Cold stratification,light and high seed density enhance the germination of Ottelia alismoides

The effects of cold stratification, light and seed clustering in petri dish on Ottelia alismoides seed germination were investigated. The seeds required light and an extended cold period in order to germinate, but neither treatment alone was effective. Seed germination significantly increased with length of the 4 °C cold stratification period. Freshly collected seeds failed to germinate while a 5-month period at 4 °C yielded 29 ± 9% germination in the light, but none in the dark. Treatment with sodium nitroprusside, a nitric oxide source, failed to promote germination in the light or dark. Seeds of O. alismoides showed an unusual and significant positive response to aggregation. Germination in the light, after 5-month 4 °C cold stratification, was stimulated to almost five-fold in the dishes that were more densely sown with seed (20 seeds versus 200 seeds). Likewise, clustering seeds in dense aggregations stimulated germination significantly. Germination more than quadrupled with an increase from 1 to 50 seeds per cluster (200 seeds per dish), reaching a value of 72 ± 4%. Linear regression analysis shows the correlation between seed cluster density (no. per cluster) and germination rate (%) was highly significant (R² = 0.85, P = 0.000). The extended cold stratification requirement is probably an over-wintering device. The mechanism of the density-dependent stimulation is unclear.     

Seed germination in Marathrum schiedeanum and M. rubrum (Podostemaceae)

Marathrum schiedeanum and Marathrum rubrum are annual Podostemaceae, thus their seeds are important to their dispersal and persistence in their habitat. We assessed the effect on germination of (1) light (white, red and far red) and darkness, (2) temperature (15, 20, 25, 30 °C and alternating 20/30 °C), (3) osmotic potential (0 to −0.8 MPa), (4) proximity to moisture sources and (5) seed storage. Seeds of M. schiedeanum and M. rubrum were non-dormant and had a high germination capacity (96%). Seeds were positive photoblastic; at 15 °C germination drop to zero, and germination rate was slower at 20 °C and at 20/30 °C than at 25 °C. A small proportion of seeds of both species germinated even at osmotic potentials as low as −0.6 MPa (11%) for M. rubrum and −0.8 MPa (70%) for M. schiedeanum. Seeds germinated only when near to the source of moisture (91.3–87.1% and 53.3–35.6% for M. schiedeanum and M. rubrum, respectively) and 2 years in dry storage did not modify their capacity to germinate. At the beginning of the rainy season, light and temperature in the rivers may be high enough for germination. The ability to germinate at low osmotic potential may be related to early germination during the rainy season. This may be because the seed mucilage assists in diffusion of water from the substrate to the seed. Both species germinated faster at −0.06 MPa, than in distilled water, which may indicate appropriate conditions for germination of these short-lived species.     

The effect of temperature, water level and burial depth on seed germination of Myriophyllum spicatum and Potamogeton malaianus

The effects of temperature, water level and burial depth on seed germination of two submerged species, Myriophyllum spicatum and Potamogeton malaianus, were investigated under controlled laboratory conditions. There was no significant difference in final germination of M. spicatum among water level treatments, but P. malaianus germinations at 1 cm and 12 cm water levels were better than at 0 cm water level at temperatures of 20 °C and 30 °C. Little to no germination was observed for either species at the temperature of 10 °C. At 15 °C, however, germination increased significantly to 66.3-70.6% for M. spicatum and to 29.4-48.1% for P. malaianus under all three water level treatments. Increased temperature from 15 °C to 30 °C had no significant effect on the final germination of M. spicatum except at the 1 cm water level, but enhanced significantly the germination of P. malaianus. Analysis of the mean time to germination revealed that M. spicatum was a faster germinator relative to P. malaianus. The two species’ germination differed markedly in response to burial depth. Germination percentage of M. spicatum was 71.3% at 0 cm burial depth, but decreased to 5.0% and to 2.5% at depths of 1 cm and 2 cm, respectively; whereas germination percentages of P. malaianus were 40.0%, 23.8%, 12.5%, 7.5% and 1.3% at depths of 0 cm, 1 cm, 2 cm, 3 cm and 5 cm, respectively. We concluded that the two species respond differently to germination strategies. The findings provided further insight into how germination strategy contributes to the seed bank formation and species invasion.     

