Parental environment changes the dormancy state and karrikinolide response of Brassica tournefortii seeds

Background and Aims

The smoke-derived chemical karrikinolide (KAR₁) shows potential as a tool to synchronize the germination of seeds for weed management and restoration. To assess its feasibility we need to understand why seeds from different populations of a species exhibit distinct responses to KAR₁. Environmental conditions during seed development, known as the parental environment, influence seed dormancy so we predicted that parental environment would also drive the KAR₁-responses of seeds. Specifically, we hypothesized that (a) a common environment will unify the KAR₁-responses of different populations, (b) a single population grown under different environmental conditions will exhibit different KAR₁-responses, and (c) drought stress, as a particular feature of the parental environment, will make seeds less dormant and more responsive to KAR₁.

Methods

Seeds of the weed Brassica tournefortii were collected from four locations in Western Australia and were sown in common gardens at two field sites, to test whether their KAR₁-responses could be unified by a common environment. To test the effects of drought on KAR₁-response, plants were grown in a glasshouse and subjected to water stress. For each trial, the germination responses of the next generation of seeds were assessed.

Key Results

The KAR₁-responses of seeds differed among populations, but this variation was reduced when seeds developed in a common environment. The KAR₁-responses of each population changed when seeds developed in different environments. Different parental environments affected germination responses of the populations differently, showing that parental environment interacts with genetics to determine KAR₁-responses. Seeds from droughted plants were 5 % more responsive to KAR₁ and 5 % less dormant than seeds from well-watered plants, but KAR₁-responses and dormancy state were not intrinsically linked in all experiments.

Conclusions

The parental environment in which seeds develop is one of the key drivers of the KAR₁-responses of seeds.     

Seed germination of agricultural weeds is promoted by the butenolide 3-methyl-2H-furo[2,3-c]pyran-2-one under laboratory and field conditions

Here we report that a synthesised form of a naturally occurring chemical (a butenolide, 3-methyl-2H-furo[2,3-c]pyran-2-one) found in smoke can stimulate seedling emergence of the economically important weed species Avena fatua L. (Poaceae), Arctotheca calendula (L.) Levyns (Asteraceae), Brassica tournefortii Gouan (Brassicaceae), and Raphanus raphanistrum L. (Brassicaceae) under field conditions at rates equivalent to 2–20 g/ha a.i. The butenolide also stimulates germination of freshly collected seeds from wild populations of these species, as well as those of Sisymbrium orientale L. (Brassicaceae), Hordeum leporinum Link (Poaceae) and Echium plantagineum L. (Boraginaceae) under laboratory conditions, consistently greater than that of smoke water. Experiments using B. tournefortii seeds collected from several locations across Western Australia and in different growing seasons found that these factors significantly influence the butenolide response, implying a role of the maternal environment in seed germination/dormancy characteristics. This research highlights the potential of butenolide as an agent for broad acre weed control and land restoration.     

Prior hydration of Brassica tournefortii seeds reduces the stimulatory effect of karrikinolide on germination and increases seed sensitivity to abscisic acid

Background and Aims

The smoke-derived compound karrikinolide (KAR₁) shows significant potential as a trigger for the synchronous germination of seeds in a variety of plant-management contexts, from weed seeds in paddocks, to native seeds when restoring degraded lands. Understanding how KAR₁ interacts with seed physiology is a necessary precursor to the development of the compound as an efficient and effective management tool. This study tested the ability of KAR₁ to stimulate germination of seeds of the global agronomic weed Brassica tournefortii, at different hydration states, to gain insight into how the timing of KAR₁ applications in the field should be managed relative to rain events.

Methods

Seeds of B. tournefortii were brought to five different hydration states [equilibrated at 15 % relative humidity (RH), 47 % RH, 96 % RH, fully imbibed, or re-dried to 15 % RH following maximum imbibition] then exposed to 1 nm or 1 µm KAR₁ for one of five durations (3 min, 1 h, 24 h, 14 d or no exposure).

