新疆短命植物小拟南芥(Arabidopsis pumila)种子萌发特性及其生态适应性

通过显微结构及不同处理条件下种子萌发率的观察,对早春短命植物小拟南芥(Arabidopsis pumila)种子萌发特性及影响因素进行了研究,并对其生态适应性进行了讨论。结果表明:(1)温度和光照变化对自然生境和温室收获种子的萌发率影响均不显著,说明此种群在前期萌发阶段对光、温不敏感;(2)自然生境中采收的小拟南芥种子萌发率显著低于温室收获种子,说明环境条件的变化对短命植物种子的发育具有重要作用,可显著改变种子的萌发行为;(3)赤霉素使自然生境收获种子胚活性增强从而对萌发有较大促进作用,可使萌发率增加50%以上;(4)对种皮进行各种机械损伤处理使得种皮松弛或透气,可以显著提高自然生境种子的萌发率(超过70%);(5)盐和干旱胁迫对种子萌发均具有明显的抑制作用,但复水后部分被抑制种子可重新萌发,显示盐和干旱胁迫可导致种子产生浅度休眠。结合小拟南芥自然生存环境及本研究的结果,显示其种子萌发特性与生境具有高度适应性。     

Conditioning period, CO2 and GR24 influence ethylene biosynthesis and germination of Striga hermonthica

Germination of witchweed ( Striga hermonthica [Del.] Benth), an important root parasite on poaceous crops, requires pretreatment 'conditioning' in a warm moist environment and a subsequent exposure to a stimulant. The roles of conditioning period, CO₂ and a strigol analogue (GR24) in ethylene biosynthesis and germination of the parasite were investigated. Conditioning increased the seeds' capacity to oxidize exogenous 1-aminocyclopropane-1-carboxylic acid (ACC). Exogenous CO₂ increased the seeds capacity to oxidize ACC by 3- to 9-fold. A combination of GR24 and ACC increased ethylene production by more than 3-fold in comparison with the rates obtained using these compounds separately. Aminoethoxyvinylglycine (AVG) completely inhibited ethylene induction by GR24, but not by ACC. A GR24 treatment, made subsequent to conditioning in GR24, did not induce ethylene. However, seeds conditioned in GR24 and then given 1 m M ACC produced 293 nl l⁻¹ ethylene. ACC oxidase (ACCO) activity in crude extracts was increased by conditioning and CO₂. The enzyme displayed an absolute requirement for ascorbate. Absence of exogenous Fe²⁺ reduced enzyme activity only by 14%. GR24 applied during conditioning reduced germination in response to a subsequent GR24 treatment. ACC was, invariably, less effective in inducing S. hermonthica germination than GR24 even at concentrations which induce more ethylene than concurrent GR24 treatments. The results are consistent with a model in which conditioning removes a restriction on the ethylene biosynthetic pathway in S. hermonthica seeds. GR24 modulates the key enzymes in ethylene biosynthesis. The stimulant suppresses ethylene biosynthesis in unconditioned seeds and promotes it in conditioned ones. Germination of S. hermonthica results from the joint action of GR24 and the ethylene it induces.     

外源信号物质对肉苁蓉种子萌发与吸器形成的影响

研究氟草敏（norflurazon）、氟啶酮（fluridone）、GR24、赤霉素（GA3）4种外源信号物质对肉苁蓉种子萌发的影响,以及2,6-二甲氧基-对-苯醌（2,6-DMBQ）、5,8-二羟基萘醌（5,8-DHNQ）、阿魏酸（ferulic acid）3种外源信号物质对萌发的肉苁蓉种子吸器形成的影响,结果表明：氟草敏、氟啶酮、GR24对肉苁蓉种子的萌发均具有明显的促进作用,其中氟草敏作用最为显著,处理168h后肉苁蓉种子开始萌发,萌发率最高达65%;2,6-DMBQ对肉苁蓉种子吸器形成具有显著的促进作用,处理48h后肉苁蓉种子开始形成吸器,吸器形成率最高达50%。     

An improved axenic system for studying pre-infection development of the parasitic plant Orobanche ramosa

