The effect of excess moisture on the germination of Spinacia oleracea L.

Summary The reversible inhibition of the germination of spinach (Spinacia oleracea L.) seeds in conditions which are even slightly wetter than optimal has been traced to the production, in a wet environment, of a layer of mucilage around and within the fruit coat which surrounds the true seed. Such wet seeds may however germinate readily when the temperature is lowered, or the oxygen pressure of the environment is raised, or the intact seeds are placed for a short time in hydrogen peroxide before being transferred to what normally would be an excess of water. Even in the absence of an increased oxygen supply the seeds will germinate under water provided the fruit coat, or even a small part of it where it covers the radicle, is crefully removed. No evidence has been found of a water soluble inhibitor and the findings are consistent with the hypothesis that germination is dependent on a sufficiently high rate of supply of oxygen to the sites embryonic respiration. The mucilage which is formed under wet conditions forms a barrier which prevents the transfer of oxygen to the embryo by gaseous diffusion or aqueous convection currents and restricts it to the process of aqueous diffusion, and under these conditions the rate of oxygen supply may not reach the threshold level required for germination.     

Alleviation by Gibberellic Acid and Kinetin of the Inhibition of Seed Germination in Maize (Zea mays L.) under Submerged Conditions

Under submerged conditions the germination of maize seeds isinhibited. Under normal conditions, i.e. on moist filter paper,more than 80 per cent of the seeds can germinate whereas lessthan 24 per cent of the seeds germinate under submerged conditions.The inhibition of germination under submerged conditions canbe fully overcome by the application of an appropriate concentrationof GA₂, and KN. The possible role of these hormones in overcomingthe inhibition of seed germination under an oxygen deficit dueto waterlogging is discussed. Zea mays L, maize, gibberellic acid, kinetin, germination     

The Role of Germination Inhibitors and Oxygen in the Dormancy of the Light-densitive Seed of Betula spp.

Although unchilled, intact seeds of Betula pubescens and B.verrucosa require light for germination, isolated embryos germinateequally well in both light and darkness. An aqueous extract of these seeds has germination-inhibitoryproperties correlated with the presence of a non-fluorescent,single substance. The light requirement of isolated embryosis restored by the inhibitor. When intact seeds are leachedwith water to remove some inhibitor, it is found that the lightrequirement is reduced, short days and single light periodsthen eliciting greater germination than in unleached seeds. It has been found that scratching, pricking, and cutting theseed coat increases the germination of intact seeds in darkness,and that this is probably due to enhanced oxygen entry. Further,it has been found that germination in short days is increasedin oxygen-enriched atmospheres. It has been found that although the inhibitory effect of theseed coat in intact seeds is partially due to the reductionof the oxygen supply to the embryo, a low oxygen concentrationdoes not prevent germination of isolated embryos. Experimentalresults suggest that the inhibitor in the seed coat increasesthe oxygen requirement of the embryo.     

Contrasted Effects of CO2 on the Regulation of Dormancy and Germination in Xanthium pennsylvanicum and Setaria faberi Seeds

The effects of CO₂ on dormancy and germination were examinedusing seeds of cocklebur (Xanthium pennsylvanicum Wallr.) andgiant foxtail (Setaria faberi Herrm.). The rate of germinationof the giant foxtail seeds as well as cocklebur was promotedby exogenously applied CO₂ at a concentration of 30 mmol mol^-1regardless of the sowing conditions. However, seeds which failedto germinate in the presence of CO₂, entered a secondary phaseof dormancy under unfavourable germination conditions. If CO₂was applied to seeds under conditions such as water stress imposedwith a 200 mol m^-3 mannitol solution, a hypoxic atmosphere of100 mmol mol^-1 O₂ or a treatment of 0·1 mol m^-3 ABA,development of secondary dormancy was accelerated. These contrastedeffects of CO₂ were observed in ecological studies. Under naturalfield conditions germination of buried giant foxtail seeds respondedpositively to CO₂ during a period of release from primary dormancyfrom Feb. to May, but CO₂ accelerated secondary dormancy commencingin early Jun. In other words, in the presence of CO₂, both theenvironmental conditions and the germination states of the seedsclearly showed secondary dormancy-inducing effects. Thus, itseems that CO₂ has contrasted effects on regulation of dormancyand germination of seeds depending on the germination conditions.Copyright1995, 1999 Academic Press Xanthium pennsylvanicum, cocklebur, Setaria faberi, giant foxtail, CO₂, water stress, hypoxia, ABA, germination, secondary dormancy     

