Alleviation of Salinity-Induced Dormancy in Perennial Grasses

All seeds of Aeluropus lagopoides and Urochondra setulosa germinated under non-saline conditions except for Sporobolus ioclados which showed only 40 % germination. Increase in salinity substantially inhibited germination and few seeds germinated at 400 mM NaCl. Germination at 200 mM NaCl was alleviated in U. setulosa by the application of gibberellic acid and fusicoccin, in A. lagopoides by thiourea, betaine, kinetin, fusicoccin and ethephon, and in S. ioclados by gibberellin and ethephon. High salinity (400 mM NaCl) induced germination inhibition was alleviated by proline, kinetin, fusicoccin and ethephon only in A. lagopoides.     

Seed Germination of Triglochin Maritima as Influenced by Salinity and Dormancy Relieving Compounds

Triglochin maritima had only 40 % germination in distilled water, but germination was substantially enhanced when seeds were exposed to ethephon, fusicoccin, proline, kinetin, and thiourea. Also, the effect of low salinity on germination was alleviated by fusicoccin, kinetin, nitrate and thiourea, whereas, the reduction in germination at high salinity was partially countered by ethephon, kinetin, thiourea and nitrate.     

Effects of Dormancy Regulating Chemicals on Innate and Salinity Induced Dormancy in the Invasive <Emphasis Type="Italic">Prosopis juliflora</Emphasis> (Sw.) DC. Shrub

The effect of different types and concentrations of dormancy regulating chemicals (DRCs) on innate and induced dormancy was evaluated under optimal germination conditions in the invasive Prosopis juliflora shrub. Lower concentrations of gibberellic acid (0.3 mM) and kinetin (0.05 mM) were more effective in enhancing germination % and rate at higher concentrations of NaCl, but the reverse was true for thiourea. None of the DRCs alleviated innate dormancy of P. juliflora. Germination % and rate decreased as salinity increased. Percent final germination of non-treated seeds was significantly reduced at 500 mM NaCl and virtually inhibited in 600 mM NaCl. Germination reduction in 500 mM NaCl was not alleviated by any of the DRCs, but inhibition induced at 600 mM NaCl was partially alleviated by all the DRCs. Gibberellic acid had a significantly greater effect than kinetin in alleviating germination inhibition. For restoration of saline soil through the use of P. juliflora, results suggest using DRCs, particularly gibberellic acid and thiourea, as a preseeding treatment can overcome the problem of reduced germination.     

Alleviation of Seed Dormancy in the Desert ForbZygophyllum simplexL. from Pakistan

Zygophyllum simplexL. is a succulent annual that grows on thecoastal and inland saline flats around Karachi, Pakistan. Theseeds are moderately salt tolerant during germination. GerminationofZygophyllum simplexseeds under various salinity, proline,betaine, GA and kinetin treatments was determined. Proline (0.1and 1 mM) and betaine (0.1 and 1 mM) alleviated the innate dormancyof seeds, and germination reached 60–70% compared to 12%in the control set. At low salinity compatible osmotica alleviatedsome effects of salinity, but at higher NaCl concentrationsboth proline and betaine were ineffective. Gibberellic acid(0.3 and 3 mM) and kinetin (0.05 and 0.5 mM) substantially alleviatedboth innate as well as salinity-induced seed dormancy. At highersalinity (125 mM), low concentrations of kinetin (0.05 mM) andhigh concentrations of GA (3 mM) were more effective. GA completelyalleviated the effect of salinity at all concentrations used. Betaine; desert; dormancy; forb; GA; germination; halophyte; kinetin; proline; seeds; Zygophyllum simplex     

Seed Germination in Chenopodium album L: Relationships between Nitrate and the Effects of Plant Hormones

Effects of ethylene, gibberellins, and kinetin on the germination of two lots of Chenopodium album L. seeds, collected from the field in 1982 and 1983, were studied in relation to the availability of nitrate. The experiments were conducted in darkness and at temperatures ranging from 12 to 32°C. Ethylene induced over 75% germination in the 1983 seed but had little effect on the 1982 seed. Nitrate was only slightly promotive in either of the two seed lots. A combination of ethylene and nitrate, however, acted synergistically on 1982 seed, resulting in as much germination as that induced in 1983 seed by ethylene alone. In 1983 seed, a combination of ethylene and nitrate was only marginally more effective than ethylene. A similar relationship was observed in the effects of gibberellic acid₄₊₇ (GA₄₊₇) and nitrate on seeds from the two lots. The 1982 seed, which responded synergistically to combinations of nitrate with ethylene or GA₄₊₇ was found to contain an extremely low endogenous level of nitrate as compared to 1983 seed. Thus, high levels of either endogenous or applied nitrate appeared to enhance the germination response to ethylene or GA₄₊₇.

