Seed germination behavior of five Resedaceae species from arid Arabian desert: gibberellic acid and light effects

Abstract

Light and growth-promoting compounds, such as gibberellic acids (GA₃), are among the most important factors that can break physiological seed dormancy. Here, we investigate the effects of GA₃ and light on germination of five species of Resedaceae that are known to have different levels of physiological dormancy. Seeds were incubated at 20/30?°C in both 12-hr photoperiod and complete darkness. To study the effect of growth hormone on germination, seeds were soaked for 24?h in different concentrations of GA₃ before sowing. The annuals (Reseda aucheri and Oligomeris linifolia) and the perennial Ochradenus arabicus had deep physiological dormancy, and exogenous application of GA₃ enhanced their germination in the light, but not in darkness; few or no seeds germinated in the dark in these species. Ochradenus aucheri and O. baccatus had intermediate and non-deep dormancy, respectively, and application of GA₃ enhanced their germination in both light and darkness. Germination of the annual species was much slower than that of the shrubby perennials. Overall, these results indicate that conditions under which seed developed, matured and stored on maternal plants as well as incubation conditions should be taken into consideration when assessing germination behavior of the perennial species of Resedaceae.     

金丝李果实、种子形态分化及外源物质对种子萌发和幼苗生长的影响

通过采集3个天然种群的金丝李(Garcinia paucinervis)果实,观察果实和种子的形态性状,分析其种群内和种群间的形态分化,观察不同种群种子萌发和幼苗生长的规律;采用四种植物生长调节剂和两种化学药剂,研究浸种对金丝李种子萌发和幼苗生长的影响。结果表明:金丝李种子长2.48~3.08 cm、宽1.49~1.67cm、百粒重392.50~438.18 g;3个种群果实和种子已产生明显的形态分化,胡润种群多数表型性状值在3个种群中最小,安宁种群的果实和种子偏圆,弄岗种群偏窄;在种群内部,果实和种子重量的分化较显著,整体形态较稳定;在萌发过程中,种子留存,不定根逐渐取代胚根成为主根;3个种群的萌发过程均缓慢,中间阶段几乎停滞,出苗极不整齐,萌发率表现为安宁种群(78.33%)弄岗种群(55%)胡润种群(48.33%),种子存在休眠;从种子萌发来看,以80 mg·L~(-1)的6-BA浸种24 h处理效果最好,萌发时滞最短、萌发率最高、平均萌发时间最短;结合幼苗生长情况来看,10~50 mg·L~(-1)的6-BA和500 mg·L~(-1)的GA_3处理均适宜,以50 mg·L~(-1)的6-BA效果最佳。低浓度的KNO_3和NH_4NO_3能提高萌发率,但未显著加快萌发进程,IAA和NAA对种子萌发和幼苗生长有抑制作用。该研究结果为金丝李的遗传多样性提供了形态学资料,为更好地保护、开发和利用这一珍贵树种提供了科学依据。     

海草种子休眠、萌发、幼苗生长及其影响因素的研究进展

海草床是沿岸海域重要的初级生产者,具有极其重要的生态价值和经济价值,是重要的浅海生态系统之一.本文综述了近年来国内外对海草种子休眠、萌发、幼苗生长及其影响因素的研究进展,总结了海草种子的休眠方式和休眠历期及其影响因素,探讨了盐度、温度、光、激素、溶解氧及种群等因素对海草种子萌发、幼苗存活和生长的影响,并对目前研究中存在的问题和今后的研究方向进行了展望.     

Effect of season of burning and removal of herbaceous cover on seedling emergence in a eucalypt savanna of north‐eastern Australia

Abstract Seedling emergence in a eucalypt savanna of north‐eastern Australia was documented over a 12‐month period, between May 1999 and May 2000. Seedling emergence for grasses, forbs and subshrubs was found to mainly occur in a brief pulse at the start of the wet season following fire or the removal of grass biomass. Only a minor number of tree and shrub seedlings were detected overall. Burning, or cutting away the grass layer in unburnt savanna, in both the early (i.e. May) and the late (i.e. October) dry seasons significantly increased seedling emergence over undisturbed savanna that had been unburnt for 3 years. Removing the grass layer in unburnt savanna, during either the early or the late dry season, triggered similar seedling densities to savanna burnt in the early dry season. Late dry season fires promoted the greatest seedling density. We attribute this to the higher intensity, late dry season fires releasing a greater proportion of seed from dormancy, coupled with the higher density of soil seed reserves present in the late dry season.     

