Toward understanding the ecological role of mucilage in seed germination of a desert shrub Henophyton deserti: interactive effects of temperature, salinity and osmotic stress

Aims

Seeds of Henophyton deserti (Brassicaceae), an endemic saharan shrub in south Tunisia, produce a pectinaceous mucilage layer that can imbibe a large amount of water when wetted. The aim of this study was to explore the role of mucilage in seed germination of this shrub under heterogeneous stressful environments.

Methods

Germination of both intact and demucilaged seeds was tested over wide ranges of temperature, and in iso-osmotic solutions of NaCl and PEG. Recovery of germination after NaCl and Polyethylene Glycol (PEG)-6000 treatment was also tested. The effect of mucilage on water uptake was measured and the structure of the seed investigated.

Results

A considerable proportion of seed mass (30 %) is made up of mucilage, which is extremely hydrophilic and able to increase seed mass by 550 % over dry seeds. Mucilage water uptake appears to be unaffected by salt concentration, while higher concentrations of PEG inhibit mucilage hydration. Mucilage decreases germination specifically at 10 °C and this effect can be interpreted in relation to oxygen uptake. High concentrations of NaCl and PEG decrease both germination percentage and rate, with some greater tolerance at 15 °C and 20 °C versus 25 °C. Recovery was higher from higher concentrations of NaCl and PEG and lower temperatures, with a clear inhibitory effect of mucilage.

Conclusions

The study has shown that the mucilage of H. deserti may act as a physical barrier for regulating diffusion of water and oxygen to the inner tissue of the seed and thereby prevent germination under unsuitable conditions.     

Seed Germination Traits of Loquat (<i>Eriobotrya japonica</i> Lindl.) as Affected by Various Pre-Sowing Treatments (Cutting of Cotyledons,Removal of Perisperm,Moist Chilling and/or Exogenous Application of Gibberellin)

The purpose of this study was to investigate the effects of various presowing treatments on the germinability (final germination percentage) and germination rate of loquat seeds in order to increase seedling production in nurseries (applied research) as well as provide answers for important physiological issues related to loquat seeds and their seed coat (basic research). Three experiments were carried out with various pre-sowing treatments. These treatments included full or partial removal of seed coat (perisperm), partial cutting of cotyledons as well as moist chilling at 5°C for 13 days and/or soaking the seeds in water or 250 ppm gibberellic acid (GA3) solution for 24 h. According to the results, cotyledons excision resulted in delayed germination, regardless of the presence or absence of the seed coat in comparison with the decoated seeds that demonstrated the highest germination rate amongst them. In addition, even the partial excision of seed coats affected positively both the germinability and the germination rate, compared to the control-intact seeds. Furthermore, control-intact seeds had a higher germination percentage when exposed to moist chilling independently of the application or not of gibberellin; while the combination of gibberellin application and moist chilling improved both the percentage and the rate of germination of decoated seeds. In conclusion, the role of perisperm (seed coat) in the germination procedure of loquat seeds seems to be important, indicating the existence of seed coat-imposed dormancy on loquat seeds. Finally, the existence of a mild endogenous embryo-dormancy on loquat is also discussed.     

Water Relations of Tomato Seeds During Imbibition and Osmotic Priming

Water uptake of tomato (Lycopersicon esculentum Mill. cv. Moneymaker) seeds during germination was obviously triphasic. The completion of the first phase of water uptake by whole seed could not be realized until 10~12 h later after sowing though varies in different parts of seed. The mechanical resistance of endosperm and seed coat restricted water uptake of the embryo envoleped by the endosperm. Water potential of the intact embryo was still 0. 6~0. 9 Mpa lower than the whole seed when the equilibrium between seed and imbibing solution was established. GA and ABA had no direct effects on the water uptake of tomato seeds. The water potential of embryo was positively correlated with its moisture content. The osmotic potential of tomato embryos decreased slowly during imbibition in water and osmotic solution as well.     

Lucerne Saponins as Inhibitors of Cotton Seed Germination: THEIR EFFECT ON DIFFUSION OF OXYGEN THROUGH THE SEED COATS

The site of inhibition of cotton-seed germination by lucernesaponins seems to be associated with tissues other than theembryo. The rate of water uptake during imbibition was similarfor intact seeds immersed in water and for those in 0.5 percent saponin solution. Seeds previously immersed in saponinsolution showed a lower rate of respiration, absorbing about60 per cent less oxygen than those pre-immersed in water. Yetthe respiration rate of excised embryos from both treatmentswas the same. The extent of the inhibition of germination wasnot affected when oxygen was either bubbled through the saponin-containingimmersion-solution or passed through the flasks in which theseeds were germinated after 24 h of pre-immersion. The rates of oxygen diffusion through the seed coats and membranesof seeds pre-immersed in water or in saponin solution were measured.They were distinctly lower for seed coats and membranes whichhad been exposed to the saponin treatment. It has been concludedthat the seed coat and/or the membrane of intact cotton seedspre-immersed in saponin solution serve as a barrier for oxygendiffusion to the embryo, resulting in inhibition of germination.     

