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: I. ACQUISITION OF DESICCATION-TOLERANCE AND GERMINABILITY DURING DEVELOPMENT 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.1. Acquisition of desiccation–tolerance and germinabilityduring development of Ricinus communis L. seeds.—J. exp.Bot. 36: 1906–1915. Seeds of Ricinus communis L. cv. Hale(castor bean) undergo a transition from desiccation–intoleranceto desiccation–tolerance approximately midway throughtheir development. Tolerance of slow desiccation is gained overonly a few days of development (between 20 and 25 d) and isachieved well before the completion of major developmental events,such as reserve deposition and the onset of normal maturationdrying. A tolerance of very rapid water loss brought about bydrying over silica gel is not acquired by this seed until nearmaturity. Coincident with the acquisition of tolerance to slowdesiccation the seeds gain the capacity to germinate upon subsequentrehydration. Germinability and capacity for normal post–germinativegrowth during the tolerant phase are not fully expressed unlessthe seed is dried at an optimal rate, which is dependent uponthe developmental stage of the seed. Drying presumably actsto terminate developmental processes and to initiate those metabolicprocesses necessary to prepare the seed for germination andgrowth. Key words: Desiccation-tolerance, germinability, seed development, castor bean     

DEVELOPMENTAL CHANGES IN THE COTYLEDONS OF LUPINUS LUTEUS L. DURING AND AFTER GERMINATION

Cotyledons of Lupinus luteus were sampled from 1 to 21 days after sowing and processed for light microscopy and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Length, width, and surface area of the cotyledons increased gradually until day 10. The thickness of the cotyledons increased from day 7 to day 12 and decreased thereafter. Morphometric analyses showed that the increase in length, width, and thickness of the cotyledon was due to cell expansion, and the decrease in thickness of the cotyledon was due to the decrease in the length of abaxial cells and in the total number of cells. Mesophyll development accompanied schizogenous and lysigenous air space formation. There were two structurally distinct types of protein bodies. Protein bodies in five to six layers of cells on the abaxial side did not contain globoids, while globoids were prominent in protein bodies in the center and adaxial side. Storage protein mobilization occurred first in the abaxial side of the cotyledon and proceeded toward the adaxial side. SDS-PAGE analysis showed that proteins ranged from 97 to 14 kD. High molecular weight α- and ß-conglutinins were more abundant in the abaxial region, whereas γ-conglutinin occurred in both abaxial and adaxial regions. In addition, there were five minor bands between 97 and 43 kD unique to abaxial region and five minor bands between 43 and 14 kD unique to adaxial region in the nonreduced protein profiles. The α- and ß-conglutinins began to decrease after imbibition and disappeared by day 7 after sowing. At this stage the subunits of ribulose-l,5-bisphosphate carboxylase/oxygenase and four new minor bands appeared.     

The Role of Maturation Drying in the Transition from Seed Development to Germination: V. RESPONSES OF THE IMMATURE CASTOR BEAN EMBRYO TO ISOLATION FROM THE WHOLE SEED: A COMPARISON WITH PREMATURE DESICCATION

Kennode, A. R, and Bewley, J. D. 1988. The role of maturationdrying in the transition from seed development to germination.V. Responses of the immature castor bean embryo to isolationfrom the whole seed; a comparison with premature desiccation.—J.exp. Bot. 39: 487–497. Desiccation is an absolute requirement for germination and post-germinativegrowth of whole seeds of the castor bean, whether desiccationis imposed prematurely during development, at 35 d after pollination(DAP) or occurs naturally during late maturation (50–60DAP). Desiccation also plays a direct role in the inductionof post-germinative enzyme synthesis in the cotyledons of embryosin the intact seed; this event is not simply due to the presenceof a growing axis. Isolation of embryos from the developingcastor bean seed at 35 DAP results in both germination and growth,despite the absence of a desiccation event. We have comparedthe metabolic consequences of premature drying of whole seeds(35 DAP) and isolation of the developing 35 DAP embryos. Inboth cases, hydrolytic events involved in the mobilization ofstored protein reserves proceed in a similar manner and mirrorthose events occurring within germinated mature seeds. Thereare differences, however, for post-germinative enzyme (LeuNAaseand isocitrate lyase) production occurs to a lesser extent innon-dried isolated embryos than in those from prematurely dried(35 DAP) whole seeds, or from mature dry (whole) seeds. Desiccationof the 35 DAP whole seed does not alter the subsequent responseof the embryo upon isolation. Thus, while drying does not affectthe metabolism of isolated embryos, it has a profound effecton that of embryos within the intact seed. Tissues surroundingthe embryo in the developing intact seed (viz. the endosperm)maintain its metabolism in a developmental mode and inhibitgermination. This effect of the surrounding tissues can onlybe overcome by drying or by their removal. Key words: Metabolism, isolation, desiccation, embryo, endosperm, castor bean, development, germination     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): VIII. DEVELOPMENT OF OSMOTICALLY DISTENDED SEEDS

