The Role of Hormones in Controlling the Mechanically Induced Dormancy of Suaeda spp.

Seeds of several taxa in the genus Suaeda with a mechanically resistant testa were stimulated to germinate with applications: of 1 × 10^?4M gibberellic acid (GAg). The barley endosperm bioassay indicated that the non-dormant taxa, S. macrocarpa, had high initial gibberellin-like activity while the dormant varieties, S. flexilis and S. vulgaris, had not. Soaking for 2 days increased the gibberellin-like activity of the dormant taxa. At 20 days hormonal activity was repressed, and few seeds germinated. The barley endosperm bioassay also revealed an inhibitor activity in the dormant varieties. The wheat coleoptile bioassay and UV irradiation of thin layer chromatograms indicated that an inhibitor occurred at the Rf of cochromatographed ABA and that it had similar inhibitory characteristics.     

Endogenous plant hormones of the broad bean,Vicia faba L. (-)-jasmonic acid,a plant growth inhibitor in pericarp

(-)-Jasmonic acid was identified as a plant growth inhibitor of the pericarp of Vicia faba by means of gas-liquid chromatography, high resolution mass spectrometry, ¹H-nuclear magnetic resonance (¹H-NMR), and ¹³C-NMR. Additionally, the pericarp contains very small amounts of abscisic acid (ABA) and 4-dihydrophaseic acid. The highest level of jasmonic acid was reached prior to full pericarp length. This amount (3 g g^-1 fresh weight) is similar to the maximal ABA content in the developing seed. Jasmonic acid is a plant growth inhibitor possessing a relative activity in the wheat seedling bioassay of 1–2.5%, compared to ABA. Contrary to ABA, jasmonic acid does not cause retardation of leaf emergence. The possible physiological role of jasmonic acid in the pericarp is discussed and compared with the assumed function of ABA in developing seeds.Abbreviations ABA abscisic acid - DPA 4-dihydrophaseic acid - DPAMeTMS methyl ester trimethylsilyl ether of DPA - EtOAc ethyl acetate - Et₂O ether - MS mass spectrometry - NMR nuclear magnetic resonance - GLC gas-liquid chromatography - TLC thin-layer chromatography - UV ultraviolet light     

Evidence for the accumulation of a germination inhibitor during progressive thermoinhibition of seeds of celery (Apium graveolens L.)

The germination of seeds of celery (Apium graveolens L.) becomes progressively thermoinhibited on incubation in the dark at high temperatures, the inhibitory temperature being dependent on the cultivar used. In two high-dormancy cultivars of celery, the production of germination inhibitors in seeds incubated in the dark at 26°C gradually increased over a 7-day period. Inhibitor production was measured by incubating seeds of the low-dormancy cultivar Florida 683 in homogenates of the thermoinhibited seeds of the high-dormancy cultivars and recording germination either in the light or with the gibberellins A₄ and A₇ (GA_4/7) in the dark. Most Florida 683 seeds which failed to germinate in the homogenates after 15 days were induced to germinate by addition of N⁶-benzyladenine (BA). The presence of BA in addition to GA_4/7 throughout incubation in the dark completely overcame the inhibitory effects of homogenates. This indicates that thermoinhibition of celery seeds is associated with the accumulation of a germination inhibitor which interacts with cytokinins. This does not appear to be abscisic acid (ABA) since ABA levels in thermoinhibited seeds were lower than in untreated seeds and did not increase with duration of high temperature treatment.Abbreviations ABA Abscisic acid - BA N⁶-benzyladenine - GA_4/7 a mixture of the gibberellins A₄ and A₇ - HTP high-temperature pretreatment     

Dormancy in somatic embryos and seeds ofVitis: changes in endogenous abscisic acid during embryogeny and germination

Abscisic acid (ABA) in extracts of somatic embryos and seeds of Gloryvine (Vitis vinifera L.xV. rupestris Scheele) was measured by gas chromatography-mass spectrometry-selected ion monitoring using deuterated ABA, (±)-[C-3Me-²H₃]ABA, ([²H₃]ABA) as internal standard. The ABA content increased rapidly during embryogeny (0.035 ng/embryo at the globular stage to 0.22 ng/embryo at the mature stage). The level of ABA in the tissues of somatic embryos, expressed in ng/mg dry weight, decreased from the globular stage (0.76 ng/mg) to the mature stage (0.25 ng/mg). Chilling (4° C) induced normal germination of seeds and mature somatic embryos and precocious germination of globular, heart-shaped and torpedoshaped somatic embryos. In all cases chilling led to a marked reduction in endogenous ABA. Exogenous (±)-ABA inhibited the germination of chilled somatic embryos.Abbreviations ABA abscisic acid - [²H₃]ABA (±)-[C-3Me-²H₃]-abscisic acid - BHT 2,6-di-t-butyl-4-methylphenol - GC-MS gas chromatography-mass spectrometry - Me-ABA and Me-[²H₃]ABA methyl esters of ABA and [²H₃]ABA, respectively - SIM selected ion monitoring     

