Combinational dormancy in seeds of Sicyos angulatus (Cucurbitaceae,tribe Sicyeae)

Seeds with a water‐impermeable seed coat and a physiologically dormant embryo are classified as having combinational dormancy. Seeds of Sicyos angulatus (burcucumber) have been clearly shown to have a water‐impermeable seed coat (physical dormancy [PY]). The primary aim of the present study was to confirm (or not) that physiological dormancy (PD) is also present in seeds of S. angulatus. The highest germination of scarified fresh (38%) and 3‐month dry‐stored (36%) seeds occurred at 35/20°C. The rate (speed) of germination was faster in scarified dry‐stored seeds than in scarified fresh seeds. Removal of the seed coat, but leaving the membrane surrounding the embryo intact, increased germination of both fresh and dry‐stored seeds to > 85% at 35/20°C. Germination (80–100%) of excised embryos (both seed coat and membrane removed) occurred at 15/6, 25/15 and 35/20°C and reached 95–100% after 4 days of incubation at 25/15 and 35/20°C. Dry storage (after‐ripening) caused an increase in the germination percentage of scarified and of decoated seeds at 25/15°C and in both germination percentage and rate of excised embryos at 15/6°C. Eight weeks of cold stratification resulted in a significant increase in the germination of scarified seeds at 25/15 and 35/20°C and of decoated seeds at 15/6 and 25/15°C. Based on the results of our study and on information reported in the literature, we conclude that seeds of S. angulatus not only have PY, but also non‐deep PD, that is, combinational dormancy (PY + PD).     

Effects of seed maturation time and dry storage on light and temperature requirements during germination in invasive Prosopis juliflora

The effects of time of seed maturation and dry seed storage and of light and temperature requirements during seed incubation on final germination percentage and germination rate were assessed for the invasive shrub Prosopis juliflora (Sw.) D.C., grown under desert environmental conditions of the United Arab Emirates (UAE). Seeds were collected from Fujira on the northern coast of the UAE at different times during the growing seasons (autumn, winter and spring) and were germinated immediately and after 8 months of dry storage under room temperature (20±3 °C). Seeds were germinated at three temperatures (15, 25 and 40 °C) in both continuous light and darkness. The results showed significant effects for time of seed collection, seed storage, light and temperature of seed incubation and many of their interactions on both germination percentage and rate. Fresh seeds matured during autumn and winter germinated significantly greater at 40 °C and in light than at lower temperatures and in dark. Storage significantly increased germination percentage and rate; the increase was greater for seeds matured during winter than for seeds matured during spring. This indicates that dormancy breakage was greater in seeds of winter than seeds of spring. The need for high temperature to achieve greater germination was significantly reduced after seed storage, especially for seeds matured in autumn and winter.     

Physiological dormancy in seeds of tropical montane woody species in Hawai`i

Worldwide, there is relatively little information on seed dormancy and germination of tropical montane species. Our aim was to help fill this knowledge gap by conducting seed dormancy/germination studies on woody species from this vegetation zone in Hawai`i. All species had water-permeable seeds with a fully developed embryo. Seeds of 29 species (23 genera) were incubated in light/dark at 15/6, 20/10 and 25/15°C and germination monitored at 2-week intervals for 16–128 weeks. Seeds of Chenopodium oahuense, Dubautia menziesii and Silene lanceolata were non-dormant (ND) and those of 26 other species had physiological dormancy (PD); 10 of the 26 species had conditional PD. The optimum germination temperature regime(s) was (were) 25/15°C, 17 species; 25/10 and 20/10°C, 2; 20/10°C, 6; 20/10 and 15/6°C, 2; and 15/6°C, 2. Worldwide, PD in the woody genera included in our study is more common than ND. In addition to its contribution to the world biogeography of seed dormancy/germination, this study will be useful to conservation biologists who need to germinate seeds of tropical montane species.     

Releasing primary dormancy in <Emphasis Type="Italic">Avena fatua</Emphasis> L. caryopses by smoke-derived butenolide

The effect of smoke and smoke-derived butenolide in releasing dormancy of caryopses (referred to as seeds) of the economically important weed Avena fatua L. was studied. Seeds of A. fatua are dormant after harvest. Both smoke-water and butenolide, applied continuously, removed dormancy in darkness at 15, 20 and 25°C and slightly at 30°C. Butenolide was very active at a concentration of 10⁻⁸ M. Butenolide at 10⁻⁸ M was also able to remove dormancy at 20°C when applied for 12 or 24 h at 4°C or for 3 to 24 h at 20°C. Sensitivity to butenolide decreased with longer preincubation times in water. This compound was less effective in releasing dormancy in the light than in darkness. Dormancy release by butenolide involves induction of cell-cycle activity just before coleorhiza protrusion. Stimulatory effects of smoke-water and butenolide were also observed in respect of seedling growth and vigor.     

