Seeds of Kosteletzkya virginica (Malvaceae): their structure,germination, and salt tolerance. II. Germination and salt tolerance

Kosteletzkya virginica (L.) Presl. (Malvaceae) is a perennial that grows in saline or brackish water, and is salt-tolerant in its mature state, but less tolerant during germination. The seeds show a very low permeability to water that increases during storage. The permeability to water differs in seeds harvested in different years. Optimal temperature for germination is 28–30 C. The effect of salinity on imbibition is largely osmotic, but germination is inhibited, apparently, by the combined osmotic and “ionic” effects, especially at high NaCl concentrations. Inhibition of germination by high NaCl concentrations is relatively more severe in scarified than in intact seeds, indicating that the seed coat acts as a partial barrier to Na⁺ influx. External application of proline or betaine did not improve germination under saline conditions. Dry seeds contain a significant amount of betaine and low levels of proline, but during germination and in the presence of NaCl the betaine content decreased while the proline content increased. Thus, the likely compatible solute in the germinating seed seems to be proline.     

Osmotic sensitivity in relation to salt sensitivity in germinating barley seeds

Abstract Cultivars of barley (Hordeum vulgare L.) were tested for germination sensitivity to progressively higher concentrations of salt, mannitol, and betaine. The three solutes were equally inhibitory at equal osmotic potential, but there was a consistent difference in osmotic sensitivity between two cultivars, CM-67 and Briggs (Briggs was the most sensitive). There was no difference between the two cultivars in salt or water uptake from salt solutions during imbibition. Brief presoaking in water did not improve salt resistance, indicating that a hydration-dependent decrease in membrane permeability is not involved in salt tolerance. The calcium content of Briggs was higher than CM-67. These results suggest that salt inhibits barley germination primarily by osmotic effects, and that salt influx during imbibition does not play a role in this inhibition. A hypothesis regarding salt effects on germination is discussed.     

Effect of Salinity on Germination and Seedling Growth of twoAtriplexspecies (Chenopodiaceae)

Salinity is one of the environmental factors that has a criticalinfluence on the germination of halophyte seeds and plant establishment.Salinity affects imbibition, germination and root elongation.However, the way in which NaCl exerts its influence on thesevital processes, whether it is through an osmotic effect ora specific ion toxicity, is still not resolved. Dimorphic seedsof the halophytesAtriplex prostrataandA. patulawere treatedwith various iso-osmotic solutions of NaCl and polyethyleneglycol (PEG). For each treatment, imbibition, germination rate,percent germination, germination recovery and nuclear area ofroot tip cells were compared. Higher concentrations of NaCl(-1.0 MPa) were more inhibitory to imbibition, germination andseedling root elongation than iso-osmotic PEG solutions. Allseeds recovered from a pre-treatment with -2.0 MPa NaCl andPEG solutions, except large seeds ofA. prostratawhich failedto germinate following transfer from -2.0 MPa NaCl. NaCl causeda greater increase in nuclear volume than iso-osmotic PEG solutions.These data suggest that the influence of NaCl is a combinationof an osmotic effect and a specific ion effect.Copyright 1998Annals of Botany Company Atriplex patula,Atriplex prostrata,cytophotometry, osmotic potential, salinity, seed germination.     

大麦种子对盐的发芽响应模型

为了明确盐对种子发芽影响的渗透效应和离子效应共同作用方式以及量化种子发芽对盐的响应, 以两个大麦(Hordeum vulgare)品种‘Cask’和‘County’为研究对象, 设置4个恒定温度(5、12、20和27 ℃)、5个等渗的NaCl和聚乙二醇(PEG)浓度梯度(-0.45、-0.88、-1.32、-1.76和-2.20 MPa, 蒸馏水作对照), 做常规发芽实验。结果显示: (1)两个品种在NaCl溶液中比在等渗的PEG溶液中发芽率高且发芽速度快; (2) NaCl和PEG分别作为渗透剂计算出的水势模型参数值差异很大, 说明水势模型不能用来描述种子发芽对盐的响应; (3)大麦种子在盐溶液中的发芽速率与盐浓度成显著的负相关直线关系, 因此我们修订了水势模型, 将修订后的模型命名为盐度模型, 用来量化盐对大麦种子发芽的影响。与水势模型计算出的发芽时间相比, 盐度模型计算出的50%种子发芽时间与大麦种子实际发芽时间更接近; (4)大麦种子在等渗的NaCl和PEG溶液中发芽速率差异随着水势降低, 先增加后降低。据此我们提出盐的渗透效应和离子效应共同作用于种子发芽的3种情况: 第一种在低盐条件下, 主要是渗透效应起负作用; 第二种情况在中盐条件下, 渗透效应和离子效应共同起作用, 离子效用的正作用强于渗透效应的负作用; 第三种情况在高盐条件下, 离子效应逐渐开始起离子毒害的负作用。     

