DORMANCY FACTORS IN IRIS (IRIDACEAE) SEEDS

Utilizing a newly developed radish seed bioassay, it has been demonstrated that Iris seed dormancy is caused by water-soluble inhibitor(s). Leached Iris seeds germinate freely when planted in soil without previous chilling. The inhibitor(s) can prevent germination of representative species of both monocotyledonous and dicotyledonous seeds.     

铜尾矿对5种豆科植物种子萌发和幼苗生长影响的初步研究

通过水培实验和土培实验,研究了铜陵铜尾矿对5种豆科植物种子萌发和幼苗生长的影响。结果表明,五种豆科植物种子在尾矿浸提液中均能萌发,但萌发率比对照组低,而且浸提液对种子萌发产生一定的阻滞作用,酸化尾矿浸提液对种子萌发初期的吸胀吸水有促进作用。尾矿与土壤5种不同改良方式的基质试验也发现铜尾矿对种子萌发着阻滞作用,其中大豆、赤豆、赤小豆在70d内未发现死苗现象。     

Drought tolerance and germination response to light and temperature for seeds of saline and non-saline habitats of the habitat-indifferent desert halophyte <Emphasis Type="Italic">Suaeda vermiculata</Emphasis>

Few plants are habitat-indifferent halophytes (i.e., grow well in both saline and non-saline soils). These plants offer a good opportunity to study drought and salinity tolerances during germination for seeds developed and matured in soils differ in salinity. Here, we assessed drought tolerance during germination, as simulated with PEG, and response of germination to light and temperature for Suaeda vermiculata, a habitat-indifferent shrub. Seeds matured in saline and non-saline soils were germinated in six PEG concentrations (0 to ? 1.0 MPa) and put in three incubators adjusted at different temperatures in both light and dark regimes. Drought tolerance was greater for seeds of the non-saline than those of saline soils, especially at higher temperatures. Seeds of the saline soils germinated in the lowest osmotic potentials (? 0.8 and ??1.0 MPa) only at lower temperatures, but seeds of the non-saline soils germinated to higher levels at all temperatures. Tolerances to drought and high temperatures were greater in light for seeds of saline soils, but in darkness for seeds of non-saline soils. Germination rate index did not differ significantly between seeds of the two soil types in higher osmotic potentials, but was significantly greater in seeds of non-saline at lower osmotic potentials. Most seeds that failed to germinate in the PEG concentrations recovered their germination when transferred to distilled water. Germination recovery levels and speeds increased with the decrease in osmotic potentials. Seeds of the saline soil postpone their germination until arrival of suitable temperatures and effective rainfalls that ensure seedling survival in salty habitats of the arid unpredictable deserts.     

Phytotoxicity Assay to Assess Plant Species for Phytoremediation of Petroleum-Contaminated Soil

A phytotoxicity bioassay was used to select plant species for phytoremediation that were able to germinate and grow in petroleum-contaminated soil from an industrial site in Canada. Perennial ryegrass (Lolium perenne var. “Affinity”) and alfalfa (Medicago sativa L.) were more successful at germination and root growth than were little bluestem (Schizachyrum scoparium) and crown vetch (Coronilla varia). The phytotoxicity assay provides a rapid, efficient mechanism of prescreening potential plant species and eliminating those not able to germinate and establish in soil conditions present at the contaminated site. This bioassay can potentially reduce the number of pot or greenhouse degradation studies that need to be conducted before plant species can be chosen for petroleum phytoremediation.     

Reproductive allocation,seed dispersal and germination of <Emphasis Type="Italic">Myricaria laxiflora</Emphasis>, an endangered species in the Three Gorges Reservoir area

