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

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

Desiccation studies in relation to the storage of Araucaria seed

Relationships between seed moisture content (fresh weight basis) and germination were examined for nine Araucaria species by desiccation under mild environmental conditions. The lowest safe moisture content, below which germination percentage begins to decline, was estimated in each case. Seeds can be grouped into three moisture content categories: the first group (including A. araucana, A. angustifolia, A. hunsteinii and A. bidwillii) cannot be safely dried to below 25–40%; the second group (including A. columnaris, A. rulei, A. nemorosa and A. scopulorum) cannot be dried to below about 12% without damage; the third category contains A. cunninghamii, which can be dried to 2% without damage. Seeds in the first group should be stored at 0–5 °C with moisture contents above the lowest-safe value. Provided freezing damage does not exceed 10%, seeds in the second group should be kept at - 18°C or lower with about 7% moisture content for long-term storage and at 0–5 °C with about 12% moisture content in the short term. Seed of A. cunninghamii is best retained at near 5% moisture content and in -18°C or lower. The lowest-safe moisture content was found to be associated with seed size and weight, higher moisture content values coinciding with greater size and weight of seed. Food reserve materials also differed among the groups; seeds of the first group were mainly starchy, whilst those in the other categories possessed a high lipid content.     

Extracts of the Brown Alga Dictyota dichotoma (Hudson) J.V. Lamouroux Alleviate Salt Stress in Rice (Oryza sativa L.) During Germination

Algal extracts provide a safe regime for enhancing crop productivity under stressful conditions. The present study evaluated the efficiency of aqueous and ethanolic extracts of the brown alga Dictyota dichotoma in alleviation of salt stress on germination of rice seeds. Firstly, seeds were germinated using the aqueous extract of D. dichotoma at concentrations of 0, 5, 10, 20, and 50 g L⁻¹, prepared either at room temperature (RTE) or by boiling (BLE). The % germination of rice increased from 84% in non-treated seeds to 100% when treated with 20 g L⁻¹ BLE, although this treatment caused reduced uniformity of germination. Embryo growth was maximum at 20 g L⁻¹ of both extracts with superiority of BLE over RTE. In the second experiment, the effect of 20 g L⁻¹ aqueous and ethanolic extracts relative to a balanced nutrient supply on germination of seeds treated with 0, 40, 90, and 170 mM NaCl was investigated. Salinity reduced % germination with delayed onset but high uniformity of germination, whereas algal amendments counterbalanced the effect of salinity to a greater extent relative to the nutrient supply. Upon withdrawal of salt stress, seeds promptly recovered, with more efficient recovery of seeds exposed to 170 mM than from 90 mM NaCl. The lower recovery of salt-treated seeds compared with the control seed germination suggests that rice suffered from the toxic ion effect of salinity on embryo rather than from the osmotic effect. Extracts of D. dichotoma can enhance and also alleviate salinity stress on rice seed germination.

     

Relationship between Position on the Parent Plant and Dormancy Characteristics of Seeds of Three Cultivars of Celery (Apium graveolens)

Germination and seedling emergence studies were made on seeds harvested from four different umbel positions of three cultivars of celery (Apium graveolens L.). Although heavier seeds were produced from primary umbels than from other umbels, these were less viable as measured by the germination percentage at I8°C in the light. However, germination of viable seeds from quaternary umbels was lower than that of seeds from primary umbels at 18°C in the dark when incubated with GA₄, (2 × 10 ^?4M) and seed from secondary and tertiary umbels tended to be intermediate in response. All viable seeds germinated when N⁶-benzyladenine (10^?2M) was used in combination with GA₄. Seeds from quaternary umbels of two of the cultivars had a lower high-temperature limit for germination in the dark than did seeds from other umbels. In glasshouse experiments the emergence of viable ‘quaternary’ seeds of these cultivars was higher than that of ‘primary’ seeds. Under these conditions the time to 50% of the final emergence as determined after 42 days was similar for seeds from all umbel positions within each cultivar. In two varieties seedling weights were greater from seeds of primary as compared to quaternary umbels, and in general, the largest seedlings arose from the heaviest seeds and the smallest from the lightest seeds in all three cultivars.     