BACKGROUND AND AIMS: Broomrapes (Orobanche spp.) are holoparasitic weeds that cause devastating losses in many economically important crops. The molecular mechanisms that control early stages of host infection in Orobanche are poorly understood, partly due to the lack of experimentally tractable in vitro systems that allow the efficient application of molecular tools. Here an improved axenic system for the analysis of pre-infection stages in O. ramosa in the absence of the host plant is described. METHODS: An optimized protocol for seed disinfection, based on formaldehyde, was developed. Orobanche ramosa seeds were conditioned in Petri dishes with filter paper, stimulated by addition of the synthetic strigol analogue GR24, and the percentage of germination as well as attachment-organ formation was determined. KEY RESULTS: Treatment of O. ramosa seeds with tobacco-root exudate or with GR24 resulted in highly reproducible germination rates around 70 %. A conditioning period of 8 d was both necessary and sufficient to allow optimal germination in response to GR24. Conditioned seeds that were dehydrated for several months remained fully responsive to GR24 without the need of a new conditioning period. Treatments as short as 5 min with GR24 were sufficient to fully and irreversibly induce the seed germination response. Approximately half of the germinated seeds initiated attachment-organ development. Similar rates of attachment organ induction were also detected in the rare cases of seeds that had germinated spontaneously on water. CONCLUSIONS: The results suggest that the conditioning period produces persistent changes in the seeds required for responsiveness to external stimulants. The rapid action of GR24 suggests that it may act via a receptor-mediated signalling mechanism. While germination in O. ramosa is induced by exogenous stimuli, attachment organ differentiation appears to be triggered by unknown endogenous signals. The new in vitro culture system will have useful applications for the molecular analysis of early stages of parasitic development in Orobanche.     

A standardized bioassay for evaluation of potential germination stimulants for seeds of parasitic weeds

A standard bioassay for the evaluation of the biological activity of potential germination stimulants for seeds of parasitic weeds has been designed by carefully reconsidering all steps of a literature procedure. Addition of a surfactant to the solution for sterilization of the seeds gave a considerable reduction of contamination during the conditioning and stimulation process. Furthermore, it was shown that the water/seed ratio during conditioning affects the germination results. For the seed conditioning and stimulation process, the sandwich technique was introduced, whereby the seeds were placed between two layers of glass fiber filter paper discs. The standardized bioassay has been used for the evaluation of the stimulatory activity of numerous (new) synthetic analogues of strigol (the natural germination stimulant). It is essential to include a reference compound—GR24, an analogue of strigol, is recommended—in every test series, because it was observed that, although a standard bioassay was used, germination percentages obtained with GR24 solutions vary from test to test. For seeds of Striga hermonthica, seasonal effects were found in the germination percentages obtained with GR24 as stimulant. Test results with strigol analogues having modifications in ring D reveal that structural variations in this part of the molecule have dramatic effects on the biological activity of strigol analogues.     

Thermoinhibition uncovers a role for strigolactones in Arabidopsis seed germination

Strigolactones are host factors that stimulate seed germination of parasitic plant species such as Striga and Orobanche. This hormone is also important in shoot branching architecture and photomorphogenic development. Strigolactone biosynthetic and signaling mutants in model systems, unlike parasitic plants, only show seed germination phenotypes under limited growth condition. To understand the roles of strigolactones in seed germination, it is necessary to develop a tractable experimental system using model plants such as Arabidopsis. Here, we report that thermoinhibition, which involves exposing seeds to high temperatures, uncovers a clear role for strigolactones in promoting Arabidopsis seed germination. Both strigolactone biosynthetic and signaling mutants showed increased sensitivity to seed thermoinhibition. The synthetic strigolactone GR24 rescued germination of thermoinbibited biosynthetic mutant seeds but not a signaling mutant. Hormone analysis revealed that strigolactones alleviate thermoinhibition by modulating levels of the two plant hormones, GA and ABA. We also showed that GR24 was able to counteract secondary dormancy in Arabidopsis ecotype Columbia (Col) and Cape Verde island (Cvi). Systematic hormone analysis of germinating Striga helmonthica seeds suggested a common mechanism between the parasitic and non-parasitic seeds with respect to how hormones regulate germination. Thus, our simple assay system using Arabidopsis thermoinhibition allows comparisons to determine similarities and differences between parasitic plants and model experimental systems for the use of strigolactones.     