Myricaria laxiflora is an endangered plant that grows in the flood zone along the Yangtze River in the Three Gorges area from 70 m to 155 m above sea level. To understand the spatial distribution patterns of the species and to provide information for developing conservation strategies, we used field surveys to study its seed reproduction and dispersion, and used growth chambers to study seed germination. Results showed that M. laxiflora produced many flowering branches, inflorescences and seeds. Seeds were very small and output was high although biomass allocation to reproduction was low (∼4%). Reproductive allocation was strongly correlated with the biomass of stems and leaves. Seeds were dispersed either by the wind or the river current. Wind-dispersed seeds usually settled within 25 m from parent plants leading to a clumped distribution of individuals in populations. Water-dispersed seeds often landed and established on strands of firth where the fine sediment and gentle sloping were available. Seedlings that emerged from water-dispersed seeds were distributed along the water flood line. The life-span of M. laxiflora seeds was about 7 days. Seeds could germinate within 24 h when they absorbed adequate amounts of water. Soil water content was a key factor limiting the establishment ability of M. laxiflora. Experiments showed that the minimum soil water content for germination to occur was 10% on sand or 17% on sandy soil substrates, and the optimal conditions were on saturated soils. The water content of sandy soils on the riverbank was lower than 10% in autumn, the dry season, and seeds were able to germinate only on sandy beaches that were intermittently inundated by the fluctuating river current. These characteristics of seed dispersal and germination limit the ability for M. laxiflora to expand its distribution. These results provide information essential for the conservation and reintroduction of this endangered species.     

培养基质、储藏方式和盐度对三种海滨植物种子萌发的影响

研究了培养基质、储藏方式和盐度对3种海滨植物互花米草(Spartina alterniflora)、盐地碱蓬(Suaeda salsa)和芦苇(Phragmites australis)种子萌发的影响,探索在潮间带环境下海滨植物种子萌发适应策略。结果表明:3种植物的干藏种子和湿藏芦苇种子随着盐度的升高,萌发率和萌发速率均显著下降,湿藏互花米草和盐地碱蓬种子在各盐度下萌发率和萌发速率差异不显著。各盐度-土培-干藏互花米草,中、高盐度-土培-干藏盐地碱蓬,土培各处理,中、高盐度-水培-干藏,高盐度-水培-湿藏芦苇种子萌发失败。湿藏提高了各盐度处理下土培互花米草,中、高盐度-水培和土培盐地碱蓬,淡水、中盐度-水培芦苇种子的萌发率和萌发速率。干藏互花米草种子在中、高盐度和土埋条件下种子的萌发受到抑制,限制了互花米草向高潮带与潮上带的扩展;而经常受潮水浸淹保持湿润的种子能抵抗高盐和泥沙沉积,导致互花米草种群逐步向低潮带方向发展;湿藏芦苇种子在淡水中萌发率和萌发速率最高,当潮上带盐度降低时,芦苇具有很强的竞争优势,但是对盐度和土埋敏感,限制了其向海的拓展;盐地碱蓬在中、高盐度和土培条件下萌发速率最高,快速萌发的适应策略和广适应性在盐地碱蓬占据高潮带和中潮带广大区域的过程中起到了重要的作用。     

模拟水分胁迫对不同种源麻楝种子萌发能力的影响

以麻楝6个种源种子为试验材料,用不同浓度的聚乙二醇(PEG)溶液模拟干旱胁迫,探讨干旱胁迫对种子发芽率、发芽势、发芽指数、活力指数以及幼苗苗高和胚根长及根苗比的影响,为麻楝的引种和推广种植提供依据。结果显示:(1)不同水势胁迫处理均降低了麻楝种子的发芽率和发芽势,当水势为-0.40MPa时延缓了种子萌发进程;种子的发芽率、发芽势、发芽指数和活力指数均随干旱胁迫强度的增加呈明显下降的趋势;当胁迫水势为-0.86MPa时,干旱胁迫处理的种子在试验结束时仍未能萌发,即-0.86MPa是麻楝种子萌发的临界水势。(2)当胁迫水势高于-0.40MPa时,麻楝幼苗的胚根长度与对照组差异不显著且长于对照组,说明高于-0.40MPa的水势有利于麻楝种子胚根的生长;麻楝幼苗苗高生长则是随着PEG浓度的升高而逐渐减缓。(3)适当的干旱胁迫可以增大各种源麻楝幼苗根苗比,且在胁迫水势高于-0.20MPa时都达到最大值。研究表明,麻楝种子具有一定的抗干旱胁迫的萌发能力,并以来自缅甸的Khin Aye Pale和泰国的Phu Wiang材料较强,来源于中国三亚和马来西亚Ulu Tranan的较弱。     

