The Influence of Temperature on Seed Germination Rate in Grain Legumes: II. INTRASPECIFIC VARIATION IN CHICKPEA (Cicer arietinum L.) AT CONSTANT TEMPERATURES

Positive linear relationships were shown between constant temperaturesand the rates of progress of germination to different percentiles,G, for single populations of each of five genotypes of chickpea(Cicer anetinum L.). The base temperature, T_b, at which therate of germination is zero, was 0·0°C for all germinationpercentiles of all genotypes. The optimum temperature, T_o(G),at which rate of germination is most rapid, varied between thefive genotypes and also between percentiles within at leastone population. Over the sub-optimal temperature range, i.e.from T_b to T_o(G), the distribution of thermal times within eachpopulation was normal. Consequently a single equation was appliedto describe the influence of sub-optimal temperatures on rateof germination of all seeds within each population of each genotype.The precision with which optimum temperature, T_b(G), could bedefined varied between populations. In each of three genotypesthere was a negative linear relationship between temperatureabove T_b(G) and rate of germination. For all seeds within anyof these three populations thermal time at supra-optimal temperatureswas constant. Variation in the time taken to germinate at supra-optimaltemperatures was a consequence of normal variation in the ceilingtemperature, T_o(G)—the temperature at or above which rateof progress to germination percentile G is zero. A new approachto defining the response of seed germination rate to temperatureis proposed for use in germplasm screening programmes. In two populations final percentage germination was influencedby temperature. The optimum constant temperature for maximumfinal germination was between 10°C and 15°C in thesepopulations; approximately 15°C cooler than the optimumtemperature for rate of germination. It is suggested that laboratorytests of chickpea germination should be carried out at temperaturesbetween 10°C and 15°C. Key words: Chickpea, seed germination rate, temperature     

A Model of the Effects of a Wide Range of Constant and Alternating Temperatures on Seed Germination of FourOrobanche Species

Seeds of the obligate parasitic plants, Orobanche spp., wereconditioned in water or GA₃for 2 or 12 weeks and then stimulatedto germinate by the synthetic stimulant GR24. Temperature treatmentsduring the germination tests comprised 169 different constantand alternating temperature regimes on a two-dimensional gradientplate. Optimum temperatures for germination of seeds of O. aegyptiacaand O. crenata were 18–21 °C and 18 °C, respectively.However, longer conditioning periods slightly lowered the optimain both species, and the maximum germination percentage wasalso reduced due to an induction of secondary dormancy. At agiven mean temperature, more seeds germinated at constant thanat alternating temperatures. Results were analysed in termsof characteristics of alternating temperatures that appearedto control germination, i.e. mean temperature, maximum temperature,amplitude (difference between daily maximum and minimum temperatures)and thermoperiod (the time spent at the maximum temperatureeach day). Final germination was modelled on the basis of therebeing two prerequisites for germination: a minimum mean temperaturewhich must be exceeded and a maximum temperature above whichthe seed will not germinate. These two requirements were assumedto be independent and to be normally distributed in the seedpopulation so that final germination could be described by amultiplicative probability model. Because of the response tomaximum temperature, inhibitory effects were more evident atalternating temperatures. Amplitude and thermoperiod influencedthis effect of maximum temperature. The implications of thedetrimental effect of alternating temperatures for germinationofOrobanche spp. in the field are discussed. Copyright 1999Annals of Botany Company Orobanche aegyptiaca, O. crenata, O. cernua, O. minor, broomrape, seed germination, temperature, germination model, secondary dormancy.     