生态因子对碱茅种子萌发期耐盐性影响的数量分析

 以种子在盐溶液中的相对发芽率作为种子萌发期耐盐性指标,定量分析了种子生产条件与萌发期温度,盐分(类型与浓度)等生态因子对碱茅(Puccinellia tenuiflora)种子萌发期耐盐性的影响,生产条件选取了3个生产年份或贮藏时间(年)。用3个不同的种批表示,处理溶液有不同浓度(或渗透势)的NaCl,CaCl2与Na2SO4 3种盐溶液和渗透胁迫剂PEG(6000)组成,处理温度有两个变温10(16h)～25℃(8h)与15(16h)～25℃(8h)条件组成。随溶液渗透势降低,种子相对发芽率线性下降,线性回归关系式中的回归系数与回归截距分别反映溶液的渗透与离子效应的相对大小。本试验条件下、碱茅种子生产条件对种子活性(以水中的发芽率表示)有显著影响,但对耐盐(NaCl)性无显著影响。溶液类型与温度条件主要通过改变溶液的离子效应影响种子耐盐性,对渗透效应无显著影,两种变温条件下,4种溶液对碱茅种子的渗透效应是溶液渗透势每降低1.0Mpa,相对发芽率降低52.31％。10～25℃变温条件下,与PEG溶液相比,3种盐溶液的离子效应是使碱茅种子相对发芽率分别增加14.0％。15.1％与21.6％,表现为对种子萌发的促进效应;15～25℃变温条件下,NaCl溶液的离子效应比10～25℃下约低17.0％。     

Protein Patterns, Characterized by Computer Image Analysis, of Lentil Embryo Axes Germinating Under Salt Stress

Following 16, 40 and 64 h exposure to 0.33 M NaCl given after 8 h water imbibition, lentil seeds showed a gradual decrease of germination upon their transfer to water. These salt related changes were accompanied by modifications in the protein patterns of embryo axes as revealed by two-dimensional electrophoresis separation and by the computer image analysis of protein spots. In comparison with 8 h water imbibed seeds, prominent proteins comprised between the 5.1 – 7.6 pH isoelectric point in the first dimension and 75 – 50 kDa molecular mass in the second dimension showed a significant increase in their abundance as salt exposure increased. On transfer to water to complete germination, the content of many of these proteins decreased at 24h in 2 – 3 cm length embryo axes in comparison with the corresponding embryo axes of seeds continuously imbibed in water for 24 h. Some groups of proteins ranging between 15.5 – 17.3 kDa, already present after 8 h water imbibition, were not detectable after 24 h but were expressed in seeds exposed to NaCl and transferred to water for 24 h. Up- and down-regulated proteins in lentil embryo axes, imbibed under non-lethal salt stress conditions, have been tentatively identified by comparison with the protein map of germinating seeds of the model plant Arabidopsis. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of salinity and osmotic stress on barley germination rate: sodium as an osmotic regulator

Background and Aims

Seed germination is negatively affected by salinity, which is thought to be due to both osmotic and ion-toxicity effects. We hypothesize that salt is absorbed by seeds, allowing them to generate additional osmotic potential, and to germinate in conditions under which they would otherwise not be able to germinate.

