为外部休眠、内部休眠和综合休眠。植物种类不同休眠特性也不同;同种植物的种子来源于不同的居群和植株时,若采集时期不同,其休眠也可能不同;甚至在同一果实中的不同种子,休眠特性亦可能有差异。影响休眠性状表达的基因既有核基因,也有质基因,休眠通常表现为一种受多基因控制的数量性状。种子休眠具有重要的生态学意义,能有效地调节种子萌发的时空分布。研究种子的休眠特性和机理及其解除方法,有助于农业生产和植物多样性保护。     

毛莨科药用植物种子发芽的研究

本文报导了不同温度对毛莨科药用植物种子萌发和休眠的影响,提出了不同种的种子发芽的温度范围,发芽适温,发芽所需天数及发芽率,对于中药材生产中掌握不同种的种子发芽适温,确定合适的播种期具有指导意义。     

Advances in Understanding Seed Dormancy at the Whole-seed Level:An Ecological, Biogeographical and Phylogenetic Perspective

Following a brief account of the early foundations of seed germination ecology sensu lato, some historical and recent developments pertaining to the ecology, biogeography and phylogeny of seed dormancy are discussed.     

Factors affecting the induction and release of secondary dormancy in Kalanchoë seeds

Abstract. Several short daily R irradiations are required from the first day of incubation on water to induce germination of Kalanchoë seeds. When the same light treatment is given after a prolonged dark incubation period at 20°C, secondary dormancy prevents germination. Factors controlling the induction and breaking of secondary dormancy have been investigated. The induction of secondary dormancy is very temperature dependent. Locally puncturing the seed coat strongly delays it. Secondary dormancy is not induced in the presence of GA₃ during the first 10 d of dark incubation, although this growth substance cannot induce dark germination. Prolonged or cyclic daily R irradiations can relieve secondary dormancy of seeds kept on water, even after a dark period of 20 d. A 24 h treatment at 4°C restores responsiveness to short R exposures of slightly secondarily dormant seeds. The synergism between GA₃ and Pfr in non-dormant Kalanchoë seeds, leading to high effectiveness of even one short FR irradiation, still occurs in seeds made secondarily dormant before transfer to GA₃, but more R or FR irradiations, in combination with GA₃, are required for the release of secondary dormancy. A combination of red light and 6-benzyl-aminopurine is ineffective in removing dormancy.     

植物种子休眠的原因及休眠的多形性

概述了植物种子休眠的原因及种子休眠的多形性。种壳障碍、胚形态发育不全和生理后熟以及种子中含有化学抑制剂都可导致种子休眠。根据不同的分类标准可将种子休眠可分成不同类型,但通常将休眠分为外源休眠、内源休眠和综合休眠。影响休眠的因素是复杂的,植物种类不同,休眠特性不同;同种植物的种子,来源于不同居群和植株,在不同时期采集,位于母株不同位置,其休眠有可能不同;甚至同一果实中的不同种子,休眠特性都会有差异。影响休眠性状表达的基因既有核基因,又有质基因,休眠通常表现为一种受多基因控制的数量性状。种子休眠的多形性有利于调节种子萌发的时空分布。     

Taxonomic complexity,population genetics,and plant conservation in Scotland

Summary

Groups of plants that are undergoing active diversification often do not fall into neat and tidy taxonomies. In such groups it can sometimes be very difficult to establish what does, and what does not, constitute a species. This presents problems for species-based conservation programmes that are based around prioritised species-lists (e.g. the UK Biodiversity Action Plans; BAPs), particularly as the inclusion or exclusion of taxa on these lists largely determines the allocation of conservation resources. This is an important issue as almost half of the BAP priority higher plant species for which Scotland has prime responsibility are taxonomically controversial.

Recent research using population genetic approaches to tackle some taxonomically complex plant groups has enhanced our understanding of their biology. Such approaches provide objective and independent assessments of whether a given entity is distinct or not. This information can then be used to contribute towards the decision making process of which taxa to prioritise for conservation, and address specific questions regarding BAP listed species. In the long term, however, a broader issue needs tackling. Actively evolving groups often contain a series of localised lineages, as well as complex populations that exhibit atypical levels of morphological diversity. These types of diversity do not fit well into a ‘standard’ species-based conservation system. In most cases protection will best be supplied by designated site protection or wider countryside habitat schemes. Where additional protection is need, a conservation policy is required that accepts the diversity in these actively evolving groups for what it is, rather than trying to squeeze it into conservation legislation derived for taxa whose delimitation is routine.     

Effect of light on abscisic acid content in photosensitive Scots pine (Pinus sylvestris L.) seed

Dormancy-breaking treatment of the photosensitive Scots pine (Pinus sylvestris L.) seed by white light incubation or a 15-min exposure to red light decreased the abscisic acid content prior to radicle protrusion. Incubation in the dark or exposure to red light followed by a 5-min far-red light irradiation did not cause as great a decrease in abscisic acid content nor was the dormancy relieved. The ability of the far-red light to keep the ABA level high and to prevent germination gradually disappeared as the length of the dark period between the red and far-red treatments was increased to 24 h. ABA was quantified on a gas chromatograph with an electron capture detector.     

Environmental and hormonal regulation of seed dormancy and germination in Cape fynbos Leucospermum R.Br. (Proteaceae) species

The endogenous levels of abscisic acid (ABA), cytokinins (CKs) and gibberellins (GA₁/GA₃ combined) in Leucospermum glabrum embryos were monitored in axes and cotyledons separately during normal germination. Plant growth substance changes were correlated with known morphological, structural and ultrastructural events in the embryo of Proteaceae. The effect of exogenous application of 6-benzyladenine (BA) and GA₄₊₇ under three known dormancy-enforcing environmental conditions were studied in L. glabrum and L. cordifolium. The endogenous levels of the hormone classes GAs and CKs changed phasically during normal germination under a single alternating temperature regime. GA₁/GA₃ levels increased in cotyledons within 3 d of hydration while at the same time initial CK levels decreased. Following this transient peak GAs fell to a low level throughout the germinative period. Subsequently the CKs, Z and ZR, and to a lesser extent their dihydro-derivatives, appeared in both the axes and the cotyledons as fluctuating, transient peaks. Early increases in GAs are thought to control the induction of the germination process. The CK pattern suggests that CKs control at least three major processes of germination sensu stricto following induction: 1) early mobilization of protein and lipid reserves in the axis and later in cotyledons, 2) cotyledon expansion which causes the endotesta to split permitting radicle protrusion and 3) later, radicle growth.Our results indicate that dormancy in intact Leucospermum seeds is enforced by embryo anoxia, regulated by the impermeable exotesta. In addition synthesis of or tissue sensitizing to both hormone classes GAs and CKs depends on moderately low temperature as the primary environmental requirement. For GA synthesis a secondary, daily pulse of high temperature is required. Inhibitory hormones, specifically ABA, appear not to play a role.Abbreviations ABA Abscisic acid - BA 6-benzyladenine - CK Cytokinin - DHZ Dihydrozeatin - DHZR Dihydrozeatin riboside - GA Gibberellin - HPLC High performance liquid chromatography - iP Isopentenyladenine - IPA Isopentenyladenosine - PGS Plant growth substance - RIA Radioimmunoassay - Z Zeatin - ZR Zeatin riboside