Alternating Temperatures and Rate of Seed Germination in Lentil

The effect of alternating temperatures on the times taken byseeds of lentil (Lens culinaris Medikus) to germinate was investigatedusing a two-way temperature-gradient plate. Between 5 and 25°C,warmer temperatures increased the rate of germination. Variationamong the individual seeds in the times required for germinationat different constant temperatures within this range were describedwell by a log-normal distribution of thermal times, accumulatedabove a base temperature of 1·5°C. Even with amplitudesas great as 20°C, no effect of alternation per se on thethermal time required for germination was detected—whetherthe cool temperature was applied for 8 or 16 h d^-1. Similarly,in alternating temperature regimes where the minimum temperatureof the diurnal cycle was between 0°C and the base temperature,the thermal times required for germination (where no thermaltime accrued during the periods when temperature was below T_b)were in close agreement with those values provided by the modeldetermined at warmer constant temperatures. However, where theminimum temperature applied was < 0°C the germinationof all but the earliest germinators was delayed beyond modelpredictions, and more so where the sub-zero minimum temperaturewas applied for 16 rather than 8 h d^-1. The results, therefore,contradict the view that alternation in temperature per se reducesthe thermal time required for seed germination. Rather, rateof germination responds instantaneously to current temperature,but prolonged exposure to sub-zero temperatures can result indamage sufficient to delay germination when seeds are returnedto regimes warmer than the base temperature.Copyright 1994,1999 Academic Press Lens culinaris Medikus, lentil, seed germination, alternating temperatures, thermal time, temperature-gradient plate     

The Effects of Priming and 'Natural' Differences in Quality amongst Onion Seed Lots on the Response of the Rate of Germination to Temperature and the Identification of the Characteristics under Genotypic Control

Ellis, R. H. and Butcher, P. D. 1988. The effects of primingand ‘natural’ differences in quality amongst onionseed lots on the response of the rate of germination to temperatureand the identification of the characteristics under genotypiccontrol —J. exp. Bot. 39: 935–950. A screening procedure was applied to define the response ofthe rate of seed germination to sub-and supra-optimal temperaturesfor different lots or sub-lots of two onion (Allium cepa L.)cultivars.Three sub-lots of the cultivar White Lisbon were derived froma control lot by osmotic priming (–1.4 MPa, 20 °C.7 d) alone, by priming and drying and by priming, drying andsubsequently storing the seeds for 7 weeks at 2–5 °C.The major effect of priming was to reduce the thermal time forgermination at both sub- and supra-optimal temperatures. Primingalone also altered the distribution of thermal times at sub-optimaltemperatures. A new equation is presented to describe this variation.In contrast, priming had no consistent effect on base temperature(T_b and little effect on the distribution of ceiling temperatures[T_e(G)]. For the control lot of White Lisbon T_b was 4°C,whilst the best common estimate of T_b for all four sub-lotswas 3.5°C. The mean estimate of T_c(50) for the control,primed and primed and dried sub-lots was 35.5°C.Comparisonof three lots of the cultivar Senshyu Semi Globe Yellow of widely-differingviability showed substantial differences in the thermal timefor germination at sub-optimal temperatures, but no significantdifferences in T_b (P>0.10), the common estimate being 4°C.There was a significant negative correlation between probitpercentage viability and the logarithm of the thermal time for50% germination at sub-optimal temperatures amongst the threelots (P<0.05). The work suggests that base temperature forgermination is a genotypic characteristic which is unaffectedby differences in seed quality. It also shows that the effectof priming, quantified as a reduction in thermal time requirementsfor germination, varies amongst the seeds within a lot. Key words: -Onion, seed germination rate, temperature, priming     

Effects of Temperature and Water Potential on Germination, Radicle Elongation and Emergence of Mungbean

Controlled environment experiments were performed to determinethe effects of temperature and water potential on germination,radicle elongation and emergence of mungbean (Vigna radiata(L.) Wilczek cv. IPB-M79-17-79). The effects of a range of constant temperatures (15–45°C) and water potentials (0 to –2.2 MPa) on germinationand radicle elongation rates were studied using an osmoticumtechnique, in which seeds were held against a semi-permeablemembrane sac containing a polyethylene glycol solution. Linearrelationships were established between median germination time(Gt₅₀) and water potential at different temperatures, and betweenreciprocal Gt₅₀ (germination rate) and temperature at differentwater potentials. Germination occurred at potentials as lowas –2.2 MPa at favourable temperatures (30–40 °C),but was fastest at 40 °C when water was not limiting, withan estimated base temperature (T_b) of about 10 °C. Subsequentradicle elongation, however, was restricted to a slightly narrowertemperature range and was fastest at 35 °C. The conceptof thermal time was used to develop an equation to model thecombined effects of water potential and temperature on germination.Predictions made using this model were compared with the actualgermination obtained in a related series of experiments in columnsof soil. Some differences observed suggested the additionalimportance of the seed/soil/water contact zone in influencingseed germination in soil. Seedling emergence appeared to reflectfurther the radicle elongation results by occurring within anarrower range of temperatures and water potentials than germination.Emergence had an estimated T_b of 12.6 °C and was fastestat 35 °C. A soil matric potential of not less than about–0.5 MPa at sowing was required to obtain 50% or moreseedling emergence. Key words: Germination, temperature, water potential     