东北刺人参种子萌发影响因子的研究

东北刺人参(Oplopanax elatus Nakai)种子透水性良好,休眠后萌发不受其影响.种皮和胚乳的水提取物中存在萌发抑制物质,胚乳中提取物对白菜种子萌发的抑制效果比种皮更明显.种子自然脱落时胚尚未分化完全,处于心形胚阶段.种子需要先温暖层积以完成胚的分化与生长,然后转入低温层积完成生理后熟.同批种子胚的发育不完全同步,变温层积处理7个月有极少数种子萌发,连续变温层积处理17个月大部分种子萌发.不同年份受气候条件影响,种子产量和发芽率差异较大.种子耐贮性较强,贮藏2年的种子生活力变化不大,仍具有较高的萌发潜力.     

Characterization of water distribution and activities of enzymes during germination in magnetically-exposed maize (Zea mays L) seeds

Magnetic seed treatment is one of the physical pre-sowing seed treatments to enhance the performance of crop plants. In our earlier experiment, we found significant increase in germination and vigour characteristics of maize (Zea mays L.) seeds subjected to magnetic fields. Among various combinations of magnetic field (MF) strength and duration, best results were obtained with MF of 100 mT for 2 h and 200 mT for 1 h exposure. The quicker germination in magnetically-exposed seeds might be due to greater activities of germination related enzymes, early hydration of membranes as well as greater molecular mobility of bulk and hydration water fractions. Thus, in the present study, changes in water uptake during imbibition and its distribution and activities of germinating enzymes during germination were investigated in maize seeds exposed to static magnetic fields of 100 and 200 mT for 2 and 1 h respectively by nuclear magnetic resonance (NMR) spectroscopy. The magnetically-exposed seed showed higher water uptake in phase II and III than unexposed seed. The longitudinal relaxation time T1 of seed water showed significantly higher values and hence greater molecular mobility of cellular water in magnetically-exposed seeds as compared to unexposed. Component analysis of T2 relaxation times revealed the early appearance of hydration water with least mobility and higher values of relaxation times of cytoplasmic bulk water and hydration water in magnetically-exposed over unexposed seeds. Activities of alpha-amylase, dehydorgenase and protease during germination were higher in magnetically-exposed seeds as compared to unexposed. The quicker germination in magnetically-exposed seeds might be due to greater activities of germination related enzymes, early hydration of membranes as well as greater molecular mobility of bulk and hydration water fractions.     

Water Uptake and Germination of Leguminous Seeds in Soils of Changing Matric and Osmotic Water Potential

Water uptake and germination rate of chickpea and pea seedswere compared under changing water potentials in sand and soilaggregate columns and osmotic solutions. The final water uptake and germination were the same in allcases for a given water potential, but the rates were lowerfor seeds planted in sand columns, probably due to mechanicalconstraints imposed on the swelling seed by the dense sand,since the capillary conductivity, and the diffusivity to waterof the sand were very high. The area of the seed in contact with soil is not of importanceif soil aggregates are small as compared to the seeds but increasesin importance when the seeds and the soil aggregates are ofthe same size and at low water potentials.     

东北刺人参种子萌发影响因子的研究

东北刺人参(Oplopanax elatus Nakai)种子透水性良好,休眠后萌发不受其影响。种皮和胚乳的水提取物中存在萌发抑制物质,胚乳中提取物对白菜种子萌发的抑制效果比种皮更明显。种子自然脱落时胚尚未分化完全,处于心形胚阶段。种子需要先温暖层积以完成胚的分化与生长,然后转入低温层积完成生理后熟。同批种子胚的发育不完全同步,变温层积处理7个月有极少数种子萌发,连续变温层积处理17个月大部分种子萌发。不同年份受气候条件影响,种子产量和发芽率差异较大。种子耐贮性较强,贮藏2年的种子生活力变化不大,仍具有较高的萌发潜力。     

Possible involvement of aquaporins in water uptake by pea seeds differing in quality