Key Results

Dry seeds with no history of imbibition were the most sensitive to KAR₁; sensitivity was lower in seeds that were fully imbibed or fully imbibed then re-dried. In addition, reduced sensitivity to KAR₁ was associated with an increased sensitivity to exogenously applied abscisic acid (ABA).

Conclusions

Seed water content and history of imbibition were found to significantly influence whether seeds germinate in response to KAR₁. To optimize the germination response of seeds, KAR₁ should be applied to dry seeds, when sensitivity to ABA is minimized.     

Seed germination of the carnivorous plant Byblis gigantea (Byblidaceae) is cued by warm stratification and karrikinolide

Byblidaceae is one of the most poorly studied carnivorous plant families, with seed dormancy and germination biology remaining unresolved. This knowledge deficit has significant conservation and management implications, particularly as the most southerly distributed species, the south‐west Western Australian endemic Byblis gigantea, is listed as critically endangered. This study examined the ecophysiology of seed dormancy and germination in B. gigantea in concert with a study of the population dynamics of a single plant community. Mass seedling emergence and plant establishment were observed after a wildfire in 2007 in the natural population, followed by a rapid decline in mature individuals (91%) over a 4‐year monitoring period, with almost no inter‐fire recruitment (1.4% of all emergence) observed. Seeds possessed a fully developed embryo, and the germination characteristics of fresh seeds classified them as showing physiological dormancy. Seed dormancy was partially alleviated by warm stratification (30 °C) for 8 weeks prior to incubation at 15 °C, with c. 40% germination observed. With the additional exposure of seeds to the germination‐active chemical in smoke, karrikinolide, the germination of warm‐stratified seeds increased to 89%. Seeds also displayed orthodox storage behaviour and appeared to be amenable to long‐term seed banking for conservation. These results present the first observation of the stimulation of the germination of a carnivorous plant by a smoke‐derived compound. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 143–152.     

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.     

准噶尔荒漠异苞滨藜(Atriplex micrantha)的种子二型性及其萌发行为

异苞滨藜的果实(种子)存在二型性,这两种类型的果实在形状、大小、颜色及包被其苞片的大小上均有差异。黑色果实果皮光滑,有光泽,直径1.481mm±0.186mm,包被果实的苞片较小;褐色果实扁平,直径2.642mm±0.254mm,包被果实的苞片较大。以异苞滨藜的两种果实(种子)为材料,在3个变温条件(5/25℃、5/15℃、15/25℃,暗12h/光12h)下进行萌发实验,褐色种子成熟后即具有一定的萌发能力,最终萌发率都在80%以上。黑色种子仅在低的夜间温度(5℃)和高的昼间温度(25℃)条件下有较高的萌发率(>70%),而在5/15℃、15/25℃条件下,种子的最终萌发率较低(<20%),2星期的低温层积处理能够有效地加速和提高黑色种子在3个变温条件下的萌发,划破果皮和种皮也能不同程度的加速和促进黑色种子的萌发,表明黑色种子处于非深度生理休眠状态。苞片中盐含量低,苞片对褐色种子萌发无抑制作用。异苞滨藜的果实(种子)二型性及其萌发行为是对荒漠异质环境的适应。     

Morphological side effects of using gibberellic acid to induce germination: consequences for the study of seed dormancy

To assess the evolutionary significance of persistent seed banks, phenotypes of naturally germinating seeds must be compared with those that remain dormant under the same environmental conditions. Dormant seeds can often be induced to germinate by application of gibberellic acid (GA). However, this method is valid only if there are no phenotypic “side effects” of GA that could confound comparisons between dormant and naturally germinating seeds. We examined this assumption in Lesquerella fendleri, a short-lived perennial mustard of the desert Southwest. We exposed 3840 seeds from 16 maternal sibships to two different GA treatments (0 or 1 g/L GA) in two different germination environments (greenhouse and growth chamber), and measured germination and postgermination traits. As expected, application of GA increased germination. GA also had strong and long-lasting effects on seedling morphology. Seeds that received GA developed into seedlings that were taller, with fewer but longer leaves, than seeds that did not receive GA. Effects of GA on both dormancy and postgermination traits varied among maternal sibships. Our results indicate that for this species and this concentration of GA, morphological effects can be substantial. Further study is required to determine whether such side effects are found for lower concentrations of GA, or under conditions that encourage faster seedling growth. Nonetheless, the present results illustrate the importance of testing potential confounding effects of GA in studies of the evolution of seed dormancy and its influence on postgermination traits.     