Methods

Seeds of barley, Hordeum vulgare, were germinated in the presence of either pure water or one of five iso-osmotic solutions of polyethylene-glycol (PEG) or NaCl at 5, 12, 20 or 27 °C. Germination time courses were recorded and germination indices were calculated. Dry mass, water content and sodium concentration of germinating and non-germinating seeds in the NaCl treatments at 12 °C were measured. Fifty supplemental seeds were used to evaluate the changes in seed properties with time.

Key Results

Seeds incubated in saline conditions were able to germinate at lower osmotic potentials than those incubated in iso-osmotic PEG solutions and generally germinated faster. A positive correlation existed between external salinity and seed salt content in the saline-incubated seeds. Water content and sodium concentration increased with time for seeds incubated in NaCl. At higher temperatures, germination percentage and dry mass decreased whereas germination index and sodium concentration increased.

Conclusions

The results suggest that barley seeds can take up sodium, allowing them to generate additional osmotic potential, absorb more water and germinate more rapidly in environments of lower water potential. This may have ecological implications, allowing halophytic species and varieties to out-compete glycophytes in saline soils.     

Germination response of black and yellow seed coated canola (<Emphasis Type="Italic">Brassica napus</Emphasis>) lines to chemical treatments under cold temperature conditions

Seed quality is a key critical component to produce well established and vigorous seedlings under cool soil (<10°C) conditions experienced in Western Canada. A simple, relatively quick germination assay is required to separate small differences in seed germination which can have a significant impact on seedling growth. It has long been established that phytohormones regulate seed germination: abscisic acid inhibits germination whereas gibberellins enhance germination. We investigated the effects of ABA, GA, ethylene and inhibitors of these phytohormones alone and in combination on the germination rate of a black and a yellow seed canola (Brassica napus) imbibed at 8°C. The effects of either saline solutions, osmotic solutions, fusicoccin or testa on the germination of canola seeds imbibed at 8°C were also investigated. This temperature is representative of the soil temperatures experienced in the early spring of Western Canada. The two canola seed lines, especially the yellow seed line, were very sensitive to increasing concentration of saline solutions at 8°C, but not at 23°C; however, iso-osmotic solutions that reduced water potential were more inhibitory. The seed coat (testa) including the endosperm was a major factor affecting the germination rate of the yellow seed line at 8°C, however, GA₄₊₇ overcame the inhibitory effect of the testa, whereas ABA exacerbated it. Fusicoccin was more stimulatory to germination than GA₄₊₇, however, unlike GA₄₊₇, it was unable to overcome the inhibitory effect of paclobutrazol, a GA biosynthesis inhibitor. Fluridone, an ABA biosynthesis inhibitor, was unable to overcome the inhibitory effects of a saline solution suggesting that the inhibitory effect was not due to elevated ABA levels. Ethylene, a stimulator of germination did not appear to be involved in the germination of these two lines. Controlled deterioration at 35°C, 85% RH could be either partially or completely overcome by exogenous GA₄₊₇. This study demonstrated the effect of hormones, salinity and testa on the germination of canola seeds under less than ideal environmental conditions.     

Phytochrome-mediated germination control of maize caryopses

Maize caryopses sown in water germinate equally well either in darkness or under any light regime. However, when they are imbibed in mannitol solutions, continuous far-red light proves to be strongly inhibitory on the final germination as compared to darkness. Similar but less pronounced inhibition is also exhibited by continuous red or blue light. Intermittent far-red light can partially substitute for continuous far-red light in inhibiting maize caryopsis germination, and its effect is reversed to the intermittent red light level when red light is given immediately after each far-red illumination. These results are interpreted as a proof of existence and involvement of phytochrome in the germination control of maize caryopses, though its manifestation is realized only under osmotic stress.Abbreviations D darkness - FR far-red - R red - B blue - c-FR, c-R, c-B continuous FR, R, B, resp. - i-FR, i-R intermittent FR, R, resp.     

