Role of cAMP in Gibberellin Promotion of Seed Germination in <Emphasis Type="Italic">Orobanche minor</Emphasis> Smith

Adenosine 3′,5′-cyclic monophosphate (cAMP) is known as a key second messenger in many living organisms, regulating a wide range of cellular responses. In higher plants the function of cAMP is poorly understood. In this study, we examined the role of cAMP in seed germination of the root parasitic plant Orobanche minor whose seeds require preincubation in warm moist environments for several days, termed conditioning, prior to exposure to germination stimulants released from roots of host plants. Accumulation of endogenous cAMP was observed in the conditioned O. minor seeds. When the seeds were exposed to light or supraoptimal temperature during the conditioning period, cAMP did not accumulate and the seeds showed low germination rates after stimulation with strigol, a germination stimulant. Addition of membrane-permeable cAMP to the medium restored the germination rates of the seeds treated with light or supraoptimal temperature during the conditioning period, suggesting that cAMP functions during the conditioning period. The endogenous cAMP levels of the seeds conditioned in the light or at a supraoptimal temperature were elevated by treatment of the seeds with gibberellin (GA) during the conditioning period. Uniconazole, a potent inhibitor of GA biosynthesis, blocked elevation of the cAMP level. Furthermore, a correlation between the endogenous cAMP level and GA level was observed during the conditioning period. These results suggest that GAs elevate the cAMP level, which is required for the germination of O. minor seeds.     

STIMULATION OF GERMINATION IN RICE (ORYZA SATIVA L.) BY A STATIC MAGNETIC FIELD

This study evaluates the percentage and rate of germination of rice (Oryza sativa L.) seeds, when exposed to magnetic treatment in laboratory conditions. The seeds were exposed to 150 and 250 mT magnetic fields both chronically and for 20 min after seeding. Nonexposed seeds were used as control. Chronic exposure to a 150-mT magnetic field increased (p < 0.05) both the rate and percentage of germination relative to nonexposed seeds (18% at 48 h). Significant differences were also obtained for seeds exposed to a 250-mT magnetic field for 20 min (12% at 48 h). Additionally, seeds were moistened with water magnetically treated by static and dynamic methods. Dynamic and static treatment of water improved the germination of seeds related to the control, but significant differences (p < 0.05) were only obtained for the dynamic method (16% at 48 h).     

Growth characteristics of mung beans and water convolvuluses exposed to 425‐MHz electromagnetic fields

Effects of high‐frequency, continuous wave (CW) electromagnetic fields on mung beans (Vigna radiata L.) and water convovuluses (Ipomoea aquatica Forssk.) were studied at different growth stages (pre‐sown seed and early seedling). Specifically, the effects of the electromagnetic source's power and duration (defined as power‐duration level) on the growth of the two species were studied. Mung beans and water convolvuluses were exposed to electromagnetic fields inside a specially designed chamber for optimum field absorption, and the responses of the seeds to a constant frequency at various power levels and durations of exposure were monitored. The frequency used in the experiments was 425 MHz, the field strengths were 1 mW, 100 mW, and 10 W, and the exposure durations were 1, 2, and 4 h. Results show that germination enhancement is optimum for the mung beans at 100 mW/1 h power‐duration level, while for water convolvuluses the optimum germination power‐duration level was 1 mW/2 h. When both seed types were exposed at the early sprouting phase with their respective optimum power‐duration levels for optimum seed growth, water convolvuluses showed growth enhancement while mung bean sprouts showed no effects. Water content analysis of the seeds suggests thermal effects only at higher field strength. Bioelectromagnetics 31:519–527, 2010. © 2010 Wiley‐Liss, Inc.     