Effects of seed moisture content,warm, chilling,and exogenous hormone treatments and germination temperature on the germination of blackthorn seeds

Blackthorn (Prunus spinosa L.) germination is often low, so new methods need to be developed with a view to improving nursery yields and to inform decision-making on natural regeneration. To this end, the effects of seed moisture content (MC) levels in combination with warm and chilling treatments on blackthorn seed dormancy release were investigated. In another experiment, the effect on seed germination of warm and chilling treatments in combination with exogenous hormones was investigated. Following treatment, the seeds were allowed to germinate at a constant 15°C with 8 h lighting per day or 20 (dark)/30°C (light). Seed lot effects were evident, but were consistent across treatments. Seeds adjusted to the lower target MC level (TMC) maintained high germination potential over a longer period of treatment than in those held in the fully imbibed (FI) state. The highest germination was achieved in the TMC seeds that were given six weeks warm treatment followed by 32 weeks chilling. Hormone treatments significantly reduced the amount of chilling needed to release dormancy in TMC seeds, but not in the FI seeds. Overall, germination response was better at 15°C test temperature than at 20/30°C.     

Density-dependent germination and the role of seed leachate

Abstract While density dependence is a central issue in much of plant ecology, it is often overlooked during the crucial seed germination period of the plant life-cycle. Here, patterns of germination in relation to initial seed density for 12 phylogenetically-diverse perennial plant species are described from laboratory experiments. When each of the 12 species was analysed individually, seeds of Alysicarpus rugosus, Callistemon citrinus, Eragrostis curvula and Panicum miliaceum showed a significant decrease in the proportion of seeds germinating at high densities of conspecifics. A meta-analysis carried out by grouping 11 of the 12 species together revealed an overall significant effect for a decrease in the proportion of seeds germinating at high conspecific densities compared with low con-specific densities. Significant decreases in the proportion of seeds germinating are interpreted as risk reappraisal by seeds through dormancy in response to potentially hazardous conditions imposed by high density clusters of seeds all germinating at once. The four species that responded significantly to high densities individually were each treated at low densities with a leachate solution obtained from high density conspecifics. For Alysicarpus rugosus and Panicum miliaceum, this resulted in a significant decrease in the proportion of seeds germinating at simulated high densities implicating the leachate as a causative agent. Heterospecific effects were investigated similarly for A. rugosus and E. curvula by the addition of leachate from high density clusters of seeds of one species upon the other. Only A. rugosus decreased germination significantly through the addition of leachate. These results demonstrate the ability of seeds to predict environmental conditions of the habitat into which they will emerge in terms of potential competitive interactions from neighbouring seedlings.     

紫花苜蓿种子萌发及幼苗生理特性对PEG6000模拟渗透势的响应

用不同质量浓度PEG6000(0%、5%、10%、15%、20%、25%、30%,渗透势分别为0、-0.06、-0.17、-0.32、-0.53、-0.79、-1.10 MPa)控制渗透势,研究紫花苜蓿种子萌发及幼苗生理特性对不同渗透势的响应.结果表明: 种子5项萌发指标均随渗透势降低呈先升后降趋势,-0.06 MPa时萌发指数和活力指数最高,-0.17 MPa时发芽率、发芽势和发芽指数最高;幼苗过氧化物酶、超氧化物歧化酶、过氧化氢酶活性和叶绿素含量均随渗透势降低呈先升后降趋势,-0.17 MPa时各指标值最高;叶绿素a/b随渗透势降低呈先降后升趋势,-0.06 MPa时最低;游离脯氨酸、丙二醛含量和相对电导率随渗透势降低而持续升高.渗透势为-0.06～-0.17 MPa时,种子萌发和幼苗生理综合评价结果最优,是最适宜种子萌发的渗透势条件,而当渗透势低于-0.79 MPa时,对种子萌发产生抑制.     