Seed germination ecology of the threatened endemic Iberian <Emphasis Type="Italic">Delphinium fissum</Emphasis> subsp. <Emphasis Type="Italic">sordidum</Emphasis> (Ranunculaceae)

Seeds of Delphinium fissum subsp. sordidum are physiologically dormant at maturity, with underdeveloped embryos; thus they have morphophysiological dormancy (MPD). The aims of this study were to determine the requirements for embryo growth, dormancy break and germination, to characterise the type of seed dormancy and to evaluate the effects of light, seed age, pollination mechanism, and inter-annual and inter-population variability on germinative ability. After 3 months of incubation at 5°C (cold stratification) in darkness conditions, the mean embryo length increased from 5.6 to 2.07 mm, with 76% of seeds germinating. Conversely, embryos of seeds incubated during 3 months at 20/7 or 28/14°C hardly grew and no germination was recorded. Since cold stratification was the only requirement for the loss of MPD, and both dry storage in laboratory conditions and warm stratification prior to cold stratification shortened the cold stratification period required for germination, it could be concluded that D. fissum subsp. sordidum seeds have intermediate complex MPD. Cold stratification and incubation in darkness conditions promoted higher germination percentages than those in light. In addition, germinative ability increased with seed age up to 8 months (reaching 96% at 5°C in darkness), showed a pronounced inter-annual and inter-population variability, as well as a significant decrease in seeds coming from pollination by geitonogamy. High temperatures (25/10 or 28/14°C) induced seeds to secondary dormancy, so seedling emergence in the greenhouse was restricted to February–March. The requirements for dormancy break and germination reflect an adaptation to trigger germination in late winter. This study is the first one to document a gradual increase in germination percentage with seed age for plant species with intermediate complex MPD.     

Seed germination ecology of the annual grass Leptochloa panicea ssp. mucronata and a comparison with L. panicoides and L. fusca

Leptochloa panicea ssp. mucronata is an annual grass that grows in relatively dry habitats. Requirements for dormancy loss and germination were determined for seeds of this species and compared to those of two species from wet habitats. Seeds of L. panicea were dormant at maturity in autumn, but when exposed to actual or simulated autumn temperatures (e.g. 20/10, 15/6 °C), they entered conditional dormancy and thus germinated to high percentages in light at 35/20 °C. Seeds buried in non-flooded soil exposed to natural seasonal temperature changes in Kentucky (USA) were non-dormant by the following summer and germinated to 80–100 % in light at 25/15, 30/15 and 35/20 °C. Seeds buried in non-flooded soil exhibited an annual conditional dormancy/non-dormancy cycle, with seeds mostly germinating to 80–100 % in light at 30/15 and 35/20 °C throughout the year but to 80–100 % in light at 25/15 °C only in summer. Results for L. panicea were compared to published data for L. panicoides and L. fusca. Whereas seeds of L. panicea buried in flooded soil failed to come out of dormancy, those of L. panicoides, an annual of moist habitats such as mudflats, exhibited an annual conditional dormancy/non-dormancy cycle, and those of L. fusca, a semi-aquatic, required flooding for both dormancy loss and germination. Differences in dormancy breaking and germination responses of seeds of Leptochloa species may help to explain why this genus occupies a wide range of habitats with regard to soil moisture conditions.     

