Ultrahigh-Temperature Activation of a Low-Temperature Bacillus subtilis Spore Germination System

Exposure of Bacillus subtilis A spores to 115 to 125 C for several seconds activated a low-temperature germination system that remained dormant after a heat treatment that activated the normal l-alanine- and glucose-stimulated germination systems. The low-temperature germination system was characterized by an optimum temperature lower than that of the l-alanine or glucose germination systems (30 C versus 45 C), germination in the absence of exogenous germination stimulants, and the capacity for heat-induced deactivation and subsequent reactivation. The rates of activation at 115 to 125 C were exponential and were not influenced by a previous heat treatment that activated the l-alanine- or glucose-stimulated germination systems. Although activation of the low-temperature germination system was accompanied by suppression of l-alanine-stimulated germination, it did not appear to be a modification of the l-alanine germination system.     

Modelling the germination of Stellaria media using the concept of hydrothermal time

The germination characteristics of Stellaria media (common chickweed) were investigated over a range of constant temperatures and degrees of moisture stress in order to assess the suitability of hydrothermal time as a basis for modelling germination under field conditions. Maximum percentage germination occurred over a much narrower temperature range around the optimum temperature than previously seen for cultivated crop seed. The entire final percentage germination response to temperature in water was well described by two probit curves, and this model was extended to describe the data at all water potentials at a temperature close to the optimum. The implications of the reduction in germination at nonoptimal temperatures are discussed with respect to the interpretation of germination progress curves and conditional dormancy. After adjusting for maximum percentage germination, a hydrothermal time model was found to fit the data set well within the conditions normally encountered in horticultural seedbeds. This separation of the final percentage germination presents a flexible modelling approach that allows for the different levels of dormancy typically expressed within weed populations. By contrast with many previously reported species, S. media had a synchronous germination rate within the population at any given temperature/water potential combination. This synchronous germination of at least a proportion of the population over a wide range of temperature and water potentials might have ecological significance for the opportunistic germination behaviour of this weed species.     

画眉草种子萌发对策及生态适应性

研究了画眉草种子在不同贮藏条件以及光照、温度和降雨等环境因素下的萌发对策.结果表明,画眉草新种子具有较强的内在休眠;4个月的干藏和冷藏处理对解除种子休眠作用不明显,但较长时间的贮藏（干藏1年）则能促进种子成熟.画眉草种子在光照和黑暗条件下都能萌发,但较强的光照更有利于种子萌发.种子萌发适宜温度是28 ℃,温度升高和降低都会导致画眉草种子萌发率下降;变温条件下（16～28 ℃）种子萌发率高于恒温28 ℃条件,但两个处理间的萌发率没有显著差异.种子萌发降雨阈值是10 mm,种子萌发率和萌发持续时间均随降雨量的增加而增加.画眉草种子具有迅速萌发和推迟萌发时间超过1年以上两种萌发对策.根据种子形态特征和萌发策略,推断画眉草具有持久土壤种子库.     

不同前处理条件对薄荷种子萌发的影响

研究了不同质量浓度(10～250 mg·L~(-1))赤霉素(GA_3)以及清水浸种不同时间(6～36 h)、层积不同时间(5～20 d)和超声波处理不同时间(5～25 min)对薄荷(Mentha haplocalyx Briq. )种子萌发的影响. 结果表明, 用100～200 mg·L~(-1) GA_3处理6 h, 薄荷种子的发芽启动时间缩短且发芽率和发芽势均显著高于对照, 其中, 用150 mg·L~(-1)GA_3浸种,薄荷种子的发芽率最高(57.3%).用清水浸种6～36 h后,薄荷种子的发芽启动时间和发芽持续时间与对照无显著差异,但浸种12 h的薄荷种子发芽率极显著高于对照.于10 ℃层积5～15 d后,薄荷种子的发芽率和发芽势极显著高于对照,发芽启动时间也与对照差异显著,其中层积5～10 d的种子发芽率较高,达47.8%～52.4%.用功率50 W、频率40 kHz超声波处理5～20 min后,薄荷种子发芽率较对照有极显著提高,其中用超声波处理10 min的薄荷种子发芽率最高,达到68.3%.研究结果显示,使用功率50 W、频率40 kHz的超声波处理10 min是打破薄荷种子休眠的最佳方法,可显著提高薄荷种子的发芽率.     