植物种子大小与幼苗生长策略研究进展

种子大小和幼苗更新对策是植物生活史策略的重要组成部分.本文从不同侧面综述了当前国内外关于种子大小和幼苗之间关系的生态学研究,包括:种子大小对萌发出土的影响,种子大小与幼苗形态生长特性之间的关系,种子大小与幼苗存活、竞争能力之间关系等,并对今后的相关研究进行了展望.在不同的微环境和植被类型下,种子大小与幼苗生长之间的关系可能有所差异;种子大小对植物幼苗生长的影响导致种子大小不同的植物对植被幼苗更新补充的贡献不同;种子大小与幼苗生活史策略关系在大尺度的群落空间水平上和小尺度的物种间与物种内的研究对于天然植被的更新恢复研究具有重要意义.     

种子特征和播种深度对辽东栎种子萌发和幼苗生长的影响

该文在玻璃温室内的遮阴环境下,采用盆播方法研究了辽东栎种子特征(大小和种皮)和播种深度(0、3、6、10 cm)对种子萌发和幼苗生长的影响。结果表明:(1)辽东栎大种子萌发率、萌发速率、萌发值和萌发指数在所有播种深度均高于小种子。其中非去皮种子萌发率、萌发速率和萌发指数在0 cm播种深度的不同大小种子间差异显著,去皮种子所有萌发参数在6和10 cm播种深度的不同大小种子间均差异显著;去皮可促进大种子萌发,但抑制小种子萌发;不同大小种子所有萌发参数均在0 cm播种深度最大,在10cm播种深度最小。(2)不论有无种皮,大种子萌发幼苗的叶片数、单株叶面积、总干物质质量和根冠比在所有播种深度均大于小种子萌发幼苗;去皮种子萌发幼苗的株高、基径、叶片数、单株叶面积和总干物质质量在所有播种深度均不同程度地小于非去皮种子萌发幼苗,但前者根冠比在0、3、6 cm播种深度大于后者;随着播种深度增大,幼苗株高、叶片数、单株叶面积、总干物质质量和根冠比等生长参数均呈减小趋势,但基径随播种深度增大而增大。     

Relationships among cytokinins, ethylene and poly amines during the stratification-germination process in seeds of Acer saccharum

Relatively high levels of dihydrozeatin and trans-zeatin were detected in unstratified seeds of Acer saccharum Marsh. Both cytokinins increased substantially over the first 20 days of stratification at 5°C and then fell rapidly to values well below original levels by first germination on day 55. In seeds held at 20°C, a non-afterripening temperature, cytokinin levels remained constant for the first 10 days and then declined to their lowest levels by day 20. Levels of putrescine, spermidine and spermine in the radicles and cotyledons did not change during the full course of the afterripening process, but large increments were noted during radicle emergence. A large increase in ethylene production at germination suggests that competition for S-adenosyl-methionine by the ethylene and polyamine biosynthetic pathways did not inhibit synthesis of ethylene or polyamines during seedling emergence and establishment. In seeds stratified at 20°C, ethylene showed an exceptionally large peak early in the stratification period, but polyamine contents remained low throughout the test. The present results are consistent with the hypothesis that cytokinins play a significant role in overcoming the metabolic block present in dormant seeds. This conclusion is supported by data showing that high levels of cytokinins develop concurrently with the start of tissue differentiation and at the time when abscisic acid and phenolic inhibitors decline in stratifying seeds. Changes in ethylene and polyamine contents did not correlate with any events in the afterripening process; however, large increases in levels of these substances were closely associated with the germinative process and, in the case of polyamines, specifically with the start of cell division.     

Assessing the risks of transgene escape through time and crop-wild hybrid persistence

Transgenes introduced into crops can escape in time, as well as space, via the seed bank. For annual plants, especially ruderals, seed bank behaviour may be the most important factor determining population persistence. Crop seeds may exhibit some dormancy and germination cueing in the soil but are expected to be less able to persist than their wild relatives, which often have considerable dormancy and longevity, as well as effective germination cueing responses. Crop-wild hybrids may have seed bank characteristics more suited to persistence, and maternal effects may favour persistence of hybrids having wild plants for their female parent. Escape of transgenes via crop-wild hybrids presents unique concerns not present for crops. Hybrids can undergo natural selection and may back-cross with wild plants. We suggest methods that can be used in conjunction with evaluation of the relative fitness of crop-wild hybrids that will determine the likelihood of back-crossing. Accurate assessment of escape in time and transgene persistence via crop-wild hybrids requires proper plant materials. We emphasize the use of null segregants as controls for transgenic crops and for generating crop-wild hybrid controls for transgenic hybrids. Since good empirical and theoretical understanding of how individual genes influence the fate of plants in different environments is lacking, evaluation of escape in time and the persistence of transgenes via crop-wild hybrids should be on a case-by-case basis.     