Acclimation and adaptive responses of woody plants to environmental stresses

The predominant emphasis on harmful effects of environmental stresses on growth of woody plants has obscured some very beneficial effects of such stresses. Slowly increasing stresses may induce physiological adjustment that protects plants from the growth inhibition and/or injury that follow when environmental stresses are abruptly imposed. In addition, short exposures of woody plants to extreme environmental conditions at critical times in their development often improve growth. Furthermore, maintaining harvested seedlings and plant products at very low temperatures extends their longevity. Drought tolerance: Seedlings previously exposed to water stress often undergo less inhibition of growth and other processes following transplanting than do seedlings not previously exposed to such stress. Controlled wetting and drying cycles often promote early budset, dormancy, and drought tolerance. In many species increased drought tolerance following such cycles is associated with osmotic adjustment that involves accumulation of osmotically active substances. Maintenance of leaf turgor often is linked to osmotic adjustment. A reduction in osmotic volume at full turgor also results in reduced osmotic potential, even in the absence of solute accumulation. Changes in tissue elasticity may be important for turgor maintenance and drought tolerance of plants that do not adjust osmotically. Water deficits and nutrient deficiencies promote greater relative allocation of photosynthate to root growth, ultimately resulting in plants that have higher root:shoot ratios and greater capacity to absorb water and minerals relative to the shoots that must be supported. At the molecular level, plants respond to water stress by synthesis of certain new proteins and increased levels of synthesis of some proteins produced under well-watered conditions. Evidence has been obtained for enhanced synthesis under water stress of water-channel proteins and other proteins that may protect membranes and other important macromolecules from damage and denaturation as cells dehydrate. Flood tolerance: Both artificial and natural flooding sometimes benefit woody plants. Flooding of orchard soils has been an essential management practice for centuries to increase fruit yields and improve fruit quality. Also, annual advances and recessions of floods are crucial for maintaining valuable riparian forests. Intermittent flooding protects bottomland forests by increasing groundwater supplies, transporting sediments necessary for creating favorable seedbeds, and regulating decomposition of organic matter. Major adaptations for flood tolerance of some woody plants include high capacity for producing adventitious roots that compensate physiologically for decay of original roots under soil anaerobiosis, facilitation of oxygen uptake through stomata and newly formed lenticels, and metabolic adjustments. Halophytes can adapt to saline water by salt tolerance, salt avoidance, or both. Cold hardiness: Environmental stresses that inhibit plant growth, including low temperature, drought, short days, and combinations of these, induce cold hardening and hardiness in many species. Cold hardiness develops in two stages: at temperatures between 10° and 20°C in the autumn, when carbohydrates and lipids accumulate; and at subsequent freezing temperatures. The sum of many biochemical processes determines the degree of cold tolerance. Some of these processes are hormone dependent and induced by short days; others that are linked to activity of enzyme systems are temperature dependent. Short days are important for development of cold hardiness in species that set buds or respond strongly to photoperiod. Nursery managers often expose tree seedlings to moderate water stress at or near the end of the growing season. This accelerates budset, induces early dormancy, and increases cold hardiness. Pollution tolerance: Absorption of gaseous air pollutants varies with resistance to flow along the pollutant’s diffusion path. Hence, the amount of pollutant absorbed by leaves depends on stomatal aperture, stomatal size, and stomatal frequency. Pollution tolerance is increased when drought, dry air, or flooding of soil close stomatal pores. Heat tolerance: Exposure to sublethal high temperature can increase the thermotolerance of plants. Potential mechanisms of response include synthesis of heat-shock proteins and isoprene and antioxidant production to protect the photosynthetic apparatus and cellular metabolism. Breaking of dormancy: Seed dormancy can be broken by cold or heat. Embryo dormancy is broken by prolonged exposure of most seeds to temperatures of 1° to 15°C. The efficiency of treatment depends on interactions between temperature and seed moisture content. Germination can be postponed by partially dehydrating seeds or altering the temperature during seed stratification. Seed-coat dormancy can be broken by fires that rupture seed coats or melt seedcoat waxes, hence promoting water uptake. Seeds with both embryo dormancy and seed-coat dormancy may require exposure to both high and low temperatures to break dormancy. Exposure to smoke itself can also serve as a germination cue in breaking seed dormancy in some species. Bud dormancy of temperate-zone trees is broken by winter cold. The specific chilling requirement varies widely with species and genotype, type of bud (e.g., vegetative or floral bud), depth of dormancy, temperature, duration of chilling, stage of plant development, and daylength. Interruption of a cold regime by high temperature may negate the effect of sustained chilling or breaking of bud dormancy. Near-lethal heat stress may release buds from both endodormancy and ecodormancy. Pollen shedding: Dehiscence of anthers and release of pollen result from dehydration of walls of anther sacs. Both seasonal and diurnal pollen shedding are commonly associated with shrinkage and rupture of anther walls by low relative humidity. Pollen shedding typically is maximal near midday (low relative humidity) and low at night (high relative humidity). Pollen shedding is low or negligible during rainy periods. Seed dispersal: Gymnosperm