濒危植物秦岭冷杉种子萌发特性的研究

 秦岭冷杉(Abies chensiensis)为中国特有种,主要分布于中国秦巴山地,现为渐危种,被列为国家二级保护植物。经测定,秦岭冷杉种子千粒重为(33.92±1.01)g,与其它冷杉属的种子比较,其种子千粒重较大。四唑（TTC,1.0 %）染色测种子生活力的结果表明:有生活力的种子占26.00%,空粒占20.50%,涩粒占33.75%,说明秦岭冷杉种子饱满度很差,反映了比较高的种子败育率;染色结果与对比发芽实验的结果很接近,说明用四唑染色来测定秦岭冷杉种子的生活力是较准确的方法。把种子进行0、14、21、28d低温(4℃)层积处理,发现低温层积可以显著提高种子发芽率和发芽势,但是层积21d与28d发芽势没有差异。设置恒温20℃、25℃和变温20～30℃ 3种温度条件下发芽比较,发现最终的发芽率并没有差异,但是发芽势差异显著,恒温25℃达到最大发芽率的90%的时间要比另外两种温度下提前9d,可见25℃是秦岭冷杉种子发芽的适宜温度。光照(8 h·d-1,100μmol·m-2·s-1)和黑暗下种子的最后发芽率差异不显著,但是光照发芽势高,可见光照可以促进秦岭冷杉种子发芽迅速、整齐。实验证明,用砂床做发芽基质与用纸床做发芽基质相比,前者的发芽率和发芽势均比后者高。     

条叶百合种子萌发的研究

研究了不同光、温对条叶百合(Lilium callosum)种子萌发的影响。研究结果表明:(1)避光条件下温度对栽培4年生条叶百合种子萌发影响最大,其种子萌发最适宜温度为25℃, 4~5天开始萌动, 1~2周萌发完全。随着温度的升高或降低其种子萌发率下降。但在5℃时萌发率又有大幅升高, 35℃种子萌发完全受到抑制。(2)同一果序不同位置果实的种子萌发以最下部果实为好,中间果实次之,上部最差。(3)同一果实内中部种子萌发最好,下部种子次之,上部种子最差,上、中、下三部分种子萌发率与其千粒重呈正相关。(4)在相同实验条件下,野生条叶百合与栽培4年生条叶百合种子萌发率一致,但萌发完全时间比栽培条叶百合多14天。(5)贮藏一年后条叶百合种子萌发率没有下降。     

温水浸种对蒙古黄芪种子萌发特性的影响

研究温水浸种破除蒙古黄芪（Astragalus membranaceus Bge.var.mongholicus（Bge.） Hsiao）种子休眠的适宜条件,采用恒温和变温2种浸种方式,测定蒙古黄芪种子在不同时间、不同温度梯度条件下的发芽率、发芽势和发芽指数。结果表明,温水浸种破除蒙古黄芪种子休眠的效果显著,变温浸种效果略优于恒温浸种。不同温度破除休眠效果排序依次为60℃> 70℃> 80℃,其中60℃变温浸种2 min和5 min的发芽率分别为对照的2.87倍和2.31倍。浸种时间、浸种温度均可显著影响蒙古黄芪种子萌发,与对照相比,随着浸种时间增加,发芽率总体呈现出先急速升高后逐渐降低的趋势;发芽指数与浸种温度极显著正相关;浸种温度与发芽势和发芽指数均显著正相关。本研究结果表明温水浸种可以提高种子发芽率,保持种子活力。     

盐胁迫对两种无芒雀麦种子萌发的影响

 在实验室中对两种无芒雀麦本地种（Bromus inermis cv. Xilinguole）和引进种 (Bromus stamineus)种子在浓度为0.5%、1.0%、1.5%的Na₂SO₄、NaCl和MgCl₂ 3种单盐胁迫下进行发芽实验，结果表明：与对照相比，在以上3种盐胁迫下，随着胁迫浓度的增加，两种无芒雀麦种子的发芽率、发芽指数和发芽值均有不同程度的降低，相对盐害率升高，种子开始发芽的时间推迟且其发芽过程延长；在3种盐中，NaCl的胁迫对两种植物种子萌发的抑制作用最大，其中浓度为1.0% NaCl的胁迫对引进种和本地种无芒雀麦发芽率的抑制分别达到了68.67%和14%，在浓度为1.5%的NaCl胁迫下两种供试植物的发芽率均为零；通过建立不同盐分处理与两种无芒雀麦种子发芽率之间的回归方程得出，引进无芒雀麦种子芽期的耐盐性较本地无芒雀麦强。     