The ecophysiology of seed persistence: a mechanistic view of the journey to germination or demise

Seed persistence is the survival of seeds in the environment once they have reached maturity. Seed persistence allows a species, population or genotype to survive long after the death of parent plants, thus distributing genetic diversity through time. The ability to predict seed persistence accurately is critical to inform long‐term weed management and flora rehabilitation programs, as well as to allow a greater understanding of plant community dynamics. Indeed, each of the 420000 seed‐bearing plant species has a unique set of seed characteristics that determine its propensity to develop a persistent soil seed bank. The duration of seed persistence varies among species and populations, and depends on the physical and physiological characteristics of seeds and how they are affected by the biotic and abiotic environment. An integrated understanding of the ecophysiological mechanisms of seed persistence is essential if we are to improve our ability to predict how long seeds can survive in soils, both now and under future climatic conditions. In this review we present an holistic overview of the seed, species, climate, soil, and other site factors that contribute mechanistically to seed persistence, incorporating physiological, biochemical and ecological perspectives. We focus on current knowledge of the seed and species traits that influence seed longevity under ex situ controlled storage conditions, and explore how this inherent longevity is moderated by changeable biotic and abiotic conditions in situ, both before and after seeds are dispersed. We argue that the persistence of a given seed population in any environment depends on its resistance to exiting the seed bank via germination or death, and on its exposure to environmental conditions that are conducive to those fates. By synthesising knowledge of how the environment affects seeds to determine when and how they leave the soil seed bank into a resistance–exposure model, we provide a new framework for developing experimental and modelling approaches to predict how long seeds will persist in a range of environments.     

盐生植物角果碱蓬种子二型性对环境的适应策略

角果碱蓬(Suaeda corniculata)是藜科一年生盐生植物, 在我国分布于北方盐碱滩涂和盐碱荒漠地区。角果碱蓬具有棕色和黑色两种异型体种子(简称棕色和黑色种子)。对采自内蒙古鄂托克前旗盐渍化生境的角果碱蓬二型种子的形态、休眠和萌发特性开展对比研究, 测定了二型种子休眠和萌发行为对温度、光照和盐分(NaCl)的响应, 以揭示盐生植物异型种子对温带盐漠生境的适应对策。结果表明: (1)二型性种子在大小、种皮特性和结实比例方面有显著差异。与黑色种子相比, 棕色种子个体较大, 种皮透水性强。黑色种子与棕色种子的结实比例约为5.6 : 1。(2)新成熟的棕色种子的萌发对各温度梯度和光照条件不敏感, 萌发率较高(84%-100%); 而新成熟的黑色种子萌发率较低(8%-78%), 萌发对光照敏感。(3)黑色种子具有浅度生理休眠, 种皮划破、赤霉素处理和低温层积均可有效地提高种子的萌发率。(4)二型种子萌发对土壤盐分的胁迫具有不同的响应。与黑色种子相比, 棕色种子对盐分胁迫不敏感, 在较高的盐分浓度下仍有较高的萌发率, 低温层积处理能够降低黑色种子对盐胁迫的敏感性, 有效地提高种子的初始萌发率、萌发恢复率和最终萌发率。角果碱蓬二型种子不同的形态、休眠和萌发特性, 提高了该物种在高度异质性生境中的适合度, 对种群成功地适应温带盐漠环境具有重要的意义。     

