Patterns of seed after-ripening in Bromus tectorum L

For grass seeds that lose dormancy through after ripening indry storage, the probability of germination following a particularwetting event can be predicted only if the relationship betweenstorage temperature and change in after-ripening status is known.This study examined patterns of seed dormancy loss in Bromustectorum L., quantifying changes in germination percentage,speed, and uniformity through time. Seed collections from threesemi-arid habitats were stored at temperatures from 10–40C. At monthly intervals, subsamples were incubated at 5/15,10/20, 15/25, and 20/30 C. For recently harvested seeds, germinationpercentage, mean germination time, and days between 10% and90% of total germination (D90–D10) ranged from 1–75%,10–24 d, and 10–20 d, respectively. Recently harvestedseeds were generally most dormant, slowest to germinate andleast uniform at high incubation temperatures. In contrast,after ripened seeds for all collections had nearly 100% germination,mean germination times <5 d, and D90–D10 values <5d. Three indices were used to characterize after-ripening ratesfor each seedlot at each incubation temperature. The mean dormancyperiod, the mean rate index, and the mean uniformity index definedthe storage period required for seedlots to become half as dormantas at harvest, to progress half-way to the fastest speed, andto progress half-way to the greatest uniformity, respectively.Seeds required longer storage to germinate uniformly than togerminate completely or quickly, because germination time-coursecurves for incompletely after-ripened seeds were positivelyskewed rather than sigmoidal. Mathematically, the three indiceswere described as negative exponential functions of storagetemperature, which suggests that after-ripening is likely completedin late summer or early autumn regardless of summer conditions. Key words: Seed dormancy, germination timing     

The Effect of Ethylene and Temperature on ATP Accumulation from Various Substrates in Peanut (Arachis hypogaea L. ) Seeds

Peanut (Arachis hypogaea L. ) seed powder accumulated ATP fromAMP and phosphoenolpyruvate (PEP) at a rate of approx. 100 pmolmin^–1mg^– powder at 35° C. When peanut seed powderwas incubated with various substrates, which may result in PEPor AMP (ADP) synthesis, then ATP accumulated. The best substratecombinations examined so far were AMP + succinate, NADH₂, andAMP + malate + NAD, with activities of 33, 12 and 12 pmol min^–mg^–1powder,respectively; AMP + malate showed very low activity. Some combinationsexhibited linear activities with time, while others had an exponential-typeprofile. The temperature dependence of the ATP accumulationdemonstrated by the Ahrrenius plot had a double phase with atransition point at 25° C. The Ea values between 15°C and 25° C were 25 000–50 000 cal/mol, while above25° C the Ea values fluctuated between 6000 and 8000 cal/mol(depending on the substrate). The AMP + PEP combination exhibiteda single-phase profile between 15° C and 40° C, withan Ea value of 22 000 cal/mol. In the presence of some substrates,ethephon (ethylene) had a stimulatory effect and caused an increasein the Ea values at the high temperature phase. A comparisonof seed powder from dormant seeds with that from non-dormantseeds revealed that some substrate combinations accumulate ATPfaster in non-dormant seeds and others do so in dormant seeds. Key words: Arachis hypogaea, ATP, Ethylene, Dormancy, Peanut, Seed     

The Role of Maturation Drying in the Transition from Seed Development to Germination: II. POST-GERMINATIVE ENZYME PRODUCTION AND SOLUBLE PROTEIN SYNTHETIC PATTERN CHANGES WITHIN THE ENDOSPERM OF Ricinus communis L. SEEDS

Kermode, A. R. and Bewley, J. D. 1985. The role of maturationdrying in the transition from seed development to germination.II. Post–germinative enzyme production and soluble proteinsynthetic pattern changes within the endosperm of Ricinus communisL. seeds.—J. exp. Bot. 36: 1916–1927. Immature seedsof Ricinus communis L. cv. Hale (castor bean) removed from thecapsule at 30 or 40 d after pollination (DAP) do not germinateunless first subjected to a desiccation treatment. This changefrom development to germination elicited by premature desiccationis also mirrored by a change, upon subsequent rehydration, inthe pattern of soluble protein synthesis within the endospermstorage tissue. Following rehydration of prematurely dried 30or 40 DAP seeds, soluble proteins characteristic of developmentcease to be synthesized after 5 h of imbibition, and those uniquelyassociated with germination and growth are then produced. Apattern of soluble storage protein breakdown comparable to thatfound in endosperms from mature seeds following imbibition isalso observed. In contrast, hydration of 40 DAP seeds immediatelyfollowing detachment from the mother plant results in a continuationof the developmental pattern of protein synthesis. Prematuredesiccation at 40 DAP elicits the production within the endospermof enzymes involved in protein reserve breakdown (leucyl ß–naphthylamidase;LeuNAase) and lipid utilization (isocitrate lyase; ICL) to levelscomparable to those observed in mature–hydrated endosperms.It is proposed that drying plays a role in redirecting metabolismfrom a developmental to a germinative mode; it also appearsto be a prerequisite for the induction of hydrolytic enzymesessential to the post–germinative (growth) phase of seedlingdevelopment. Key words: Desiccation-tolerance, germinability, seed development, castor bean     