Using the method of room temperature phosphorescence (RTP), we divided air-dry pea (Pisum sativum L.) seeds subjected to accelerated ageing (40°C, 85% relative humidity) into three fractions: (I) high-quality seeds, (II) weakened seeds, and (III) dead seeds. In the process of ageing, seed germinability firstly decreased and then increased due to so-called “improved” seeds of fraction II, which returned to fraction I as judged from the RTP level; the germinability of these seeds became equal to that of fraction I seeds. Seeds capable of germination (fractions I and II) differed in the rates of imbibition, which depended on plasma membrane permeability (opened or closed water channels) but not on the presence of the seed coat. A low activation energy of seed imbibition in fraction II (less than 5 kcal/mol) indicates that water channels are open. A mercury-containing compound (5 μM p-chloromercuribenzoate (PCMB) reduced the rate of water uptake by these seeds, and dithiothreitol restored it. A high activation energy of fraction I seed imbibition (more than 12 kcal/mol) corresponded to the water uptake mainly across the lipid bilayer when water channels are closed. PCMB did not affect the rate of fraction I seed imbibition. We supposed that mature air-dry pea seeds had open water channels. During the first stages of fraction I seed imbibition, these channels were closed, limiting water uptake. NaF (100 μM), an inhibitor of phosphatase, prevented channel closing and accelerated the imbibition of fraction I seeds. It did not affect the imbibition rate of fraction II seeds, indicating their water channels to be opened. However, NaF did not affect the water uptake of “improved” fraction II seeds as well. It seems likely that their channels were closed during accelerated ageing but otherwise than via dephosphorylation. The results obtained indicate the possibility of water inflow regulation in the weakened seeds via the state of aquaporins, which form water channels in the membranes.     

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。     

Variation in temperature and light but not salinity invokes antioxidant enzyme activities in germinating seeds of Salsola drummondii

Seeds with efficient antioxidant defence system show higher germination under stress conditions; however, such information is limited for the halophyte seeds. We therefore studied lipid peroxidation and antioxidant responses of a leaf-succulent halophyte Salsola drummondii during seed germination under different salinity levels (0, 200 and 800 mM NaCl), temperature (10/20, 20/30 and 25/35°C) and light regimes. Seeds absorbed water and germinated in less than 1 h in non-saline control while increases in salinity decreased the rate of water uptake as well as seed germination. Non-optimal temperatures (10/20 and 25/35°C) and complete dark condition reduced seed germination in comparison to those seeds germinated under optimal temperature (20/30°C) and 12-h photoperiod, respectively. Generally, higher lipid peroxidation and antioxidant enzyme activities were observed in seeds at non-optimal temperature and in those seeds germinated in dark. Decrease in reduced ascorbic acid content was found in highest salinity and temperature treatments, while reduced glutathione content did not change significantly with changes in salinity, temperature and light regimes. These results indicate variation in temperature and light but not salinity enhances antioxidant enzyme activities in germinating seeds of Salsola drummondii.     

Uptake of Gibberellic Acid in Intact and Scarified Seeds of Barbarea vulgaris

Uptake of gibberellic acid as a function of duration of exposure, external concentration, and seed lot was measured in seeds of yellow rocket (Barbarea vulgaris R. Br.) by means of lettuce hypocotyl bioassays of the acidic, basic, or neutral fractions of seed extracts and by uptake of ¹⁴C-GA₃. In intact seeds, where mM levels of GA₃ promoted only 25% germination, uptake was completed within 24 h of exposure. The maximum uptake was about 0.2% of external amount. Although germination promotion by GA₃ differed among seedlots of yellow rocket, relative uptake (percentage of the external GA₃) was nearly the same. The relative rate of uptake of GA₃ was similar for scarified and intact seeds, but germination was promoted in scarified seeds by much lower levels of GA₃ than in intact seeds. Total uptake in scarified seeds was much higher, however (about 10% of the external amount). In seeds imbibed in H₂O, practically no endogenous GA-like activity was detected in either the acidic, basic, or neutral fractions. It was also apparent that intact seeds could take up quantities of GA₃ that failed to promote germination, but were comparable to quantities that promoted germination in scarified seeds.     

The role of the persistent fruit wall in seed water regulation in Raphanus raphanistrum (Brassicaceae)

Background and Aims

Dry fruits remain around the seeds at dispersal in a number of species, especially the Brassicaceae. Explanations for this vary, but usually involve mechanisms of innate dormancy. We speculate that, instead, a persistent fruit may give additional protection through control of dehydration, to species growing in arid or Mediterranean environments where water is sporadic.