Germination biology of selected central Australian plants

Abstract Risk spreading of germination may be particularly common in environments with unpredictable climates. Germinability, propensity to germinate at different temperatures and germination speed were classified for seeds of 105 species from the central Australian arid zone, and related to plant growth form, perenniality, seed size and seed dispersal mode. Almost all species had at least some seeds which were dormant, consistent with the idea that risk spreading is important in arid zones. Dispersal mode and plant perenniality were not found to be associated with germinability. Seeds of most species germinated rapidly relative to what has been recorded from higher-rainfall environments, as might be expected in an environment where wet soils are usually temporary. Faster germination tended to be associated with low germinability, suggesting a spectrum of strategies from species that risk a small number of their seeds in many rainfall events, to those that germinate only in large rainfall events but then risk large numbers of seeds.     

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。     

Cold stratification,light and high seed density enhance the germination of Ottelia alismoides

The effects of cold stratification, light and seed clustering in petri dish on Ottelia alismoides seed germination were investigated. The seeds required light and an extended cold period in order to germinate, but neither treatment alone was effective. Seed germination significantly increased with length of the 4 °C cold stratification period. Freshly collected seeds failed to germinate while a 5-month period at 4 °C yielded 29 ± 9% germination in the light, but none in the dark. Treatment with sodium nitroprusside, a nitric oxide source, failed to promote germination in the light or dark. Seeds of O. alismoides showed an unusual and significant positive response to aggregation. Germination in the light, after 5-month 4 °C cold stratification, was stimulated to almost five-fold in the dishes that were more densely sown with seed (20 seeds versus 200 seeds). Likewise, clustering seeds in dense aggregations stimulated germination significantly. Germination more than quadrupled with an increase from 1 to 50 seeds per cluster (200 seeds per dish), reaching a value of 72 ± 4%. Linear regression analysis shows the correlation between seed cluster density (no. per cluster) and germination rate (%) was highly significant (R² = 0.85, P = 0.000). The extended cold stratification requirement is probably an over-wintering device. The mechanism of the density-dependent stimulation is unclear.     

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 effect of leachates from grass trash on establishment of ryegrass

These experiments have shown that whilst leachates from grass trash produced by killing grass with glyphosate can significantly affect germination and seedling growth of both perennial and Italian ryegrass on germination paper and on inert media, they had no effect when added to seeds on soil. This suggests that these leachates are unlikely to inhibit germination in direct drilled sowings in the field unless seeds are sown in direct contact with grass trash and in conditions of sufficient moisture availability to enable production of the leachates. Comparisons of the effect of leachates from grass killed with herbicides or by drying, both before and after passing through a soil column further confirmed this and suggested that the effect of these leachates could partly though not wholly be attributed to herbicide residues on the trash. Glyphosate was less toxic to germination than paraquat. However on sandy soils, glyphosate residues could still cause a reduction in germination. Surface trash produced by spraying with glyphosate had no effect when seeds were sown at a depth of 1 cm, again confirming that seeds must be in close proximity to grass trash before germination and establishment is reduced.     

Alleviation by Gibberellic Acid and Kinetin of the Inhibition of Seed Germination in Maize (Zea mays L.) under Submerged Conditions

Under submerged conditions the germination of maize seeds isinhibited. Under normal conditions, i.e. on moist filter paper,more than 80 per cent of the seeds can germinate whereas lessthan 24 per cent of the seeds germinate under submerged conditions.The inhibition of germination under submerged conditions canbe fully overcome by the application of an appropriate concentrationof GA₂, and KN. The possible role of these hormones in overcomingthe inhibition of seed germination under an oxygen deficit dueto waterlogging is discussed. Zea mays L, maize, gibberellic acid, kinetin, germination     

Plant protection and rhizosphere colonization of barley by seed inoculated herbicide degrading Burkholderia (Pseudomonas) cepacia DBO1(pRO101) in 2,4-D contaminated soil