Evidence of a role for tyrosine dephosphorylation in the control of postgermination arrest of development by abscisic acid in Arabidopsis thaliana L

In the present paper evidence is presented indicating that tyrosine dephosphorylation is a key regulatory mechanism in postgermination arrest of Arabidopsis thaliana L. seed development mediated by abscisic acid (ABA). By using phenylarsine oxide (PAO), an inhibitor of tyrosine phosphatases, the sensitivity to the inhibitory effect of ABA on seed germination is enhanced. Consistent with this finding, we demonstrate that the ABA-responsive gene, RAB18, is hyperinduced in seeds imbibed in ABA plus PAO, compared with seeds imbibed only with ABA.     

Control of seed dormancy in Nicotiana plumbaginifolia: post-imbibition abscisic acid synthesis imposes dormancy maintenance

The physiological characteristics of seed dormancy in Nicotiana plumbaginifolia Viv. are described. The level of seed dormancy is defined by the delay in seed germination (i.e the time required prior to germination) under favourable environmental conditions. A wild-type line shows a clear primary dormancy, which is suppressed by afterripening, whereas an abscisic acid (ABA)-deficient mutant shows a non-dormant phenotype. We have investigated the role of ABA and gibberellic acid (GA₃) in the control of dormancy maintenance or breakage during imbibition in suitable conditions. It was found that fluridone, a carotenoid biosynthesis inhibitor, is almost as efficient as GA₃ in breaking dormancy. Dry dormant seeds contained more ABA than dry afterripened seeds and, during early imbibition, there was an accumulation of ABA in dormant seeds, but not in afterripened seeds. In addition, fluridone and exogenous GA₃ inhibited the accumulation of ABA in imbibed dormant seeds. This reveals an important role for ABA synthesis in dormancy maintenance in imbibed seeds. Received: 31 December 1998 / Accepted: 9 July 1999     

Does Seed Priming Induce Changes in the Levels of Some Endogenous Plant Hormones in Hexaploid Wheat Plants Under Salt Stress？

In order to assess whether salt tolerance could be Improved In spring wheat （Triticum aestivum L.）, the present study was performed by soaking the seeds of two cultlvars, namely MH-97 （salt sensitive） and Inqlab-91 （salt tolerant）, for 12 h In distilled water or 100 mol/m^3 CaCl2, KCI, or NaCI. Primed seeds from each treatment group and non-primed seeds were sown In a field In which NaCI salinity of 15 dS/m was developed. Priming of seeds with CaCl2, followed by priming with KCI and NaCI, was found to be effective In alleviating the adverse effects of salt stress on both wheat cultivars In terms of shoot fresh and dry weights and grain yield. Priming with CaCl2 alleviated the adverse effects of salt stress on hormonal balance In plants of both cultlvars. In MH-97 plants, CaCl2 pretreatment considerably reduced leaf absclslc acid （ABA） concentrations and Increased leaf free salicylic acid （SA） concentrations under both saline and non-saline conditions. In contrast, In the Inqlab-91 plant, CaCl2 Increased free Indoleacetic acid （IAA） and indolebutyrlc acid （IBA） content. However, priming of seeds with CaCl2 did not alter free polyamlne levels in either cultlvar, although spermldlne levels were considerably lower In plants raised from seeds treated with CaCl2 for both cultlvars under saline conditions. Priming with KCI Increased growth In Inqlab-91 plants, but not In MH-97 plants, under saline conditions. The salinity Induced reducUon In auxins （IAA and IBA） was alleviated by NaCI priming In both cultlvars under saline conditions. However, NaCI Increased leaf free ABA content and lowered leaf SA and putresclne levels In Inqlab-91 plants under saline conditions. In conclusion, although all three priming agents （I.e. CaCl2, KCI, and NaCI） were effective In alleviating the adverse effects of salt stress on wheat plants, their effects on altering the levels of different plant hormones were different In the two cuItlvars.     