水分胁迫对蔓性千斤拔种子萌发和生理指标的响应

利用不同浓度的聚乙二醇(PEG)模拟水分胁迫条件,测定蔓性千斤拔种子发芽率、发芽指数、平均发芽速度、苗长等萌发特性及渗透调节物质、保护酶活性等生理指标。结果显示,随着PEG浓度的增加,苗长受到明显抑制,发芽率影响不大,降低了平均发芽速度,在4%浓度范围内提高了发芽指数;可溶性糖、脯氨酸、可溶性蛋白含量呈上升趋势,超氧化物歧化酶(SOD)、过氧化物酶(POD)活性呈逐渐上升的趋势。这些结果表明,在一定的PEG胁迫浓度范围内,蔓性千斤拔种子萌发有较高的膜保护酶系统及渗透调节能力,并能不同程度的提高其萌发的整齐度。     

The laboratory germination of crisp lettuce seeds under moisture stress

Seeds of the crisp lettuce cultivar Pennlake were germinated using all combinations of six ‘initial’ solutions of polyethylene glycol 6000 (PEG) with osmotic potentials ranging from 0 to -8 bars and seven ‘secondary’ solutions of PEG with osmotic potentials ranging from 0 to -10 bars, to which seeds were moved after 24 or 48 h in the ‘initial’ solution. The number of seeds germinating decreased at more negative osmotic potentials of both ‘initial’ and ‘secondary’ solutions but there was an interaction between germination temperature and the osmotic potential of the ‘initial’ solution. At an ‘initial’ solution osmotic potential of 0 bars germination at 20°C exceeded that at 10°C. As the osmotic potential of the ‘initial’ solution decreased germination at 20°C decreased more than at 10°C so that at the more negative osmotic potentials germination at 10°C exceeded that at 20°C. However seeds ungerminated after 14 days germinated normally when transferred back to water, so that the average final germination was 99.5%. The results suggest that major fluctuations in soil water potential in a seedbed are unlikely to influence seed germination per se provided that a period of 24 to 48 h at 0 bars tension is available at some time. The timing of such a period relative to sowing will have a considerable effect on the time of germination and hence the time of emergence. It is concluded that factors other than the direct effect of soil moisture content on germination are involved in reducing seedling emergence under fluctuating soil moisture conditions in the field.     

Osmotic and specific ion effects on the germination of Prosopis strombulifera

BACKGROUND AND AIMS: Salinity can affect germination of seeds either by creating osmotic potentials that prevent water uptake or by toxic effects of specific ions. Most studies have only used monosaline solutions, although these limit the extent to which one can interpret the results or relate them to field conditions. The aim of this work was to evaluate the germination of Prosopis strombulifera seeds under increasing salinity by using the most abundant salts in central Argentina in monosaline or bisaline iso-osmotic solutions, or in solutions of mannitol and polyethylene glycol. METHODS: Seeds were allowed to germinate under controlled conditions in a germination chamber at 30 +/- 1 degrees C and at 80 % r.h. Salinizing agents were KCl, NaCl, Na(2)SO(4), K(2)SO(4), NaCl + Na(2)SO(4) and KCl + K(2)SO(4) and osmotic agents were polyethylene glycol 6000 and mannitol. Treatments for all osmotica consisted of 0.0, -0.4, -0.8, -1.2, -1.5, -1.9 and -2.2 MPa solutions. KEY RESULTS: The percentage of germination decreased as salinity increased. SO(4)(2-) in monosaline solutions, with osmotic potentials -1.2 MPa and lower, was more inhibitory than Cl(-) at iso-osmotic concentrations. This SO(4)(2-) toxicity was alleviated in salt mixtures and was more noticeable in higher concentrations. K(+) was more inhibitory than Na(+) independently of the accompanying anion. CONCLUSIONS: Different responses to different compositions of iso-osmotic salt solutions and to both osmotic agents indicate specific ionic effects. This study demonstrates that the germination of P. strombulifera is strongly influenced by the nature of the ions in the salt solutions and their interactions. Comparative studies of Cl(-) and SO(4)(2-) effects and the interaction between SO(4)(2-) and Cl(-) in salt mixtures indicate that extrapolation of results obtained with monosaline solutions in the laboratory to field conditions can be speculative.     