不同处理对银沙槐种子休眠破除和幼苗生长的影响

对银沙槐种子破除休眠的适宜方法及其幼苗生长进行研究。结果表明:破口和沙磨处理休眠破除效果最好,但容易引起种子腐烂死亡;分别用65、80和95℃热水处理种子,以95℃1 min破除种子休眠效果最好,且幼苗长势好,65℃效果最差,80℃可破除部分种子休眠,除80℃外延长热水处理时间可导致死种子数增加,95℃则引致大部分种子死亡;液氮浸种处理效果均显著,其中以液氮处理10 min效果最好,但幼苗多为不正常苗而致死;硫酸处理以浸种120 min效果最好,但处理时间过长可导致死种子数增多,且造成少数幼苗根部腐蚀死亡。综上所述,打破银沙槐种子休眠的较优处理方法是硫酸120 min浸种处理和95℃1 min热水处理。     

埋藏对65种半干旱草地植物种子萌发特性的影响

比较了半干旱草原科尔沁沙地65种植物新采种子和埋藏1年种子的萌发特性.结果表明：埋藏1年后,有38种植物的种子仍具有活力.新采种子萌发率>80%的植物种子埋藏后萌发率下降；而萌发率<80%的植物种子埋藏后萌发率均有较大幅度的提高.埋藏对种子萌发特性的影响因植物生态类群(杂草、草原植物、草甸植物、沙生植物)而异.种子埋藏1年后,多年生植物萌发率没有明显提高,而1年生植物萌发率显著提高(P<0.05).对于新采种子和埋藏1年种子萌发率间相差10%以下的物种,可根据萌发格局将植物种分为3类：埋藏促进型(如差巴嘎蒿)、埋藏抑制型(如大籽蒿)和埋藏不变型(如鹤虱).     

围封沙质草甸土壤种子库与幼苗库的特征

采用野外定点取样和萌发实验相结合的方法,研究了科尔沁沙地围封沙质草甸土壤种子库和幼苗库的特征.结果表明:土壤种子库总密度为13854±1651有效种子数/m2,而幼苗库的总密度为808±164株/m2,仅为土壤种子库总密度的6%,土壤种子库与幼苗库总密度之间存在显著的差异 F=36.0,n=219,P<0.001 .土壤种子库与幼苗库的植物种数分别为37和44,其中一、二年生草本植物分别占种子库与幼苗库植物种数的62%和50%,而多年生草本植物所占的比例分别为24%和41%,灌木所占的比例很小,分别为14%和9%.土壤种子库与幼苗库种类组成上的相似性系数为0.667,表现出较小的异质性.土壤种子库密度与幼苗库密度之间存在显著的相关性,其间关系可用三次曲线来描述.     

Seed germination and in vitro propagation of Maytenus canariensis through regeneration of adventitious shoots from axillary and apical buds

Seed germination and micropropagation protocols of the medicinal species Maytenus canariensis (Loes.) G. Kunkel & Sunding were optimized. In vitro seed germination occurred (86 to 94.7 %) only after treatment of the seeds with H₂SO₄, followed by surface sterilization and culture on solid nutrient medium without any growth regulators. Micropropagation failed when explants were taken from mature trees, and browning of the nutrient medium frequently occurred despite testing many growth media. Nonetheless, adventitious shoot regeneration was achieved employing axillary or apical buds taken from 2–2.5 months old plantlets obtained after in vitro germination of seeds, following culture on nutrient media supplemented with benzylaminopurine, kinetin and naphthalenacetic acid (NAA), attaining up to 3.9 shoots per explant, after 4–6 months. Root induction was best on a medium containing 4.0 mg dm⁻³ NAA, achieving a 100 % induction. After hardening of rooted plants, survival after transfer to soil was 71.43 %.     

