Primary dormancy in tomato (Lycopersicon esculentum cv. Moneymaker): studies with the sitiens mutant

Intact wild-type tomato (Lycopersicon esculentum cv. Moneymaker)seeds do not complete germination to the same percentage orat the same speed as intact ABA-deficient sitiens (sit^w) mutantseeds when seeds of both genotypes are imbibed on polyethyleneglycol (PEG) solutions of –0.3 to –1.5 MPa osmoticpotential. However, if the thicker testas of wild-type seedsare removed (stripped) from the micropyle without damaging theendosperm, both the percentage and speed of germination at lowexternal water potential are similar to that of sit^w mutantseeds. Removing the micropylar end of the testa from sit^w seedsdid not enhance either the speed or percentage of germinationon PEG solution. Despite similar germination percentage and speed between strippedwild-type seeds and either stripped or intact sit^w seeds underosmotic stress, some differences in seed metabolism are evidentbetween genotypes. The activity of endo-ß-mannanasewas greater in the endosperm of sit^w mutant seeds compared tothe endosperm of wild-type seeds when seeds were exposed toosmotic stress. Although     

Nuclear replication activities during imbibition of abscisic acid- and gibberellin-deficient tomato (Lycopersicon esculentum Mill.) seeds

The role of cis-abscisic acid (ABA) and gibberellins (GAs) in the induction of cell-cycle activities has been studied during imbibition and subsequent germination of tomato seeds. Using flow cytometry, nuclear replication activity was investigated in embryo root tips isolated from seeds of the ABA-deficient mutant sit ^w , the GA-deficient mutant gib-1, and the wild-type (MM) tomato (Lycopersicon esculentum Mill. cv. Moneymaker) upon imbibition in water, 10 μM GA₄₊₇, 5 μM ABA or 5 μM ABA+10 μM GA₄₊₇. The nuclei of fully matured dry MM, sit ^w and gib-1 seeds predominantly showed 2C DNA signals, indicating that the cell-cycle activity of most root-tip cells had been arrested at the G₁ phase of nuclear division. However, ABA-deficient sit ^w seeds contained a significantly higher amount of G₂ cells (4C DNA) compared with the other genotypes, suggesting that, during maturation, cell-cycle activity in sit ^w seeds is less efficiently arrested in G₁. Upon imbibition in water, an induction of the 4C signal, indicating nuclear replication, was observed in the root tip cells of both MM and sit ^w embroys. The augmentation in the 4C signal occurred before visible germination. Gib-1 seeds did not show cell-cycle activity and did not germinate in water. Upon imbibition in GA₄₊₇, both cell-cycle activity and subsequent germination were enhanced in MM and sit ^w seeds, and were induced in gib-1. In ABA, the germination of MM and sit ^w seeds was inhibited while nuclear replication of these seeds was not affected. It is concluded that GA influences germination by acting upon processes that precede cell-cycle activation, while ABA affects growth by acting upon processes that follow cell-cycle activation.     

Flow Cytometric Determination of Nuclear Replication Stages in Tomato Seeds during Priming and Germination

Flow cytometric determination of DNA levels in embryos of fullymatured dry tomato (Lycopersicon esculenium) seeds revealedlarge amounts of 2C DNA signals, indicating that most cellshad arrested in the cell cycle at the presynthetic G₁ phaseof nuclear division. After imbibition in water, an augmentationof the 4C signal in the embryonic root tip region was found.This increase could be ascribed to cells entering the syntheticphase of nuclear division leading towards the doubling of chromosomalmaterial. In the root tip cells, 4C:2C ratios increased I dafter imbibition in water though radicle emergence started 2d later. Apparently, DNA synthesis preceded germination. Onlya small increase in the number of cells with 4C DNA levels wasfound in the rest of the embryonic tissues. In whole dry seeds,DNA histograms revealed both a 2C signal and a considerable6C peak, the latter originating from the endoreduplicated endosperm. A priming period of 14 d in PEG-6000 considerably enhanced therate and uniformity of germination. In the ungerminated seeds,the 4C DNA signal of root tip cells started to increase after3 d incubation in PEG. The ratio of 4C:2C steadily increasedduring the 14 d priming period, though did not reach the levelobtained after hydration in water. Upon priming, the 4C:2C ratiowas constant after redrying the seeds towards the original moisturecontent, indicating that the chromosomal material in the rootcells had stably ceased cell cycle activity at the G² phase.The present results indicate that the beneficial effects ofpriming on seedling performance are associated with the actionof replicative DNA synthetic processes prior to germination. Lycopersicon esculeniumMill, tomato, DNA content, flow cytometry, priming, seed, nuclear replication stage, C levels     