Gravitational stress on germinating Pinus pinea seeds

In the germination of lipid-rich seeds, the glyoxylate cycle plays a control role in that, bypassing the two decarboxylative steps of the Krebs cycle; it allows the net synthesis of carbohydrates from lipids. The activity of isocitrate lyase, the key enzyme of the glyoxylate cycle, is an indicator of the state of seed germination: stage of germination, growth of embryo, activation and progress of protein synthesis, depletion of lipidic supplies. In order to investigate the effects of gravity on seed germination, we carried out a study on the time pattern of germination of Pinus pinea seeds that were subjected to a hypergravitational stress (1000 g for 64 h at 4 degrees C), either in a dry or in a wet environment, before to be placed in germination plates. During the whole time of germination, we monitored the state of embryo growth and the most representative enzymes of the main metabolic pathways. In treated wet seeds, we observed an average germination of only 20% with a slowdown of the enzyme activities assayed and a noticeable degradation of lipidic reserves with respect to the controls. These differences in germination are not found for dry seeds.     

Seed germination traits of Ailanthus altissima,Phytolacca americana and Robinia pseudoacacia in response to different thermal and light requirements

Invasion of alien plant species (IAS) represents a serious environmental problem, particularly in Europe, where it mainly pertains to urban areas. Seed germination traits contribute to clarification of invasion dynamics. The objective of this research was to analyze how different light conditions (i.e., 12-hr light/12-hr darkness and continuous darkness) and temperature regimes (i.e., 15/6°C, 20/10°C and 30/20°C) trigger seed germination of Ailanthus altissima (AA), Phytolacca americana (PA) and Robinia pseudoacacia (RP). The relationship between seed germination and seed morphometric traits was also analyzed. Our findings highlight that temperature rather than light was the main environmental factor affecting germination. RP germinated at all tested temperatures, whereas at 15/6°C seeds of AA and PA showed physiological dormancy. RP had a higher germination capacity at a lower temperature, unlike AA and PA, which performed better at the highest temperatures. Light had a minor role in seed germination of the three species. Light promoted germination only for seeds of PA, and final germination percentage was 1.5-fold higher in light than in continuous darkness. Seed morphometric traits (thickness [T], area [A] and volume [V]) had a significant role in explaining germination trait variations. The results highlight the importance of increasing our knowledge on seed germination requirements to predict future invasiveness trends. The increase in global temperature could further advantage AA and PA in terms of germinated seeds, as well as RP by enhancing the germination velocity, therefore compensating for a lower germination percentage of this species at the highest temperatures.     

Germination responses of Reaumuria vermiculata to salinity and temperature

Reaumuria vermiculata is a xerohalophytic perennial dwarf shrub distributed in many gypseous and saline areas in southern Tunisia. A laboratory experiment was carried out to assess the effects of temperature and salinity on germination. The germination responses of the seeds in darkness were determined under a range of salinity and temperature regimes. Temperatures between 10°C and 30°C seem to be favourable for the germination of this species. Germination was inhibited by either an increase or a decrease in temperature from the optimal temperature (15°C). Highest germination percentages were obtained under non-saline conditions and increases in salinity inhibited seed germination. Salt stress decreased both the germination percentage and the germination speed (increase of the mean time to germinate). Seed germination decreased with an increase in NaCl concentrations at all temperatures. An interaction between salinity and temperature yielded no germination at salinity of 300 mM, whereas some seeds germinated under the optimal temperature.     

WATER POTENTIAL,TEMPERATURE, AND KINETIN EFFECTS ON SEED GERMINATION IN SOIL AND SOLUTE SYSTEMS

Germination of lettuce and wheat in soil is reduced by a decrease in water potential, but a significant temperature-water potential interaction exists for lettuce. At 35 C kinetin permits lettuce germination at 0 and —1.1 bars, and at 25 C and 15 C it enhances germination at lower water potentials, causing 30% germination at —8.0 bars. Wheat germinates well at —8.0 bars, but no germination occurs at —14.9 bars; temperature had little effect on wheat germination. Germination in soil and solute systems was compared to determine the usefulness of solute germination data for predicting germination in dry soil. Total germination of lettuce in polyethylene glycol-6000 may approximate total germination in soil at the same water potential, but germination rates differ widely for the two systems. Kinetin-treated lettuce seeds nearly completed germination in two days in polyethylene glycol solutions, but five days were required for similar germination percentages in the soil. Sucrose is not useful for simulating soil water stress; wheat seeds germinate at —14.9 bars in sucrose but fail to germinate in soil at the same potential, and germination is more rapid in sucrose than in the soil.     