甘蓝型油菜种子发芽率QTL定位及相关生理性状

利用GH06×P174组合衍生的183个重组自交系进行种子发芽率遗传分析及种子发芽期间种子生理性状分析。用复合区间作图法对在室温下保存两年的种子(STY)、保存1年的种子(SOY)与新收获种子(FS)发芽率进行QTL定位。另外对保存两年的种子及新收获的种子萌发期间脂肪酶活性、电导率、还原糖含量、总糖含量及根系活力进行了测定, 并对结果进行分析。结果表明3批种子的发芽率QTL位点各不相同, 保存两年的种子在第9、14、17条连锁群上分别检测到1个位点, 保存1年的种子在第5、9条连锁群上各检测到1个位点, 新收获的种子在第4、18条连锁群上分别测检到1个位点。研究发现, 3批种子的发芽率相关性不显著, 发芽率差异达到极显著水平, 同时保存不同年份种子的发芽率QTL各不相同, 这表明甘蓝型油菜发芽率受很多不同因素所控制。保存两年及新收获种子的发芽率与电导率之间的相关性均达到极显著负相关, 表明可以通过电导率的测定估测发芽率, 电导率的研究对种子发芽率的研究具有重要意义。     

Germination strategy of Striga hermonthica involves regulation of ethylene biosynthesis

Ethylene involvement in germination of Striga hermonthica (Del.) Benth., an important root parasitic weed on poaceous crops, was investigated at the physiological and molecular levels. Seeds, conditioned at 30°C for 14 days, were treated with ethylene, ethephon or 1-aminocyclopropane-1-carboxylic acid (ACC). Ethylene consistently induced low germination. Ethephon and ACC effectively stimulated germination at concentrations of 0.01 and 1 m M , respectively. In contrast to ethylene, both ethephon and ACC acted in a concentration-dependent manner. Germination induced by the synthetic strigolactone GR24 was inhibited by aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene. ACC reversed the inhibition caused by AVG. When seeds were treated with GR24 in sealed vials, ethylene concentration in headspace gas increased prior to the onset of germination. Total RNA extracted from germinating seeds 12 h after GR24 treatment was used for PCR-based amplification of cDNA fragments encoding the ACC synthase- and oxidase-active site domains. Two distinct cDNA fragments encoding ACC synthase ( SHACS1 and SHACS2 ) and one encoding ACC oxidase ( SHACO1 ) were cloned and sequenced. Southern analysis suggested that each of the cloned genes was present as a single copy in the genome of S. hermonthica . Northern analyses showed that SHACS1 exhibited a temporal change in expression peaking at 10 h after GR24 treatment, which coincided with a steady increase in ethylene concentration. SHACS2 was expressed at a low level with a similar trend. SHACO1 exhibited a temporal change in expression peaking at 15 days during conditioning, when seed response to GR24 was maximal. In summary, expression of ACC synthase and ACC oxidase genes was found to be responsive to a germination stimulant and to conditioning, respectively. The implications of these findings with respect to germination of S. hermonthica under field conditions are discussed.     

Stimulation of weed seed germination by 1–(3-chlorophthalirnido) cyclohexanecarboxamide (AC 94377)

The N-substituted phthalimide, AC 94377, promoted the germination of dry-stored seeds of 17 out of 24 weed species in Petri-dish tests maintained at 22°C. In a further test it was able to substitute for light and/or alternating temperatures in promoting the germination of some species. AC 94377 was more active than GA, in stimulating Solanum nigrum seed to germinate. When mixed with soil in the laboratory, AC 94377 again promoted germination of S. nigrum but the level and persistence of activity differed between soils. In the glasshouse, with soil containing a natural weed seed population, more seedlings emerged from treated than from untreated soil but this number represented fewer than half of the apparently viable seeds present. Field applications of AC 94377 promoted the germination of hand-sown seeds of certain weed species but did not increase the number of seedlings emerging from the natural weed seed bank.     