The Role of Maturation Drying in the Transition from Seed Development to Germination: III. INSOLUBLE PROTEIN SYNTHETIC PATTERN CHANGES WITHIN THE ENDOSPERM OF Ricinus communis L. SEEDS

Kermode, A. R., Gifford, D. J. and Bewley, J. D. 1985. The roleof maturation drying in the transition from seed developmentto germination. III. Insoluble protein synthetic pattern changeswithin the endosperm of Ricinus communis L. seeds.—J.exp. Bot. 36: 1928–1936. Immature seeds of Ricinus communisL. cv. Hale (castor bean) removed from the capsule at 30 or40 days after pollination (DAP) can be induced to germinateby being subjected to drying. This desiccation–inducedswitch from development to germination is mirrored by a change,upon subsequent rehydration, in the pattern of insoluble proteinsynthesis within the endosperm storage tissue. During normaldevelopment from 25–40 DAP there is rapid synthesis ofthe insoluble (11S) crystalloid storage protein. At later stagesof development (45 and 50 DAP), crystalloid protein synthesisdeclines markedly and synthesis of new insoluble proteins commences.Following premature drying at 30 or 40 DAP, the pattern of insolubleprotein synthesis upon rehydration is virtually identical tothat following imbibition of the mature seed. Proteins synthesizedduring normal late development (at 45 and 50 DAP) are producedup to 48 h after imbibition; a subsequent change in the patternof insoluble protein synthesis occurs between 48 and 72 h. Thus,in contrast to the rapid switch in the pattern of soluble proteinsynthesis induced by drying, insoluble protein syntheses withinthe endosperm are redirected towards those uniquely associatedwith a germination/growth programme only after a considerabledelay following mature seed imbibition, or following rehydrationof the prematurely dried seed. Nevertheless, these results supportour contention that drying plays a role in the suppression ofthe developmental metabolic programme and in the permanent inductionof a germination/growth programme. Key words: Desiccation, crystalloid storage proteins, castor bean, seed development, seed germination     

Germination and Food Reserves in Bambarra Groundnut Seeds (Voandzeia subterranea Thouars) after Different Periods of Storage

Studies were made on bambarranut seeds (Voandzeia subterraneaThouars) after 0, 6, 12, 18 and 24 months of storage in gunnybags under laboratory conditions (25–35 °C). Seeddeterioration during storage was indicated by delayed germination,reduced germinability, reduced growth of seedlings and increasednumber of stunted seedlings culminating in a total failure ofgermination after two years. Slight depletion of food reserves occurred during seed storage.The loss in fat was higher than starch or protein. Total solublesugars decreased while the content of total fatty acids andamino acids and soluble protein increased. Total nitrogen (N)remained unaffected while soluble-N and amino-N increased. Allthese components showed a rapid change (increase or decrease)from 12 months to 18 months of storage which was associatedwith commencement of rapid decline in germinability of the seedsand growth of the seedlings. Initial rapid imbibition of water was observed in viable aswell as non-viable seeds, though at a higher rate in the latterand followed by a lag period in both. At the end of 24 h ofimbibition, water content in non-viable seeds was less thanthat in viable ones. Key words: Voandzeia subterranea, Seed germination, Seed storage     

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     

Water as a Storage Medium for Elaeis guineensis (pisifera) Seeds under Aseptic Conditions

Over 50 per cent germination has been obtained from Elaeis guineensisform pisifera seeds stored in unaerated sterile distilled waterfor 6 months. The moisture levels of the seeds and excised embryoswere of the same order (20–30 and 60–70 per cent,respectively) as those of fully imbibed fresh seeds. The implicationsof an apparent lower oxygen requirement by seeds stored underwater as against germinating seeds are discussed in the contextof the successful storage. Elaeis guineensis, pisifera, germination, seed dormancy, embryo     

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     

Protein Synthesis During Rehydration, Germination and Seedling Growth of Naturally and Precociously Matured Soybean Seeds (Glycine max)