Dormancy and germination in Stachys germanica L. subsp. bithynica (Boiss.) Bhattacharjee seeds: Effects of short-time moist chilling and plant growth regulators

We investigated the germination requirements of the species Stachys germanica L. subsp. bithynica (Boiss.) Bhattacharjee (Lamiaceae). We studied the effects of scarification, short-time moist chilling (+4 °C) for 15 and 30 days, and various doses of gibberellic acid (GA₃; 0, 100, 150 and 250 ppm), Kinetin (KIN; 50 ppm) and a combination of 250 ppm GA₃ and 50 ppm KIN. The hormone and moist chilling treatments were carried out under both continuous darkness (20 °C) and photoperiodic (20/10 °C; 12/12 h, respectively) conditions. Seeds failed to germinate in response to short-time moist chilling treatments with distilled water under both continuous darkness and photoperiodic conditions. Seeds were found to have dormancy. Treatments with GA₃ or a combination of GA₃ and KIN were successful at breaking seed dormancy. A maximum of 37% of the seeds germinated after GA₃ application in all series. When only KIN was applied at a 50 ppm concentration, germination (12%) was found only with moist chilling for 30 days under continuous darkness. The highest germination rates were found in seeds treated with combination of 250 ppm GA₃ and 50 ppm KIN. In the combination treatments, while the moist chilling treatments for 15 days resulted in 68 and 73% germination, respectively, these rates were up to 95% in the moist chilling treatments for 30 days under continuous darkness and photoperiodic conditions. Mean germination time (MGT) in GA₃ and KIN combinations was lower than in other treatments. Scarification with 80% sulphuric acid did not promote germination. The characteristics of physiological dormancy of S. germanica ssp. bithynica seeds are consistent with conditions of existence in the in alpine habitat of this species.     

Influence of environmental factors on Vallisneria americana seed germination

Over the course of a growing season (April–October) water quality (water temperature, light, salinity, dissolved oxygen) and reproductive phenology (biomass, production of flowering shoots and seed pods, seed bank densities) were quantified in three Vallisneria americana beds in Nanjemoy Creek, MD, a tributary to the Chesapeake Bay. Clonal production of V. americana biomass increased at all sites when water temperatures rose above 25 °C. Flowering occurred during peak biomass (August–September) and resulted in the production of up to 16,000 seeds m⁻² at the end of the growing season. However, observed seed bank densities represented <1% of seed production. Laboratory experiments quantified the effects of dissolved oxygen (0.29–8.00 mg l⁻¹), light (0–160 μmol m² s⁻¹), temperature (13–29 °C), salinity (0.1–17.4 psu), sediment composition (3–86% sand; 0.9–8.3% sediment organic content), and burial depth (0.2–10 cm) on V. americana seed germination. Germination of V. americana seeds was enhanced (greater overall germination and shorter time to germination) under oxygenated conditions (8.00 mg l⁻¹), temperatures >22 °C, salinities of <1 psu, and in sediments composed of ≤3% organic content and >40% sand. Light (<160 μmol m⁻² s⁻¹) and burial depth (0.2–10 cm) had no significant effects on germination. Temperatures most favorable for seed germination (>22 °C) occurred in June, 2 months in the growing season just prior to development of peak vegetative standing stock. Seedlings were therefore at a distinct disadvantage to plants developed from over wintering buds. A lack of viable seed retention and inadequate environmental conditions at critical times in the growing season may be limiting seed germination success and subsequent seedling establishment within V. americana beds in the Chesapeake Bay. However, ungerminated seeds were found to maintain high viability, especially at salinities of 10 psu that can have significant negative effects of shoot growth survival. This suggests that seeds may serve as a source of reproductive material for bed recovery after periods of drought or other stressful conditions in estuarine systems.     