Kinetin had no effect on 1982 seed and only a small promotive effect on 1983 seed. There was no synergism between kinetin and nitrate in either of the seed lots.

     

Variation in seed dormancy and germination among populations of Silybum marianum (Asteraceae)

Milk thistle (Silybum marianum) is a medicinal plant; however, lack of consistency in past dormancy studies has hindered propagation of this species from seeds. We tested the germination responses of freshly harvested and after-ripened (stored for 2 and 7 months; 25°C at 50% relative humidity) seeds from three populations (P1, P2 and P3) in Iran at varying constant or alternating temperatures, with or without GA₃ and in light and continuous darkness. No germination occurred in freshly harvested seeds incubated at any condition without GA₃ application, indicating that all the seeds were dormant. Seeds from P1 and P2, which developed under relatively dry, warm conditions, germinated over a wider range of temperatures after 2 months of dry storage, indicating type 6 of non-deep physiological dormancy (PD). Seeds from P3, which developed under relatively wet, cool conditions, incubated at constant temperatures (especially on GA₃), exhibited an increase in maximum temperature for germination, indicating type 1 of non-deep PD. Light improved germination of after-ripened seeds, and GA₃ application substituted for the light requirement for germination. This is the first report that environmental conditions during seed development may be correlated with differences in the type of non-deep PD. We conclude that milk thistle seeds are positively photoblastic and photodormant and the germination responses of after-ripened seeds from different populations are different under darkness. Therefore, the impacts of genetic differences and maternal effects on the induction of dormancy during seed development should be considered in attempts to domesticate this medicinal plant.     

The role of gibberellic acid (GA3) in the removal of dormancy inFraxinus excelsior L. seeds

The seeds ofFraxinus excelsior L. were stratified at 17-20 °C (warm stratification), at 4-6 °C (cold stratification) and at alternating temperature (warm — cold stratification). The seeds subjected to warm stratification only, remained dormant. The seeds stratified only at 4-6 °C germinated gradually during a long period of time. The seeds subjected to warm — cold stratification, however, germinated with great intensity within a relatively short period of time. GA₃ was shown to stimulate the growth of embryos markedly, and its effect on the germination of seeds depended on the temperature of stratification. GA₃ applied during the cold stratification accelerated the removal of dormancy by shortening the period of stratification and by influencing the germination of seeds. The results obtained indicate a similarity between the effect of temperature 17-20 °C during the warm stratification and that of gibberellic acid. Both those factors applied separately affect favourably after-ripening of the embryos and accelerate the germination of seeds.     

Effect of Dormancy Relieving Compounds on the Seed Germination of Non-dormantAllenrolfea occidentalisunder Salinity Stress

Allenrolfea occidentalis(Chenopodiaceae) is a highly salt tolerantplant species that is widely distributed in inland salt marshesand salt playas of the western United States. We investigatedthe influence of dormancy-relieving compounds (fusicoccin, ethephon,nitrate and thiourea) in alleviating salinity stress on theseed germination ofA. occidentalis. Seed germination decreasedwith an increase in salinity and no seed germinated at 800 mMNaCl.Fusicoccin (5 µM), ethephon (10 mM) and nitrogenous compounds(20 mMnitrate and 10 mMthiourea) were able to counteract theinhibition produced by salinity treatments. All dormancy relievingcompounds significantly (P<0.0001) promoted germination atall salinity concentations. Fusicoccin completely reversed theinhibitory effects of salinity on seed germination ofA. occidentalis.Ethephon application significantly promoted germination at allsalinities. Nitrate and thiourea were relatively less effectivein alleviating the effects of high salinity on germination.Copyright1998 Annals of Botany Company Allenrolfea occidentalis, ethephon, fusicoccin, halophyte, dormancy, nitrate, salinity, seed germination, thiourea.     