cones typically dehydrate before opening. The cones open and shed seeds because of differential shrinkage between the adaxial and abaxial tissues of cone scales. Once opened, cones may close and reopen with changes in relative humidity. Both dehydration and heat are necessary for seed dispersal from serotinous (late-to-open) cones. Seeds are stored in serotinous cones because resinous bonds of scales prevent cone opening. After fire melts the resinous material, the cone scales can open on drying. Fires also stimulate germination of seeds of some species. Some heath plants require fire to open their serotinous follicles and shed seeds. Fire destroys the resin at the valves of follicles, and the valves then reflex to release the seeds. Following fire the follicles of some species require alternate wetting and drying for efficient seed dispersal. Stimulation of reproductive growth: Vegetative and reproductive growth of woody plants are negatively correlated. A heavy crop of fruits, cones, and seeds is associated with reduced vegetative growth in the same or following year (or even years). Subjecting trees to drought during early stages of fruit development to inhibit vegetative growth, followed by normal irrigation, sometimes favors reproductive growth. Short periods of drought at critical times not only induce formation of flower buds but also break dormancy of flower buds in some species. Water deficits may induce flowering directly or by inhibiting shoot flushing, thereby limiting the capacity of young leaves to inhibit floral induction. Postharvest water stress often results in abundant return bloom over that in well-irrigated plants. Fruit yields of some species are not reduced or are increased by withholding irrigation during the period of shoot elongation. In several species, osmotic adjustment occurs during deficit irrigation. In other species, increased fruit growth by imposed drought is not associated largely with osmotic adjustment and maintenance of leaf turgor. Seedling storage: Tree seedlings typically are stored at temperatures just above or below freezing. Growth and survival of cold-stored seedlings depend on such factors as: date of lifting from the nursery; species and genotype; storage temperature, humidity, and illumination; duration of storage; and handling of planting stock after storage. Seedlings to be stored over winter should be lifted from the nursery as late as possible. Dehydration of seedlings before, during, and after storage adversely affects growth of outplanted seedlings. Long-term storage of seedlings may result in depletion of stored carbohydrates by respiration and decrease of root growth potential. Although many seedlings are stored in darkness, a daily photoperiod during cold storage may stimulate subsequent growth and increase survival of outplanted seedlings. For some species, rapid thawing may decrease respiratory consumption of carbohydrates (over slowly thawed seedlings) and decrease development of molds. Pollen storage: Preservation of pollen is necessary for insurance against poor flowering years, for gene conservation, and for physiological and biochemical studies. Storage temperature and pollen moisture content largely determine longevity of stored pollen. Pollen can be stored successfully for many years in deep freezers at temperatures near −15°C or in liquid nitrogen (−196°C). Cryopreservation of pollen with a high moisture content is difficult because ice crystals may destroy the cells. Pollens of many species do not survive at temperatures below −40°C if their moisture contents exceed 20–30%. Pollen generally is air dried, vacuum dried, or freeze dried before it is stored. To preserve the germination capacity of stored pollen, rehydration at high humidity often is necessary. Seed storage: Seeds are routinely stored to provide a seed supply during years of poor seed production, to maintain genetic diversity, and to breed plants. For a long time, seeds were classified as either orthodox (relatively long-lived, with capacity for dehydration to very low moisture contents without losing viability) or recalcitrant (short-lived and requiring a high moisture content for retention of viability). More recently, some seeds have been reclassified as suborthodox or intermediate because they retain viability when carefully dried. True orthodox seeds are preserved much more easily than are nonorthodox seeds. Orthodox seeds can be stored for a long time at temperatures between 2° and −20°C, with temperatures below −5°C preferable. Some orthodox seeds have been stored at superlow temperatures, although temperatures of −40°, −70°, or −196°C have not been appreciably better than −20°C for storage of seeds of a number of species. Only relatively short-term storage protocols have been developed for nonorthodox seeds. These treatments typically extend seed viability to as much as a year. The methods often require cryopreservation of excised embryos. Responses to cryopreservation of nonorthodox seeds or embryos vary with species and genotype, rate of drying, use of cryoprotectants, rates of freezing and thawing, and rate of rehydration. Fruit storage: Storing fruits at low temperatures above freezing, increasing the CO₂ concentration, and lowering the O₂ concentration of fruit storage delays senescence of fruits and prolongs their life. Fruits continue to senesce and decay while in storage and become increasingly susceptible to diseases. Both temperate-zone and tropical fruits may develop chilling injury characterized by lesions, internal discoloration, greater susceptibility to decay, and shortened storage life. Chilling injury can be controlled by chemicals, temperature conditioning, and intermittent warming during storage. Stored fruits may become increasingly susceptible to disease organisms. Fruit diseases can be controlled by cold, which inhibits growth of microorganisms and maintains host resistance. Exposure of fruits to high CO₂ and low O₂ during storage directly suppresses disease-causing fungi. Pathogens also can be controlled by exposing fruits to heat before, during, and after storage. Scald that often develops during low-temperature storage can be controlled by chemicals and by heat treatments.     