Seed Viability Constants for Lettuce

Seeds of two lettuce cultivars (Lactuca sativa L., cv. Meikoninginand cv. Grand Rapids) were hermetically stored with constantmoisture contents ranging between 3.6 and 17.9 per cent (freshweight basis) at constant temperatures ranging between 5 and75 °C. The decline with time in percentage germination andpercentage normal seedlings was determined for each storagetreatment. The data were fitted to an equation which containsthe constants: K₁, the probit of the initial percentage germinationor normal seedlings; K_E, a species constant; C_W, the constantof a logarithmic moisture term; C_H, the constant of a lineartemperature term and C_Q, the constant of a quadratic temperatureterm. Regression analysis of data from storage periods up to5.5 years at temperatures of 5–75 °C and seed moisturecontents of 3.6–13.6 per cent yielded the following values:K_E= 8.218, C_W=4.797±0.163, C_H=0.0489±0.0050 andC_Q=0.000365±0.000056. Although this equation consistentlyprovided a better fit, simplified equations, assuming eithera log-linear relationship between seed longevity and temperature,or a log-linear relationship between seed longevity and bothmoisture content and temperature, accounted for more than 94per cent of the variation at the restricted temperature rangeof 5–40 °C. Longevity of the same seed lots at sub-zero temperatures (–5,–10 and –20 °C) was studied in separate tests.Freezing damage, resulting in abnormal seedlings in the germinationtest, occurred at –20 °C when the moisture contentof the seeds exceeded 12 per cent. No decline in percentagenormal seedlings was observed after a storage period of 18 monthsor longer at –20 °C, provided the seed moisture contentdid not exceed 9.5 per cent. For seeds stored at –5 and–10 °C with 9.6–12.5 per cent moisture content,the observed rate of decline of percentage normal seedlingswas adequately predicted by the viability equation, using theabove values for the constants. This suggests that for low moisturecontents the viability equation can be applied to estimate longevityat sub-zero temperatures. Lettuce, Lactuca sativa (L.), seed longevity, seed storage, viability constants, storage conditions     

The Influence of Temperature on Seed Germination in Cultivars of Common Bean

Common bean (Phaseolus vulgaris L.) is grown over a wide rangeof environments, including sites with low or high soil temperaturesat sowing time. To describe the temperature responseof seedgermination, 20 bean genotypes were evaluated using a rolledpaper towel system with 11 constant temperatures ranging from12 to 34 °C. Germination response was characterized by fittingcumulative counts using a maximum-likelihood analysis. Rateof germination increased from abase temperature (T_b) typicallynear 8 °C to an optimal development temperature (T_o) of29 to 34 °C. T_b did not differ among common bean genotypes.Mesoamerican germplasm showed slightlyhigher T_o than Andeangermplasm, but there was large variation in T_o within each ofthe two gene pools. The single accession of tepary bean (P.acutifolius) evaluated appeared to be the mosttolerant to highgermination temperatures. Key words: Common bean, seed germination rate, temperature     

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     

The effect of temperature and CO2 on seed quality development in wheat (Triticum aestivum L.)