Profile of Plant Hormones and their Metabolites in Germinated and Ungerminated Canola (Brassica napus) Seeds Imbibed at 8°C in either GA4+7, ABA, or a Saline Solution

Abscisic acid (ABA) and gibberellins (GAs) are two major phytohormones that regulate seed germination in response to internal and external factors. In this study we used HPLC-ESI/MS/MS to investigate hormone profiles in canola (Brassica napus) seeds that were 25, 50, and 75% germinated and their ungerminated counterparts imbibed at 8°C in either water, 25 μM GA₄₊₇, a 80 mM saline solution, or 50 μM ABA, respectively. During germination, ABA levels declined while GA₄ levels increased. Higher ABA levels appeared in ungerminated seeds compared to germinated seeds. GA₄ levels were lower in seeds imbibed in the saline solution compared to seeds imbibed in water. Ungerminated seeds imbibed in ABA had lower GA₄ levels compared to ungerminated seeds imbibed in water; however, the levels of GA₄ were similar for germinated seeds imbibed in either water or ABA. The ABA metabolites PA and DPA increased in seeds imbibed in either water, the saline solution, or ABA, but decreased in GA₄₊₇-imbibed seeds. In addition, ABA inhibited GA₄ accumulation, whereas GA had no effect on ABA accumulation but altered the ABA catabolism pathway. Information from our studies strongly supports the concept that the balance of ABA and GA is a major factor controlling germination.     

Response interactions in grape somatic embryogenic cultures to cold and gibberellic acid treatments to overcome embryo dormancy

Somatic embryogenesis (SE) is a widely used method in grape (Vitis vinifera) biotechnology as it permits the rapid multiplication of clonal material from a single explant source. A commonly observed difficulty with this technique, however, is that many of the newly derived embryos either cease development entirely or they develop abnormally and fail to form a plantlet capable of survival beyond the in vitro environment. Previous studies have reported that somatic embryos of grape enter into a state of endodormancy similar to that seen in grape seeds. Grape seeds require a cold period of several weeks to induce germination and the release of the embryo from dormancy is associated with a rapid rise in endogenous gibberellins. We tested the influence of cold and/or a pulse treatment of gibberellic acid (GA₃) on embryogenic callus cultures of the variety Pinot noir. In the most efficient treatment tested (8 weeks in cold), a 4.6-fold improvement in plantlet recovery was recorded compared with that in the untreated controls. The improvement in yield was the result of combined increases in embryo differentiation and embryo germination. Treatment with GA₃ improved embryo germination compared to the untreated controls, but only when GA₃ was used in combination with sub-optimal cold treatments. The GA₃ pulse treatments tested had no measurable impact on embryo differentiation or on the differentiation of plantlets from young germinated embryos.     

Light and temperature control of germination in Agropyron smithii seeds

In darkness, A. smithii seeds germinated poorly at constanttemperatures but well at alternating temperatures. Prolongedperiods on the high part of the temperature cycles reduced germination;the higher the temperature the shorter was the period requiredon the high part of the temperature cycles for optimum germination.Continuous, unfiltered, incandescent illumination and intermittentfar red at 15?–25?C alternation also inhibited germination;the inhibitory effects were similar to those caused by the highintensity reaction. Far red inhibited germination when appliedafter 1 and 2 complete 15?–25?C cycles in darkness butnot after 3 cycles. Less than 20% of the seeds were under phytochromecontrol at constant 20?C. When red light was applied directlyafter far red that was applied in intermittent cycles at 15?–25?C,however, 50% of the seeds caused to germinate by the alternatingtemperature were shown to be controlled by the reversible phytochromereaction. The induced high-temperature dormancy was overcome by gibberellicacid (GA₃) plus kinetin. The hormonal treatment was much moreeffective than light for breaking dormancy. Inhibition fromprolonged illumination was alleviated or eliminated by GA₃+kinetin.The failure of red light to promote good germination at 20?Cwas also overcome with GA₃+kinetin; effects of light plus thehormone treatments were more than additive. These data suggestthat optimum alternating temperatures facilitate a proper balanceand interaction of hormones, enzymes, substrates and possiblypreexistent P_fr so that the germination of A. smithii seedscan proceed without benefit of a light treatment. (Received July 7, 1976; )     