Variation in seed germination between populations of five sub-alpine woody species from eastern Qinghai-Tibet Plateau following dry storage at low temperatures

Effects of cold-dry storage on dormancy break and viability were determined for seeds of the five sub-alpine woody species Philadelphus incanus, Berberis vernae, Berberis dubia, Betula utilis, and Picea purpurea collected along an altitudinal gradient on the eastern part of the Qinghai-Tibet Plateau in China. Germination tests were conducted at 20/5°C for seeds stored dry at ambient room temperature for 4 weeks and then at 3–4°C for 0, 6, 12, and 24 weeks. Dormancy break during dry storage, i.e., afterripening, was indicated by an increase in germination percentages and rates. Duration of cold-dry storage and altitude of seed collection had significant effects on germination. With an increase in duration of storage, germination percentages and rates of P. incanus and B. vernae increased with a decrease in altitude of seed collection, while they increased with an increase in altitude for seeds of B. utilis and P. purpurea. Seeds of B. dubia did not exhibit changes in germination percentages and rates with altitude because a high number of seeds remained dormant during storage. Seed viability after 24 weeks of storage ranged from high (88, 93.3, 92.7%) for B. utilis to low (15% for high altitude) for P. incanus. The potential for dormancy break to occur during cold-dry storage should be considered when studies on basic seed dormancy are conducted or when seeds from various locations are stored prior to propagating plants from them.     

Seed dormancy-breaking and germination requirements ofDrosera anglica,an insectivorous species of the Northern Hemisphere

Seeds of Drosera anglica collected in Sweden were dormant at maturity in late summer, and dormancy break occurred during cold stratification. Stratified seeds required light for germination, but light had to be given after temperatures were high enough to be favorable for germination. Seeds stratified in darkness at 5/1 °C and incubated in light at 12/12 h daily temperature regimes of 15/6, 20/10 and 25/15 °C germinated slower and to a significantly lower percentage at each temperature regime than those stratified in light and incubated in light. Length of the stratification period required before seeds would germinate to high percentages depended on (1) whether seeds were in light or in darkness during stratification and during the subsequent incubation period, and (2) the temperature regime during incubation. Seeds collected in 1999 germinated to 4, 24 and 92 % in light at 15/6, 20/10 and 25/15 °C, respectively, after 2 weeks of stratification in light. Seeds stratified in light for 18 weeks and incubated in light at 15/6, 20/10 and 25/15 °C germinated to 87, 95 and 100 %, respectively, while those stratified in darkness for 18 weeks and incubated in light germinated to 6, 82 and 91 %, respectively. Seeds collected from the same site in 1998 and 1999, stratified in light at 5/1 °C and incubated in light at 15/6 °C germinated to 22 and 87 %, respectively, indicating year-to-year variation in degree of dormancy. As dormancy break occurred, the minimum temperature for germination decreased. Thus, seed dormancy is broken in nature by cold stratification during winter, and by spring, seeds are capable of germinating at low habitat temperatures, if they are exposed to light.     

Temperature Dependence of Viability and Dormancy of Zizania palustris var. interior Seeds Stored at High Moisture Contents

Seeds (caryopses) of North American wild rice (Zizania palustrisvar. interior), a temperate aquatic grass, have been thoughtto require storage at low temperatures and high moisture contentsto preserve viability. The seeds are also deeply dormant atmaturity and require up to 6 months of stratification to breakdormancy. We report here that wild rice seeds can retain viabilityat moisture contents 30% (f. wt. basis) for up to 6 monthsat temperatures as high as 30 °C, and for at least 1 yearat temperatures below 20 °C. Dormancy is not broken at temperaturesabove 10 °C, but subsequent stratification requirementsare unaffected by prior warm storage. Cold storage is thereforenot required to maintain viability of wild rice seeds, but isnecessary to break dormancy. Hydrated wild rice seeds can befrozen to –10 °C without damage, but dormancy is notlost at subfreezing temperatures. These results provide newoptions for long-term storage of wild rice seeds. Zizania palustris var. interior (Fassett) Dore, wild rice, seed, germination, dormancy, storage, moisture content     

Patterns of Testa-imposed Seed Dormancy in Native Australian Legumes

The testa-imposed seed dormancy of 34 native Australian speciesof Faboideae and Mimosoideae was examined immediately afterthe seeds matured and again after 3.5 years of dry storage inthe laboratory. Three groups of dormancy patterns are recognized:17 species (of the Mirbelieae and Acacieae) that have a relativelysmall nondormant fraction (0–10%) of their ripe seedsand that maintain this fraction through time; ten species (ofthe Mirbelieae) that have a relatively large non-dormant fraction(10–40%) of their ripe seeds and that maintain this fractionthrough time; and seven species (of the Bossiaeeae and Phaseoleae)that have a relatively small non-dormant fraction when the seedsripen, and have this fraction increase significantly throughtime. The species in the second group have smaller seeds thando those of the first and third groups, while the species inthe third group have a different testa construction from thosein the first and second groups. For all of the non-dormant seedstested, the water permeability is not localized only at thelens. Leguminosae, Fabaceae, Mimosoideae, Papilionoideae, Faboideae, legume seeds, seed dormancy, hard-seededness, dormancy loss, germination     