Winter wheat (Triticum aestivum L.) cv. Hereward was grown inthe field in two double-walled polyethylene-covered tunnelswithin each of which a temperature gradient was superimposedon diurnal and seasonal fluctuations in temperature. The meantemperature between anthesis and harvest maturity varied from14.3 to 18.4C among plots within these tunnels. The CO₂ concentrationwas controlled at different values in each tunnel; seasonalmean concentrations were 380 and 684 µmol CO₂ mol^–1air. Crops were also grown outside the tunnels at ambient temperaturesand CO₂. Samples of seeds were harvested sequentially from eachplot between anthesis and harvest maturity. Seed germinationand seed survival during subsequent air-dry storage were determinedfor each sample. The onset of both ability to germinate anddesiccation tolerance (ability to germinate after rapid desiccationto 10–15% moisture content and subsequent rehydration)coincided in all environments. Full germination capacity (>97%, determined at 10C) was reached 4–18 d before theend of the seed-filling phase (mass maturity) in most cases.There was little or no decline in germination capacity duringsubsequent seed development and maturation. Differences in seedquality were evident, however, throughout seed development andmaturation when seed survival curves during subsequent storagewere compared. Potential longevity in air-dry storage (assessedby the value K₁ of the seed viability equation) improved consistentlyboth before and after mass maturity. There was a significantpositive relation between the rate of increase in potentiallongevity (dK₁Idt) and temperature (the minimum temperaturefor seed quality development was 4.8 C), but neither CO₂ concentrationnor production within the polyethylene tunnels affected thisrelation. Key words: Wheat, Triticum aestivum L., seed development, seed longevity, carbon dioxide, temperature     

Dormancy in Rice Seed: IV. VARIETAL RESPONSES TO STORAGE AND GERMINATION TEMPERATURES

Serial germination tests were carried out on dormant seeds ofsix rice varieties (four varieties of Oryza sativa L. and twovarieties of O. glaberrima Steud.) stored at several differentconstant temperatures within the range 27° C to 57°C. Probit analyses of the results were carried out to determmethe mean dormancy period for each variety at each temperature.Regression lines fitted to these data showed that there is adirect negative relationship between storage temperature andlog mean dormancy period over the range 27° C to 47°C, thus confirming a previous result obtained on a single variety.At 7° C there were indications of a slight departure fromthis relationship in that the mean dormancy periods at thistemperature were slightly longer than would have been predictedby extrapolation of the regressions calculated from the resultsobtained at lower temperatures. In all cases where the resultswere unambiguous (i.e. in all the sativa varieties and one ofthe glaberrima varieties) a constant Q₁₀ of 3.13 was shown forthe rate of loss of dormancy over the range of storage temperaturesfrom 27° C to 47° C. In the remaining glaberrima variety,where the results were less reliable, a Q₁₀ of 2.54 was found. Germination tests on all varieties were carried out at 32°C, but in the case of one sativa variety germination tests forall storage treatments were also duplicated at 27° C. Thisinvestigation showed that, in contrast to the effect of storagetemperature, the higher temperature during the germination testconsistently resulted in a lower percentage germination. Inaddition the results demonstrated that there is no interactionbetween storage temperature and germination temperature: consequentlythe storage-temperature coefficient has the same value irrespectiveof germination temperature. Some theoretical implications ofthe results are discussed.     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): VII. INFLUENCE OF AFTER-RIPENING AND AGEING ON GERMINATION RESPONSES TO TEMPERATURE AND WATER POTENTIAL

The effects of storage conditions on the germination of developingmuskmelon (Cucumis melo L.) seeds were tested to determine whetherafter-ripening is required to obtain maximum seed vigour. Seedswere harvested at 5 d intervals from 35 (immature) to 60 (fullymature) days after anthesis (DAA), washed, dried, and storedat water contents of 3·3 to 19% (dry weight basis) at6, 20, or 30°C for up to one year. Germination was testedin water and in polyethylene glycol 8000 solutions ( –0·2to –1·2 MPa osmotic potential) at 15, 20, 25 or30°C. Germination percentages and rates (inverse of meantimes to radicle emergence) were compared to those of newlyharvested, washed and dried seeds. For 40 and 60 DAA seeds,one year of storage at 20°C and water contents <6·5%significantly increased germination percentages and rates at20°C, but had little effect on germination at 25 and 30°C.Storage reduced the estimated base temperature (T_b) and meanbase water potential (_b) for germination of both 40 and 60 DAAseeds by approximately 5°C and 0·3 MPa, respectively.Immature 35 DAA seeds showed the greatest benefit from storageat 3 to 5% water content and 30°C, as germination percentagesand rates increased at all water potentials (). Storage underthese same conditions had little effect on the germination ofmature seeds in water, but increased germination percentagesand rates at reduced 's. Accelerated ageing for one month at30°C and water contents from 15 to 19° increased germinationrates and percentages of mature seeds at reduced 's, but longerdurations resulted in sharp declines in both parameters. Immatureseeds lost viability within one month under accelerated ageingconditions. An after-ripening period is required at all stagesof muskmelon seed development to expand the temperature andwater potential ranges allowing germination and to achieve maximumgerminability and vigour. Post-harvest dormancy is deepest atthe point of maximum seed dry weight accumulation and declinesthereafter, both in situ within the ripening fruit and duringdry storage. Key words: Muskmelon, Cucumis melo L., seed, development, dormancy, germination, vigour, after-ripening     