Role of some growth regulators on cytogenetic activity of barley under salt stress

The effects of gibberellic acid (GA₃), kinetin (KIN), benzyladenine and ethylene (E) on mitotic activity and chromosomal aberrations in root tips of barley seeds (Hordeum vulgare L. cv. “Bülbül 89”) germinated under salt stress were investigated. It was determined that all of these plant growth regulators (PGRs) decreased mitotic index in root tips of barley seeds germinated at 20 °C and in distilled water. Furthermore, some of the PGRs studied increased significantly the frequency of chromosomal aberrations. The frequency of chromosomal aberrations in seeds treated with E and KIN was considerably higher than in the seeds germinated under nonstress conditions. The inhibitory effect of salt stress on mitotic index increased with increasing salt concentration (0.30, 0.35, 0.40 and 0.45 molal, m). GA₃ and KIN pretreatments showed a successful performance in ameliorating the negative effects of increasing salinity on mitotic activity. The number of chromosomal aberrations also increased with increasing NaCl concentration. However, most of the PGR pretreatments studied alleviated the detrimental effects of increasing salinity on chromosomal aberrations. KIN pretreatment at 0.30 and 0.35 m salinity could not rescued the cytogenetic activity of salt stress on this parameter.     

Germination Promotion of Loblolly Pine and Baldcypress Seeds by Stratification and Chemical Treatments

The effects of 4 chemicals on the germination promotion of stratified and unstratified seeds of loblolly pine (Pinus taeda) and baldcypress (Taxodium distichum) were studied. The chemicals used were gibberellic acid, kinetin, potassium nitrate and thiourea, each at 3 different concentrations. Stratification promoted the germination of both seed species. Certain concentrations of gibberellic acid, potassium nitrate and thiourea improved the germination of unstratified loblolly pine and baldcypress seeds while kinetin had no stimulatory effect. All 4 chemicals at specific concentrations promoted the germination of loblolly pine seeds stratified for a short period of time. Considering both speed and completeness of germination, best results were obtained when 21-day stratified seeds were treated with either gibberellic acid (100 mg/1) or kinetin (10 mg/1). In baldcypress, on the other hand, none of these chemicals had any stimulatory effect on the germination of stratified seeds. Germination of both species of seeds was either partially or completely inhibited by the highest concentration of thiourea (30,000 mg/1) used.     

Induction of Secondary Dormancy in Chenopodium bonus-henricus L. Seeds by Osmotic and High Temperature Treatments and Its Prevention by Light and Growth Regulators

Factors controlling the establishment and removal of secondary dormancy in Chenopodium bonus-henricus L. seeds were investigated. Unchilled seeds required light for germination. A moist-chilling treatment at 4 C for 28 to 30 days removed this primary dormancy. Chilled seeds now germinated in the dark. When chilled seeds were held in the dark in −8.6 bars polyethylene glycol 6000 solution at 15 C or in water at 29 C a secondary dormancy was induced which increased progressively with time as determined by subsequent germination. These seeds now failed to germinate under the condition (darkness) which previously allowed their germination. Continuous light or daily brief red light irradiations during prolonged imbibition in polyethylene glycol solution at 15 C or in water at 29 C prevented the establishment of the secondary dormancy and caused an advancement of subsequent germination. Far red irradiations immediately following red irradiation reestablished the secondary dormancy indicating phytochrome participation in “pregerminative” processes. The growth regulator combination, kinetin + ethephon + gibberellin A₄+A₇ (GA₄₊₇), and to a relatively lesser extent GA₄₊₇, was effective in preventing the establishment of the secondary dormancy and in advancing the germination or emergence time. Following the establishment of the secondary dormancy by osmotic or high temperature treatments the regulator combination was relatively more active than light or GA₄₊₇ in removing the dormancy. Prolonged dark treatment at 29 C seemed to induce changes that were partially independent of light or GA₄₊₇ control. The data presented here indicate that changes during germination preventing dark treatment determine whether the seed will germinate, show an advancement effect, or will become secondarily dormant. These changes appear to be modulated by light and hormones.     