Seed germination of Pilosocereus arrabidae (Cactaceae) from a semiarid region of south‐east Brazil

We evaluated the effect of temperature regimes (six constant and four alternating temperatures), light qualities (five red : far red ratios) and water potentials (ΨW; seven NaCl and polyethylene glycol 6000 [PEG] solutions) on the percentage and germination rate, as well as the post‐seminal development morphology, that allow Pilosocereus arrabidae seeds to germinate in a hot semiarid climate on the south‐eastern Brazilian coast. The results showed that seeds germinated similarly between constant and alternating temperatures, with an optimal germination at 25/20°C and 20°C. Pilosocereus arrabidae seeds were photoblastic positive and the final germination percentage was inhibited at low red : far red ratios. Maximum germination was obtained in distilled water (0 MPa) and decreases of Ψ_W in the solutions reduced the germination, which was lower in NaCl than in iso‐osmotic PEG solutions. Germination inhibition appears to be osmotic because the recovery response was high when non‐germinated seeds from both iso‐osmotic solutions were transferred to water. Seeds of P. arrabidae are small and germination is phaneroepigeal. Despite the slow growth typically seen in seedlings and adults of Cactaceae, germination in this species depends on the ability of the seeds to appropriately sense and react to environmental cues that correlate with times and places under low‐risk growth conditions.     

Canola seed germination and seedling emergence from pre-hydrated and re-dried seeds subjected to salt and water stresses at low temperatures

Low soil temperatures and low water potentials reduce and delay the seed germination of canola (Brassica rapa L., B. napus L.) in western Canada. Germination is also very sensitive to the salinity effects of nitrogen fertiliser placed with the seed, especially when the seed bed is relatively dry. The effects of pre-hydration and re-drying treatment on canola (Brassica rapa L. cv. Tobin) seed germination and seedling emergence at 10°C subjected to either a water or salt stress were determined. Low water potentials, induced by polyethylene glycol (PEG 8000), low soil moisture, or high concentrations of salts, reduced both germination and seedling emergence, and increased the time to 50% germination and emergence of seeds at 10°C. At equal osmotic potentials, Na₂SO₄ was less inhibitory on low temperature germination than either NaCl or PEG, suggesting that the sulphate ion partially alleviated the inhibitory effects of low water potential. Solutions of NaCI produced more abnormal seedlings compared to Na₂SO₄, suggesting that NaCl was more toxic than Na₂SO₄ during seedling development. Pre-hydration and re-drying partially overcame the inhibitory effects of both low water potential and salts on seed germination and seedling emergence at 10°C. The seed treatment increased the germination rate in Petri dishes and seedling emergence from a sandy loam soil. Water potentials or soil water contents required to inhibit 50% germination or emergence at 10°C were lower for treated seeds compared to control seeds. Salt concentrations inhibiting 50% emergence were higher for treated seeds than control seeds. Neither treated nor control seeds produced seedlings which emerged if the soil water content was lower than 9% or when the soil was continuously irrigated with salt solutions of 100 mmol kg^-1 of NaCl or 50 mmol kg^-1 of Na₂SO₄. These results suggest that the pre-hydration and re-drying treatment did not lower the base water potentials at which seedling emergence could occur. Abnormal seedlings were observed in both treated and control seeds, particularly if the soil was watered with NaCl solutions; however, the seed treatment reduced the number of abnormal seedlings.     

Strategies for adaptation of Suaeda physophora, Haloxylon ammodendron and Haloxylon persicum to a saline environment during seed-germination stage