PHYSIOLOGY OF LIGHT-REQUIRING GERMINATION IN ERAGROSTIS SEEDS

The photorequirement for the germination of Eragrostis seedsdecreases with the progress of their after-ripening, and thegermination occurs whether in continuous light or in darknessat the final stage of after-ripening. The dehydration of seedsor the puncturing of seed coats also results in a decrease ofphotorequirement for germination. The rate of water absorptionof seeds increases with the germination capacity under continuousdark condition. However, there is no correlation between therespiration rate and the germination capacity; respiration isstimulated in the punctured seeds, but not in the after-ripenedseeds. The after-ripened or punctured seeds which no longer have aphotorequirement become light-sensitive again, when they areallowed to germinate in the air of low oxygen concentrations.The assumption is presented that the permeability to oxygenof the seed coat may be a factor controlling the seed germinationof this species. (Received August 21, 1964; )     

Influence of Salinity and Temperature on the Germination of Haloxylon recurvum Bunge ex. Boiss.

The stem succulent perennial halophyteHaloxylon recurvum Bungeex. Boiss. grows and produces seed under highly saline conditionsand seeds are deposited in saline soils. Experiments were conductedto determine the effect of salinity and temperature on the germinationof seeds. Results indicate that seeds can germinate at veryhigh salt concentrations (500 mM). However, highest germinationpercentages were obtained in distilled water. Cooler thermoperiodspromoted germination, while high temperatures significantlyinhibited the germination of seeds at all NaCl concentrationstested. Rate of germination decreased with increases in salinity.At higher thermoperiods the rate of germination was significantlylower in comparison to lower thermoperiods. Seeds recover afterbeing transferred to distilled water and recovery was higherfrom higher salinity concentrations and lower thermoperiods.Final recovery germination percentages in high salt treatmentswere significantly lower than non-saline controls, indicatingthat exposure to high concentration of NaCl permanently inhibitedgermination. Germination; halophyte; Haloxylon recurvum recovery of germination; salinity; temperature     

Germination Rate of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] Seeds Affected by Their Orientation

Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seeds developwith the adaxial surface continuous with the cone scale. Onseparation, the scale side of the seed is lighter coloured andflatter than the side not previously in contact with the scale.Seeds oriented scale-side-up on a moist surface germinate morerapidly than seeds placed scale-side-down. When seeds were germinatedunder laboratory conditions, the response to orientation variedamong seeds of different geographic origin. Most of the geographicvariation in germination rate occurred when seeds were orientedscale-side-up. Pseudotsuga menziesii (Mirb.) Franco, Douglas-fir germination, orientation of seeds     

Some Aspects of the Reproductive Biology of Limonium vulgare Mill., and Limonium humile Mill.

The germination of two species of salt-marsh plants Limoniumvulgare Mill., and L. humile Mill., is investigated in relationto their ecology. Germination is inhibited by sea water, butgermination even in fresh water is low. Inhibition of germinationby sea water is negatively correlated with water uptake. However,a treatment in sea water stimulates subsequent germination infresh water. The effect of the sea-water treatment appears tobe one of osmotic shock which weakens the seed coat. Variationin response to the treatment is partly genetical and partlyenvironmental. Seeds in different parts of the salt-marsh willbe subject to differing conditions, both during seed developmentand during the interval between seed maturation and seed dispersal.In connection with this the effect of leaching by sea waterand fresh water is considered. The response to a sea-water treatmentvaries with time. Considered in the long term it shows somecyclical variation which might correspond with the tidal cycle.It is shown that seeds of Limonium can survive long periodsin sea water. There is a slow rate of germination during immersion.Most of those seeds which do not germinate in sea water surviveto germinate rapidly in fresh water. The response to oxygenconcentration, light, and temperature is also investigated.Experiments on seedling growth and establishment show the needfor fresh water and a suitable substrate. Mud gives a lowergermination but a higher survival, while sand gives a highergermination but a lower survival. The dispersal of Limoniumseeds in nature is investigated. Seeds of Limonium are mostabundant in the drift line, but even these only represent asmall fraction of the total produced. It is considered thatreproduction by seed is only important when a new area is beinginvaded. Subsequent reproduction is largely by vegetative spread.The ecological implications of the germination experiments arediscussed.     