Roles of Soluble Sugars in Protecting Phytochrome- and Gibberellin A3-Mediated Germination Control in Skotodormant Lettuce Seeds

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A₃ (GA₃). Soluble sugars in the imbibition solutions influenced the depth of skotodormancy. Ten-day DS seeds, imbibed in 50–500 mm sucrose or 100–500 mm glucose and given terminal GA₃ germinated completely and germinated about 80% when imbibed in 100 mm galactose, mannose, lactose, or maltose. In contrast, terminal R applied to 10-day DS seeds caused only 20–50% germination. If given R at day 0 and imbibed for 10 days in darkness in 500 mm sucrose or glucose, seeds washed free of exogenous glucose or sucrose then germinated about 50% in darkness in water. These seeds responded to terminal R or GA₃ with complete germination. When seeds were given FR at day 0, germination responses following terminal R or GA₃ were significantly lower when the duration of DS was increased from 7–10 day DS to 15 days. In 10-day DS seeds given initial FR and imbibed in either solutions of 50 or 100 mm sucrose and KNO₃, either terminal R or GA₃ treatment gave complete or near complete germination. It is concluded that seed exposure to certain soluble sugars and/or nitrate during a 10-day DS protected certain substrates and thereby extended the sensitivity of the seeds to terminal R or GA₃ treatment. The study provides substantial evidence for nonhormonal factors associated with light and GA action in the control of seed skotodormancy. Received October 30, 1996; accepted April 22, 1997     

Effects of salt,alkali and salt–alkali mixed stresses on seed germination of the halophyte Salsola ferganica (Chenopodiaceae)

Salsola ferganica L. (Chenopodianceae) is an annual halophytic species. Experiments were carried out in laboratory to determine the effects of temperature, perianths and various types of salinity on seed germination and germination recovery. Seeds were germinated at 6 levels of temperature with perianths, plus perianths and removed perianths in complete darkness for 9 days. The germination responses of the seeds without perianths at 25 °C were determined over a wide range of NaCl, NaHCO₃ or NaCl–NaHCO₃ mixed stress for 13 days. Perianths seriously affected germination as a barrier for seed germination and the optimal temperature was at 25 °C. Highest germination percentage was obtained under control and seed germination was progressively inhibited with the increase of salinity concentration. The negative effect of NaHCO₃ at the same concentration on germination was stronger than that of NaCl and NaCl–NaHCO₃ mixed. When substrate salinity was removed, seeds exposed to a high NaCl concentration (400–800 mM), NaHCO₃ (50–200 mM) and NaCl–NaHCO₃ mixed (100–400 mM) germinated well. Final germination of Salsola ferganica seeds was significantly affected by types of salt at the low salinity (?200 mM) and with increased salinity it was influenced mainly by salinity concentration for various proportion of salt–alkali mixed stress.     

The roles of inorganic nitrogen salts in maintaining phytochrome- and gibberellin A3-mediated germination control in skotodormant lettuce seeds

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A₃ (GA₃). Inorganic nitrogen salts in the imbibition solutions reduced seed skotodormancy. Ten-day DS seeds, imbibed in 25 mm salt solutions followed by terminal R, germinated 99% if imbibed in NH₄NO₃, 70% if imbibed in KNO₃ or NH₄Cl, and 55% if imbibed in NaNO₃. Seeds imbibed in higher salt concentrations germinated fully upon terminal R treatment. Seeds imbibed in 25 mm NH₄Cl or in 50 mm NH₄NO₃ germinated completely upon GA₃ treatment. Osmotic effects of imbibition media accounted for only part of the effect, since seeds imbibed in 50 mm CaCl₂ or NaCl germinated poorly following R or GA₃ treatment. Seeds imbibed in 500 mm polyethylene glycol (PEG) 1000 or mannitol solutions for 10 days still exhibited skotodormancy. Treatments of R or GA₃ did not stimulate germination in seeds imbibed in mannitol, but germination was complete if seeds were given 1-h acid immersion plus a water rinse before the terminal R or GA₃ treatment. Seeds imbibed in 50–500 mm PEG during 10-day DS germinated significantly better in response to terminal R. Terminal GA₃ significantly improved germination only in seeds imbibed at 500 mm PEG. P_fr appeared to function in mannitol-imbibed seed only after an acid treatment. Seed exposure to inorganic nitrogen salts during the 10-day DS maintained seed sensitivity to terminal R or GA₃ treatment. The depth of seed skotodormancy was related to the availability of inorganic nitrogen and also involved the levels of P_fr or endogenous GA₃.Abbreviations FR far red - DS dark storage - R red - GA₃ gibberellin A₃ - PEG polyethylene glycol - SHAM salicylhydroxamic acid - ANOVA analysis of variance - GLM general linear model - LSD least squares difference - P_fr far-red absorbing form of phytochrome     