Dead seeds that expand to nearly twice their normal volume whenfully hydrated are called osmotically distended (OD). Theseseeds swell osmotically in response to a water potential ()gradient created by solutes trapped in the free space betweenthe embryo and the surrounding endosperm or perisperm tissues.The formation of OD seeds in planta is poorly understood, althoughthey often occur in newly harvested muskmelon (Cucumis meloL. Reticulatus group) seed lots. Muskmelon fruit senescenceand seed germinability were contrasted with Armenian cucumber(Cucumis melo L. Flexuosus group) from 50 d after anthesis (DAA)to when seeds were released from the fruit. Fifty DAA muskmelonseeds were incubated in the laboratory for 30 d at 15, 25, and35 °C in factorial combinations of ethanol, acetic acid,and to simulate conditions in decaying fruits. Seed releasefrom Armenian cucumber occurred 20 d earlier than muskmelon.In both years of the study, less than 25% of the muskmelon seedsreleased from the fruit were viable, and 52% and 24% of thedead seeds were OD in year one and two, respectively. All Armeniancucumber seeds were viable or had germinated precociously atseed release. From 50 to 60 DAA, soluble solids in muskmelonfruit pericarp tissue declined from 11·4 to 7·8° Brix, pH declined from 6·2 to 5·1, increasedfrom –1·76 to –1·36 MPa, acetic acidincreased to 61 mol m^–3;, and ethanol content rose from0·1% to 0·3%. O₂ and CO₂ partial pressures inthe seed cavities of 40 to 55 DAA fruits were generally 12 and8 kPa, respectively, at midday. All 50 DAA muskmelon seeds incubatedin acetic acid and ethanol germinated, because these chemicalscould not penetrate the perisperm tissue. Incubating 50 DAAmuskmelon seeds in the laboratory for 30 d at 15 or 25 °Chad little effect on germinability, regardless of . Germinationpercentages of muskmelon seeds incubated at 35 °C and 's<–1·28MPa were less than 50%. Muskmelon seeds died and became OD insidedecaying fruits in the field because of the combined effectsof low , high temperature, and low O₂ partial pressures. Fruitsof muskmelon cultivars bred to resist decomposition and to havehigh sugar content showed decreased reproductive capacity comparedto Armenian cucumber which decomposed more rapidly. Key words: Muskmelon, seed, fruit, germination, senescence, water potential, temperature, oxygen, carbon dioxide     

THE DIFFERENTIATION OF PIGMENTATION IN FLOWER PARTS. VIII. THE EFFECT OF INHIBITORS OF PROTEIN AND RNA SYNTHESIS ON DEVELOPMENTAL CHANGES OF ANTHOCYANINS IN CULTURED PETALS OF IMPATIENS BALSAMINA

If inhibitors of protein or RNA synthesis are administered to flower petals of the red genotype (HHHP^rP^r) of Impatiens balsamina at a very early stage of development, an alteration in the normal pattern of anthocyanin pigmentation results. Whereas control petals are mainly pigmented with acyl pelargonidin-3,5-diglucoside and pelargonidin-3,5-diglucoside, petals cultured in the presence of inhibitors are mainly pigmented with pelargonidin-3-monoglucoside. The complete absence of the more highly substituted forms of pelargonidin in treated petals suggests that the biochemical reactions required for the addition of glucosyl and hydroxycinnamoyl residues to pelargonidin-3-monoglucoside have been prevented. The ability to block the normal developmental pattern of pigmentation with these inhibitors suggests that de novo synthesis of active enzymes is required, and as indicated by the effectiveness of actinomycin D, specific RNA synthesis is a necessary prerequisite for the synthesis of the normal anthocyanin complement in this tissue. The ability of the white flowered genotype (llhhpp) to metabolize exogenously supplied pelargonidin-3-monoglucoside was found to be prevented by prior culture of immature petals in the presence of DL-ethionine. The data indicate that the enzymes required for this ability are not products of induction by the substrate but rather their presence is a normal feature of petal development. Treatment with inhibitors has failed to produce any inhibition in the formation of specific anthocyanins found in the flower petals of some other genotypes of I. balsamina.     