Effects of Temperature and dl-Strigol on Seed Conditioning and Germination of Witchweed (Striga asiatica)

Seed conditioning and germination in witchweed (Striga asiatica(L.) Kuntze) were temperature-dependent. With higher conditioningtemperatures, shorter conditioning time was required for germinationwith terminal dl-strigol (strigol) treatment at 30 °C. Maximumgermination (80–100%) was obtained by conditioning inwater at 20, 25, 30 and 35 °C for 14, 7, 5 and 3 d, respectively,and terminally treating with 10^–6 M strigol at 30 °C.Seeds conditioned in 10^–8 M strigol instead of water germinatedmuch less with the same terminal strigol treatment. Generally,conditioning was slower when seeds were conditioned in strigolrather than water. The reduction in germination rate by pretreatmentin strigol or pretreatment at low temperatures could be overcomeby increasing the terminal strigol concentration in the germinationtest. Conditioned seeds did not germinate at 10 and 15 °Cwith a terminal 10^–6 M strigol treatment but yielded closeto maximum germination at 25, 30 and 35 °C with the sameterminal strigol treatment. To obtain maximum germination, boththe minimum conditioning temperature and the minimum germinationtemperature for conditioned seeds were 20 °C. Factors suchas conditioning time, and strigol concentration and temperatureduring conditioning and/or germination determine whether seedsremain in the conditioning phase or shift to a germination phase. dl-Strigol, germination stimulation, parasitic plants, seed conditioning, seed germination, Striga asiatica, temperature, weed control     

A Mathematical Model to Utilize the Logistic Function in Germination and Seedling Growth

Several models have been proposed to describe germination rates,but most are limited in statistical analysis and biologicalmeaning of indices. Therefore, a mathematical model is proposedto utilize the logistic function. The function was defined asan overall response including time, temperature, and the interactionbetween time and temperature. Cumulative germination percentagesover time were used to develop the model. Germination tests were conducted on indiangrass (Sorghastrumnutans (L.) Nash) strain ‘IG-2C-F1’, at constanttemperatures of 9, 12, 15, 20, 25, and 30 °C. The functionfitted the observed data over six temperatures at r² = 0.99.Time to reach 10% of final germination (Gt₁₀) increased from2.5 d at 30 °C to 44.0 d at 9 °C, and Gt₅₀ (time toreach 50% of final germination) increased from 3.6 d at 30 °Cto 53.8 d at 9 °C. True germination rate (% d^–1) foreach temperature was maximum at Gt₅₀. A linear model of 1/Gt₅₀versus temperature was used to estimate the base temperatureof 8.3 °C for germination. An Arrhenius plot indicated achange occurred between 20 °C and 25 °C for temperatureresponse of germination. Published data on hypocotyl growthof Cucumis melo L. were recalculated using the model. Absolutegrowth rates showed a temperature response similar to the publishedweighted-mean elongation rates. Base temperature for hypocotylgrowth of C. melo was estimated as 8.8 °C. The proposedmodel proved to be useful in calculating and interpreting germinationand growth kinetics. Key words: Indiangrass, Sorghastrum nutans (L.) Nash, Germination rate, Threshold temperature, Arrhenius plot, Growth rate, Cucumis melo L     