A comparison of methods for delivering DNA to wheat: the application of wheat dwarf virus DNA to seeds with exposed apical meristems

The apical meristems in dry wheat seeds were exposed (dissected seeds) to provide a target for DNA uptake. Using wheat, dwarf virus as the marker DNA, various methods of delivery were compared. Dry dissected seeds imbided in wheat dwarf virus DNA solution gave infection in 16% of the seedlings growing from them. A wheat dwarf virus dimer placed between the T-DNA borders of a vector plasmid inAgrobacterium tumefaciens (disarmed C58) andA. rhizogenes (LBA 9402) gave high levels of infection (79%) when dissected seeds were soaked in theAgrobacterium inoculum (agroinfection). Bombardment of dry dissected seeds with tungsten particles coated in wheat dwarf virus DNA did not give infection, but when softened by presoaking in water for 14 h, infection was observed at a low level (3%). The exposure of the apical meristem in all three methods gave a higher frequency of infection compared with treating intact seeds and in some cases the difference was substantial. The significance of the approach for DNA uptake studies is discussed along with its relevance to achieving stable transformation with non-viral constructs.     

The effect of extended exposure to hypersaline conditions on the germination of five inland halophyte species

In order to determine how salinity and exposure time affect seed viability and germination, seeds of five halophytes, Atriplex prostrata, Hordeum jubatum, Salicornia europaea, Spergularia marina, and Suaeda calceoliformis were exposed to 3.0, 5.0, and 10.0% NaCl solutions for 30, 60, 90, 365, and 730 d. Recovery experiments in distilled water indicated significantly different species responses to salinity over time. Percentage germination and rate of germination in H. jubatum were dramatically reduced following extended exposure and all seeds exposed to 10% NaCl for > 1 yr failed to germinate. Spergularia marina seeds were stimulated following short-term exposure to 3% NaCl; however, germination was delayed and overall germination was significantly reduced with exposure time in the two higher salinity levels. Percentage germination in A. prostrata decreased over time, but salinity level was not related to this reduction. Germination of S. europaea and S. calceoliformis, the most salt-tolerant species being tested, was stimulated by exposure to high salinity. Both species had a significant increase in percentage germination and in the germination rate when compared to seeds germinated in distilled water. Baseline germination data from seeds placed in 0, 1, 2, and 3% NaCl solutions indicated that S. europaea and S. calceoliformis were the only species to germinate in the 3% NaCl solution. Spergularia marina failed to germinate in the 2% NaCl treatment, and germination of A. prostrata and H. jubatum was significantly reduced at this salinity level. It is concluded that prolonged exposure to saline solutions can inhibit or stimulate germination in certain species, and the resulting germination and recovery responses are related to the duration and intensity of their exposure to salt in their natural habitats.     

Aflatoxins in sunflower seeds: Influence of Alternaria alternata on aflatoxin production by Aspergillus parasiticus

The aim of the present work was to determine the influence of Alternaria alternata upon aflatoxin production by Aspergillus parasiticus.A mixture of spores of both strains was inoculated in sunflower seeds at 0,90 a_w, and incubated for 42 days at 28 °C ±1.The cultures were observed and analyzed every 7 days to determine the infection level of the seeds and the production of aflatoxins. Results showed that when the seeds were inoculated only with Aspergillus parasiticus, 100% were infected from the 7th day.When Aspergillus parasiticus and Alternaria alternata were simultaneously inoculated the infection level of the seeds was 100% for Aspergillus parasiticus following 7 days of inoculation and 0% for Alternaria alternata. After the 14th day of inoculation there was no significant difference in the infection percentage of both strains (approximately 80% of each one). As far as toxin production is concerned a remarkable decrease was observed when seeds were inoculated with both strains simultaneously.In accordance to the results, Alternaria alternata would not compete with Aspergillus parasiticus in colonization of seeds but would either degrade the aflatoxins by Aspergillus parasiticus or compete for aflatoxin biosynthesis precursors. Alternaria alternata could also secrete some substance that specifically inhibits aflatoxin synthesis.     

Transmission of Alternaria macrospora in Cotton Seeds

Alternaria macrospora was isolated from seeds only after the natural opening of the bolls and exposure of seeds to an environment in which the fungus was present. The fungus lacks the ability to penetrate the boll wall and reach the seed site. Attempts to isolate the pathogen from seeds of immature bolls at different developmental stages failed. Internal infection by slow injection resulted in seed infection and partial shedding of the injected plant parts which was high in buds and decreased with the ripening to mature bolls. Severity of seed infection was not dependent on either inoculum level, boll physiological age or even if the boll itself was not diseased. Infection of flowers under field conditions caused flower shedding. Naturally infected seeds or inoculated seeds with inoculum levels of 100 spores/ml and above resulted in diseased cotyledons, the incidence of which was, for inoculated seeds, positively correlated with inoculum level. A small difference was observed between cultivars in susceptibility to artificial inoculation at the cotyledon stage. A. macrospora survived on commercial cotton seeds and on post-season plants left growing at the field edges. Survival in plant debris under field conditions was minimal and may only have a minor effect on field reinfestation.     