Dormancy removal of apple seeds by cold stratification is associated with fluctuation in H2O2, NO production and protein carbonylation level

Reactive oxygen (ROS) and nitrogen (RNS) species play a signaling role in seed dormancy alleviation and germination. Their action may be described by the oxidative/nitrosative “window/door”. ROS accumulation in embryos could lead to oxidative modification of protein through carbonylation. Mature apple (Malus domestica Borkh.) seeds are dormant and do not germinate. Their dormancy may be overcome by 70–90 days long cold stratification. The aim of this work was to analyze the relationship between germinability of embryos isolated from cold (5 °C) or warm (25 °C) stratified apple seeds and ROS or nitric oxide (NO) production and accumulation of protein carbonyl groups. A biphasic pattern of variation in H₂O₂ concentration in the embryos during cold stratification was detected. H₂O₂ content increased markedly after 7 days of seeds imbibition at 5 °C. After an additional two months of cold stratification, the H₂O₂ concentration in embryos reached the maximum. NO production by the embryos was low during entire period of stratification, but increased significantly in germination sensu stricto (i.e. phase II of the germination process). The highest content of protein carbonyl groups was detected after 6 weeks of cold stratification treatment. Fluctuation of H₂O₂ and protein carbonylation seems to play a pivotal role in seed dormancy alleviation by cold stratification, while NO appears to be necessary for seed germination.     

Effects of pre-treatments and temperature on seed viability and germination of Juniperus macrocarpa Sm.

The effects of collecting season, collection site, laboratory pre-treatments and temperatures on seed viability and germination of Juniperus macrocarpa were investigated. Ripe cones were collected in four Sardinian dune systems, in two seasons, from plant and soil. Warm (W) and cold (C) stratifications, two combinations of them (W + C, C + W), and no pre-treatment (0) were applied. Seeds were incubated in a range of constant (10–25 °C) and an alternating (25/10 °C) temperature regime. Seed viability was low (ca. 40%) and varied significantly according to the collecting season. Seed germination was also low (ca. 10%), the 0 and W were the most effective pre-treatments on stimulating germination. The best germination temperature, without any pre-treatment, was 15 °C (ca. 20%). J. macrocarpa seeds are dormant and the achieved results suggested that the presence of secondary dormancy is induced by cold stratification. Spring appeared to be the best season for seed collecting, whereas autumn was the best for sowing. These results give new findings for restoration activities on this species.     

Ecological and morphological seed traits of Polygala sardoa and P. sinisica: A comparative study on two endemic species of Sardinia

Polygala sardoa Chodat and P. sinisica Arrigoni (Polygalaceae) are two exclusive endemics to Sardinia and P. sinisica is affiliated under “Critically Endangered” in the IUCN Red Lists. In this work comparative studies on two populations of P. sardoa and in the only one of P. sinisica were carried out. In particular, seed output calculations and morphometric measurements on seed and elaiosome sizes were carried out. The effect of chipping, constant (15 °C) and alternating (25/10 °C) temperature regimes and light (8 h irradiance/day and dark) on germination were investigated. Seedling vigor assessments and a study on seed persistence in the soil were also carried out. P. sinisica had a higher seed output than P. sardoa and P. sinisica seeds were smaller than those of P. sardoa, with lower elaiosome area and elaiosome ratio values. Neither species had alternating temperature or light requirements for germination. P. sardoa achieved high germination percentages (> 80%) at all the tested conditions. P. sinisica had a lower maximum germination (<60%), suggesting the presence of physiological dormancy, and took more than twice as long to reach the maximum germination percentage. Seedlings of P. sardoa were larger than those of P. sinisica, and neither species formed a persistent soil seed bank. These new data may help implement effective conservation measures for these two species and, more generally, for threatened endemic species of this genus.     

Morphological characteristics of annual Zostera marina shoots at various germination temperatures