CHANGES IN MITOTIC ACTIVITY AND CELL SIZE IN THE APICAL MERISTEM OF HELIANTHUS ANNUUS L. DURING THE TRANSITION TO FLOWERING

Cellular changes in the shoot apical meristem of Helianthus annuus L. have been investigated in relation to its progress towards flowering. During the strictly vegetative phase, lasting for 6–7 days from sowing, mitotic divisions were confined to the peripheral zone, while the central mother cells zone proper, together with the distal cells positioned above the mother zone and also the central portion of the tunica, were relatively quiescent. Mitotic activity increased in the distal cells zone on day 8 and reached the level of that in the peripheral zone by day 12. This was accompanied by an enlargement of this zone and the consequent recession of the mother zone away from the central tunica. At the same time there was a substantial increase in the amount of cytoplasm in the cells of the central tunica. Mitotic activity in the central tunica began on day 12 and reached a peak on day 16. This zone then lost its distinct entity and was replaced by a uniform dome-shaped meristematic layer that became apparent by day 16. The cells of the mother zone remained quiescent during the transition period.     

THE SYNTHESIS OF DNA, RNA, AND NUCLEAR PROTEIN IN NORMAL AND TUMOR STRAIN CELLS : IV. HeLa Tumor Strain Cells

Interferometric and photometric measurements have been made on HeLa cells, a strain of cells originally derived from a human carcinoma. From a study of the relations between successive physical measurements on individual cells, it was confirmed that, whereas the net syntheses of nuclear RNA and nuclear protein are closely associated during interphase, they are dissociated from DNA replication to a significant extent. These results on nuclear metabolism agree with others previously reported in cell strains derived from tumors; they contrast with results from freshly prepared normal cells, where the net syntheses of DNA, nuclear RNA, and protein are closely associated during interphase. Cytoplasmic measurements on HeLa cells showed that much of the net synthesis of cytoplasmic RNA is associated with DNA replication as in normal cells, and they failed to detect transfer from the nucleus of a stable RNA component synthesized independently from DNA replication. In auxiliary experiments, an inhibition of the onset of DNA synthesis was produced by a dose of X-rays; under these conditions it was shown that the major part of the accumulation of nuclear protein was independent of DNA replication and that the accumulation of nuclear RNA was equivalent to or slightly less than that of nuclear protein. About half the accumulation of cytoplasmic RNA was inhibited when DNA synthesis was blocked.     

Seed Dormancy in Acer: CHANGES IN ENDOGENOUS GERMINATION INHIBITORS, CYTOKININS, AND GIBBERELLINS DURING THE BREAKING OF DORMANCY IN ACER PSEUDOPLATANUS L.

Changes in germination inhibitors, cytokinins, and gibberellin-likesubstances during the breaking of coat-imposed dormancy of sycamoreseeds at low temperature suggest that dormancy may be controlledby the presence of endogenous germination inhibitors. Stratificationat 5°C led to a greater loss of neutral inhibitor(s) fromthe embryo than did incubation at 20°C. No marked differenceswere observed in the level of cytokinins and gibberellin-likesubstances between treatments. However, a gradual decrease inthe level of cytokinins was observed during stratification.Whether a cytokinin-inhibitor interaction is involved in thecontrol of dormancy of sycamore seeds, as was previously suggested,remains to be determined.     

The Utilization of Cotyledonary Reserves in Phaseolus vulgaris L. cv. Carioca: I. CHANGES IN TOTAL AMYLOLYTIC AND PROTEOLYTIC ACTIVITY AND THE EFFECTS OF 6-BENZYLADENINE AND GIBBERELLIC ACID UPON WHOLE SEEDLINGS