Desiccation and storage studies on Dipterocarpm seeds

The relationship of seed moisture content (fresh weight basis) to germination, and the effect on viability of various storage conditions were examined for five species of the tropical forest tree genus Dipterocarpus. It was shown that seeds fall into two groups with regard to desiccation tolerance. Firstly, D. obtusifolius and D. turbinatus cannot be dried below about 45% moisture content without damage; a sigmoid curve was found to fit the relationship between germination and moisture content for the latter species. Secondly, D. intricatus, D. tuberculatus and D. alatus can be safely dried to 10%, 12% and 17% moisture contents respectively, but desiccation to near 7% moisture content reduced viability by at least a half. Storage studies showed that seed of D. intricatus and D. tuberculatus possessed increased longevity as moisture contents were reduced within the range 6–20%. It was concluded that seeds in the first group are ‘recalcitrant’ and that those in the second group are ‘orthodox’ in their storage physiology, according to the categories described by Roberts (1973). Wide differences between species in seed desiccation rates were observed. In 15% relative humidity D. intricatus dried to 7% moisture content within a week, whilst D. obtusifolius retained 30% moisture content even after 5 wk; other species had intermediate desiccation rates. Seed size and structure may partly account for the differences observed. Correlations were observed between seed storage physiology and other factors which were investigated. ‘Orthodox’ seeds had quicker desiccation rates, were derived from drier habitats, and had smaller embryos than those of ‘recalcitrant’ seeds. ‘Orthodox’ seeds, with the possible exception of D. alatus, should be kept at 0–3°C with about 12% moisture content in the short term and, provided less than 10% germination is lost on freezing, at-18°C with about 8% moisture content in the long term. ‘Recalcitrant’ seeds should be stored in ventilated containers at 21°C and with moisture contents above 45–50%.     

Effect of desiccation on physiological and biochemical indicators associated with the germination and vigor of cryopreserved seeds of <Emphasis Type="Italic">Nicotiana tabacum</Emphasis> L. cv. Sancti Spíritus 96

Cryopreservation is a valuable technique for the long-term conservation of plant germplasm and complementary to traditional seed storage methods. However, critical factors such as seed moisture content should be optimized before using this technique as a safe strategy for storing seeds such as those of Nicotiana spp. This study aimed to determine the effect of desiccation on physiological and biochemical indicators associated with germination and vigor in cryopreserved seeds of Nicotiana tabacum cv. Sancti Spíritus 96 (SS-96). The germination and vigor of seeds with a range of moisture content were assessed using electrolyte leakage and accelerated aging tests. In addition, these physiological indicators were related to the oxidative state of the seeds, in terms of the rate of O₂ ^·? generation and the H₂O₂ content, and the activity of enzymatic antioxidants superoxide dismutase and catalase. The cryopreserved seeds of N. tabacum SS-96 with a moisture content of 2.1% exhibited higher vigor probably due to the retention of membrane integrity, reflected by lower levels of lipid peroxidation and electrolyte leakage associated with the absence of oxidative stress. The results suggest 2.1% as the optimal moisture content for the storage of seeds of this cultivar, both at cryogenic temperatures and at 5°C.     

The effects of soil conditions, soil sterilisation and seed treatmen on the emergence of cabbage in controlled temperature cabinets and the field

Previous cropping history of the soil and the changes that occurred in soil moisture content and temperature were the major factors determining the emergence of cabbage seedlings from pathogen-free seeds. Seedling losses caused by soil-borne pathogens could be high but these losses were prevented by seed treatment with metalaxyl or soil sterilisation with methyl bromide prior to sowing. The beneficial effects of metalaxyl and methyl bromide treatments were confirmed in field experiments involving repeated sowings of cabbage seeds. In experiments with sterilised soil and cabbage seed infected with Alternaria brassicicola emergence at – 0·2 bars soil moisture potential was reduced by 7·8–23.5% at 5, 10, 20, and 25°C. In the field, losses due to A. brassicicola were greatest when the soil became capped after sowing. The results show that recently developed fungicides may facilitate emergence under conditions extremely favourable for seed- and soil-borne pathogens. For maximum benefit, selection of seed treatments should be based on knowledge of the range of pathogens likely to reduce emergence.     