Factors influencing the storability of Fagus sylvatica L. seeds after release from dormancy

Seeds of beech (Fagus sylvatica L.) that have been subjected to dormancy breaking consisting of 10 weeks of prechilling at 3 °C and 34 % water content (WC) and then desiccation to 10 % WC, are non-dormant (ND). ND seeds are characterised by greater sensitivity to storage conditions, than no prechilled, dormant (D) seeds. The aim of the present work was to investigate factors affecting the loss of seed viability during storage of D and ND beech seeds at different temperatures (4 and 20 °C) and humidity levels (45 and 75 % RH) for 3 weeks. In general, both D and ND seeds maintained a high germination capacity after storage at 4 °C. At 20 °C and 45 and 75 % RH the germination capacity of D seeds diminished to 80 and 28 %, respectively. Under the same conditions, ND seeds lost germination capacity to a greater degree, with only 62 and 7 % germinated seeds, respectively. At 20 °C, an increase in production of reactive oxygen species was observed, and the increase was significantly higher in ND seeds. The loss of germination capacity was coincident with an increase in electrolyte leakage and accumulation of free fatty acids, which suggests that membrane deterioration was the cause of the decline in germinability. ND seeds stored at 20 °C and 45 and 75 % RH showed a greater decrease than D seeds in contents of the primary phospholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE) as well as in polyunsaturated fatty acids (18:2 and 18:3). ND seeds possessed more unsaturated fatty acids, especially 18:3, than D seeds in the phospholipid fraction before storage. D seeds were characterised by a significantly higher level of α-tocopherol and UV-absorbing phenols. The level of ascorbate was similar in D and ND seeds. D seeds contained glutathione in both reduced (GSH) and oxidised (GSSG) forms, and GSSG dominated GSH. ND seeds contained more GSSG form than D seeds. We concluded that the membranes of ND seeds are exposed to greater oxidative stress during storage due to higher levels of unsaturation and lower levels of α-tocopherol, the main antioxidant that protects membranes against free radical attack.     

Tolerance of kikuyu grass to long term salt stress is associated with induction of antioxidant defences

Primary dormancy in A. retroflexus seeds wascompletely broken by dry storage or ethylene treatment and partially removedwith GA₃. Norbornadiene counteracted the dormancy breaking action ofethylene and GA₃. The GA₃ effect was lowered bycobaltous ions. ABA increased the ethylene requirement in primary dormant seeds.Dormant seeds had a similar or different ability to produce ethylene and ACCoxidase in vivo activity than did non-dormant seeds,depending on the period of incubation. Dormant seeds contained less endogenousACC than non-dormant seeds. Thus, ethylene seems to play an essential role inthe release of primary dormancy in A. retroflexus seeds.Ethylene also participates in the release of dormancy achieved by GA₃treatment. The results indicate that both ethylene biosynthesis and action isinvolved in the control of primary dormancy in Amaranthusretroflexus seeds.     

Deep and intermediate complex morphophysiological dormancy in seeds of Ferula gummosa (Apiaceae)

We tested the hypothesis that seeds of the monocarpic perennial Ferula gummosa from the Mediterranean area and central Asia have deep complex morphophysiological dormancy. We determined the water permeability of seeds, embryo morphology, temperature requirements for embryo growth and seed germination and responses of seeds to warm and cold stratification and to different concentrations of GA₃. The embryo has differentiated organs, but it is small (underdeveloped) and must grow inside the seed, reaching a critical embryo length, seed length ratio of 0.65–0.7, before the seed can germinate. Seeds required 9 weeks of cold stratification at <10°C for embryo growth, dormancy break and germination to occur. Thus, seeds have morphophysiological dormancy (MPD). Furthermore, GA₃ improved the germination percentage and rate at 5°C and promoted 20 and 5% germination of seeds incubated at 15 and 20°C, respectively. Thus, about 20% of the seeds had intermediate complex MPD. For the other seeds in the seed lot, cold stratification (5°C) was the only requirement for dormancy break and germination and GA₃ could not substitute for cold stratification. Thus, about 80% of the seeds had deep complex MPD.     