Germination of seeds in Jussiaea suffruticosa

Seeds of Jussiaea suffruticosa reach high germination percentagesonly when exposed to long periods of continuous illumination.The light reaction may be repeatedly reversed by short exposuresto red and far red light, thus being mediated by the phytochromesystem. Seeds also germinate at high percentages if exposedto various cycles of 1 hr light and 24 hr of darkness at 20°C.If the temperature in the periods of darkness is raised up to30°C or lowered to 10°C the promotive effect of lightis inhibited. High temperatures (35°C) during imbibitionhave a promotive effect, whereas a pure O₂ atmosphere decreasesthe response to light. KNO₃ and kinetin enhance the responseto light but do not provoke germination in the dark. Only ifseed coats are punctured or removed does germination in thedark occur. (Received January 14, 1969; )     

Light and temperature control of germination in Agropyron smithii seeds

In darkness, A. smithii seeds germinated poorly at constanttemperatures but well at alternating temperatures. Prolongedperiods on the high part of the temperature cycles reduced germination;the higher the temperature the shorter was the period requiredon the high part of the temperature cycles for optimum germination.Continuous, unfiltered, incandescent illumination and intermittentfar red at 15?–25?C alternation also inhibited germination;the inhibitory effects were similar to those caused by the highintensity reaction. Far red inhibited germination when appliedafter 1 and 2 complete 15?–25?C cycles in darkness butnot after 3 cycles. Less than 20% of the seeds were under phytochromecontrol at constant 20?C. When red light was applied directlyafter far red that was applied in intermittent cycles at 15?–25?C,however, 50% of the seeds caused to germinate by the alternatingtemperature were shown to be controlled by the reversible phytochromereaction. The induced high-temperature dormancy was overcome by gibberellicacid (GA₃) plus kinetin. The hormonal treatment was much moreeffective than light for breaking dormancy. Inhibition fromprolonged illumination was alleviated or eliminated by GA₃+kinetin.The failure of red light to promote good germination at 20?Cwas also overcome with GA₃+kinetin; effects of light plus thehormone treatments were more than additive. These data suggestthat optimum alternating temperatures facilitate a proper balanceand interaction of hormones, enzymes, substrates and possiblypreexistent P_fr so that the germination of A. smithii seedscan proceed without benefit of a light treatment. (Received July 7, 1976; )     

Effects of High Temperatures on the Permeability and Germinability of the Hard Seeds of Rhus javanica L.

The effects of temperature, 40–85 °C, on the permeabilityand germinability of the hard seeds of the pioneer tree Rhusjavanica L. with a fire syndrome were studied. The temperatureeffective for removal of the water-impermeable coat dormancyof the seeds was 55 ± 7·4 °C. With increasingtemperature, shorter exposure became sufficient to render theseeds permeable, but at temperatures above 75 °C, heat impairmentof germinability resulted in less than 60% germinability, evenwith long exposure. The most favourable regimes among thosetested were temperatures of 65–75 °C for durationsof 30–120 min, which frequently occur on denuded groundduring the midday hours of clear spring or summer days. Rhus javanica L., water-impermeable coat dormancy, seed germination, high temperature     

Theoretical Basis of Protocols for Seed Storage III. Optimum Moisture Contents for Pea Seeds Stored at Different Temperatures

In previous work, we demonstrated that there was an optimummoisture level for seed storage at a given temperature (Vertucciand Roos, 1990), and suggested, using thermodynamic considerations,that the optimum moisture content increased as the storage temperaturedecreased (Vertucci and Roos, 1993b). In this paper, we presentdata from a two year study of aging rates in pea (Pisum sativum)seeds supporting the hypothesis that the optimum moisture contentfor storage varies with temperature. Seed viability and vigourwere monitored during storage under dark or lighted conditionsat relative humidities between 1 and 90%, and temperatures between-5 and 65°C. The optimum moisture content varied from 0·015g H₂O g^-1 d.wt at 65°C to 0·101 g H₂O g^-1 d.wt at15°C under dark conditions and from 0·057 at 35°Cto 0·092 g H₂O g^-1 d.wt at -5°C under lighted conditions.Our results suggest that optimum moisture contents cannot beconsidered independently of temperature. This conclusion hasimportant implications for 'ultra-dry' and cryopreservationtechnologies.Copyright 1994, 1999 Academic Press Seed storage, seed aging, seed longevity, water content, temperature, glass, desiccation damage, ultradry, Pisum sativum L., pea, cryopreservation     