BACKGROUND AND AIMS: Germination is very important for plant establishment in arid regions. The strategies taken by halophytes during the seed germination stage to adapt to saline environments in an arid zone were investigated in Suaeda physophora (euhalophyte), Haloxylon ammodendron (xero-halophyte) and Haloxylon persicum (xerophyte). METHODS: Seeds of S. physophora, H. ammodendron and H. persicum were exposed to a range of iso-osmotic NaCl and PEG solutions. Seed germination in, and recovery germination from, high NaCl were recorded. The effects of iso-osmotic NaCl and PEG on seed water uptake and changes in ion content were measured. In addition, the structure of seeds and Na+ distribution in the seed coat and embryos of dry seeds were investigated. KEY RESULTS: The relative increase in fresh weight of germinating seeds was markedly reduced in -2.24 MPa PEG compared with that in -2.24 MPa NaCl, while the opposite trend was found in concentration of K+ during the initial 9 h for all species. Haloxylon ammodendron and S. physophora had a higher recovery germination from -3.13 MPa NaCl compared with H. persicum. Seeds of all species had no endosperm. More Na+ was compartmentalized in the seed coats of the two halophytic species compared with that in the xerophyte H. persicum. CONCLUSIONS: The effect of NaCl on seed germination was due to both osmotic stress and ion toxicity for the three species. High soil salinity and a high content of Na+ in seeds may induce more seeds to remain ungerminated in S. physophora and H. ammodendron. Morphological structure and adaptation to salinity during seed germination may determine the geographical distribution of H. ammodendron and S. physophora in certain saline regions.     

Two Tomato Expansin Genes Show Divergent Expression and Localization in Embryos during Seed Development and Germination

Expansins are plant proteins that can induce extension of isolated cell walls and are proposed to mediate cell expansion. Three expansin genes were expressed in germinating tomato (Lycopersicon esculentum Mill.) seeds, one of which (LeEXP4) was expressed specifically in the endosperm cap tissue enclosing the radicle tip. The other two genes (LeEXP8 and LeEXP10) were expressed in the embryo and are further characterized here. LeEXP8 mRNA was not detected in developing or mature seeds but accumulated specifically in the radicle cortex during and after germination. In contrast, LeEXP10 mRNA was abundant at an early stage of seed development corresponding to the period of rapid embryo expansion; it then decreased during seed maturation and increased again during germination. When gibberellin-deficient (gib-1) mutant seeds were imbibed in water, LeEXP8 mRNA was not detected, but a low level of LeEXP10 mRNA was present. Expression of both genes increased when gib-1 seeds were imbibed in gibberellin. Abscisic acid did not prevent the initial expression of LeEXP8 and LeEXP10, but mRNA abundance of both genes subsequently decreased during extended incubation. The initial increase in LeEXP8, but not LeEXP10, mRNA accumulation was blocked by low water potential, but LeEXP10 mRNA amounts fell after longer incubation. When seeds were transferred from abscisic acid or low water potential solutions to water, abundance of both LeEXP8 and LeEXP10 mRNAs increased in association with germination. The tissue localization and expression patterns of both LeEXP8 and LeEXP10 suggest developmentally specific roles during embryo and seedling growth.     

Effetto del « water stress » su semi germinanti di Haplopappus gracilis (Nutt.) Gray pretrattati con gibberellina e fusicoccina

Abstract

Water stress effects on germinating seeds of Haplopappus gracilis (Nutt.) Gray pretreated with gibberellin and fusicoccin.—Achenes of Haplopappus gracilis, deprived of their coats, were germinated for various times, dried and then rehydrated. After this procedure many seeds were not able to resume regular germination and to overcome the water stress.

After having examined the morphological changes consequent to the water stress treatments we have checked if, as suggested by some Authors, there was a correlation between the resumption of DNA synthesis in the apical meristems of the rootlets and irreversible drought sensitivity.

To this purpose, embryos were pre-imbibed in water and in solutions of gibberellin (GA₃), which in Haplopappus promotes resumption of DNA synthesis, and fusicoccin (FC) which strongly stimulates germination and embryo elongation, without altering the pattern of DNA synthesis.

Our data show that embryos pre-imbibed in water or GA₃ and then dried, do not show any difference in their ability to resume germination, while embryos pre-hydrated in FC are always damaged more precociously and more severely by the dehydration treatments.

These results suggest that, since fusicoccin promotes embryo elongation through an activation of cell membranes, the physiological condition of these may be more critical for resumption of growth after the water stress than DNA replication activity.     