The system modulating ROS content in germinating seeds of two Brazilian savanna tree species exposed to As and Zn

The effects of increasing arsenic (0, 10, 50, 100 mg L^?1) and zinc (0, 50, 80, 120, 200 mg L^?1) doses on germination and oxidative stress markers (H₂O₂, MDA, SOD, CAT, APX, and GR) were examined in two Brazilian savanna tree species (Anadenanthera peregrina and Myracrodruon urundeuva) commonly used to remediate contaminated soils. The deleterious effects of As and Zn on seed germination were due to As- and Zn-induced H₂O₂ accumulation and inhibition of APX and GR activities, which lead to oxidative damage by lipid peroxidation. SOD and CAT did not show any As- and Zn-induced inhibition of their activities as was seen with APX and GR. We investigated the close relationships between seed germination success under As and Zn stress in terms of GR and, especially, APX activities. Increased germination of A. peregrina seeds exposed to 50 mg L^?1 of Zn was related to increased APX activity, and germination in the presence of As (10 mg L^?1) was observed only in M. urundeuva seeds that demonstrated increased APX activity. All the treatments for both species in which germination decreased or was inhibited showed decreases in APX activity. A. peregrina seeds showed higher Zn-tolerance than M. urundeuva, while the reverse was observed with arsenic up to exposures of 10 mg L^?1.     

Effects of microhabitat,light and temperature on seed germination of a critically endangered Himalayan medicinal herb,Swertia chirayita: Conservation implications

Abstract

Swertia chirayita, a critically endangered medicinal herb, is being over-harvested in the wild. Understanding seed germination is a pre-requisite to ensure species conservation. The germination of seeds collected from six microhabitats was studied at 20°C, 25°C, and 30°C, both under a 14/10 h light/dark photoperiod and in continuous darkness. Two-way ANOVA indicated that microhabitat and temperature significantly affect seed germination, germination rate, germination recovery (GR), and GR rate. Overall, the seeds collected from under canopy showed a significantly (p < 0.05) higher germination than those from open habitats, at 20°C, 25°C, and 30°C (14/10 h light/dark photoperiod). Germination was negligible in continuous darkness but after transfer to a 14/10 h light/dark photoperiod, the seeds from under canopy significantly recovered at 20°C and at 25°C (p < 0.05), and showed the highest germination percentage compared to seeds collected from tree base, stump base, shrubberies, and grassy slope. Similarly, at 30°C, seeds from under canopy recorded the highest GR percentage. In general, seed germination, mean germination rate, seed GR, and GR rate were significantly greater (p < 0.05) at 25°C. Among the microhabitats tested, variation in GR rate was significant (p < 0.05). Seeds were confirmed to be positively photoblastic.     

The Activity of Principal Antioxidant Enzymes and the Content of Metabolites in Dormancy Breaking and Germination of Davidia involucrate Seeds

The principal antioxidant enzymes and metabolites were reported to play a very important role in eliminating reactive oxygen species and maintaining vigour in dormancy breaking and germination of Davidia involucrate seeds. However, the researches on the change laws of content and activity are seldom. In present study, we chose Davidia involucrate seeds which collected from the Mabian Nature Reserve as experimental materials, and then investigated the activity of principal antioxidant enzymes and the content of metabolites in dormancy breaking and germination of the seeds. The results showed that the activity of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR) exhibited an increasing trend but the activity of total antioxidant capacity (T AOC) decreased greatly in early stage of stratification. Comparing with the decrease of protein (Pr), the content of ascorbic acid (Vc) and free amino acid (FAA) significantly increased. In middle stage of stratification, the activity of SOD and T AOC increased firstly and then decreased at last. The activity of POD always maintained a higher level although the activity of CAT and GR decreased greatly. In terminal stage of stratification, the activities of POD, GR, T AOC and the content of FAA and Vc exhibited an increasing trend, while the activity of CAT and SOD maintained a low level. In germination stage, the activity of all antioxidant enzymes and the content of Vc and FAA were increased obviously (P < 005), but the content of the protein was decreased. These results suggested that Davidia involucrata seeds may have a good ability to efficiently remove the effects on cell structure caused by reactive oxygen species (ROS) by keeping the interaction of antioxidant enzymes and metabolites successively during the period of dormancy breaking and germination. This adjustment helps to ensure the germination of seeds by acceleration the post ripening in morphological and physiological of progresses.     