Growth Capacity of Embryo Axes Excised from Dormant and Germinating Horse Chestnut Seeds and Their Response to Exogenous Abscisic Acid

In embryo axes excised from mature horse chestnut (Aesculus hippocastanum L.) seeds, both freshly-fallen and subjected to cold stratification, the ability for growth was studied. While excised axes were kept on water at 28°C for 3 days, their fresh weight and length increased, the polypeptide composition of soluble proteins changed, the content of some heat-stable polypeptides decreased, and the capacity for protein synthesis in vivo retained. All these processes were similar to those in the axes of intact seeds during stratification until radicle protrusion. Growth of excised axes accelerated with the increasing duration of stratification. Cycloheximide (50 mg/l) and -amanitin (7 mg/l) inhibited axis growth, but an inhibitor of ABA synthesis fluridone (5 mg/l) and a natural cytokinin dihydrozeatin (10^–5 M) did not influence the growth rate. The growth capacity of axes excised from dormant and germinating horse chestnut seeds indicates the absence of dormancy in the axes of mature seeds. ABA (10^–5 M) suppressed completely the growth of axes detached from seeds experiencing cold stratification but still not germinating, although protein synthesis was not inhibited. The axes excised from the seeds after radicle emergence were insensitive to ABA and grew actively in its presence. ABA-induced growth inhibition might be related to the suppressed synthesis of minor polypeptides required for growth or to the activated synthesis of some growth-retarding proteins. The conclusion was drawn that the excised axes could be used as a model for studying the processes preceding visible germination of recalcitrant seeds.     

刺楸种子中性与酸性抑制物质的研究

本文研究了刺楸种子抑制物质的提取,分离和鉴定方法,并测定了抑制物质的相对活性及其含量。结果表明,刺揪种子中除含高水平的酸性抑制物外,还存在一种中性抑制物。该中性抑制物同酸性抑制物相似,有较强的生物活性,不但可以抑制白菜种子的萌发与胚根生长,而且对已解除休眠的刺楸种子也有显著作用。利用纸层析,薄层层析,颜色反应和高效液相色谱等手段,证明中性抑制物质为香豆素类物质;酸性抑制物质的主要成分为脱落酸。种子各部位均含这两种抑制物质,但含量有所不同,随种子贮藏时间的延长,抑制物会发生转移。本文还讨论了用不同溶剂提取中性抑制物的效果。     

Inhibition of ABA-mediated Responses by Dithiothreitol in Plants

In plants, abscisic acid (ABA)-mediated responses during abiotic stress, growth, and development have been well studied. Many chemicals which modulate ABA responses have been identified. In this study, we report that dithiothreitol (DTT), an inducer of endoplasmic reticulum (ER) stress, can overcome ABA-mediated responses in plants. In rice seedlings, combined treatment of ABA and DTT increased shoot growth compared to ABA alone. The phenotype correlated with the expression pattern of ABA and ER stress-responsive genes. In finger millet, increase in root growth was observed in combined treatment, compared to ABA treatment. Experiments using dimethyl sulfoxide indicated that the phenotype observed was specific to DTT. Priming of germinated rice seeds with DTT followed by salinity stress indicated that DTT can mask the ABA effect. In ABA bioassay using cotton petioles, an increase in intact petioles in combined treatment of ABA and DTT was observed compared to ABA treatment. The expression of OsWRKY48, an ABA-responsive gene, was down-regulated in combined treatment, indicating that the target of DTT-induced ER stress is upstream of OsWRKY48 in the ABA signaling pathway. The study demonstrated that DTT-induced ER stress can be a potential mechanism to regulate ABA-mediated responses in plants.

     

A Preliminary Study on Neutral and Acid Inhibitors in the Seed of Kalopanax scptemlobus

The method of extraction, isolation, purification and identification of the neutral and acid inhibitors in the seeds of Kalopanax Septemlobus was given. It is proved that the neutral inhibitor is coumarin, the acid inhibitor is abscisic acid (ABA) by means of paper chromatograph, thin layer chromatograph, high performance liquid chromatograph (HPLC), color reaction and bioassay. The neutral inhibitor can strongly inhibite not only the seed germination of Brassica Chinensis and the radical elongation, but also that of the seed of Kalopanax septemlobus. The study showed that ABA and coumarin exist in the seed coat, endosperm and pericarp of the Kalopanax Septemlobus seed. Both ABA and coumarin can transport from seed cover (pericarp, seed coat)to the interior (endosperm, embryo) as the seeds were stored in refrigerator. In addition, the different results of extracting neutral inhibitor with water, methanol, and alcohol were compared in this paper.     