The 2,4-dichlorophenoxyacetic acid (2,4-D) degrading bacterium, Burkholderia cepacia (formerly Pseudomonas cepacia) DBO1(pRO101) was coated on non-sterile barley (Hordeum vulgare) seeds, which were planted in two non-sterile soils amended with varying amounts of 2,4-D herbicide. In the presence of 10 or 100 mg 2,4-D per kg soil B. cepacia DBO1(pRO101) readily colonized the root at densities up to 10⁷ CFU per cm root. In soil without 2,4-D the bacterium showed weak root colonization. The seeds coated with B. cepacia DBO1(pRO101) were able to germinate and grow in soils containing 10 or 100 mg kg^–1 2,4-D, while non-coated seeds either did not germinate or quickly withered after germination. The results suggest that colonization of the plant roots by the herbicide-degrading B. cepacia DBO1(pRO101) can protect the plant by degradation of the herbicide in the rhizosphere soil. The study shows that the ability to degrade certain pesticides should be considered, when searching for potential plant growth-promoting rhizobacteria. The role of root colonization by xenobiotic degrading bacteria is further discussed in relation to bioremediation of contaminated soils.     

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.     

苜蓿种子萌发和幼苗生长对温度、光照和埋深的响应

紫花苜蓿(Medicagosativa)是世界人工草地重要的优良牧草.研究其种子萌发和幼苗生长对温度、光照及埋深等环境因子的响应,对苜蓿草地的种植及管理具有重要的实践指导意义.采用室内控制实验,分析了紫花苜蓿种子萌发和幼苗生长对恒温(10、15、20、25、30℃)、变温(6/15、10/20、15/25、15/30、...     

Antimicrobial solid media for screening non-sterile Arabidopsis thaliana seeds

Stable genetic transformation of plants is a low-efficiency process, and identification of positive transformants usually relies on screening for expression of a co-transformed marker gene. Often this involves germinating seeds on solid media containing a selection reagent. Germination on solid media requires surface sterilization of seeds and careful aseptic technique to prevent microbial contamination, but surface sterilization techniques are time consuming and can cause seed mortality if not performed carefully. We developed an antimicrobial cocktail that can be added to solid media to inhibit bacterial and fungal growth without impairing germination, allowing us to bypass the surface sterilization step. Adding a combination of terbinafine (1 μM) and timentin (200 mg l⁻¹) to Murashige and Skoog agar delayed the onset of observable microbial growth and did not affect germination of non-sterile seeds from 10 different wild-type and mutant Arabidopsis thaliana accessions. We named this antimicrobial solid medium “MSTT agar”. Seedlings sown in non-sterile conditions could be maintained on MSTT agar for up to a week without observable contamination. This medium was compatible with rapid screening methods for hygromycin B, phosphinothricin (BASTA) and nourseothricin resistance genes, meaning that positive transformants can be identified from non-sterile seeds in as little as 4 days after stratification, and transferred to soil before the onset of visible microbial contamination. By using MSTT agar we were able to select genetic transformants on solid media without seed surface sterilization, eliminating a tedious and time-consuming step.     

SOIL-PLANT PHYTOTOXICITY AND ITS POSSIBLE SIGNIFICANCE IN PATTERNING OF HERBACEOUS VEGETATION IN A BOTTOMLAND FOREST

Plant growth inhibitors, which are known to exert synergistic effects on herbaceous vegetation, were isolated and quantified from the soils under hackberry trees. Ferulic, caffeic, and p-coumaric acids were isolated from the soils under hackberry trees collected in January, April, and September from 0–15 and 15–30 cm soil depths. Seed germination bioassay indicated considerably higher phytotoxicity levels of individual plant growth inhibitors in January and April soils, and this toxicity level was more drastic when inhibitors were applied accumulatively. Individual phytotoxins extracted from soil in September were not very inhibitory to seed germination of selected test species; however, accumulative effects were still allelopathic to seed germination. Toxicity levels of individual compounds may reduce or disappear in a given time, but the combined action of these chemicals would still be toxic in croplands or in natural communities. Ecological implications of allelopathy in terms of soil-plant interaction are discussed.