The Effects of Ethanol on the Germination of Seeds of Japonica and Indica Rice (Oryza sativa L.) under Anaerobic and Aerobic Conditions

An examination was made of the effects of ethanol at 0.2–6.0%(v/v) on the germination, under aerobic conditions, of intactand dehusked seeds of indica rice (cv. Assam IV), which hadbeen harvested 14, 21 and 28 d after anthesis, and of the japonicarice (cv. Sasanishiki), which had been harvested 30 and 60 dafter anthesis. The inhibition of germination caused by dehuskingjaponica rice was overcome by 0.5–5% ethanol, with maximumgermination (frequently 100%) achieved at 3–5% (30 d afteranthesis) or 1–4.5% (60 d after anthesis) ethanol. Furtherincreases in the ethanol concentration reduced germination.The germination of dehusked indica rice was slightly inhibitedat 0.5 and 1% ethanol, whilst the promotion of germination by2% ethanol increased as the seeds matured. At all harvests germinationwas greatest at 3% ethanol, and at 5–6% ethanol germinationfell to 0%. Inhibition, no effect, or minimal stimulation ofthe germination of intact seeds of both japonica and indicarice by ethanol was observed at the concentrations examined.The absence of oxygen stimulated germination of dehusked japonicarice, but this germination was inhibited by ethanol. In contrastethanol had little or no effect on the failure of dehusked indicaseeds to germinate in anaerobic conditions. Thus ethanol treatmentmay help break the strong dormancy of dehusked seeds of indicaand japonica rice. The possible role of ethanol in stimulatinggermination in rice is discussed. Rice; Oryza sativa L.; seed germination; dehusking treatment; ethanol; indica; japonica; oxygen; dormancy; germination inhibition; seed formation     

Seed Dormancy in Acer pseudoplatanus L.: the Role of the Covering Structures

The present studies with Acer pseudoplatanus L. suggest thatthe covering structures play an important and multiple rolein the dormancy of the fruit. Whole fruits and seeds with thetesta intact required a period of chilling at 5 °C beforedormancy was broken whereas bare embryos germinated immediatelyat 20 °C without pretreatment. This suggested that dormancywas coat-imposed and that the testa was responsible for thiseffect. Germination of dormant seeds was inhibited by lightwhereas the non-dormant bare embryos showed little response.Studies on the manner in which the testa imposed dormancy onthe embryo indicated that restriction on oxygen uptake, wateruptake, mechanical restriction to embryo enlargement, and thepresence of germination inhibitors in the testa were not limitingfactors at this stage of dormancy. Results from leaching experimentssuggest that dormancy was the result of the restriction by thetesta of the outward diffusion of a germination inhibitor(s)present in the embryo. In seeds that had nearly completed theirstratification requirements, the covering structures seemedto act in a manner other than by preventing the leaching ofan inhibitor from the embryo. At this point the physical propertiesof the covering structures seem to determine any further delaysin germination by the mechanical restriction of embryo enlargementby the testa and by restriction of oxygen uptake by the pericarp.     