Phytochrome-mediated changes in the ATP content of Kalanchoë blossfeldiana seeds

One short red (R) irradiation increases the ATP content of Kalanchoë blossfeldiana Poelln. cv Feuerblüte seeds before onset of germination. Phytochrome control is demonstrated by the full R/far-red light (FR) reversibility of the effect in water imbibed seeds. In seeds imbibed in the presence of gibberellin A₃ (GA₃, one short R exposure already increases the ATP content when given 2h after start of imbibition, showing phytochrome control at the energy-metabolic level when one R pulse cannot yet induce germination. After longer imbibition periods in the presence of GA₃, one short FR irradiation also increases the ATP content of ungerminated Kalanchoë seeds. The time course of the ATP levels after a R or FR germination inducing irradiation shows an initial increase that clearly preceeds germination. A second increase starts about 15 h after irradiation and is most probably the consequence of the germination itself. The results suggest that, in Kalanchoë seeds, the increase in ATP levels, induced by irradiation(s) and preceding germination, is a phytochrome-mediated process, supplying energy, required for germination.     

Non-lethal freezing effects on seed degreening in Brassica napus

The effects of a non-lethal freezing stress on chlorophyll content, moisture level and distribution, and abscisic acid (ABA) levels were examined in siliques and seeds of Brassica napus (canola). A non-lethal freezing stress resulted in the retention of chlorophyll in seed at harvest that was most pronounced for seeds 28, 32 and 36 days after flowering (DAF). This increase was primarily due to an increased retention of chlorophyll a relative to chlorophyll b. Chlorophyll retention in seeds exposed to a non-lethal freezing stress correlated with an increased ABA catabolism, as measured 1, 3 or 7 days after the stress treatment. Although the non-lethal freezing stress had no significant effect on moisture content in seeds of siliques stressed at 28–44 DAF, moisture distribution, as viewed by magnetic resonance imaging, showed an uneven drying of 32 and 40 DAF siliques after exposure to the non-lethal freezing stress. Moisture was initially lost more rapidly from the silique wall between seeds, than in control non-stressed siliques. Increased moisture loss was not due to structural changes in the vasculature of the silique/seed of stressed tissues. These results are consistent with the hypothesis that a non-lethal freezing stress-induced decrease in ABA level, during seed maturation, effects an inhibition of normal chlorophyll a catabolism resulting in mature but green B. napus seed.     

Changes in endogenous abscisic acid levels during dormancy release and maintenance of mature seeds: studies with the Cape Verde Islands ecotype,the dormant model of<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

Mature seeds of the Cape Verde Islands (Cvi) ecotype of Arabidopsis thaliana (L.) Heynh. show a very marked dormancy. Dormant (D) seeds completely fail to germinate in conditions that are favourable for germination whereas non-dormant (ND) seeds germinate easily. Cvi seed dormancy is alleviated by after-ripening, stratification, and also by nitrate or fluridone treatment. Addition of gibberellins to D seeds does not suppress dormancy efficiently, suggesting that gibberellins are not directly involved in the breaking of dormancy. Dormancy expression of Cvi seeds is strongly dependent on temperature: D seeds do not germinate at warm temperatures (20–27°C) but do so easily at a low temperature (13°C) or when a fluridone treatment is given to D seeds sown at high temperature. To investigate the role of abscisic acid (ABA) in dormancy release and maintenance, we measured the ABA content in both ND and D seeds imbibed using various dormancy-breaking conditions. It was found that dry D seeds contained higher amounts of ABA than dry ND after-ripened seeds. During early imbibition in standard conditions, there was a decrease in ABA content in both seeds, the rate of which was slower in D seeds. Three days after sowing, the ABA content in D seeds increased specifically and then remained at a high level. When imbibed with fluridone, nitrate or stratified, the ABA content of D seeds decreased and reached a level very near to that of ND seeds. In contrast, gibberellic acid (GA₃) treatment caused a transient increase in ABA content. When D seeds were sown at low optimal temperature their ABA content also decreased to the level observed in ND seeds. The present study indicates that Cvi D and ND seeds can be easily distinguished by their ability to synthesize ABA following imbibition. Treatments used here to break dormancy reduced the ABA level in imbibed D seeds to the level observed in ND seeds, with the exception of GA₃ treatment, which was active in promoting germination only when ABA synthesis was inhibited.Abbreviations ABA Abscisic acid - Cvi Cape Verde Islands - D Dormant - GA Gibberellin - GA₃ Gibberellic acid - ND Non dormant     