根瘤菌对广金钱草种子萌发及幼苗生长的影响

为探求促进广金钱草萌发及生长的有效途径,该文使用不同浓度的费氏中华根瘤菌、放射型根瘤菌以及田菁茎瘤固氮根瘤菌菌液分别浸染广金钱草种子,以蒸馏水浸泡种子为空白处理,研究其对广金钱草种子萌发指标(发芽率、发芽势、发芽指数、活力指数)的影响,并在温室培养40、60、80 d后分别测定广金钱草幼苗的生长指标(叶片数、分枝数、株高)及部分生理指标(叶绿素含量、含氮量)的变化。结果表明:(1)在1×10⁷ CFU·mL^-1浓度条件下,三种菌液浸种均获得最大萌发指标,其中田菁茎瘤固氮根瘤菌实验组效果最显著,发芽率、发芽势、发芽指数和活力指数高于对照组16.00%、9.33%、9.51和41.34%。(2)除田菁茎瘤固氮根瘤菌实验组外,其余实验组的广金钱草幼苗叶片数、分枝数及株高均低于对照组。(3)放射型根瘤菌实验组和田菁茎瘤固氮根瘤菌实验组幼苗叶绿素含量相比对照组分别增加1.47%和7.47%,含氮量分别增加0.57%和5.17%。综上所述,三种根瘤菌菌液浸种均可在不同程度上提高广金钱草种子的发芽能力和植株生长期的叶绿素和含氮量,其中田菁茎瘤固氮根瘤菌具有最大正向影响,可有效提高种子萌发能力并促进植株生长。该研究可为不同地区广金钱草的种植和栽培提供技术指导,为开发田菁茎瘤固氮根瘤菌作为植物促生长菌剂提供理论支持。     

The effects of ripening and drying of carrot seed (Daucus carota) crops on germination

Carrot seeds taken from the parent plant were capable of germinating before the stage when maximum seed dry weight was reached but even after this stage, when the seed moisture content had fallen below 20%, improvement in seed germination characteristics continued. In the latter stages of seed growth losses by shedding were 12–20 kg/ha/day. For low density crops (10 plants/m²) the yield of viable seed was at a maximum in crops whose seed was harvested with a moisture content of between 20 and 40% but no consistent relationship could be established for high density crops (80 plants/m²). There were no effects of umbel order or plant density on mean germination time or spread of germination. At any early harvest, percentage germination was highest for primary-umbel-seeds and seeds from low density crops but the differences between the seed origins diminished with later harvests. Drying the seeds on the umbels improved the percentage germination, reduced the mean germination time and the spread of germination particularly at the early harvests compared with seeds removed from the umbels and germinated immediately without drying.     

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.     

Seed development and germination ecophysiology of the invasive tree <Emphasis Type="Italic">Prunus serotina</Emphasis> (Rosaceae) in a temperate forest in Western Europe

Seed development, dormancy and germination of the American invasive tree species, Prunus serotina, are described for plants growing in a large forest in Belgium. Seeds of P. serotina were collected following anthesis in the first week of July and thereafter at fortnightly intervals. Seed dormancy, temperature requirements for germination and the soil seed bank were investigated. At maturation (about 105 days after anthesis), seed moisture content had decreased to around 13.7%, and 44% of the seeds had attained the capacity to germinate. Mature seeds of P. serotina exhibited physiological dormancy, germinating only after a long cold, moist stratification period. Highest germination percentage occurred in seeds treated with gibberellic acid (GA₃), at 10°C. We found no evidence that P. serotina forms a persistent seed bank but noticed a persistent seedling bank in the field.     