Seed Germination and Seedling Development in Cyclamen persicum

Cyclamen persicum Mill, seeds germinate in a narrow range oftemperature and germination is strongly inhibited by continuousirradiation with white light. The thermal optimum is approx.15 °C in both darkness and light. Seed germination is alsovery sensitive to oxygen deprivation and this sensitivity ismore pronounced at 20 °C than at the optimum 15 °C.Very immature seeds cannot germinate at any temperature, butgerminability increases during seed maturation Seedling development is unusual since seed reserves are usedimmediately for tuber formation. Tuberization is optimal at15–20 °C in light and in darkness. Supra-optimal temperatures(25–30 °C) or hypoxia inhibit tuber formation andlead to very elongated tubers These results allow the producers to improve the productionof homogeneous populations of cyclamen seedlings Wheat seeds, Triticum aestwum L., acetylcholinesterase, electrophoresis, germination, assay     

Effect of high temperature on moisture loss,imbibition and germination in the seeds ofTrianthema Crystallina Vahl. and its distribution

Summary The germination behaviour of the seeds ofT. crystallina in relation to its frequent distribution in arid and semi-arid belt of Rajasthan has been investigated. In nature, the seed germination in this weed is definitely effected and to some extent controlled by certain features like light, environmental temperature fluctuations, germination temperature and seed age, and their complex effect seems to be responsible for the complex germination behaviour, and also for the common occurrence and distribution of this species in arid and semi-arid areas of low rainfall in Rajasthan and also in the dry habitats of Australia, Arabia and West Pakistan. The seeds possess endogenous seed coat inhibitor which is removed by washing with running water. Germination is also inhibited by total light and dark conditions, but for the diffused light. Constant low (10 °C) and high temperatures (40 °C and above) have also more or less deleterious effect on germination. However, if the seeds are given some intermittent treatment like low temperature (10 °C) or dilute acid (1%) before germination, they show better germination at slightly higher (35 or 40 °C) temperatures (64% and 40.3% respectively). The older seeds show a quick and higher germination percentage (89.6%) while fresh ones show a sufficiently poor percentage (36.3%) when both were germinated under uniform conditions of temperature (35 °C) and germination duration (96 hours). This is due to a slower moisture depletion and higher as well as faster water imbibition capability of old seeds than the fresh ones under identical treatments and conditions. Thus, the older seeds can retain more moisture for long than fresh seeds at all higher temperatures as the old seeds lose moisture slower than the fresh ones (87.2% and 91.6% respectively) when kept for drying under uniform conditions. The increase in water absorption after imbibition is faster in old seeds (48.4%) as compared to fresh ones (24.3%) and that the former which germinate faster, absorb two times more water than the latter when both are put for imbibition under similar conditions of temperature and duration.     

Ethylene, Nitrate and Nitrite Interactions in the Promotion of Dark Germination of Common Purslane Seeds

Ethylene (10 µ1^–1) caused about one-third of highlydark-dormant seeds of common purslane (Portulaca oleracea L.)to germinate in the dark. Attempts were made to increase germinationin the dark with nitrate and ethylene combinations. When applieddirectly to the seeds, KNO₃ did not stimulate germination andKNO₃ plus ethylene did not increase germination above that ofethylene alone. Pre-incubation of seeds in KNO₃ for 4 to 7 dbefore the ethylene applications significantly increased germination.The effects of the KNO₃ pre-incubation were additive at eachof four ethylene concentrations (0.1–100 µ11^–1).Potassium nitrate was effective only when ethylene followedthe KNO₃ pre-incubation period. Potassium nitrite stimulatedabout 25 per cent of the seeds to germinate without a pre-incubationperiod and without ethylene. Also, ethylene plus KNO₂ enhancedgermination above that achieved by either stimulus alone. Silvernitrate did not block the ethylene promotion of germination,but reversed the typical ethylene inhibition of seedling growthfollowing germination. The results support the views that nitrateexerted its effect via conversion to nitrite within the seedand that the rate of nitrate conversion may be a limiting factorin the dark germination of common purslane seeds. Ethylene mayfacilitate nitrite activity by increasing seed sensitivity tothe stimulus. Common purslane, Portulaca oleracea L., ethylene, nitrate, nitrite, germination, dormancy     

Further Studies on Glucose Catabolism in the Early Phases of Germination of Phaseolus mungo Seeds

In the early stage of germination of Phaseolus mungo seeds,oxygen uptake was little inhibited by iodoacetate and sodiumfluoride, yet carbon dioxide output was strongly inhibited.The inhibitors also decreased alcohol formation severely inthis stage. It was shown that NaF attacked its target (enolase)and curtailed the glycolytic activity. On the basis of theseresults, a mechanism for the insensitivity of oxygen uptakeis proposed.     