Methods

X-rays and weight measurements were used to determine the extent to which Raphanus raphanistrum seeds within mature fruits imbibe water, and germination tests determined the roles of the fruit and seed coat in seed dormancy. Rates of water uptake and desiccation, and seedling emergence were compared with and without the fruit. Finally, germinability of seeds extracted from fruits was determined after various periods of moist conditions followed by a range of dry conditions.

Key Results

Most seeds rapidly take up water within the fruit, but they do not fully imbibe when compared with naked seeds. The seed coat is more important than the dry fruit wall in maintaining seed dormancy. The presence of a dry fruit slows emergence from the soil by up to 6–8 weeks. The fruit slows the rate of desiccation of the seed to a limited extent. The presence of the fruit for a few days during imbibition somehow primes more seeds to germinate than if the fruit is absent; longer moist periods within the pod appear to induce dormancy.

Conclusions

The fruit certainly modifies the seed environment as external conditions change between wet and dry, but not to a great extent. The major role seems to be: (a) the physical restriction of imbibition and germination; and (b) the release and then re-imposition of dormancy within the seed. The ecological significance of the results requires more research under field conditions.     

Water uptake in germinating pecan (Carya illinoinensis) seed

• Water uptake is the fundamental and essential requirement for seed germination. Pecan seed has a hard woody endocarp that plays an important role during water uptake.
• To explore water uptake during germination, the spatiotemporal pattern of water and effect of the endocarp were analysed using high-field MRI, dye-tracing, wax blocking and SEM of water uptake.
• Isolated seeds completed water uptake in 8 h while whole seeds required 6 days, hence, cracking the endocarp plays an important role. The hilum is the channel through which water enters the seed, while the remainder of the seed coat consist of cells covered with a waxy layer that act as a barrier to water absorption. The region with the highest water content in pecan seed is the edge of the U-shaped region, and water can progressively diffuse from this U-shaped region into the whole kernel.
• We report a new water absorption stage between phase II and phase III of the triphasic model of water uptake of pecan seeds. Cracking the endocarp changed water distribution in pecan seeds, which may trigger further water absorption and radicle elongation.

     

红皮糙果茶种子生活力测定与发芽试验

选取饱满有光泽的红皮糙果茶Camellia crapnelliana种子,进行种子贮存生活力测定、种子发芽试验及种皮解剖结构观察等研究,就种子繁殖探讨其濒危原因。结果表明,有利于保持种子生活力的贮存方式为：4 ℃贮存>常温贮存>－10 ℃贮存;种子发芽试验中,采用不同浓度赤霉素(GA₃)、吲哚丁酸(IBA)和不同温度温水处理,种子发芽率均不高,最高为40%;不同因素对种子发芽的影响不同,种子发芽最佳处理为800 mg·L^-1GA₃浸泡6 h;种皮解剖结构观察到红皮糙果茶种皮坚硬,由栓化壁和骨状石细胞组成,内、外部石细胞垂直交错排列,这可能是造成种子萌发困难的机械阻碍原因。     

SEEDS OF KOSTELETZKYA VIRGINICA (MALVACEAE): THEIR STRUCTURE,GERMINATION, AND SALT TOLERANCE. I. SEED STRUCTURE AND GERMINATION

Dormancy of Kosteletzkya virginica (L.) Presl. seeds is primarily due to the impermeability of the seed coat to water. The impermeable structure is assumed to be, in other Malvaceae, the palisade layer of the seed coat. The percentage of seeds capable of imbibition and germination increased with increasing time of storage at low temperatures, but the release from dormancy was not accompanied by decreased seed coat resistance to pressure. Under natural conditions, mechanical damage to the seed coat due to changes in temperature and/or abrasion may render the seeds water permeable. It is not clear what causes water permeability during storage under laboratory conditions. During seed maturation and drying, the inner epidermis of the tegmen partly separates from the rest of the seed coat and an air space, which makes the seed buoyant, is formed around the region of the chalazal cleft. The optimal temperature for germination of K. virginica seeds is between 28 and 30 C in light or darkness.     

干旱胁迫与不同储藏时间对杠柳种子萌发的影响

为了阐明干旱胁迫与不同储藏时间对杠柳种子萌发的影响机理,在室内采用不同浓度的聚乙二醇（PEG）模拟干旱胁迫条件,对3种不同储藏时间的杠柳种子进行了萌发期对比试验,观测了种子的总萌发率、发芽势、活力指数和胚根的生长情况,分析了抗旱特性,结果表明：不同程度的干旱胁迫与储藏时间对杠柳种子萌发均有一定的影响,当PEG-6000浓度为5%,对储藏1年杠柳种子的萌芽率和发芽势起促进作用,对储藏2年种子萌芽率轻度抑制,对储藏3年种子抑制影响较大,当PEG-6000浓度>5%,3种种子的萌芽率和发芽势均呈下降趋势,但当胁迫浓度增大到25%时,种子基本没有萌发。在不同的水分胁迫处理中,3种种子的活力指数和胚根生长速度一直呈下降趋势,尤其3年种子的下降幅度最大。不同储藏时间杠柳种子对干旱胁迫的适应性有差异,储藏1~2年的杠柳种子在PEG-6000浓度为5%~15%中萌发效果较好,且储藏1年种子好于2年种子,3年种子较差。3种种子的耐旱能力由强到弱依次为：1年种子>2年种子>3年种子。     