The timing of the transition from seed, seedlings and development into flowering is paramount importance in annual-type Zostera marina, because flowering is the first step of sexual reproduction. A majority of plants use environmental cues to regulate the transition to their developmental stages because plants must flower synchronously for successful outcrossing and must complete their sexual reproduction under favorable external conditions. The morphological characteristics (seeds and lateral shoot production, branch number, and inflorescence length) of reproductive shoots of Z. marina L. were examined in outdoor mesocosms to better understand the reproductive strategies of annual populations. Seeds in the germination experiment were divided into two groups: those exposed to cold (7 °C; vernalized group) and those left untreated (25-21 °C; non-vernalized group). All 600 seeds (300 from each group) were cultured for 2 months at 7, 10, 15, 20, and 25 °C in an indoor incubator. In the vernalized group, the germination rates were almost significantly higher than in the non-vernalized group. However, germination rates were not significantly affected by germination temperature. In outdoor mesocosms, production of vegetative shoots was observed in plants germinated at 15 and 20 °C in the vernalized group and at 10, 15 and 20 °C in the non-vernalized group. The highest number of vegetative shoots produced (35) was observed in plants germinated at 20 °C in the vernalized group, whereas seeds of either group failed to produce vegetative shoots when germinated at a low temperature (7 °C).In the flowering phase, the number of branches per shoot in the vernalized group was significantly higher than in the non-vernalized group. The total number of spadices on the 1st branches of plants in the vernalized group (germination at 20 °C) was significantly lower than that in the non-vernalized group at the same germination temperature. The total number of spadices per reproductive shoot in the vernalized group (germination at 10 °C) was also higher than in the non-vernalized group. Thus, both low temperature (vernalization) and seed germination temperature have implications for the sexual and asexual propagation of annual Z. marina populations.     

Combined effects of temperature and salinity on critical thermal minima of pacific white shrimp Litopenaeus vannamei (Crustacea: Penaeidae)

Critical thermal minima (CTMin) were determined for the Pacific white shrimp Litopenaeus vannamei juveniles from four different acclimation temperatures (15, 20, 25, and 30 °C) and salinities (10‰, 20‰, 30‰, and 40‰). The lowest and highest CTMin of shrimp ranged between 7.2 °C at 15 °C/30‰ and 11.44 °C at 30 °C/20‰ at the cooling rate of 1 °C h⁻¹. Acclimation temperature and salinity, as well as the interaction of both parameters, had significant effects on the CTMin values of L. vannamei (P<0.01). Yet, the results showed a much more profound effect of temperature on low thermal tolerance of juveniles. Only 40‰ salinity had an influence on the CTMin values (P<0.01). As the acclimation temperature was lowered from 30 to 15 °C thermal tolerance of the shrimp significantly increased by 3.25–4.14 °C. The acclimation response ratio (ARR) of the Pacific white shrimp exposed to different combinations of salinity and temperature ranged between 0.25 and 0.27. When this species is farmed in sub-tropical regions, its pond water temperature in the over-wintering facilities (regardless of the water salinity level) must never fall below 12 °C throughout the cold season to prevent mortalities.     

Responses of dormant heather (Calluna vulgaris) seeds to light, temperature, chemical and advancement treatments

Two seed lots of Calluna vulgaris were obtainedfrom English Nature (seed of Cornish provenance) (EN) and John ChambersWildflower Seeds (JCWS). In laboratory tests, under continuous light untreatedseeds of both seed lots were partially dormant at temperatures between14–35 °C, but JCWS seeds were more deeply dormant thanENseeds. The optimum temperature for germination for both lots was ca 18°C. Germination of EN seeds was much lower in the dark than inthe light at all temperatures; JCWS seeds did not germinate in the dark. In thelight at 22 °C, dormancy of both seed lots was broken whenseeds were incubated in GA_4/7 solution(2×10^–4 M). Dormancy ofJCWSseeds at 22 °C in the light was broken when seeds wereincubated in four different smoke solutions but more so when used incombinationwith GA_4/7. Soaking seeds for 4h insmoke/GA_4/7solutions before sowing improved both the speed andpercentage germination in pot experiments on a mist bench in the glasshouse byat least 10-fold. Soaking with GA_4/7 alone produced a 5-fold increasein germination but seedlings were more etiolated than with thesmoke/GA_4/7 mixtures. A seed advancement treatment modified from thatused commercially on sugar beet seeds also promoted germination in bothlaboratory and glasshouse tests. This entailed soaking seeds in 0.2% thiramsuspension for 4h followed by incubation in excess solution at 22°C for 4 days. This treatment was not as effective as thesmoke/GA_4/7 seed soaks.     