Axis growth commenced only 20 h from imbibition in Phaseolusvulgaris when both uptake of water and oxygen were levellingoff. Cotyledonary dry material was exhausted by day 9, the greatestrates of transfer occurring from day 2. Utilization of reserveprotein proceeded relatively faster than dry matter and proportionatelymore was translocated to the shoot, particularly the leaf blades.Lamina protein and chlorophyll content showed a biphasic increasewith rapid synthesis prior to day 7 being followed by slowerrates up to maximum leaf area on day 17. The level of free aminoacids in the cotyledons fell continuously from day 3 and roseto peak levels in the axis between days 5 and 7. Soluble sugarsincreased throughout the period examined in the axis and accumulatedin the cotyledons prior to day 7. Exogenous application of GA₃ had marked morphological effectsupon the seedling though did not significantly alter the distributionof dry matter or protein reserves: 6-BA, in addition to distinctmorphological effects, delayed the mobilization of reservesto the axis. Total amylolytic activity in the cotyledon, optimal at pH 5.5,increased continually from day 3 to 9 whereupon activity abruptlydeclined. This increase was due to the appearance of -amylase;ß-amylase, while present, remained at a constant andcomparatively low level. Peak proteolytic activity occurredprior to that for amylases between days 5 and 7. 6-BA significantlyincreased both amylolytic and proteolytic activities in vitrothough did not alter the changes in levels of free amino acidsor sugars in the reserve tissue and axis. The discrepancy betweenin vivo and in vitro effects of 6-BA may be attributed to concomitanteffects upon seedling development whereby sink capacity is reduced.     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): II. DEVELOPMENT OF GERMINABILITY, VIGOUR, AND DESICCATION TOLERANCE

The germinability, vigour, and desiccation tolerance of muskmelon(Cucumis melo L. cv. Top Mark) seeds was studied in relationto changes in seed water content during development within thefleshy fruit. Seed water content (fresh weight basis) declinedfrom 91% to 42% between 10 d and 35 d after anthesis (DAA) (whenmaximum dry weight was attained), then declined more slowlyto a minimum of 35% at 50 DAA before increasing again to 43%at 65 DAA. Fresh intact seeds were first germinable at 25 to30 DAA and attained maximum germination percentages at 45 DAA.Between 15 and 35 DAA, cotyledons, hypocotyls, radicles andepicotyls of isolated embryos (testa and perisperm enveloperemoved) sequentially developed the ability to grow when incubatedon water. Dehydration to water contents less that those attainedwithin the fleshy fruit is not a requirement for developmentof germination capacity of muskmelon seeds. Seeds became tolerantof rapid desiccation after 25 DAA, and drying of immature seeds(25 to 40 DAA) increased their germination percentages uponsubsequent imbibition. Washing, drying, or washing followedby drying increased seedling vigour (root length) as comparedto fresh seeds, which had very poor vigour. Water absorptionisotherms were constructed to test whether changes in water-bindingcomponents were correlated with the development of desiccationtolerance. Isotherms for seeds older than 25 DAA fit well tothe D'Arcy/Watt model, which postulates the existence of high-affinity,low-affinity and multi-molecular water-binding sites. Desiccation-intolerantseeds younger than 25 DAA lacked the component of the absorptionisotherm characteristic of the high-affinity water-binding siteswhich have been hypothesized to confer desiccation tolerance.However, we were unable to determine whether the absence ofhigh-affinity binding characteristics was specifically relatedto desiccation intolerance or was artifactual due to the lossof volatiles when immature seed samples were dried at high temperatures. Key words: Muskmelon, embryo, germination, development, vigour, desiccation     

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     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: I. RELATIONSHIP BETWEEN TUBER GROWTH RATE AND ENZYME ACTIVITIES OF THE STARCH METABOLISM

Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. Cooling (+8°C) of individualtubers decreased their growth rates and increased the growthrates of non-cooled tubers of the same plant. The carbohydrateconcentration in non-cooled and cooled tubers did not differsignificantly, but ¹⁴C-import from labelled photosynthate waslower in cooled than in non-cooled tubers. The markedly lowerconversion rate of ethanol-soluble ¹⁴C to starch in cooled,in comparison to non-cooled tubers, was not associated withsignificant differences in the in vitro activities of starchsynthase, ADPG-pyrophosphorylase and starch phosphorylase understandard assay conditions (+30°C). However, the Q₁₀-valuesof the enzymes differed in vitro in the temperature range between30°C and 8°C, leading to a marked decrease in the activityratio of ADPG-pyrophosphorylase/starch phosphorylase in cooledtubers. In tubers differing in growth rates without manipulation, 14d after tuber initiation significant positive correlations werefound between ¹⁴C-concentration of tuber tissue and the in vitroactivities of starch synthase and ADPG-pyrophosphorylase anda significant negative correlation between ¹⁴C-concentrationand starch phosphorylase. In contrast, in tubers which wereanalysed 5 d after initiation, there were only small differencesbetween tubers in growth rate, ¹⁴C import and the activity ratioADPG-pyrophosphorylase/starch phosphorylase. From various directand indirect evidence it is concluded that the growth rate ofindividual tubers, and thus the sink strength, is at least inpart controlled by the activity of starch synthesizing enzymes. Key words: Potato tuber, cooling, starch synthesizing enzymes     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: III. EFFECT OF CHANGED PHOSPHATE CONCENTRATIONS ON THE GROWTH AND DISTRIBUTION OF PHOSPHATE WITHIN PLANTS OF LOLIUM PERENNE L.