Influence of an abscisic acid (ABA) seed coating on seed germination rate and timing of Bluebunch Wheatgrass

Semi‐arid rangeland degradation is a reoccurring issue throughout the world. In the Great Basin of North America, seeds sown in the fall to restore degraded sagebrush (Artemisia spp.) steppe plant communities may experience high mortality in winter due to exposure of seedlings to freezing temperatures and other stressors. Delaying germination until early spring when conditions are more suitable for growth may increase survival. We evaluated the use of BioNik? (Valent BioSciences LLC) abscisic acid (ABA) to delay germination of bluebunch wheatgrass (Pseudoroegneria spicata). Seed was either left untreated or coated at five separate rates of ABA ranging from 0.25 to 6.0 g 100 g^?1 of seed. Seeds were incubated at five separate constant temperatures from 5 to 25°C. From the resultant germination data, we developed quadratic thermal accumulation models for each treatment and applied them to 4 years of historic soil moisture and temperature data across six sagebrush steppe sites to predict germination timing. Total germination percentage remained similar across all temperatures except at 25°C, where high ABA rates had slightly lower values. All ABA doses delayed germination, with the greatest delays at 5–10°C. For example, the time required for 50% of the seeds to germinate at 5°C was increased by 16–46 d, depending on the amount of ABA applied. Seed germination models predicted that the majority of untreated seed would germinate 5–11 weeks after a 15 October simulated planting date. In contrast, seeds treated with ABA were predicted to delay germination to late winter or early spring. These results indicate that ABA coatings may delay germination of fall planted seed until conditions are more suitable for plant survival and growth.     

A comparative study of seed morphology in relation to desiccation tolerance and other physiological responses in 71 Eastern Australian rainforest species

Seed characteristics were measured in 71 Eastern Australian rainforest species representing 30 families. Sensitivity to desiccation to low moisture contents (< 10%) occurred in 42% of species. We estimate, based on findings from 100 species from this present study and previously published reports, that 49% of Eastern Australian rainforest species have non‐orthodox seeds. Germination level and time to 50% germination were not significantly different between desiccation sensitive (DS) and desiccation tolerant (DT) seeds. The estimation of seed desiccation sensitivity based on predictors is an important tool underpinning ex situ conservation efforts. Seed characteristics differed significantly between DS and DT seeds; that is, DS seeds had: (i) larger fruits (19 949 mg vs 8322 mg); (ii) larger seeds (1663 mg vs 202 mg); (iii) higher seed moisture contents (49.7% vs 35.5% fresh weight); (iv) lower oil content (7.3% vs 24.8% yield); and (v) less investment in seed coats (0.19 vs 0.48 seed coat ratio). Only 25% of DS seeded species had oily seeds compared with 87% of DT seeded species. Most green embryos were DS. Seed coat ratio was the best predictor of seed DS (80% correctly predicted). Seed moisture content at maturity was also related to germination time. Mean seed size was correlated (?0.657, P = 0.01) with mean seed oil content in 46 species. Further research on seed storage physiology of possible oily and/or DS seeded species is crucial to ensure future long‐term security of this biodiversity, particularly for species currently threatened in situ and/or of socioeconomic importance in Eastern Australian rainforests.     

Characterisation of Soybean and Wheat Seeds by Nuclear Magnetic Resonance Spectroscopy

The effects of equilibration under different air relative humidities (RH, 1 – 90 %) and temperatures (35 and 45 °C) on soybean (Glycine max) and wheat (Triticum aestivum) seeds were studied using different techniques. Seed moisture content, electrical conductivity (EC) of seed leachate and per cent seed germination were measured following standard procedures, and compared with nuclear magnetic resonance spin-spin relaxation time (T₂) measurements. Moisture contents of soybean and wheat seeds, following the reverse sigmoidal trend, were greater at 35 than at 45 °C at any particular RH. Changes in T₂ were related to the changes in germination percentage and leachate EC of both soybean and wheat seeds. Equilibrating soybean seeds at RH 11 % decreased germination percentage with corresponding decrease in T₂. On the contrary, EC of seed leachate increased. In wheat seeds equilibrated at 45 °C, T² was maximal at RH 5.5 %. T₂ declined in seeds equilibrated at high RH (> 80 %) together with low germination percentage.     