Influence of calcium pretreatment on wheat germination on saline media

Summary Wheat grains (Triticum vulgare L. var. Lemhi 53) were pretreated for about 6 hours with various solutions. They were then rinsed and planted on filter paper moistened with NaCl solution in petri dishes. Percent germination was measured after 3 days. Germination of water pretreated seeds on 1% NaCl was 8 per cent, while pretreatment with 1% CaCl₂. 2H₂O resulted in 90 per cent germination on 1% NaCl. Pretreatment with sodium and potassium chlorides enhanced germination only slightly. The beneficial effects of calcium pretreatment could be duplicated only partially by increments of CaCl₂ to the NaCl germination medium. Preatreatment concentrations ranging from 1 to 5% CaCl₂. 2H₂O, and times ranging from 3 to 24 hours were about equally effective. The beneficial effect of pretreatment persisted even though the seeds were subsequently dried and planted several months later. Pretreatment with calcium resulted in about a 25 per cent reduction in Na²² uptake from the germination medium.United Nations F.A.O. André Meyer Post Doctoral Research Fellow, on leave from Sind University, Hyderabad, West Pakistan.     

Nitric oxide is involved in light-specific responses of tomato during germination under normal and osmotic stress conditions

Background and Aims Nitric oxide (NO) is involved in the signalling and regulation of plant growth and development and responses to biotic and abiotic stresses. The photoperiod-sensitive mutant 7B-1 in tomato (Solanum lycopersicum) showing abscisic acid (ABA) overproduction and blue light (BL)-specific tolerance to osmotic stress represents a valuable model to study the interaction between light, hormones and stress signalling. The role of NO as a regulator of seed germination and ABA-dependent responses to osmotic stress was explored in wild-type and 7B-1 tomato under white light (WL) and BL. Methods Germination data were obtained from the incubation of seeds on germinating media of different composition. Histochemical analysis of NO production in germinating seeds was performed by fluorescence microscopy using a cell-permeable NO probe, and endogenous ABA was analysed by mass spectrometry. Key Results The NO donor S-nitrosoglutathione stimulated seed germination, whereas the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) had an inhibitory effect. Under WL in both genotypes, PTIO strongly suppressed germination stimulated by fluridone, an ABA inhibitor. The stimulatory effect of the NO donor was also observed under osmotic stress for 7B-1 seeds under WL and BL. Seed germination inhibited by osmotic stress was restored by fluridone under WL, but less so under BL, in both genotypes. This effect of fluridone was further modulated by the NO donor and NO scavenger, but only to a minor extent. Fluorescence microscopy using the cell-permeable NO probe DAF-FM DA (4-amino-5-methylamino-2',7'-difluorofluorescein diacetate) revealed a higher level of NO in stressed 7B-1 compared with wild-type seeds. Conclusions As well as defective BL signalling, the differential NO-dependent responses of the 7B-1 mutant are probably associated with its high endogenous ABA concentration and related impact on hormonal cross-talk in germinating seeds. These data confirm that light-controlled seed germination and stress responses include NO-dependent signalling.     

Characterisation of germinating and non-germinating wheat seeds by nuclear magnetic resonance (NMR) spectroscopy

Experiments were conducted to characterise the changes, especially of water status in germinating and non-germinating wheat seeds by nuclear magnetic resonance (NMR) spectroscopy. NMR relaxation time (T₂) measurements showed tri-phasic or bi-phasic characteristics during different stages of hydration, depending on the seed's ability to germinate. Component analysis of T₂ data revealed the existence of only two components, bound and bulk water, in dry seeds. In contrast, both the germinating and non-germinating wheat seeds had a three-component water proton system (bound, bulk and free water) in phase I of hydration. During the lag phase (phase II) of hydration, bulk water component of non-germinating seeds disappeared completely, resulting in a two component water proton system. Nevertheless, the three component water proton system was observed in the germinating seeds in phase II. Following phase II, rapid hydration (phase III) was observed in germinating seeds only. Water protons were re-organised and there were increases in bulk and free water but decreases in bound water concomitantly. Comparison of the physical state of water in these seeds by NMR spectroscopy with that of tissue leachate conductivity measurement suggests that the seed membrane system was affected more evidently in non-germinating seeds, leading to the disorganised cell structure. The present study provides evidence that the reorganisation of physical state of water in germinating wheat seeds during hydration is essential for its subsequent event of germination.