Soybean seeds [Glycine max (L.) Merr.] synthesize de novo andaccumulate several non-storage, soluble polypeptides duringnatural and precocious seed maturation. These polypeptides havepreviously been coined ‘maturation polypeptides’.The objective of this study was to determine the fate of maturationpolypeptides in naturally and precociously matured soybean seedsduring rehydration, germination, and seedling growth. Developingsoybean seeds harvested 35 d after flowering (mid-development)were precociously matured through controlled dehydration, whereasnaturally matured soybean seeds were harvested directly fromthe plant. Seeds were rehydrated with water for various timesbetween 5 and 120 h. Total soluble proteins and proteins radio-labelledin vivo were extracted from the cotyledons and embryonic axesof precociously and naturally matured and rehydrated seed tissuesand analyzed by one-dimensional PAGE and fluorography. The resultsindicated that three of the maturation polypeptides (21, 31and 128 kDa) that had accumulated in the maturing seeds (maturationpolypeptides) continued to be synthesized during early stagesof seed rehydration and germination (5–30 h after imbibition).However, the progression from seed germination into seedlinggrowth (between 30 and 72 h after imbibition) was marked bythe cessation of synthesis of the maturation polypeptides followedby the hydrolysis of storage polypeptides that had been synthesizedand accumulated during seed development. This implied a drasticredirection in seed metabolism for the precociously maturedseeds as these seeds, if not matured early, would have continuedto synthesize storage protein reserves. Glycine max (L.) Merr, soybean, cotyledons, maturation, germination/seedling growth     

Recalcitrant Seed Storage Physiology in Three Aquatic Grasses (Zizania palustris, Spartina anglica and Porteresia coarctata)

The moisture content/probit viability relationship for storedseeds of Zizania palustris L. and Spartina anglica C. E. Hubbardwas linear and independent of the rate of embryo drying. Theseresults provide firm evidence of recalcitrant storage physiologyin these taxa. Preliminary tests strongly suggest that freshseeds of Porteresia coarctata (Roxb.) Tateoka are also intolerantof desiccation In Z. palustris apparent differences in desiccation tolerancebetween individuals can be partly explained by wide variationin individual embryo moisture contents during desiccation. Long-termstorage experiments in solutions of polyethylene glycol 6000(PEG) suggest that the actual variation in desiccation toleranceis confined to a narrow range of embryo water potentials inthe range –2 to –3 MPa. Despite the presence of prolonged dormancy in seeds of Z. palustrisand S. anglica there is no evidence of a significant effectof dormancy or storage period (up to the point of visible germination)on the limits of desiccation tolerance Aquatic grasses, seeds, storage, desiccation intolerance     

Storage Behaviour of Salix alba and Salix matsudana Seeds

Effects of dehydration, storage temperature and humidificationon germination of Salix alba andS. matsudana seeds were studied.Newly released seeds showed 100% germination before and afterdehydration to 11–12% moisture content. Germination ofthe high vigour lot (100% initial normal germination) was notaffected by dehydration to 6.7% moisture content but germinationdecreased with further dehydration to 4.3%. The lower vigourlot (75% initial normal germination) was more susceptible todehydration and germination decreased following dehydrationto 6.7% moisture content. Dry seeds of both species survivedimmersion in liquid nitrogen without loss of viability. Thegermination of seeds stored with 9% moisture content decreasedto 35–40% in 5 months at -20°C or in 2 months at 5°C.However, at 25°C seeds entirely lost viability within 2weeks. Seeds showed improved performance when stored at -70°C> - 20°C > 5°C > 25°C and tolerated dehydrationto a moisture content in equilibrium with 15% relative humidity.Results suggest that they are orthodox in storage behaviouralthough they are short-lived. Humidification treatment of lowvigour seed lots resulted in a remarkable increase in germinationpercentage. Copyright 2000 Annals of Botany Company Salix alba, Salix matsudana, willow, seed storage behaviour, dehydration, humidification, cryopreservation     

Changes in Respiratory Potential of Dormant and Non-dormant Galium aparine L. (cleavers) Seeds during Dry Storage

Hilton, J. R. and Thomas, J. A. 1987. Changes in respiratorypotential of dormant and non-dormant Galium aparine L. (cleavers)seeds during dry storage.—J. exp. Bot. 38: 1484–1490. Pre-germinative rates of O₂ uptake of two collections of Galiumaparine L. seed were compared throughout a 9 month period ofdry storage at 4 °C, 23 °C and at ambient (frost-protected)temperatures. Uptake of O₂ by the dormant seeds was generallyhigher than that of the less dormant seeds except when freshly-harvested.Moreover, changes in the O₂ consumption of seeds stored at ambienttemperatures could be associated with periods of germinationand seedling emergence in the field. The results are discussedin relation to changes in respiratory metabolism during dormancybreakage.     