Effect of temperature on sporulation of Neozygites floridana isolates from different climates and their virulence against the tomato red spider mite, Tetranychus evansi

The fungal pathogen Neozygites floridana Weiser and Muma has been evaluated as a classical biological candidate for introduction into Africa against the invasive tomato red spider mite Tetranychus evansi Baker and Pritchard. In this study, the effect of temperature on sporulation, germination and virulence of three isolates of N. floridana collected from T. evansi in three climatically distinct regions of Brazil and Argentina was determined. Six constant temperatures of 13 °C, 17 °C, 21 °C, 25 °C, 29 °C and 33 °C were tested for their effect on the ability of the three fungal isolates to sporulate, germinate and kill the mites. Six alternating-temperature regimes of 17-13 °C, 21-13 °C, 29-13 °C, 33-13 °C, 33-23 °C, 33-28 °C under a 12 h photophase were also tested to estimate virulence of the three isolates against T. evansi. The Vipos isolate discharged more conidia than isolates from Recife or Piracicaba at all temperatures and sporulation was strongly temperature dependent. Optimal sporulation rates were observed at 25 °C while optimal germination rates were observed at 25 °C and 29 °C. At 29 °C, the shortest mean survival time of T. evansi (3.16 days, 95% CI of 3.05-3.27) was observed for the isolate from Vipos, while the longest LT₅₀ (3.47 days, 95% CI 3.34-3.59) was observed for the isolate from Piracicaba. Mortality of mites increased as the differences between alternating day and night temperatures increased from 8 °C (21-13 °C), to 10 °C (33-23 °C), to 16 °C (29-13 °C), with smallest and highest temperature differences of 4 °C (17-13 °C) and 20 °C (33-13 °C), both producing low mortalities. The overall results suggest that the Vipos isolate is better adapted to a wider range of temperatures than the other isolates tested.     

Seed germination of Lasia spinosa as a function of temperature,light, desiccation,and storage

Lasia spinosa seeds were not dormant at maturity in early spring. The most favorable temperatures for germination were between 25 and 30 °C, and final percentage and rate of germination decreased with an increase or decrease in temperature. When L. spinosa seeds were transferred to 25 °C, after 60 days at 10 °C (where none of the seeds germinated), final germination increased from 0% to 78%. Seeds germinated to high percentage both in light and in dark, although dark germination took more than twice as long as in the light. During desiccation of seeds at 15 °C and 45% relatively humidity, moisture loss decreased exponentially from 2.02 to 0.13 g H₂O g⁻¹ dry wt within 16 days, and only a few seeds (12%) survived 0.13 g H₂O g⁻¹ dry wt moisture content. Seeds stored at 0.58 g H₂O g⁻¹ dry wt moisture content at four constant temperatures (4, 10, 15, and −18 °C) for up to 6 months exhibited a well-defined trend of decreasing viability with decreasing temperature. Thus, we concluded that freshly harvested L. spinosa seeds are non-dormant and recalcitrant. Also, the seeds with 0.58 g H₂O g⁻¹ dry wt moisture content could be effectively stored for a few months between 10 and 15 °C although the most appropriate temperature for wet storage appears to be 10 °C, as it is close to the minimum temperature for germination and so there will be less pre-sprouting compared to 15 °C.     

Multigenerational analysis of temperature and salinity variability affects on metabolic rate,generation time,and acute thermal and salinity tolerance in Daphnia pulex

Climate change, sea level rise, and human freshwater demands are predicted to result in elevated temperature and salinity variability in upper estuarine ecosystems. Increasing levels of environmental stresses are known to induce the cellular stress response (CSR). Energy for the CSR may be provided by an elevated overall metabolic rate. However, if metabolic rate is constant or lower under elevated stress, energy for the CSR is taken from other physiological processes, such as growth or reproduction. This study investigated the examined energetic responses to the combination of temperature and salinity variability during a multigenerational exposure of partheogenetically reproducing Daphnia pulex. We raised D. pulex in an orthogonal combination of daily fluctuations in temperature (15, 15–25, 15–30 °C) and salinity (0, 0–2, 0–5). Initially metabolic rates were lower under all variable temperature and variable salinity treatments. By the 6th generation there was little metabolic variation among low and intermediate temperature and salinity treatments, but metabolic suppression persisted at the most extreme salinity. When grown in the control condition for the 6th generation, metabolic suppression was only observed in D. pulex from the most extreme condition (15–30 °C, 0–5 salinity). Generation time was influenced by acclimation temperature but not salinity and was quickest in specimens reared at 15–25 °C, likely due to Q₁₀ effects at temperatures closer to the optima for D. pulex, and slowest in specimens reared at 15–30 °C, which may have reflected elevated CSR. Acute tolerance to temperature (LT₅₀) and salinity (LC₅₀) were both highest in D. pulex acclimated to 15–30 °C and salinity 0. LT₅₀ and LC₅₀ increased with increasing salinity in specimens raised at 15 °C and 15–25 °C, but decreased with increasing salinity in specimens raised at 15–30 °C. Thus, increasing temperature confers cross-tolerance to salinity stress, but the directionality of synergistic effects of temperature and salinity depend on the degree of environmental variability. Overall, the results of our study suggest that temperature is a stronger determinant of metabolism, growth, and tolerance thresholds, and assessment of the ecological impacts of environmental change requires explicit information regarding the degree of environmental variability.     