Effect of high temperature on moisture loss,imbibition and germination of seeds ofTrianthema Govindia Buch.-Ham. ex DC

Summary Seeds of erect and prostrate plants ofTrianthema govindia Buch. ham. ex DC., growing in shade and open respectively, differed significantly in seed weight and percentage germination. Effect of high temperature exposure to these seeds has been studied in view of water depletion, imbibition and seed germination. The seeds of both the types were subjected to temperatures of 40, 50, 60, and 70° C for 24, 48, 96, and 144 hours. The three factors viz., loss of water, water imbibition and germination of seeds were positively correlated to the duration of treatment at different temperatures. A highly significant positive correlation was also observed between moisture depletion and imbibition, and between imbibition and germination. The percentage germination was favoured at 40° C in both the types of seeds and was increased with the increase of treatment duration. However, at higher temperatures (50 and 60° C) the percentage declined while at 70° C the seeds lost their vitality.     

Interaction of light and temperature on the germination of Rumex obtusifolius L.

Seeds (nutlets) of Rumex obtusifolius L. fail to germinate in darkness at 25° C, but are stimulated by short exposure to red light (R) the effectiveness of which can be negated by a subsequent short exposure to far red light (F) indicating phytochrome control. Short periods of elevated temperature treatment (e.g. 5 min at 35° C) can induce complete germination in darkness. Although short F cannot revert the effect of 35° C treatment, cycling the phytochrome pool by exposure to short R before short F results in reversion of at least 50% of the population. Prolonged or intermittent F can also revert the germination induced by 35° C treatment. The effect of elevated temperature treatment is interpreted on the basis of two possible models; (i) that it increases the sensitivity of the seeds to a low level of pre-existing active form of phytochrome (Pfr) (ii) that it induces the appearance of Pfr in the dark. In both cases it is envisaged that elevated temperature treatment and Pfr control germination at a common point in the series of reactions that lead to germination.Abbreviations D Dark - F far red light - P phytochrome - Pr red absorbing form of P - Pfr far red absorbing form of P - R red light     

An unusual effect of the far-red absorbing form of phytochrome: Photoinhibition of seed germination inBromus sterilis L.

Seeds ofBromus sterilis L. germinated between 80–100% in darkness at 15° C but were inhibited by exposure to white or red light for 8 h per day. Exposure to far-red light resulted in germination similar to, or less than, that of seeds maintained in darkness. Germination is not permanently inhibited by light as seeds attain maximal germination when transferred back to darkness. Germination can be markedly delayed by exposure to a single pulse of red light following 4 h inhibition in darkness. The effect of the red light can be reversed by a single pulse of far-red light indicating that the photoreversible pigment phytochrome is involved in the response. The response ofB. sterilis seeds to light appears to be unique; the far-red-absorbing form of phytochrome (Pfr) actually inhibiting germination.Abbreviations Pr red absorbing form of phytochrome - Pfr far-red absorbing form of phytochrome     

Low-temperature stratification strategies and growth regulators for rapid induction of Paris polyphylla var. yunnanensis seed germination