Seed Longevity of Rice Cultivars and Strategies for their Conservation in Genebanks

Changes in seed quality during ripening were studied in sixteencultivars of rice, representing the three ecogeographic racesofOryza sativa, and one cultivar ofO. glaberrima, grown duringone dry season (Nov. –May) 1992 –1993 at Los Baños, Philippines. Mass maturity (defined as the end ofseed filling period) among the cultivars was attained between18.5 and 21.6d after anthesis (DAA). The seed moisture contentat mass maturity varied between 24 and 40%. Germination abilityof seeds in the early stages of development varied significantly,but as mass maturity approached, germination increased to themaximum and no significant differences were found among cultivars.The seeds were stored hermetically at 35 °C with 15±0.2%moisture content and the resultant seed survival data were analysedby probit analysis. Potential longevity (quantified by the valueof seed lot constantK_iof the seed viability equation) was greatestbetween 33 and 37 DAA, i.e. about 2 weeks after mass maturity.The stage during development at which seeds achieve maximumpotential longevity is described by the term storage maturity.Lowlandjaponicacultivars, large seeded accessions (seed mass40mg) andO. glaberrimahad shorter storage longevity ( , standarddeviation of the frequency of seed deaths in time=1.47 weeks)while cultivars with purple pericarp survived longer than othercultivars ( =2.33 weeks). The initial germination of thejaponicacultivarsat storage maturity was high (99 –100%) and the estimatesof maximum potential longevity (K_i) which ranged between 3.3(Shuang cheng nuo) and 4.4 (Minehikare) were close to thoseof theindicacultivars. This research suggests that seed production environment betweenNov. and May at Los Ba ños is benign for the temperatejaponicacultivars.The implications of these results on management of rice geneticresources are discussed. Oryza sativaL.; rice; germplasm conservation; seed production environment; seed development; seed longevity     

Effects of Moisture Content on Germination of Seeds of Hancornia speciosa Gom. (Apocynaceae)

Seeds of Hancornia speciosa germinated best at a temperatureof 20–30 °C. The viability of the seeds during storagewas short and the best storage conditions for viability entailedkeeping the seeds in polyethylene bags. Seed viability was maintainedonly when the seeds were stored at a moisture content above30%; storage conditions which allowed dehydration resulted ina rapid loss of viability (the seeds showed recalcitrant behaviour). Low temperature during storage did not improve longevity. Arelationship between germination and moisture content was established,but when the moisture content fell below 25% there was a drasticreduction of germination. After 9 weeks of storage, even athigh moisture content, seeds lost viability. Loss of seed viability during seed dehydration was associatedwith increased leakage of electrolytes and organic solutes,and reduced tetrazolium staining during subsequent imbibition. Hancornia speciosa, germination, recalcitrant seeds, storage, moisture     

The Potential for Newly-Germinated Cabbage Seed Survival and Storage at Sub-Zero Temperatures

The moisture content of newly germinated cabbage seed (radicles1 05 mm long) was reduced to 14% of f.wt without loss of viability.As the moisture content was reduced below 45%, the temperatureat which the germinated seeds froze, and therefore died, decreasedprogressively to a minimum of –34 C at 19% moisture content.No freezing exotherms were recorded in seeds with moisture contentsbelow 19%. Seeds with a moisture content between 14 and 16%maintained viability for at least 1 week when cooled at 26C.min^–1to –20 C and held at this temperature, indicating thepotential for prolonged storage of these low-moisture-contentgerminated (LMCG) seeds. Brassica oleracea, cabbage, germinated seed, seed storage, fluid drilling, freezing exotherm, thermal analysis     

Some Morphological and Chemical Characteristics of Developing Fruits of Raphia hookeri