Effects of bird ingestion on seed germination of Sorbus commixta

To determine the effects of ingestion by birds on seed germination, we performed germination experiments in the field and laboratory with Sorbus commixta. The germination of four groups of seeds was compared: ingested seeds, seeds defecated in feces after feeding of fruits to birds; extracted seeds, seeds deliberately extracted from the fruit pulp; juiced seeds, seeds plus the juice of the pulp after seeds had been deliberately extracted from the pulp; intact seeds, seeds in untreated intact fruits. In the laboratory, intact and juiced seeds hardly germinated, but ingested and extracted seeds germinated. Thus, the pulp and its juice appeared to inhibit germination, but seeds could germinate without ingestion by birds once the seeds had been manually extracted from the pulp. In the field, intact fruits did not germinate in the first spring, because the seed was still covered with pulp. The pulp of intact seeds decomposed during the first summer, and thus, the seeds had the potential to germinate during the second spring. In fact, most intact seeds do not germinate during the second spring either, since they lose their viability during the first summer. Thus, under natural conditions, most seeds of Sorbus commixta cannot germinate without bird ingestion. Received: 5 July 1997 / Accepted: 7 November 1997     

Germination of Geonoma brevispatha (Arecaceae) in laboratory and its relation to the palm spatial distribution in a swamp forest

Geonoma brevispatha is a clonal palm species commonly found as tussocks in swamp and riparian forests in SE Brazil, occurring in the very transition between flooded pits/channels and dry mounds. Aiming to verify whether the germination responses could explain the spatial pattern of the palm tussocks in swamp forests, we investigated the germination in relation to the main environmental factors to which the seeds are subjected in their natural habitat. The seeds are recalcitrant since germination percentage is reduced with loss of moisture content. Germination did not differ on moist filter paper, semi-immersion (water up to half of the seed diameter) or complete immersion (water up to double of the seed diameter). Seeds did not germinate when stored in a closed bottle with water (that is, under low oxygen concentration), but remained viable for up to 8 weeks under this condition. The capacity to germinate in water with minimum oxygen availability may be considered ecologically advantageous in a swamp habitat. On the other hand, the capacity to germinate in moist filter paper indicates that, in natural conditions, the seed can germinate, provided there is a critical minimum of water availability. We concluded that the germination responses per se are not enough to explain the palm tussocks spatial pattern, but they are very well tuned with the conditions of the transitional zone between channels/pits (ever flooded micro-sites) and mounds (well-drained micro-sites), in which the species occurs in the swamp forest.     

Comparative germination ecology of two altitudinal vicariant Saxifraga species endemic to the north of Spain

Seeds of high‐mountain species are thought to germinate rapidly, synchronously and at high percentages after a cold period, with limited dependence on the external environment; yet, empirical evidence only partially supports this behaviour. We performed a comparative study of the germination response of two closely related taxa along an altitude gradient in northern Spain. Seeds from several maternal families of six populations of Saxifraga trifurcata (lowland species) and S. canaliculata (highland species) were subjected to temperature and stratification treatments. Germination percentages and germination rates were analysed using generalised linear mixed modelling and accelerated failure‐time modelling. We found that germination percentages and germination rates were high and dependent on incubation temperature in both species. Within species, seeds from higher altitudes had higher germination percentages under all conditions. Cold–wet stratification negatively affected germination success, particularly in the lowland species. Overall, the highland species was less responsive to the experimental treatments and showed more synchronous germination patterns. We conclude that seeds from these two Saxifraga species germinate as efficiently as species from other habitats, but have a narrower germination response, probably due to the stronger selective pressures in their harsh environments. Finally, a cold, wet stratification period is not a prerequisite for the germination of high‐mountain S. canaliculata, and its strong negative effect on the germination of its lowland relative S. trifurcata may contribute to the altitudinal segregation of these two species.     