野生烟草种子活力检测及物候特性观察

在烟草属（Nicotiana L．）中,野生种具有抗病、抗虫及抗逆性强等性状,是烟草抗病、抗逆育种的珍贵材料。研究野生烟草种子活力及其物候特点,对于解决烟草远缘杂交过程中的花期相遇问题以及开展抗性鉴定等工作具有重要意义,是烟草抗性育种工作的基础。     

Ascorbate and glutathione metabolism in embryo axes and cotyledons of germinating lupine seeds

Changes in ascorbate and glutathione contents and the activities and isoenzyme patterns of enzymes of the ascorbate-glutathione cycle were investigated in embryo axes and cotyledons of germinating lupine (Lupinus luteus L.) seeds. Ascorbate content was not significantly affected over the initial 12 h of imbibition in embryo axes, but afterwards increased, with the most rapid accumulation coinciding with radicle emergence. A somewhat similar trend was observed for glutathione with significant increase in embryo axes shortly before radicle protrusion followed by decline in the next hours. In cotyledons the ascorbate pool rose gradually during germination but the amount of glutathione showed fluctuations during a whole germination period. The activity of ascorbate peroxidase (APX) rose progressively in embryo axes, while activities of dehydroascorbate reductase (DHAR) and glutathione reductase (GR) showed transient increase during germination. New isoforms of APX and GR were synthesized, suggesting that they play a relevant role during germination. All analyzed enzymes were already present in dry seeds which allowed them to be active immediately after imbibition.     

Sunflower (Helianthus annuus L.) response to broomrape (Orobanche cernua Loefl.) parasitism: induced synthesis and excretion of 7-hydroxylated simple coumarins

The interaction of the parasitic plant Orobanche cernua with resistant and susceptible cultivars of Helianthus annuus L. was investigated. Using different bioassays to evaluate the early stages of the parasite life cycle (germination, attachment, penetration, and establishment), differences were observed between O. cernua-resistant and O. cernua-susceptible sunflower varieties. Germination of O. cernua seeds in the presence of resistant sunflower roots was approximately half that of germination in the presence of susceptible roots, and germinated seeds displayed enhanced browning symptoms. Parasite radicles or host-tissue around the contact point turned brown after O. cernua attachment to sunflower roots, especially in the resistant varieties. These observations suggested the possible accumulation of toxic compounds as a defence strategy in the resistant sunflower varieties. Sunflower 7-hydroxylated simple coumarins may play a defensive role against O. cernua parasitism by preventing successful germination, penetration and/or connection to the host vascular system. This hypothesis is supported by the following data: (i) coumarins inhibited the in vitro germination of O. cernua seeds induced by the strigol analogue GR(24) and caused a browning reaction in germinated seeds and (ii) resistant sunflowers accumulated higher levels of coumarins in roots and excreted greater amounts than susceptible varieties in response to O. cernua infection.     

Fate of the soil seed bank of giant ragweed and its significance in preventing and controlling its invasion in grasslands

Giant ragweed (Ambrosia trifida, L. henceforth referred to as GR), an annual non‐native invasive weed, may cause health problems and can reduce agricultural productivity. Chemical control of GR in grasslands may have irreversible side effects on herbs and livestock. In an attempt to propose a solution to the harmful effects of GR on grasslands, this study explores the fate of its soil seed bank (SSB) and considers the physical control of its SSB reduction. By studying GR distributed in grasslands of the Yili Valley, Xinjiang, China, we measured the spatial and temporal changes in seed density, seed germination, dormancy, and death. We analyzed seed germination, dormancy, and death following different storage periods. The study analyzed population characteristics over time, including seed fate, and examined physical control methods for reducing the SSB density. The SSB of GR occurs in the upper 0–15 cm of soil in grasslands. Seed density in the SSB decreased by 68.1% to 82.01% from the reproductive growth period to the senescence period. More than 98.7% of the seeds were rotten, eaten, germinated, dispersed, or died within one year after being produced. The seed germination rate of the SSB decreased with the number of years after invasion. When stored for 0.5 or 3.5 years, seed germination rates fell by 40%, during which time seed death rate increased by almost 40%. When GR was completely eradicated for two consecutive years, the SSB and population densities decreased by >99%. The vast majority of GR seeds germinated or died within one year; the germination rate decreased significantly if the seeds were stored dry at room temperature for a long time. Newly produced seeds are the main source of seeds in the SSB. Therefore, thoroughly eradicating GR plants for several years before the seeds can mature provides an effective control method in grasslands.     