Ndon, B. A. 1985. Some morphological and chemical characteristicsof developing fruits of Raphia hookeri.—J. exp. Bot. 36:1817–1830. Fruits which were at different stages of development were randomlysampled from different inflorescences of Raphia hookeri palms.The morphological characteristics and chemical (the dry matter,lipid and carbohydrate) contents of the exocarp and seeds weredetermined. The results showed that the seed length, circumferenceand volume were optimal at 24 months after pollination whichindicates that Raphia seeds attained maximum size at that period.The seed endosperm was liquid or semi-liquid between 6–18months after pollination but became solid with a prominent embryoat 24 months. The seed dry matter was low at the early stagesof development but there was a rapid increase in seed dry weightat 18–33 months after pollination. The seeds were physiologicallymatured at 30–33 months after pollination, while the exocarpmatured at 24–30 months after pollination. The Raphia seeds were low in lipid (about 2%) compared to theexocarp which had 30–40% lipid at full maturity. Maximumamount of lipid was accumulated within the exocarp at 36–42months after pollination and this period indicates the timefor harvesting Raphia fruits for maximum oil which is probablythe most economic part of the fruit. The total sugar concentration increased in the exocarp withincrease in maturity. Conversely the concentration of sugarsdecreased within the seeds as the fruit matured. Maximum totalsugar concentration (about 309 mg g^–1 dry fat free sample)was found in the exocarp at 36–42 months after pollination.Mature seeds at 48 months after pollination had about 50 mgof total sugars per g of fat free sample. There was insignificantaccumulation of starch in the exocarp. The mature seeds werelow in starch (5–10% of the dry weight). Key words: Raphia hookeri, development, fruit     

The Structure of Legumin of Vicia faba L.--a Reappraisal

Two-dimensional electrophoretic studies have shown a wide rangeof heterogeneity in the subunits of legumin isolated from seedsof Vicia faba L. As many as 10 disulphide-linked subunit pairsin the mol. wt. range 37 000–79 000 have been observed.Each subunit pair separated on reduction by 2-mercaptoethanolinto a large acidic and a small basic subunit, each of whichwas shown to be heterogeneous in charge by isoelectric focusing.More heterogeneity was found in the large subunits (mol. wt.range 23 000–58 000; pl range 4.6–6.1) than in thesmall subunits (mol. wt. range 21 000–23 000; pl range8.2–8.5). Most legumin molecules seemed to be formed byrandom association of subunit pairs, although one subunit pairassociated only with itself to give a molecular type separableunder non-dissociating conditions.     

Turnover of Storage Protein in Seeds of Soya Bean and Pea

We were interested in determining whether the low protein contentof pea seeds (Pisum sativum L.) as compared to soya bean seeds(Glycine max L. Merrill) might be due to faster degradationof the pea storage proteins during development of the seed.Pea and soya bean cotyledons were subjected to a ‘pulse-chase’experiment using [³H]glycine in in-vitro cultures. In peas,legumin had a half-life of 146 days, while vicilin had a half-lifeof 39 days. There was no measureable degradation of soya beanstorage proteins. Even with the pea storage proteins, the half-liveswere so much longer than the maturation time of seeds that degradationof storage proteins could not account for the lower proteincontent of peas as compared to soya beans. The validity of theseresults was indicated by the finding that non-storage proteinshad much shorter half-lives and that omission of a carbon ora nitrogen source greatly accelerated degradation. Labelledglycine was found to be a good probe for protein turnover studiesbecause it was very rapidly metabolized. Glycine max L. Merrill, soya bean, Pisum sativum, L. pea, protein turnover, storage proteins, legumin, vicilin     

Priming and accelerated ageing affect L-isoaspartyl methyltransferase activity in tomato (Lycopersicon esculentum Mill.) seed

Damage and degradation of cellular proteins is observed duringage-induced seed deterioration. L-Isoaspartyl protein methyltransferase(EC 2.1.1.77 [EC] ) is an enzyme hypothesized to play a role in limitingand repairing age-induced damage to proteins. Tomato (Lycopersiconesculentum Mill. ‘New Yorker’) seeds were assayedfor changes in L-isoaspartyl methyl-transferase activity duringaccelerated ageing and after osmotic priming. Accelerated ageingof seeds for 1–4 d at 45C and 100% relative humidityreduced germination from 94% to 71%, increased the mean timeof germination (MTG) from 2.4 to 5.8 d, and was accompaniedby a correlative decrease in L-isoaspartyl methyltransferaseactivity (r²=0.90). Aged and untreated seeds were primed for7 d at 20C in darkness using aerated solutions of 3% KNO₃ orpolyethylene glycol 8000 (PEG) with equivalent osmotic potential(–1.25 MPa). Priming with KNO₃ decreased the MTG, butdid not improve germination percentage for untreated seeds.Priming did not affect L-isoaspartyl methyltransferase activityin untreated seeds, but restored activity in aged seeds primedin KNO₃ to levels near that of untreated seeds. Priming withPEG did not effectively improve the MTG or increase L-isoaspartylmethyltransferase activity. During germination, L-isoaspartylmethyltransferase activity remained constant for 48 h post-imbibitionand then declined, suggesting that the enzyme was developmentallyregulated and inactivated or degraded as radicle emergence occurred. Key words: L-Isoaspartyl methyltransferase, protein repair, seed priming, accelerated ageing, Lycopersicon esculentum     

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