Effects of temperature and light on germination and early seedling development of the pine pink orchid (Bletia purpurea)

Orchid seed physiology is a poorly understood phenomenon owing to an emphasis on production and the challenges associated with propagating orchids from minute seed. We investigated the role of simulated south Florida temperatures and illumination (dark and 12 h photoperiod) in regulating germination and seedling development using asymbiotic seed germination assays of Bletia purpurea. Our objectives were to determine whether in situ germination is limited by seasonal temperatures and to determine whether temperature alters responses to illumination. Bletia purpurea seeds were able to germinate to > 90% under all treatments. The greatest germination after 3 weeks was observed at 29/19°C under continual darkness and at 25°C under dark and illuminated conditions. The slowest germination was observed at simulated winter temperatures (22/11°C). Illumination initially inhibited germination and development, but resulted in equal or greater development by week six. Germination under 22/11°C was strongly inhibited by illumination, indicating an interaction between temperature and light sensing systems.     

The Effects of Kinetin and Gibberellin on the Germination of Dehusked Seeds of Indica and Japonica Rice (Oryza sativaL.) under Anaerobic and Aerobic Conditions

The effects of kinetin and gibberellin were examined under anaerobicconditions (0% oxygen) and aerobic conditions (20% oxygen) onthe germination of dehusked seeds of indica and japonica ricecultivars that had been harvested at different times duringthe formation of seeds. Surjamkhi was used as a representativeof deep dormant indica cultivars and Assam IV as a less dormantindica cultivar. Sasanishiki was used as the japonica rice cultivar.Both phytohormones were applied at a concentration of 10^-3Mwhichproved to have the greatest stimulatory effect in preliminarywork at concentrations of 10^-3–10^-5M. Under aerobic conditions,inhibition of germination by dehusking of Sasanishiki seedsthat had been harvested either 30 or 60 d after anthesis wasovercome by kinetin and all seeds germinated. Complete germinationinduced by kinetin under aerobic conditions was also achievedwith the dehusked seeds of the indica rice cultivar Assam IVthat had been harvested on two occasions and of Surjamkhi thathad been harvested 28 d after anthesis. In contrast, germinationof dehusked japonica seeds stimulated by anaerobiosis was inhibitedby kinetin. The stimulatory effects of gibberellin on the germinationof indica and japonica rice seeds were observed under aerobicand anaerobic conditions. Under anaerobic conditions, the responsesof dehusked indica and japonica rice seeds to kinetin and gibberellindiffered, being negative with kinetin and positive with gibberellin.Under aerobic conditions, the stimulatory effects of kinetinon germination of dehusked seeds were greater than those ofgibberellin. Thus, treatment with kinetin appears to be usefulfor breaking the considerable dormancy commonly observed inthe dehusked seeds of indica rice. Mechanisms are proposed toexplain the stimulatory effects of these phytohormones on thegermination of dehusked seeds of indica and japonica rice underaerobic and anaerobic conditions. Rice; Oryza sativaL.; seed germination; dehusking treatment; gibberellin; indica; japonica; kinetin; oxygen; dormancy; germination inhibition; seed formation     

Germination strategies of halophyte seeds under salinity

Halophytes are plants of saline habitats that grow under conditions that may vary in extremes of temperatures (freezing to very hot), water availability (drought to water logging) and salinity (mild to almost saturation). Halophytes may also face sudden micro-environmental variations within their habitats. In this review we examine some of the factors that determine the ability of seeds of halophytes to germinate when conditions are optimal for seedling growth and survival.Seed dormancy (innate, induced or acquired) is an important means of initiating growth under appropriate conditions. Saline environments are often wet and so the seeds of halophytes may remain un-germinated over extended periods even after imbibition if the external environment does not favour germination and seedling survival. Many perennial halophytes, however, do not possess elaborate dormancy systems because they propagate largely through ramets and have no ecological compulsions for seed germination.The seeds of halophytes also have the capacity to recover from a salinity shock and start germination once salinity is reduced, which may happen following rain. In some cases, imbibition in a low-salt solution may help in osmo-priming and improve germination. Seed heteromorphism is yet another strategy adopted by some halophytes, whereby seeds of different size and colour are produced that germinate consecutively at suitable intervals. Light-dependent germination may also help if the seed is under a dense canopy or buried in debris; germination only occurs once these restraints are removed thus increasing the chances of seedling survival.