外来杂草小花山桃草种子休眠萌发特性

种子萌发和出苗是植物一生中对环境胁迫最为敏感的阶段,外来植物在这一时期对环境条件的适应能力是决定其入侵能力大小的关键因素之一。通过室内外试验研究了小花山桃草种子休眠特性以及贮藏时间、果皮、温度、p H值、水势、盐分和埋土深度对其种子萌发、幼苗生长和出苗的影响。结果表明:小花山桃草蒴果中4粒种子的大小差异显著(P0.01),但它们的活力和萌发率差别不大,4粒种子活力均高达96%以上。休眠解除后,萌发率均高达98%以上;坚硬果皮的机械阻碍是引起种子休眠的主要原因;在室温储藏条件下,种子萌发率随贮藏时间的增加先增加后降低。贮藏1个月,萌发率提高到54%(贮藏前为0)。贮藏3—6个月时,萌发率达最大值(98.5%—99%)。贮藏1a后,萌发率和萌发速度显著下降,但萌发率仍高达90%以上;在室外,有10.5%的蒴果前两粒种子(果实柱头端)同时萌发出苗。室外埋藏1a后,蒴果中未萌发的3粒种子的发芽率分别为45.5%、90.5%和88.5%;小花山桃草种子萌发的温度范围为5—35℃,15—25℃最适于种子萌发,25℃最有利于幼苗生长;小花山桃草能忍受一定的盐胁迫和干旱胁迫,盐浓度和水势为0.15 mol/L和-0.5 MPa时,种子萌发率分别为33.5%和9%。种子萌发和幼苗生长最适宜的土壤含水量为50%;小花山桃草对p H值具有较广泛的适应性,在p H值为5—9范围内均可萌发;小花山桃草种子在土壤表面的出苗率为43%,埋土深度2 cm时,出苗率最高(89.5%),埋土深度大于10 cm时,不再出苗。小花山桃草种子休眠萌发特征以及出苗特点是其快速入侵的基础。研究结果为预测小花山桃草潜在分布范围以及提出科学合理的综合治理措施提供了理论依据。     

Light stimulation and darkness requirement for the symbiotic germination of Dactylorhiza majalis (Orchidaceae) in vitro

Germination percentage of Dactylorhiza majalis (Rchb.f.) Hunt & Summerh. (Orchidaceae) was increased by illuminating surface-sterilized, rinsed and incubated seeds with white light in 16 h photoperiods. Optimal exposures (10–14 days) raised germination from 40 to 75%. Longer light treatments resulted in reduced germination percentage and smaller seedlings. Only about 2% of the seeds could actually germinate in photoperiods; the germination of the rest was delayed by initial light and required about 14 days in constant darkness. Interruption of this darkness period with two consecutive photoperiods increased the germination percentage when the interruption occurred before day 8, but not when occurring later than that.     

The Role of Water Uptake in the Transition of Recalcitrant Seeds from Dormancy to Germination

In recalcitrant seeds of horse chestnut (Aesculus hippocastanum L.) maintaining a high water content during winter, dormancy is determined by the presence and influence of the seed coat, while the axial organs of the embryos excised from these seeds are not dormant. Such axial organs were capable for active water uptake and rapid fresh weight increase, so that their fresh weights exceeded those in intact seeds at the time of radicle protrusion. Fructose plays an essential role in the water uptake as a major osmotically active compound. ABA interferes with the water uptake by the axial organs and thus delays the commencement of their growth. The manifestation of seed response to ABA during the entire dormancy period indicates the presence of active ABA receptors and the pathways of its signal transduction. The content of endogenous ABA in the embryo axes doubled in the middle of dormancy period, which coincided with a partial suppression of water uptake by the axes. During seed dormancy release and imbibition before radicle protrusion, the level of endogenous ABA in axes declined gradually. Application of exogenous ABA can imitate dormancy by limiting water absorption by axial organs. Fusicoccin A (FC A) treatment neutralized completely this ABA effect. Endogenous FC-like ligands were detected in the seed axial organs during dormancy release and germination. Apparently, endogenous FC stimulates water uptake via the activation of plasmalemmal H⁺-ATPase, acidification of cell walls, their loosening, and turgor pressure reduction. FC can evidently counteract the ABA-induced suppression of water uptake by controlling the activity of H⁺-ATPase. It is likely that, in dormant intact recalcitrant seeds, axial organs, maintaining a high water content, are competent to elevate their water content and to start their preparation for germination under the influence of FC when coat-imposed dormancy becomes weaker.