Interactive effects of salt and alkali stresses on seed germination,germination recovery,and seedling growth of a halophyte Spartina alterniflora (Poaceae)

Soil salinization and alkalinization frequently co-occur in nature, but there is little information on the interactive effects of salt and alkali stresses on plants. Seed germination and early seedling growth are crucial stages for plant establishment. We investigated the interactive effects of salt and alkali stresses on seed germination, germination recovery and seedling growth of a halophyte Spartina alterniflora. Seed germination percentage was not significantly reduced at low salinity (≤ 200 mM) at pH 6.63–9.95, but decreased with increased salinity and pH. Ungerminated seeds germinated well after transfer to distilled water from treatment solutions, indicating that seeds can remain viable in high salt–alkaline habits. Shoot growth was stimulated at low salinity and pH, but decreased with increased salinity and pH. Radicle elongation decreased sharply with increased salinity and pH, and was significantly inhibited when pH ≥ 9.0, indicating that the radicles are very sensitive to salt–alkaline stress. The deleterious effects of salinity or high pH alone were less than when combined. A reciprocal enhancement of salt and alkali stresses is a characteristic feature for salt–alkaline stress. Stepwise regression analysis indicates that salinity is the dominant factor, while pH and buffer capacity are secondary for salt–alkaline mixed stress.     

Seed size and capitulum position drive germination and dormancy responses to projected warming for the threatened dune endemic Cirsium pitcheri (Asteraceae)

Among coastal plant species at risk from rapid environmental changes is the North American Great Lakes dune endemic Cirsium pitcheri. Despite being listed as federally threatened, little is known about how C. pitcheri seed attributes influence germination and dormancy‐break patterns in the context of climate change. Following a previous work where we found differences in the number and weight of C. pitcheri seeds among capitulum positions and study sites, here we examine the effects of seed attributes (capitulum position, seed weight, and site of origin) on the proportion and timing of C. pitcheri seed germination under temperature treatments that simulate projected warming in the Great Lakes (20/10, 25/10, and 30/10°C day/night). Our results demonstrate that C. pitcheri produces diverse cohorts of seeds with seed attributes that significantly influence the timing and probability of germination over a 3‐year soil seed bank. Cirsium pitcheri seed germination proportions were highest at 20°C and decreased successively at 25 and 30°C. Seeds from terminal capitula also had higher germination proportions and took longer to germinate than those from secondary capitula. Lastly, the effect of seed weight on germination probability depended on site of origin and capitulum position, with all effects varying in size and significance over time. Ultimately, our results highlight the considerable differences in germination patterns exhibited by seeds from different capitulum positions and sites of origin and provide insight into the dormancy‐break patterns that C. pitcheri might experience under predicted temperature rise in the Great Lakes region of North America.     