Uptake and Effect of Abscisic Acid during Induction and Progress of Radicle Growth in Seeds of Chenopodium album

In the seeds of Chenopodium album L. visible phenomena preceding the final protrusion of the radicle enable a clear distinction between the induction and the progress of growth inside the covering structures. The light-dependent induction of radicle growth is not inhibited by exogenously applied abscisic acid (ABA). Experiments with 1-¹⁴C-ABA ruled out a lack of penetration of the hormone. However, ABA does inhibit the growth of the radicle before final protrusion. This inhibition and the uptake of 1-¹⁴C-ABA are enhanced at lower pH values, indicating absorption of the undissociated molecule. The uptake of labeled hormone strongly increases during the growth of the radicle. This increase is not merely a reflection of extra water uptake. Seeds of different degrees of dormancy contain equallly low levels of endogenous ABA. Much higher levels of ABA in the seeds were obtained by exogenous application of the hormone but these levels stills do not prevent the breaking the dormancy by light. It is concluded that ABA has no function in the regulation of dormancy in C. album seeds.     

In cress roots (Lepidium sativum L.), abscisic acid prevents the development of the central cap cells into statocytes

Summary If seeds of Lepidium sativum are soaked in a 10^-4M solution of abscisic acid (ABA) for 30 min, the structural development of the central cap cells (C.C.) deviates strongly from the norm. ABA inhibits the elongation of the C.C., the sedimentation of the amyloplasts which may be caused by a higher viscosity of the cytoplasm, the formation of the stacked ER-cisternae at the distal cell pole, and the polar arrangement of the cell organelles along the gravity vector. The statistical distribution of the organelles and the arrangement of lipid droplets near the plasmalemma indicate that ABA prevents the normal development of the C.C. into statocytes.Abbreviations ABA abscisic acid - C.C. central cap cells     

Abscisic acid and gibberellin-like substances in roots and root nodules ofGlycine max

Summary The content of endogenous gibberellin (GA)-like substances of roots and root nodules of SOya, and GA production byRhizobium japonicum cultures, were investigated by a combined thin layer chromatographic (TLC)-dwarf pea epicotyl bioassay technique. GAs were more concentrated in root nodules than in the roots, totalling 1.34 and 0.16 nM GA₃ equivalents g⁻¹ dry wt. respectively. GA production byR. japonicum cultures was demonstrated (1.00 nM GA₃ equivalentsl ⁻¹) and comparison of the GA components of plant and bacterial culture medium extracts, suggested that rhizobial GA production may contribute to the nodule GA content. Cis-trans abscisic acid (ABA) was identified in root and nodule extracts by TLC-gas liquid chromatography (GLC), and amounted to 0.18 and 2.21 nM g⁻¹ dry wt. respectively, whereas 0.30 and 4.63 nM ABA equivalents g⁻¹ dry wt. were detected by a TLC-wheat embryo bioassay technique. ABA was not detected in extracts of bacterial cultures.     

A simple bioassay for abscisic acid using cucumber hypocotyls

A simple bioassay based on the inhibition by abscisic acid (ABA) of cucumber (Cucumis sativus L., cv. National Pickling) hypocotyl elongation was developed. Sections of 3-day-old dark-grown cucumber hypocotyl taken from 0–5 mm immediately below the cotyledon were used for the assay. A dark incubation period of 20 h was followed by an exposure to light for 24 h. Under these conditions, the inhibition of hypocotyl elongation is proportional to the abscisic acid applied. The minimum detectable level of abscisic acid was 10^–9 M, and the range of linear response to abscisic acid was between 10^–7 and 10^–3 M. This assay is 10 times more sensitive than the cucumber cotyledon greening bioassay for abscisic acid.     

Seed germination in a tomato male-sterile mutant is resistant to osmotic, salt and low-temperature stresses

Seed germination in a male-sterile 7B-1 mutant in tomato is reletively more resistant to the inhibitory effects of a high osmoticum induced by mannitol and polyethylene glycol, to various salts, including NaCl, Na₂SO₄, KCl and K₂SO₄, and to low-temperature stress, compared to the wild-type (WT) seeds. The inhibitory effects of various stresses could be partly or completely overcome by fluridone (FLU), an inhibitor of abscisic acid (ABA) biosynthesis. However, lower concentration of fluridone was required for the 7B-1 mutant than for WT seeds, and the mutant seeds were more sensitive to the inhibitory effects of exogenous ABA. The data suggest that 7B-1 seed has a pre-existing level of elevated ABA which imparts resistance to the various stresses. The ability to regulate male sterility in the 7B-1 mutant by photoperiod, as previously reported by Sawhney (1997), and its resistance to abiotic stresses, as reported here, makes this a useful system for tomato breeding and in hybrid programs. Received: 11 May 2000 / Accepted: 4 June 2000     