The Effect of Temperature on the Supply of Oxygen to Embryos ofIntact Acer pseudoplatanus L. Seeds

The effect of temperature on various factors affecting O₂ supplyto enclosed embryos of A. pseudoplatanus L. seeds was investigatedusing a simple model for O₂ consumption by intact seeds. Lowtemperatures which induced germination had little effect onthe diffusivity of the testa although an increase in diffusivityoccurred immediately prior to radicle emergence. The O₂ concentrationsurrounding an enclosed embryo was found to be 5–10% thatof the solution bathing the seeds at storage temperatures. Therespiratory capacity of the embryos was found to be stronglydependent on temperature and, largely as a result of this, atchilling temperatures the O₂ concentration surrounding the enclosedembryo approached that in the ambient solution. The apparentArrhenius activation energy for O₂ consumption was considerablygreater below 17 °C than above this temperature. Althoughinsufficient evidence in themselves for a relationship betweenO₂ availability and seed germination, the results do provideevidence for a mechanism by which such a relationship may beassociated with seeds requiring chilling to induce germination.     

Dormancy in Dioscorea: Rapid Germination of Detached Embryos from Dormant Seeds of D. tokoro

The intact dormant seeds of Dioscorea tokoro germinate slowlyif at all between 11-23°C; for full and rapid germinationthey require prior chilling treatment [Okagami and Kawai (1982)Bot. Mag. Tokyo 95: 155]. The germination abilities of zygoticembryos detached from dormant seeds of this species were studiedunder various nutritional and temperature regimes. For germinationof embryos, the minimum nutritional components in Murashigeand Skoog's (1962) medium that were required were sucrose andNO^–₃ or SO^2–₄. As the source of carbohydrate forgermination of detached embryos, sucrose, mannose and maltosewere effective; glucose and fructose were less effective; andrhamnose was entirely unable to support germination. Embryos detached from dormant seeds, incubated with the sucroseplus KNO₃, germinated more rapidly with increasing temperatureup to 35°C. However, application of sucrose and KNO₃ didnot induce germination of intact seeds above 26°C. Therefore,it is very possible that the endosperm exerts an inhibitoryfunction on germination at such high temperatures. When seeds were incubated after a cut was made over a smallpart of the edge of the endosperm in which the radicle of theembryo is encased, germination occurred rapidly but the increasein germination percentage was slight. This result suggests thatthe endosperm suppots part of the germination inhibition bymeans of a mechanical barrier or its impermeability to wateror gases. Physiological features of the endosperm alone or interactionsbetween the embryo and endosperm may contribute significantlyto the characteristics of dormancy of intact seeds of this species. (Received May 30, 1988; Accepted January 11, 1989)     

Thermodormancy Release of Celery Seed by Gibberellins, 6-Benzylaminopurine, and Ethephon Applied in Organic Solvent to Dry Seeds

The emergence of celery (Apium graveolens L. cv. Utah 52–70)seeds was promoted by growth regulators when exposed to hightemperatures during the germination period. The growth regulatorswere applied to dry seeds prior to sowing, by means of the organicsolvent dichloromethane (DCM). A mixture of gibberellins A₄and A₇ (GA_4/7) strongly enhanced emergence at a high day-timetemperature of 35°C alternating with night temperaturesof 20°C and 25°C; however, emergence was very poor whenthe night temperature was raised to 30°C. Under the latterregime, only mixtures of GA_4/7 with 6-benzylaminopurine (BA)or with 2-chlorophosphonic acid (ethephon) promoted seed emergence.However, BA and ethephon applied separately or in combinationwere much less effective in enhancing seed emergence withoutthe addition of GA_4/7, under all the temperature regimes.