濒危植物水青树种子的生物学特性

通过连续三年（2006～2008）对水青树种子（Tetracentron sinense）的形态特征和生理特性等指标进行检测,探讨了不同储藏温度、时间和不同基质对水青树种子萌发的影响,分析了与种子生物学特性相关的濒危机制。水青树种子很小,其形态特征、千粒重、含水量和饱满度在不同年限间差异不显著,而吸水速率却差异显著,其中2007年种子的吸水速率最快。TTC染色测得3年水青树种子的活力几乎为0,但其活力指数分别为0、0.41和0.27,表明TTC染色法不适于水青树种子活力的估算。低温储藏后,3年种子的萌发率分别为1.25%、96.5%、70.8%,发芽势分别为1%、59.8%、41.8%。随储藏时间的增加,2007年种子活力降低的速度都慢于其它2年,低温储藏的种子活力降低速度慢于常温储藏的种子。不同基质对水青树种子的萌发和幼苗的生长有一定影响。结果表明,大年水青树种子的活力明显强于小年,随储藏时间的增加其活力的丧失速度也慢于小年;低温储藏有利于种子活力的保持。种子生物学特性方面导致水青树更新困难的原因可能有以下几点：（1）长期进化形成的小种子虽有利于传播和散布,但不利于种子和幼苗的存活;（2）长期低温不适于种子萌发,难以形成应有的幼苗格局;（3）长期湿润环境不适于种子安全度过寒冷期。     

The Effects of Priming and Ageing on Resistance to Deterioration of Tomato Seeds

The influence of seed priming and ageing treatments on viabilityand rate of germination of tomato (Lycopersicon esculentum Mill.)seeds was examined under both long-term and controlled-deteriorationstorage conditions. Seeds of a single lot of tomato were eitherprimed or aged to increase or decrease the rate of germination(Argerich and Bradford, 1989). They were then stored at 6% moisturecontent (dry weight basis) at either 4 ?C or 30 ?C for 1 year.Both viability and germination rate were unaffected by eitherstorage temperature in control seeds, or by 4 ?C storage inprimed or aged seeds. At 30 ?C, however, viability and germinationrate of primed and aged seeds was markedly reduced after 6 monthsof storage. The temperature dependence of the germination rateand the spread of germination times within the population wasalso adversely affected by high temperature storage, particularlyfor primed seeds. Under controlled deterioration conditions(13.5% moisture content and 50 ?C), the rate of loss of viabilitywas greater for primed seed than for control or aged seeds.The relationship between seed viability and the mean germinationrate, however, was not influenced by the seed treatments. Thesedata are analysed in relation to current models of seed deteriorationduring storage and seed repair during priming. The results indicatethat enhancement of seed germination rates by priming treatmentssimultaneously lowers the resistance of seeds to deterioration.Primed tomato seeds must, therefore, be considered to be vigorousseeds with a reduced storage life. Key words: Tomato, controlled deterioration, seed germination rate, seed viability     

Viability of onion (Allium cega) seed as influenced by temperature during seed growth

The yield and performance of seeds from crops of winter-hardy, bolting-resistant onion grown at temperatures of 15–16, 18–19 and 22–23°C in 1979, 1980 and 1982 were compared. Yields of seed from crops grown at 22–23°C were lower than those from crops grown at lower temperatures but the seeds ripened between 11 and 32 days earlier. Seeds from crops grown at mean temperatures of above 18°C gave higher percentage germination when imbibed at 30°C than 20°C and they also gave higher percentage seedling emergence than those from crops grown at lower temperatures. Seedlings from seeds produced at mean temperatures above 18°C were heavier than those from seeds of a similar weight but produced at lower temperatures. None of these differences were associated with differences in seed weight, embryo weight or seed dormancy but were positively correlated with differences in seed N-concentration. The differences were also associated with the rate of imbibition of water as high germination, high N-content seeds had a slower rate of imbibition than low germination, low N-content seeds of the same weight.