Gibberellins and the Growth of Excised Tomato Roots: Comparison of gib-1 Mutant and Wild Type and Responses to Applied GA3 and 2S, 3S Paclobutrazol

Clones of excised roots of wild type tomato (Lycopersicon esculentum,Mill., cv. Moneymaker) and a near-isogenic GA-deficient mutant(gib-1/gib-1) were cultured in modified White's medium containing1.5% w/v sucrose. The linear elongation rate of the main axisof the gib-1 mutant was 40% less than that of the wild type.In addition, the main axis of the gib-1 mutant was thicker thanthat of the wild type but main axis volume growth was the samein both genotypes, indicating that the gib-1 allele was affectingthe orientation of root expansion. There was no evidence tosuggest that the gib-1 allele affected either the pattern ofemergence or the density of lateral roots. Elongation rate andthickness of gib-1 mutant roots were restored to those of thewild type by the addition of low concentrations (0.1–1.0µM) of gibberellic acid (GA3). These concentrations ofGA3 caused a slight reduction in extension growth of wild typeroots, indicating that endogenous GAs were not limiting elongationof normal roots in culture. The GA biosynthesis inhibitor, 2S,3S paclobutrazol, at 0.1 µM, significantly reduced elongationof wild type roots and this inhibition was counteracted by 0.1µM GA₃. It is concluded that the difference in growthbetween the gib-1 mutant and the wild type represented GA-dependentgrowth. Low concentrations of 2S, 3S paclobutrazol caused onlya small (5%) reduction in growth of the gib-1 mutant and thisgrowth inhibition was not reversed by GA₃. This observation,and the fact that gib-1 mutant roots grow in the absence ofadded GA₃, suggested that part of root growth was GA-independent.However, the possibilities that the gib-1 mutant is ‘leaky’and that paclobutrazol does not inhibit GA biosynthesis completelycannot be excluded. Key words: gib-1 mutant, gibberellic acid, Lycopersicon esculentum, 2S, 3S paclobutrazol, root growth     

Dynamics of Competition in Populations of Carrot (Daucus carota)

Populations of carrot (Daucus carota) were raised over a widerange of densities (79–5763 plants m^-2) to examine thedynamics of competition in terms of yield–density relationshipsand size variability, and to investigate the effects of nutrientsupply on competition. While the relationship between shootyield and density was asymptotic, the relationship between rootand total yield and density tended to be parabolic. For a giventime and density series the relationship between yield per unitarea and density could best be described by the model: y=w_mD_(1+aD)^b wherey is the yield per unit area,D is density,w_m, a andb arefitted parameters. The parametersw_m anda increased over timebut nutrient availability affected onlyw_m. An extension of thebasic yield-density model is proposed to describe the dynamicsof the yield–density relationship over time: y=kD_{[1+cexp(-rt)]{1+}     

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     

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: I. GERMINATION AT SUBOPTIMAL TEMPERATURE