Radiosensitivity and Biological Effects of Gamma and X-Rays on Germination and Seedling Vigour of Three Coffea arabica Varieties

Effects of gamma and X-ray treatments were studied on three varieties of Coffea arabica (Kent, Mundo Novo and Geisha) to determine their radiosensitivity and relative biological effects. The coffee varieties seeds were subjected to 0, 50, 100, 150, 200 and 400 Gy of gamma and X-rays from Cobalt 60 (⁶⁰Co) source irradiation. The irradiated seeds were pre-germinated in Petri dishes placed in a germination chamber, whilst some were sown in the greenhouse for germination studies. Data were collected on germination date and rate, root and hypocotyl length to determine the relative biological effectiveness of treatments and the optimum dose. The results showed varieties responding differently to the irradiations and doses. There was a decrease in germination with increasing doses of the irradiation. The X-ray-treated seeds had less germination percentage and seedling vigour measured at 28 days after treatment compared to the gamma-irradiated seeds. The irradiation effects on germination suggest that lower doses of X-rays give the same Relative Biological Effects as higher gamma doses for both growth chamber and greenhouse germination for Geisha at LD₅₀, where the effects were similar for the two irradiations. Whereas 50–100 Gy stimulated germination and seedling vigour, 150 Gy adversely affected germination and no germination occurred at 200–400 Gy. The study concluded that all the coffee varieties evaluated are sensitive to gamma and X-ray irradiation in terms of germination, seedling vigour and biological effects with an optimum dose of 50–100 Gy. Therefore, both gamma and X-rays could be utilized in a future mutational breeding programme for coffee seedlings.

     

Conflicting selection on the timing of germination in a natural population of Arabidopsis thaliana

The timing of germination is a key life‐history trait that may strongly influence plant fitness and that sets the stage for selection on traits expressed later in the life cycle. In seasonal environments, the period favourable for germination and the total length of the growing season are limited. The optimal timing of germination may therefore be governed by conflicting selection through survival and fecundity. We conducted a field experiment to examine the effects of timing of germination on survival, fecundity and overall fitness in a natural population of the annual herb Arabidopsis thaliana in north‐central Sweden. Seedlings were transplanted at three different times in late summer and in autumn covering the period of seed germination in the study population. Early germination was associated with low seedling survival, but also with high survival and fecundity among established plants. The advantages of germinating early more than balanced the disadvantage and selection favoured early germination. The results suggest that low survival among early germinating seeds is the main force opposing the evolution of earlier germination and that the optimal timing of germination should vary in space and time as a function of the direction and strength of selection acting during different life‐history stages.     

温带半干旱地区一年生植物种子的萌发特性

在实验室条件下研究了中国温带半干旱地区科尔沁沙地的23种1年生植物的种子萌发特性（新采集种子、冷藏和干藏种子）.大籽蒿、虎尾草、冠芒草、沙蓬和地锦的新种子萌发率达90%左右,11种植物新种子萌发率均低于70%,说明这些植物的新种子具有或多或少的休眠属性.经过150d的冷干藏后,大籽蒿、虎尾草萌发率保持在90%以上,说明这两种植物完全没有休眠机制;冠芒草、沙蓬和地锦的种子萌发率下降较多,可能是储藏的环境条件导致的2次休眠现象;冷藏和干藏处理均能使绿珠藜、毛马唐、细叶益母草、雾冰藜、金狗尾草、苋菜、马齿苋、碱地肤和水稗草的种子在生长季开始时完成生理后熟,萌发率达到80%以上;干藏有利于促进毛马唐、细叶益母草、马齿苋和鹤虱的种子成熟,冷藏有利于促进绿珠藜和金狗尾草的种子成熟;黄蒿、灰绿藜、画眉草和烛台虫实在不同处理下的萌发率都比较低,说明种子内在生理休眠作用较强,具有减少种子一次性萌发数量的风险分摊策略.大多数1年生植物均能在较短时间内达到最终萌发率的90%,表现出迅速萌发的特性;黄蒿、灰绿藜、碱地肤和沙蓬种子则在不同处理中表现出延长萌发时间的策略来适应半干旱地区不确定的环境条件.最后,探讨了几种主要1年生植物的种子萌发对策与其对环境适应机制之间的关系.     