Abscisic Acid Inhibition of Kinetin Nucleotide Formation in Germinating Lettuce Seeds

Imbibing ‘Grand Rapids’ lettuce (Lactuca saliva L.) seeds take up ¹⁴C-kinetin, and metabolize this cytokinin to the 5′-nucleotide. The identity of the labeled nucleotide in seed extracts was verified by Sephadex LH-20 column chromatography, paper and thin layer chromatography, and high voltage paper electrophoresis. Incubations with kinetin in the presence of abscisic acid lead to an apparent specific inhibition of kinetin nucleotide formation. ABA has no effect on kinetin uptake, and does not inhibit kinetin nucleotide synthesis in vitro by a cell-free preparation from lettuce seeds. Additionally, ABA does not inhibit adenylate synthesis from exogenously supplied adenine. These results represent a specific cytokinin-ABA interaction, which might play a significant role in the hormonal regulation of lettuce seed germination.     

Dormancy termination of western white pine (<Emphasis Type="Italic">Pinus monticola</Emphasis> Dougl. Ex D. Don) seeds is associated with changes in abscisic acid metabolism

Western white pine (Pinus monticola) seeds exhibit deep dormancy at maturity and seed populations require several months of moist chilling to reach their uppermost germination capacities. Abscisic acid (ABA) and its metabolites, phaseic acid (PA), dihydrophaseic acid (DPA), 7-hydroxy ABA (7OH ABA) and ABA-glucose ester (ABA-GE), were quantified in western white pine seeds during dormancy breakage (moist chilling) and germination using an HPLC–tandem mass spectrometry method with multiple reaction monitoring and internal standards incorporating deuterium-labeled analogs. In the seed coat, ABA and metabolite levels were high in dry seeds, but declined precipitously during the pre-moist-chilling water soak to relatively low levels thereafter. In the embryo and megagametophyte, ABA levels decreased significantly during moist chilling, coincident with an increase in the germination capacity of seeds. ABA catabolism occurred via several routes, depending on the stage and the seed tissue. Moist chilling of seeds led to increases in PA and DPA levels in both the embryo and megagametophyte. Within the embryo, 7OH ABA and ABA-GE also accumulated during moist chilling; however, 7OH ABA peaked early in germination. Changes in ABA flux, i.e. shifts in the ratio between biosynthesis and catabolism, occurred at three distinct stages during the transition from dormant seed to seedling. During moist chilling, the relative rate of ABA catabolism exceeded ABA biosynthesis. This trend became even more pronounced during germination, and germination was also accompanied by a decrease in the ABA catabolites DPA and PA, presumably as a result of their further metabolism and/or leaching/transport. The transition from germination to post-germinative growth was accompanied by a shift toward ABA biosynthesis. Dormant imbibed seeds, kept in warm moist conditions for 30 days (after an initial 13 days of soaking), maintained high ABA levels, while the amounts of PA, 7OH ABA, and DPA decreased or remained at steady-state levels. Thus, in the absence of conditions required to break dormancy there were no net changes in ABA biosynthesis and catabolism.Abbreviations ABA abscisic acid - ABA-GE abscisic acid glucose ester - DPA dihydrophaseic acid - 7OH ABA 7-hydroxy abscisic acid - 8OH ABA 8-hydroxy abscisic acid - MRM multiple reaction monitoring - PA phaseic acid     

Efficacy of soaking cotton seeds within salicylic acid and potassium silicate on reducing reniform nematode infection

ABSTARCT

The efficiency of soaking cotton cv. Giza 45 seeds in five concentrations of salicylic acid and potassium silicate (5, 10, 15, 20 and 25?mg?L^?1 against Rotylenchulus reniformis infection showed a significant (P?<?0.05) improvement in the tested plant parameters that was distinct in soaked seeds in salicylic acid for 24?hours compared with potassium silicate in greenhouse (28?±?5?°C). The application of concentration (20?mg?L^?1) stated the highest values of improvement of plant criteria, while high concentration (25?mg?L^?1) revealed the maximum reduction rates in the total nematode population for both potassium silicate and salicylic acid. Moreover, seed soaking in salicylic acid and potassium silicate achieved a considerable increment in nitrogen, phosphorus, potassium, phenol and chlorophyll contents in cotton leaves with changeable values.