Effects of incubation temperature on the energetics of embryonic development and hatchling morphology in the Brisbane river turtle Emydura signata

Incubation temperature and the amount of water taken up by eggs from the substrate during incubation affects hatchling size and morphology in many oviparous reptiles. The Brisbane river turtle Emydura signata lays hard-shelled eggs and hatchling mass was unaffected by the amount of water gained or lost during incubation. Constant temperature incubation of eggs at 24 °C, 26 °C, 28 °C and 31 °C had no effect on hatchling mass, yolk-free hatchling mass, residual yolk mass, carapace length, carapace width, plastron length or plastron width. However, hatchlings incubated at 26 °C and 28 °C had wider heads than hatchlings incubated at 24 °C and 31 °C. Incubation period varied inversely with incubation temperature, while the rate of increase in oxygen consumption during the first part of incubation and the peak rate of oxygen consumption varied directly with incubation temperature. The total amount of oxygen consumed during development and hatchling production cost was significantly greater at 24 °C than at 26 °C, 28 °C and 31 °C. Hatchling mass and dimensions and total embryonic energy expenditure was directly proportional to initial egg mass. Accepted: 18 March 1998     

Seed Dormancy and Germination Responses of Nine Australian Fire Ephemerals

Fire ephemerals are short-lived plants with seeds that persist in the soil and germinate after a fire or physical soil disturbance. Ex situ germination of many Australian fire ephemerals has previously been difficult. Dormancy was present in most of the nine fire ephemerals examined. Alyogyne hakeifolia (Giord.) Alef. and Alyogyne huegelii (Endl.) Fryxell (Malvaceae) seeds had physical and possibly also physiological dormancy, Actinotus leucocephalus Benth. (Apiaceae) seeds had morphophysiological dormancy, Austrostipa compressa (R.Br.) S.W.L. Jacobs & J. Everett and Austrostipa macalpinei (Reader) S.W.L. Jacobs & J. Everett (Poaceae) seeds were either non-dormant or possessed physiological dormancy, and seeds of all remaining species possessed physiological dormancy. A proportion of the Alyogyne hakeifolia, Alyogyne huegelii, Austrostipa compressa and Austrostipa macalpinei seed populations were non-dormant because some seeds could germinate at the various incubation temperatures without further treatment. At 20 °C, artificial methods of inducing germination such as manual or acid scarification were among the optimal treatments for Austrostipa compressa, Austrostipa macalpinei, Alyogyne huegelii, Actinotus leucocephalus and Grevillea scapigera A.S. George (Proteaceae), and gibberellic acid induced maximum germination of Tersonia cyathiflora (Fenzl) J.W. Green (Gyrostemonaceae) seeds. Heat (70 °C for 1 h) and smoke water was one of the most effective treatments for germinating Actinotus leucocephalus and Codonocarpus cotinifolius (Desf.) F. Muell. (Gyrostemonaceae) seeds. Germination of Grevillea scapigera, Codonocarpus cotinifolius, Gyrostemon racemiger H. Walter (Gyrostemonaceae) and Tersonia cyathiflora did not exceed 40% and may require other treatments to overcome dormancy. Although the nine fire ephemerals examined require fire to germinate under natural conditions, a range of germination responses and dormancy types was observed.     

Nondeep simple morphophysiological dormancy in seeds of Ilex maximowicziana from northern (subtropical) and southern (tropical) Taiwan

In this study, we show that seeds of Ilex maximowicziana collected from northern and southern Taiwan differ in germination responses to temperature. Seeds produced by plants growing in the tropical environment of southern Taiwan were more responsive (in a positive way) to higher incubation temperatures than those produced by plants growing in the subtropical environment of northern Taiwan. On the other hand, seeds produced in northern Taiwan were more responsive (in a positive way) to low incubation temperatures and to cold stratification than those from southern Taiwan. Germination percentages and rates of seeds from northern Taiwan were higher at 20/10°C than at 30/20°C, reaching a plateau of >80% germination after 12 weeks incubation, whereas germination of seeds from southern Taiwan reached >80% at 30/20 and 25°C but not at 20/10°C. Gibberellic acid (GA₃) increased germination rate but not germination percentage of seeds from both southern and northern Taiwan. Freshly matured seeds of I. maximowicziana have rudimentary embryos. During dormancy break, embryo length increased 11.5- and 8.0-fold in northern and southern seeds, respectively, before radicle emergence. Thus, seeds of Ilex maximowicziana have nondeep simple morphophysiological dormancy. This is the first detailed study of the germination requirements of a subtropical/tropical species of the large cosmopolitan genus Ilex.     

Ecological genetics of seed germination regulation in Bromus tectorum L.