Alleviation of salt stress by plant growth regulators and IAA producing bacteria in wheat

The action of phytohormone producing bacteria and plant growth regulators on germination and seedling growth of wheat under saline conditions were studied. Seed dormancy enforced by salinity (100 mM NaCl) was substantially alleviated and the germination was promoted by gibberellin, auxin, zeatin, and ethephon from 54 to 97%. The IAA producing bacterial strains Pseudomonas aureantiaca TSAU22, Pseudomonas extremorientalis TSAU6 and Pseudomonas extremorientalis TSAU20 significantly increased seedling root growth up to 25% in non-salinated conditions and up to 52% at 100 mM NaCl, compared to control plants. It is concluded that growth regulators considerably alleviated salinity-induced dormancy of wheat seeds. The facts mentioned above make it possible to recommend root colonizing bacteria that produce phytohormone to alleviate salt stress of wheat grown under conditions of soil salinity.     

ABA, GA3, and nitrate may control seed germination of Crithmum maritimum (Apiaceae) under saline conditions

Impaired germination is common among halophyte seeds exposed to salt stress, partly resulting from the salt-induced reduction of the growth regulator contents in seeds. Thus, the understanding of hormonal regulation during the germination process is a main key: (i) to overcome the mechanisms by which NaCl-salinity inhibit germination; and (ii) to improve the germination of these species when challenged with NaCl. In the present investigation, the effects of ABA, GA₃, NO⁻₃, and NH⁺₄ on the germination of the oilseed halophyte Crithmum maritimum (Apiaceae) were assessed under NaCl-salinity (up to 200 mM NaCl). Seeds were collected from Tabarka rocky coasts (N-W of Tunisia). The exogenous application of GA₃, nitrate (either as NaNO₃ or KNO₃), and NH₄Cl enhanced germination under NaCl salinity. The beneficial impact of KNO₃ on germination upon seed exposure to NaCl salinity was rather due to NO⁻₃ than to K⁺, since KCl failed to significantly stimulate germination. Under optimal conditions for germination (0 mM NaCl), ABA inhibited germination over time in a dose dependent manner, but KNO₃ completely restored the germination parameters. Under NaCl salinity, the application of fluridone (FLU) an inhibitor of ABA biosynthesis, stimulated substantially seed germination. Taken together, our results point out that NO⁻₃ and GA₃ mitigate the NaCl-induced reduction of seed germination, and that NO⁻₃ counteracts the inhibitory effect of ABA on germination of C. maritimum. To cite this article: A. Atia et al., C. R. Biologies 332 (2009).     

Effect of salinity and chemical factors on seed germination in the halophyte Crithmum maritimum L.

Seeds of the halophyte Crithmum maritimum L. were exposed to salt stress and chemical pretreatments in order to improve germination. Seeds submitted to salt stress did not germinate but they recovered rapidly upon transfer to distilled water, recovery being higher after a low salinity pretreatment. Chemical treatments resulted in differential effects on seed germination. Known dormancy breakers such as potassium nitrate and thiourea had no effect on sea fennel seed germination. Conversely, l-ascorbic acid (40 or 60 mM) and ethanol (96%) significantly improved germination rate by 10, 30 and 30%, respectively. Pretreatment of seeds with l-ascorbic acid at 40 mM was shown to alleviate the negative effects of low NaCl concentration on germination. These findings indicate that the application of ascorbic acid may be used to improve sea fennel seed germination, which is of great interest for cultivating this plant.