Tree fine root Ca/Al molar ratio – Indicator of Al and acidity stress

Many Aloe species are exploited as natural products. Generally, the leaves are unsustainably picked from wild plants to meet the market demand. Basic scientific information on seed biology and the ways of increasing levels of secondary metabolites in seedlings is still lacking for Aloe species. This study investigated seed germination requirements and evaluated levels of secondary metabolites in seedlings of Aloe arborescens, an important species in traditional medicine. The highest percentage germination (78%) and the fastest germination rate (GR) (10% d^? 1) with a mean germination time (MGT) of 9 days were achieved at 20°C under a 16-h photoperiod. At 25°C, maximum percentage germination (67%) (P < 0.05), higher GR (13% d^? 1) and shorter MGT (6 days) were obtained under constant light. These results indicate that temperature and light play a significant role in germination of A. arborescens seeds. Increasing osmotic pressure on seeds decreased percentage germination, whereas buffering the solution to a range of pH values (4–10) did not significantly affect germination. Smoke–water (1:500 v/v), smoke-isolated karrikinolide (10^? 8 and 10^? 9 M) and potassium nitrate (10^? 3 and 10^? 4 M) significantly promoted germination compared with the control at 25°C (supra-optimal temperature) under a 16-h photoperiod. These treatments were also effective in increasing secondary metabolite levels (flavonoids and phenolics) in A. arborescens seedlings.     

Seed Dynamics of Early and Late Successional Tree Species in Tropical Abandoned Pastures: Seed Burial as a Way of Evading Predation

We explored different treatments to enhance the probability of sowed seeds of two early successional (ES, Cecropia obtusifolia and Ochroma pyramidale) and two late successional (LS, Brosimum costaricanum and Dialium guianense) species to escape predation and germinate in abandoned cattle‐raising pasture fields in Southeastern Mexico. ES species were sown in groups of 50 seeds under three treatments: invertebrate exclusion, burial, and exposition to seedeaters. LS species were sown in groups of 10 seeds under three treatments: vertebrate exclusion, burial, and exposition to seedeaters. We registered seed predation and germination 2, 4, 8, 16, 32, and 64 days after the initial sowing. Overall, ES showed higher predation rates (mean ± SE = 0.45 ± 0.07 seed seed^?1 day^?1; n = 3) than LS species (0.09 ± 0.02 seed seed^?1 day^?1). Cecropia obtusifolia was completely predated in all treatments after 8 days. Burial and exclusion treatments reduced final predation in circa 6% for O. pyramidale, relative to that of exposed seeds (85% after 8 days); most germination occurred in buried seeds (3.7%). In B. costaricanum, burial enabled germination by 10%; exposed and excluded seeds were removed 100%. Dialium guianense showed 12% germination in buried seeds and circa 20% of the seeds were not removed after 64 days. Direct sowing would be a recommended rainforest restoration practice for species with relatively large seeds if deposited in groups and buried. Studies which address variation across numerous sites are necessary in order to generate more consistent seed predation patterns and rainforest restoration principles in tropical pastures.     