Factors influencing seed germination of medicinal plant Salvia aegyptiaca L. (Lamiaceae)

Salvia aegyptiaca is a xerophytic perennial herb belongs to the Lamiaceae family commonly used for medicinal purposes. Laboratory experiments were carried out to assess the effects of temperature and salinity on seed germination and recovery responses after transferring to distilled water. Temperatures between 10 and 40 °C seem to be favourable for the germination of this species. Germination was inhibited by either an increase or decrease in temperature from the optimum (30 °C). The highest germination percentages were obtained at 0 mM NaCl; however, the increase of solution osmolalities progressively inhibited seed germination. The germination rate decreased with an increase in salinity for most of tested temperatures, but comparatively higher rates were obtained at 30 °C. Salt stress decreased both the percentage and the rate of germination. An interaction between salinity and temperature yielded no germination at 300 mM NaCl. By experimental transfer to distilled water, S. aegyptiaca seeds that were exposed to moderately saline conditions recovered and keep their ability to germinate mostly at low temperatures. At 300 mM NaCl, germination recovery decreased with increasing temperature and it was completely inhibited at 40 °C.     

Dormancy and germination responses of halophyte seeds to the application of ethylene

Ethylene is invariably produced during seed germination but its role in regulating seed dormancy and germination is poorly understood. Seeds of 22 halophytic species having different life forms – salt secreting dicots, salt secreting monocots, stem succulents and leaf succulents were germinated in Petri dishes kept in a growth chamber set at 20/30 °C (night/day) temperature and a 12 hr light period. Sodium chloride and ethephon were added to the medium from the beginning of the experiment. Seed germination was recorded every other day for twenty days. Application of ethylene did not have any significant effect on releasing seeds from innate dormancy. However, it appeared to have a role in alleviation of salinity effects which varied from negative in certain species to almost complete alleviation of high salinity effects in others.Our data indicates that ethylene appears to have little role in breaking innate seed dormancy however, in most halophyte seeds studied, application of ethylene alleviate the salinity effect to various degrees. Halophyte seeds which could germinate under saline conditions approaching twice the salinity of seawater may offer clues to understand management of seed germination under highly saline conditions. To cite this article: M.A. Khan et al., C. R. Biologies 332 (2009).     

Effects of salinity levels and seed mass on germination in Australian species of Frankenia L. (Frankeniaceae)

Halophyte species demonstrate differing levels of salt tolerance. Understanding interspecific variation to salinity levels is of value from both the scientific perspective, which includes the identification of traits associated with salinity tolerance, as well as from an applied perspective, which includes identifying plant species for specific salinity restoration and remediation projects. This paper investigates the effects of salinity on germination of 12 Australian species of the plant genus Frankenia L. (Frankeniaceae). We use saline solutions that corresponded to the average soil–water salinity concentrations in the arid zones of inland Australia. These solutions consisted of 10 mM calcium chloride, 30 mM magnesium sulphate, and 450 mM sodium chloride. The aims of our study were: (1) to investigate the germination (germination rates, germination success) of Frankenia seeds to four salinity levels (0%, 10%, 20%, 30%), (2) to test for possible interaction effects between seed mass, germination, and salinity, and (3) to examine the effect of salinity levels on the inhibition of germination and/or seed damage. Species varied in their salt tolerance for germination rates and success. Species with larger seeds had higher germination rates and germination success for high salinity levels. Several species did not germinate well at any salinity level. Finally, no seeds were adversely affected by exposure to high salinity levels pre-germination. There is potential for including some Frankenia species in remediation and revegetation projects in areas affected by salinity, and also as garden plants in saline regions.     

Suitable water temperature for seed storage of Zostera japonica for subtropical seagrass bed restoration

Restoration of Zostera japonica is needed. Laboratory culture experiments to know the germination characteristics might be helpful for implementation of actual restoration. As a part of germination experiments, we explored suitable water temperature for long-term storage of Z. japonica seeds. This work was based on earlier reports of Zostera marina, which presumably has similar physiological properties to Z. japonica. This study consisted of two experiments: (1) preservation experiments to investigate the fate of stored Z. japonica seeds and (2) germination experiments to investigate the germination potential of the stored seeds. The results of the preservation experiments suggested that seed condition, that is, germinated, degraded, unstable, stable, etc., showed variations between the seeds stored at 4 and 23 °C. The majority of the seeds stored at 4 °C were germinated, while those at 23 °C seemed to be degraded, presumably by bacteria and mold. The germination experiments suggested high germination potential of seeds stored at 4 °C even after 302 days had elapsed. In conclusion, including previously reported results on Z. marina, low temperature was suitable for the preservation of seeds to maintain germination potential.