Perennial ryegrass (Lolium perenne L.) was grown from seed for29 d in flowing solution culture containing 0.1, 0.4 or 6.4mmol m^–3 P before the concentrations were changed (0.1and 0.4 raised to 6.4; 6.4 lowered to 0.4; controls unchanged)for an experimental period of two weeks to test the hypothesisthat after the seedling stage, the maximum rate of plant growthcould be sustained by a lower concentration of phosphate atthe root/solution interface than was necessary for the maximumrate of seedling growth. During the 29 d seedling period growthwas greatest on 6.4 mmol m^–3 P achieving 179 mg per plantdry weight compared with 122 and 26 mg on 0.4 and 0.1 mmol m^–3P respectively. During the experimental period growth on thetreatment 6.4 lowered to 0.4 mmol m^–3 P continued at thesame rate as the 6.4 control achieving 981 and 983 mg per plantdry weight respectively. Similarly growth of the treatment 0.4raised to 6.4 mol m^–3 P was unaffected by the change inconcentration and was comparable with the 0.4 control. Bothresults support the hypothesis for seedlings exceeding about100 mg per plant dry weight. In contrast the small plants ofthe treatment 0.1 raised to 6.4 mmol m^–3 P behaved similarlyto seedlings and responded rapidly to the increased concentrationof phosphate in solution, achieving high rates of phosphateuptake and increasing the growth of shoot more than the growthof root so that the ratio of root: shoot declined from 065 to0.34, a value similar to that for the seedlings grown on 6.4mmol m^–3 P. Key words: Lolium perenne L, Phosphate concentration, Seedling growth     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): VI. INFLUENCE OF PRIMING ON GERMINATION RESPONSES TO TEMPERATURE AND WATER POTENTIAL DURING SEED DEVELOPMENT

Seed priming (imbibition in water or osmotic solutions followedby redrying) generally accelerates germination rates upon subsequentre-imbibition, but the response to priming treatments can varyboth within and among seed lots. Seed maturity could influenceresponsiveness to priming, perhaps explaining variable primingeffects among developmentally heterogeneous seed lots. In thecurrent study, muskmelon (Cucumis melo L.) seeds at two stagesof development, maturing (40 d after anthesis (DAA)) and fullymature (60 DAA), were primed in 0?3 M KNO₃ for 48 h at 30 ?C,dried, and imbibed in polyethylene glycol 8000 solutions of0 to –1?2 MPa at 15, 20, 25, and 30 ?C. Germination sensitivitiesto temperature and water potential () were quantified as indicatorsof the influence of seed maturity and priming on seed vigour.Germination percentages of 40 and 60 DAA control seeds weresimilar in water at 30 ?C, but the mean germination rate (inverseof time to germination) of 40 DAA seeds was 50% less than thatof 60 DAA seeds. Germination percentages and rates of both 40and 60 DAA seeds decreased at temperatures below 25 ?C. Reductionsin also delayed and inhibited germination, with the 40 DAAseeds being more sensitive to low than the 60 DAA seeds. Primingsignificantly improved the performance of 40 DAA seeds at lowtemperatures and reduced , but had less effect on 60 DAA seeds.Priming lowered both the minimum temperature (T_b) and the minimum (_b) at which germination occurred. Overall, priming of 40 DAAseeds improved their germination performance under stress conditionsto equal or exceed that of control 60 DAA seeds, while 60 DAAseeds exhibited only modest improvements due to priming. Asthe osmotic environment inside mature fruits approximates thatof a priming solution, muskmelon seeds may be ‘primed’in situ during the late stage of development after maximum dryweight accumulation. Key words: Cucumis melo L., seed priming, germination, vigour, development, temperature