The seeds of Paris polyphylla var. yunnanensis are deeply dormant, and they remain dormant for 18 months or longer in their natural environment. Periodic exposure of the seeds to a low-temperature of 4 °C broke the dormancy in about 16 weeks (112 days). The most effective temperature stratification scheme was an interval of 14 days at 4 °C and 14 days at 22 °C. Both GA₃ and ethephon significantly enhanced the germination rate during the stratification treatment. The seed coat, particularly the mesophyll outer layer of the seed coat, strongly inhibited the germination. With removal of the seed coat and exposure of the uncoated seeds to 600 mg/l GA₃ for 48 h before the temperature stratification of 14 days at 4 °C and 14 days at 22 °C for 112 days, a germination percentage as high as 95.3% of the seeds was attained in about 160 days.     

Desiccation,Moisture Content and Germination of Zostera marina L. Seed

Zostera marina is the only seagrass species whose seeds have been successfully used in large‐scale restoration. Although progress has been made in refining Z. marina restoration protocols, additional information on Z. marina seed physiology is necessary as the science of seagrass restoration evolves. We tested the germination rates of Z. marina seeds under different relative humidities and temperatures for different periods of time. Z. marina seed moisture content (MC) and germination rates were also tested when seeds were exposed to a temperature of 25°C and relative humidity of 50%. Z. marina seeds suffered higher mortality when exposed to lower relative humidity and higher temperature for longer period of exposure time. A significant negative correlation was detected between seed germination rate and MC. Z. marina seeds are sensitive to desiccation exposure and long periods of exposure to air should be prevented to minimize seed mortality when seeds are used in restoration projects.     

A combined physical and physiological dormancy controls seasonal seedling emergence of Geranium robertianum

Temperate forest herbs with seeds exhibiting both a physical and a physiological dormancy mechanism are rare, and knowledge on the factors regulating germination of these species is fragmentary. The biennial Geranium robertianum L. grows mainly in temperate woodlands, but can also be found in exposed habitats. Seedlings of G. robertianum are known to emerge from spring until autumn, but little is known about the environmental factors regulating germination. In this study, phenology of seedling emergence and of physical dormancy loss was examined for seeds buried at shaded or sunny exposed locations. The role of temperature in regulating dormancy and germination was analysed by incubating seeds in temperature sequences simulating temperatures that seeds experience in nature. The results indicate that most seeds of G. robertianum buried in sunny conditions germinate immediately after physical dormancy loss in summer. Seeds buried in shaded conditions also lose physical dormancy mainly during summer, but remain physiologically dormant and do not germinate until late winter or early spring. Besides physical dormancy, seeds of G. robertianum also initially have a high level of physiological dormancy, which is reduced during dry storage. Physiological dormancy is reduced through chilling in winter, thus enabling the seeds to germinate at low temperatures. We conclude that a complex combination of physical and physiological dormancy ensures that G. robertianum seeds germinate in summer at exposed sites and in early spring at shaded sites.     

Early Sprouting and First Stages of Growth of Rice Seeds Exposed to a Magnetic Field

The effects of a stationary magnetic field on the germination of rice seeds (Oryza sativa, L.) and on the initial stages of growth of rice plants have been evaluated. In both tests, the seeds were exposed to one of two magnetic field strengths (125 or 250 mT) for different times (1 min, 10 min, 20 min, 1 h, 24 h, or chronic exposure) as 12 separate treatments (doses D1–D6 for 125 mT and doses D7–D12 for 250 mT). Nonexposed seeds were used as controls (C). The mean germination time (MGT) was significantly reduced compared to control when seeds were exposed to magnetic field (54.00 h for D5 and D11, and 58.56 h for control). The parameters T₁ and T₁₀, times required to obtain 1 and 10% of germinated seeds, were also reduced. The T₁₀ of control seeds was 44.40 h, while treatments D5, D6, D11, and D12 gave rise to values of 36.00, 36.96, 32.64, and 39.36 h, respectively. The higher germination rate of treated seeds obtained in the germination test is in agreement with the higher lengths and weights of rice plants exposed to a magnetic field recorded on the growth tests. All the parameters measured were over the control ones, although the highest lengths and weights of rice plants were obtained for chronic exposure to magnetic field (doses D6 and D12). Stem length of control plants (45.36 mm) measured at the tenth day was significantly lower than that obtained for doses D6 (58.58 mm) and D12 (80.63 mm); the same behavior was observed on total length, stem weight, and total weight. Our finding indicates that this type of magnetic treatment clearly affects germination and the first stages of growth of rice plants.     