The Effect of Chilling and Moisture Status on the Germination, Desiccation Tolerance and Longevity ofAesculus hippocastanumL. Seed

Effects of 2 °C chilling on the threshold moisture contentsand water potentials for various physiological processes wereestimated forAesculus hippocastanumL. seed. Seed harvested atthe time of maximum seed fall exhibited a dual response to drying:partial drying from near 50% to 32–40% moisture contentprogressively increased germination percentage (at 16 °C)up to various peak values; further desiccation was detrimental,confirming that the seeds are ‘recalcitrant’. Themoisture content for optimum germination was increased by atleast 10% as the chilling period was raised from 0 to 9 weeks.A negative linear relationship was found between log₁₀mean timeto germinate and probit final germination, regardless of pre-treatment,indicating that partial desiccation and chilling are interchangeablein promoting germination of hydrated seed. For nearly fullyhydrated seeds, increasing the chilling period from 6 to 26weeks increased the viability-loss onset point for desiccationinjury from near 40% to about 48% moisture content without alteringthe drying rates of seed tissues. Extending moist chilling invarious seed lots from 0 to 26 weeks decreased subsequent longevityat 16 °C. For 26-week-chilled seeds longevity (the periodto lose one probit of germination) differed above and belowa threshold moisture content of 48%. It remained constant inthe moisture-content range 48–38%, but increased progressivelyas moisture content was raised above 48%. This threshold moisturecontent coincided with the value above which chilled seed pre-germinatedin storage. The results indicate that post-harvest desiccationand chilling alter the water relations of various physiologicalprocesses and a schematic summary is presented which relatesthe results to an axis water sorption isotherm.Copyright 1998Annals of Botany Company Aesculus hippocastanumL., horse chestnut, chilling, moisture content, water potential, desiccation tolerance, longevity, recalcitrant seed, embryo axis, maturation, germination.     

The role of after‐ripening in promoting germination of arid zone seeds: a study on six Australian species

The effects of after‐ripening (storage under warm, dry conditions) on seed germination was examined in six plant species from the arid zone of Western Australia with the aim of improving germination and germination rate for rehabilitation objectives. Study species (Acanthocarpus preissii, Anthocercis littorea, Dioscorea hastifolia, Eremophila oldfieldii, Thryptomene baeckeacea and Zygophyllum fruticulosum) were selected based on diverse plant habits, seed types and requirements for rehabilitation. After‐ripening was investigated by adjusting seed moisture content to 13 and 50 equilibrium relative humidity (eRH) at 23 °C and storing seeds at two temperatures (30 and 45 °C) from 1 to 18 months. Following storage, seeds were incubated in water, gibberellic acid (GA₃) or karrikinolide (KAR₁; the butenolide, 3‐methyl‐2H‐furo[2,3‐c]pyran‐2‐one). All after‐ripening conditions increased germination percentage and rate of A. littorea and D. hastifolia, with A. littorea only germinating when treated with GA₃ or KAR₁. The germination of Z. fruticulosum was dependent on after‐ripening temperature and seed moisture content. After‐ripening had a limited effect on the remaining three species. The restoration implications of the findings are discussed. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161 , 411–421.     

Light effects upon dry lettuce seeds

Germination of certain dry seeds (achenes) of Lactuca sativa L. cv. Grand Rapids was increased to ca. 75% after irradiation with 665 nm red light (R; 1x10³ J m^-2); this response was eliminated by far-red light (FR) following the R. The response of dry seeds required an order of magnitude more light than that of wetted seeds, and was not maximal until 48 h after irradiation. Other seeds, which could not be stimulated by R in dry state, showed a partial response after 10 min hydration. Irradiation of dry seeds (or seeds wetted 1 h) with FR (1x10³ J m^-2) reduced dark germination from 26% to 2%. Seeds dehydrated in an oven (60°C, 90 min) showed a decrease in germination if irradiated with R (1x10⁵ J m^-2) before wetting. The results show that phytochrome is present in dry lettuce seeds (and functional in some seed lots) prior to wetting; and that in other seed lots the molecule becomes functional within minutes after wetting the seeds. Transformation of the FR absorbing from of phytochrome (P_FR) to the inactive from (P_R) occurs at lower seed moisture content than the reverse reaction. It appears that dormancy in seeds ripened in sunlight might be assured during seed drying and maturation by the more effective transformation of P_FR to P_R than vice versa as phytochrome is dehydrated.Abbreviations FR far-red - R red - CAL seeds from California - NC seeds from North Carolina (see text)     

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.