Annual dormancy cycles in buried seeds of shrub species: germination ecology of Sideritis serrata (Labiatae)

The germination ecology of Sideritis serrata was investigated in order to improve ex‐situ propagation techniques and management of their habitat. Specifically, we analysed: (i) influence of temperature, light conditions and seed age on germination patterns; (ii) phenology of germination; (iii) germinative response of buried seeds to seasonal temperature changes; (iv) temperature requirements for induction and breaking of secondary dormancy; (v) ability to form persistent soil seed banks; and (vi) seed bank dynamics. Freshly matured seeds showed conditional physiological dormancy, germinating at low and cool temperatures but not at high ones (28/14 and 32/18 °C). Germination ability increased with time of dry storage, suggesting the existence of non‐deep physiological dormancy. Under unheated shade‐house conditions, germination was concentrated in the first autumn. S. serrata seeds buried and exposed to natural seasonal temperature variations in the shade‐house, exhibited an annual conditional dormancy/non‐dormancy cycle, coming out of conditional dormancy in summer and re‐entering it in winter. Non‐dormant seeds were clearly induced into dormancy when stratified at 5 or 15/4 °C for 8 weeks. Dormant seeds, stratified at 28/14 or 32/18 °C for 16 weeks, became non‐dormant if they were subsequently incubated over a temperature range from 15/4 to 32/18 °C. S. serrata is able to form small persistent soil seed banks. The maximum seed life span in the soil was 4 years, decreasing with burial depth. This is the second report of an annual conditional dormancy/non‐dormancy cycle in seeds of shrub species.     

Seed Germination Biology of the Narrowly Endemic Species Lesquerella stonensis (Brassicaceae)

Abstract Lesquerella stonensis (Brassicaceae) is an obligate winter annual endemic to a small portion of Rutherford County in the Central Basin of Tennessee, where it grows in disturbed habitats. This species forms a persistent seed bank, and seeds remain viable in the soil for at least 6 years. Seeds are dormant at maturity in May and are dispersed as soon as they ripen. Some of the seeds produced in the current year, as well as some of those in the persistent seed bank, afterripen during late spring and summer; others do not afterripen and thus remain dormant. Seeds require actual or simulated spring/summer temperatures to come out of dormancy. Germination occurs in September and October. Fully afterripened seeds germinate over a wide range of thermoperiods (15/6–35/20°C) and to a much higher percentage in light (14 h photoperiod) than in darkness. The optimum daily thermoperiod for germination was 30/15°C. Nondormant seeds that do not germinate in autumn are induced back into dormancy (secondary dormancy) by low temperatures (e.g., 5°C) during winter, and those that are dormant do not afterripen; thus seeds cannot germinate in spring. These seed dormancy/ germination characteristics of L. stonensis do not differ from those reported for some geographically widespread, weedy species of winter annuals and thus do not help account for the narrow endemism of this species.     

Burial of canopy-stored seeds in the annual psammophyte Agriophyllum squarrosum Moq. (Chenopodiaceae) and its ecological significance

Agriophyllum squarrosum Moq. is a dominant annual on sand dunes in the arid regions of central Asia. A high percentage of seeds is retained on dead plants which become covered by moving sand, but little is known about the ecological significance of burial of canopy-stored seeds. We investigated the size and dynamics of the buried canopy-stored seed bank and effects of burial on seed germination. In March (during the windy season), May (beginning of the germination season), and July (middle of the growing season), the number of seeds per square meter in sample plots in the dunes was 623, 223 and 22, respectively, with 54.6, 30.6 and 12.9% of the total seeds retained on buried plant canopies. In a controlled experiment, more seedlings emerged from released (dispersed) than from canopy-stored seeds when burial depth was the same. No viable ungerminated released seeds were found, but 45–80% of the ungerminated canopy-stored seeds were viable. In general, with an increase in applied water germination of released seeds buried at a depth of 1 or 2 cm and of canopy-stored seeds buried at 1 cm increased, but regardless of watering regime few or no released seeds at 4 cm or canopy-stored seeds at 2 or 4 cm germinated. Significantly more seedlings emerged from plants buried in a horizontal than in a vertical position. Seedlings originating from buried canopy-stored seeds on an active dune accounted for only 5.4% of the total seedlings emerging, and most of them emerged later than those from released seeds. Thus, seed release is more effectively postponed in buried than in exposed canopies, and burial of canopy-stored seeds is a mechanism that helps regulate seed germination and seedling emergence of A. squarrosum on active dunes.