Regulation of seed germination phenology is an important aspect of the life history strategy of invading annual plant species. In the obligately selfing winter annual grass Bromus tectorum, seeds are at least conditionally dormant at dispersal in early summer and lose dormancy through dry-afterripening. Patterns of germination response at dispersal vary among populations and sometimes across years within populations. To assess the relative contribution of genotype and maturation environment to this variation, we grew progeny of ten parental lines from each of six contrasting populations in a common greenhouse environment. We then tested the germination responses of recently harvested seeds of the putative full-sib progeny at five incubation temperatures. Significant germination response differences among populations were observed in greenhouse cultivation, and major differences among full-sib families were evident for some populations and traits. Among-population variation accounted for over 90% of the variance in each trait, while within-family variance accounted for 1% or less. Germination responses of greenhouse-grown progeny were positively correlated with the responses of wild-collected seeds, but there was a tendency for lowered dormancy at higher incubation temperatures. This tendency was more marked in populations from cold desert, foothill, and plains habitats, suggesting a genotype-maturation environment interaction. Differences among populations in the amount of among-family variance were more evident at lower incubation temperatures, while among-family variance was more uniformly low at summer incubation temperatures. Populations from predictable extreme environments (subalpine meadow and warm desert margin) showed significantly less variation among families than populations from less predictable cold desert, foothill, and plains environments. Low among-family variance was not specifically associated with small population size or marginality of habitat, as small marginal populations from unpredictable environments showed variance as high as that of large populations. In populations with high among-family variance for germination traits, germination responses tended to be correlated across incubation temperatures, making it possible to characterize families in terms of their general dormancy status. The results indicate that seed germination regulation in this species is probably under strong genetic control, and that habitats with temporally varying selection are occupied by populations that tend to be more polymorphic in terms of their germination response patterns. Received: 19 May 1998 / Accepted: 27 January 1999     

Triacylglycerol phase and ‘intermediate’ seed storage physiology: a study of Cuphea carthagenensis

Seeds with ‘intermediate’ storage physiology store poorly under cold and dry conditions. We tested whether the poor shelf life can be attributed to triacylglycerol phase changes using Cuphea carthagenensis (Jacq.) seeds. Viability remained high when seeds were stored at 25°C, but was lost quickly when seeds were stored at 5°C. Deterioration was fastest in seeds with high (≥0.10 g g⁻¹) and low (0.01 g g⁻¹) water contents (g H₂O g dry mass⁻¹), and slowest in seeds containing 0.04 g g⁻¹. A 45°C treatment before imbibition restored germination of dry seeds by melting crystallized triacylglycerols. Here, we show that the rate of deterioration in C. carthagenensis seeds stored at 5°C correlated with the rate that triacylglycerols crystallized within the seeds. Lipid crystallization, measured using differential scanning calorimetry, occurred at 6°C for this species and was fastest for seeds stored at 5°C that had high and very low water contents, and slowest for seeds containing 0.04 g g⁻¹. Germination decreased to 50% (P50) when between 16 and 38% of the triacylglycerols crystallized; complete crystallization took from 10 to over 200 days depending on water content. Our results demonstrate interactions between water and triacylglycerols in seeds: (1) water content affects the propensity of triacylglycerols to crystallize and (2) hydration of seed containing crystallized triacylglycerols is lethal. We suggest that these interactions form the basis of the syndrome of damage experienced when seeds with intermediate storage physiologies are placed in long-term storage.     

How incubation temperature influences the physiology and growth of embryonic lizards

Eggs of two small Australian lizards, Lampropholis guichenoti and Bassiana duperreyi, were incubated to hatching at 25 °C and 30 °C. Incubation periods were significantly longer at 25 °C in both species, and temperature had a greater effect on the incubation period of B. duperreyi (41.0 days at 25 °C; 23.1 days at 30 °C) than L. guichenoti (40.1 days at 25 °C; 27.7 days at 30 °C). Patterns of oxygen consumption were similar in both species at both temperatures, being sigmoidal in shape with a fall in the rate of oxygen consumption just prior to hatching. The higher incubation temperature resulted in higher peak and higher pre-hatch rates of oxygen consumption in both species. Total amount of oxygen consumed during incubation was independent of temperature in B. duperreyi, in which approximately 50 ml oxygen was consumed at both temperatures, but eggs of L. guichenoti incubated at 30 °C consumed significantly more (32.6 ml) than eggs incubated at 25 °C (28.5 ml). Hatchling mass was unaffected by either incubation temperature or the amount of water absorbed by eggs during incubation in both species. The energetic production cost of hatchling B. duperreyi (3.52 kJ · g⁻¹) was independent of incubation temperature, whereas in L. guichenoti the production cost was greater at 30 °C (4.00 kJ · g⁻¹) than at 25 °C (3.47 kJ · g⁻¹). Snout-vent lengths and mass of hatchlings were unaffected by incubation temperature in both species, but hatchling B. duperreyi incubated at 30 °C had longer tails (29.3 mm) than those from eggs incubated at 25 °C (26.2 mm). These results indicate that incubation temperature can affect the quality of hatchling lizards in terms of embryonic energy consumption and hatchling morphology. Accepted: 27 January 2000