Germination ecology of drupelets of the fig (Ficus carica L.)

Abiotic and biotic factors and their effects on germination of fig drupelets were studied. The drupelets germinated between 10^oC and 30^oC.Constant humidity was necessary for germination and frequent drying out of the substrate was unfavourable. Total darkness for the whole duration of the experiments had a slighly negative effect on germination. The fastest germination occurred at constant humidity and an alternating temperature of 20/30^oC with exposure to light for 8 hours (at the higher temperature) and to darkness for 16 hours (at the lower temperature).Natural or artificial removal of drupelets from the syconium guaranteed a high germination percentage, whereas no germination occurred in drupelets left inside the syconium. Hence birds and mammals act as dispersal agents and mediators of germination. As they eat pieces of fig syconium, they free the drupelets from the flesh, eliminating the effect of inhibitors and/or microenvironments with high osmotic pressure inside the syconium. These findings support the hypothesis that germination occurs in autumn or spring depending on the climatic zone in which the species grows.     

不同种子预处理对10种沙拐枣植物萌发的影响

为了确定沙拐枣植物种子的萌发特性及最优播前预处理方法,在实验室条件下,对10种沙拐枣植物的种子进行了磨砺、硫酸和热水浸泡、冷藏、种子浸出液处理,然后进行发芽实验研究。萌发实验的结果表明,10种沙拐枣植物对于不同的种子预处理,均表现出相似的萌发反应。磨砺、硫酸浸泡和冷藏处理对种子萌发有明显地促进作用。与对照相比,种子浸出液处理对种子的发芽率、发芽速度均具有明显地抑制作用,并能增强种子的休眠。冷藏处理具有打破有活力的种子休眠、促进种子萌发的作用,但它与热水浸泡处理一样,对有活力种子表现出一定的致死作用。沙拐枣植物的萌发模式在不同种子预处理问均表现出明显的差异性。机械磨擦和硫酸处理能够促进种子的萌发率及发芽势。泡果沙拐枣(Callingonum junceum)在本项实验中表现出很强的萌发能力。     

Representing Cumulative Germination. 1. A Critical Analysis of Single-value Germination Indices

Several single-value germination indices, including Kotowski'scoefficient of velocity, Maguire's speed of germination, Czabator'sgermination value, Diavanshir and Pourbiek's germination value,Timson's cumulative germination, Lehle and Putnam's Richardsfunction index, Smith and Millett's sprouting index, and Tuckerand Wright's regression index, were evaluated to test theirability to distinguish superior from inferior germination. Allexcept Timson's cumulative germination method were essentiallyno better for ranking germination responses than data on totalgermination; Kotowski's coefficient of velocity, Smith and Millet'ssprouting index, and Lehle and Putnam's Richards function indexwere markedly inferior. Because of the ambiguity inherent inany index that combines, into a single value, data about theonset, rate and extent of germination, none of the indices couldbe recommended as a way of summarizing germination. Cumulative germination, single-value germination indices, germination index, germination     

濒危植物合柱金莲木种子萌发特性

研究了合柱金莲木种子萌发的生物学特性,以了解该物种种群自然更新困难的原因和机制。结果表明:合柱金莲木种子萌发的适宜温度为25℃,萌发率为56.67%,在20℃和30℃条件下,萌发速度和萌发率均较低,且在30℃条件下,幼苗不能正常生长,萌发在15℃受到抑制。土壤含水量在20%～30%,种子正常萌发,随着土壤含水量的升高,萌发开始时间缩短,萌发速度加快。种子萌发需要光照,为需光种子。种子在河沙、粘质壤土、沙土3种不同的基质中萌发率并无显著差异,但在粘质壤土和沙土中生长的幼苗长势较好。不同地理种源的种子,其种子质量存在差异,融水种群种子萌发率高,幼苗长势好。合柱金莲木种子萌发速度慢,萌发不整齐,幼苗生长缓慢,使得其在种间竞争中处于不利地位,且种子萌发对温度的适应范围狭窄,再加上林下光照不足限制种子萌发,这些因素是导致该物种自然更新困难的重要原因。