Accumulation and degradation of thiamin-binding protein and level of thiamin in wheat seeds during seed maturation and germination

Changes in the levels of thiamin-binding globulin and thiamin in wheat seeds during maturation and germination were studied. The thiamin-binding activity of the seed proteins increased with seed development after flowering. The thiamin content of the seeds also increased with development. Thiamin-binding activity decreased during seed germination. On the other hand, immunological analysis using an antibody directed against the thiamin-binding protein isolated from wheat seeds showed that the thiamin-binding globulin accumulated in the aleurone layer of the seeds during maturation, and then the protein was degraded and disappeared during seed germination. These results suggested that the thiamin-binding globulin of wheat seeds was synthesized and accumulated in the aleurone layer of the seeds with seed development, similar to the thiamin-binding albumin in sesame seeds, and that thiamin bound to the thiamin-binding globulin in the dormant wheat seeds for germ growth during germination.     

Physiology of Oil Seeds: II. Dormancy Release in Virginia-type Peanut Seeds by Plant Growth Regulators

Germination, ethylene production, and carbon dioxide production by dormant Virginia-type peanuts were determined during treatments with plant growth regulators. Kinetin, benzylaminopurine, and 2-chloroethylphosphonic acid induced extensive germination above the water controls. Benzylaminopurine and 2-chloroethylphosphonic acid increased the germination of the more dormant basal seeds to a larger extent above the controls than the less dormant apical seeds. Coumarin induced a slight stimulation of germination while abscisic acid, 2,4-dichlorophenoxyacetic acid, and succinic acid 2,2-dimethylhydrazide did not stimulate germination above the controls. In addition to stimulating germination, the cytokinins also stimulated ethylene production by the seeds. In the case of benzylaminopurine, where the more dormant basal seeds were stimulated to germinate above the control to a larger extent than the less dormant apical seeds, correspondingly more ethylene production was induced in the basal seeds. However, the opposite was true of kinetin for both germination and ethylene production. When germination was extensively stimulated by the cytokinins, maximal ethylene and carbon dioxide evolution occurred at 24 and 72 hours, respectively. Abscisic acid inhibited ethylene production and germinaton of the seeds while carbon dioxide evolution was comparatively high. The crucial physiological event for germination of dormant peanut seeds was enhancement of ethylene production by the seeds.     

不同脱水速率对木奶果种子脱水敏感性及抗氧化酶活性的影响

研究了脱水速率对木奶果种子脱水敏感性和抗氧化酶活性的影响。木奶果种子初始含水量高达1.72gH2O·g^-1DW,萌发率为86.67%。含水量降至0.90gH2O·g^-1DW左右时,慢速脱水种子的萌发率为97.78%,而快速脱水的种子萌发率仅为64.44%。快速脱水至含水量为0.76gH2O·g^-1DW时萌发率为21.67%,而慢速脱水至0.68gH2O·g^-1DW时,萌发率仍高达55.56%。确定了木奶果种子是对慢速脱水耐受性更高的顽拗性种子。在种子脱水过程中,相对电解质渗透速率和脂质过氧化产物（TBARs）都呈升高趋势,但慢速脱水后的种子,其TBARs升高的速率较快速脱水的慢。快速脱水的种子中超氧化岐化酶（SOD）、脱氢抗坏血酸还原酶（DHAR）和抗坏血酸过氧化物酶（APX）的活性较慢速脱水的高,而过氧化氢酶（CAT）活性较慢速脱水的低,未检测出谷胱甘肽还原酶（GR）的活性。这些结果表明,在木奶果种子脱水耐性获得过程中过氧化氢酶比其他抗氧化酶作用更大。