The effect of light on the endogenous levels of cytokinins and gibberellins in seeds of sitka spruce (Picea sitchensis Carriere)

Abstract Maximum germination of Sitka spruce seed was obtained at 22°C under continuous fluorescent light or following a single 10 min exposure to red light (RL) given after 48 h of dark imbibition. The levels of endogenous cytokinins and gibberellins were examined in seeds which were exposed to different light regimes. Cytokinin levels in Sitka spruce seeds increased approximately 1.7–fold during exposure to continuous white light, during dark stratification, or within 1 h or a 30 min exposure to RL. A single peak of activity could be eluted from the LH^?20 Sephadex column which appeared in the same volume as authentic zeatin riboside. Gibber-ellin activity in Sitka spruce seeds increased rapidly during exposure to 30 min of RL and then declined during subsequent dark incubation. Similarly, under continuous white light, gibberellin activity was at least twice as high as in the dark. Two gibberellm-like substances were found in Sitka spruce seeds which appeared to be similar to GA₇ and GA₉ on the basis of their chromato-graphic properties. The zone of gibberellin activity directly associated with photo-excitation of Sitka spruce seeds contains conjugate gibberellins, possibly glucosyl esters, which when hydrolysed with β-glucosidase form two products which are similar to the free gibberellins which were detected. The light response in Sitka spruce seed is compared to a similar response in Scots pine (Pinus sylvestris L.) seeds.     

Enhanced levels of nicotianamine promote iron accumulation and tolerance to calcareous soil in soybean

Iron (Fe) is an essential nutrient in both plants and humans. Fe deficiency on calcareous soil with low Fe availability is a major agricultural problem. Nicotianamine (NA) is one of the Fe chelator in plants, which is involved in metal translocation into seeds, and serves as an antihypertensive substance in humans. In this study, soybean plants overexpressing the barley NA synthase 1 (HvNAS1) gene driven by the constitutive CaMV 35S promoter were produced using Agrobacterium-mediated transformation. The transgenic soybean showed no growth defect and grew normally. The NA content of transgenic soybean seeds was up to four-fold greater than that of non-transgenic (NT) soybean seeds. The level of HvNAS1 expression was positively correlated with the amount of NA, and a high concentration of NA was maintained in the seeds in succeeding generations. The Fe concentration was approximately two-fold greater in transgenic soybean seeds than in NT soybean seeds. Furthermore, the transgenic soybeans showed tolerance to low Fe availability in calcareous soil. Our results suggested that increasing the NA content in soybean seeds by the overexpression of HvNAS1 offers potential benefits for both human health and agricultural productivity.     

The comparative germination ecology of nine Rumex species

The germination requirements, dormancy cycle and longevity of nine Rumexspecies were studied in field conditions and laboratory experiments to show theadaptations of the related species to their specific habitat. Within one genus,rather striking differences were observed in germination ecology. However, theclosely related species, R. acetosa and R.scutatus, are very similar: they fruit in early summer; theirseeds can germinate immediately after dispersal, and they are nondormant andshort-lived. R. acetosella also has fruits insummer, but the seeds do not germinate the first season after dispersal. Theyare long-lived, but buried seeds do not show a dormancy cycle; they mightgerminate in different seasons after exposure to light. Seeds of four species (R. conglomeratus,R. maritimus, R. sanguineus andR. crispus) are long-lived and undergo aseasonal dormancy cycle, with a low level of dormancy in winter and early springand a deep dormancy in summer as was already known for R.obtusifolius. These seeds are shed in the autumn, and they germinatemainly in the spring in consecutive years. R. maritimusalso germinates in summer and autumn on drying muddy soils. The seeds of R. hydrolapathum only germinate onwaterlogged soils, which explains its growth at the edge of streams and ponds.Its seeds are rather short-lived. The seeds of the species on very wetplaces require a higher temperature for germination.