The bases of differences in germination rates (GR_g = inverseof time to germination [t_g] of percentage g) among three cold/salt-toleranttomato (Lycopersicon esculentum Mill.) accessions (PI 341988,PI 120256, and PI 174263) and one cold/salt-sensitive tomatocultivar (T5) were investigated. The effects of seed priming(6 d imbibition in aerated –1.2 MPa polyethylene glycolsolution at 20 ?C followed by redrying) and of removing theendosperm/testa cap covering the radicle on the temperaturesensitivity of GR_g, and the interaction of these treatmentswith genotypes, were also examined. GR_g decreased linearly withdecreasing temperature for all genotypes and seed treatments.The minimum or base temperatures for germination (T_b) variedby 1 ?C among the tomato lines, so genotypic differences inGR_g were due to differing thermal time requirements for germination.The mean thermal time requirement for germination of T5 seeds was 22% and 19% greater than that of PI 341988 andPI 120256 seeds, respectively, but only 9% greater than thatof PI 174263 seeds. Seed priming did not lower Tb of any genotype,but significantly reduced by 24, 49, 41, and 49% in T5, PI 341988, PI 120256, and PI 174263, respectively,indicating that priming increased the rate at which the seedsprogressed towards germination when T>T_b, but did not lowerthe minimum temperature at which germination could occur. Primingincreased the GR_g of T5 seeds to equal or exceed those of control(non-primed) seeds of the cold/salt-tolerant genotypes at anyT>T_b, but the PI lines exhibited an even greater responseto priming. Times to germination within each seed lot were normallydistributed on a logarithmic scale. Priming increased the variancein tg within a seed lot when compared to control seeds. However,the variation in thermal time for germination between the 10thand 90th percentiles of the seed population (_T(10–90))was relatively unaffected by priming due to the reduction in in primed seeds. Removing the endosperm cap and testa opposite the radicle tip decreased almost 6-fold and and reduced T_b by 5 ?C in T5 and PI 341988,implicating processes in the endosperm/testa as the limitingfactors in germination at suboptimal temperatures. Key words: Lycopersicon esculentum Mill., tomato, genetic variation, seed priming, thermal time, germination rate     

Differential Responsiveness in Zonal Growth of Cocklebur Seed Axes to CO2, C2H4, O2 and Respiration Inhibitors

The axial growth of de-coated cocklebur (Xanthium pennsylvanicumWallr.) seeds, whose axes were divided into 4 zones, was examinedin relation to the temperature-dependent shift of the effectof C₂H₄ on germination. At 23?C, where both C₂H₄ and CO₂ stimulatedgermination, CO₂ promoted the axial growth at the radicle tipzone, whereas C₂H₄ promoted growth in the proximal portion ofthe axis. At 33?C, C₂H₄ inhibited germination, and stronglysuppressed the growth at the radicle tip, whereas the effectof CO₂ did not change. The inhibition of growth at the radicletip zone was alleviated by O₂ enrichment, which also reversedthe inhibition of germination. It is thus apparent that thetemperature-dependent shift of the action of C₂H₄ is associatedwith a temperature-dependent responsiveness of the radicle tipzone to C₂H₄. Growth of the radicle tip zone was sensitive toNaN₃, whereas the proximal portion was sensitive to benzohydroxamicacid, an inhibitor of alternative respiration, suggesting thatthere may be an increase in the operation of the alternativerespiration path along a gradient of axial tissue from the tiptowards the cotyledonary side. The effects of CO₂ and C₂H₄ arediscussed in relation to the different respiratory activitiesin each axial zone of cocklebur seeds. (Received May 9, 1986; Accepted November 6, 1986)     

Kinetics of Phenylalanine Ammonia-Lyase and the Effect of L-{alpha}-aminooxy-{beta}-phenylpropionic Acid on Enzyme Activity and Radicle Growth in Germinating Lettuce Seeds

The effects of different concentrations of L--aminooxy-ß-phenyIpropionicacid (AOPP), an analog of L-phenylalanine, on the activity ofphenylalanine ammonia-lyase (PAL, EC 4.3.1.5 [EC] ) and the growthof radicles in 24 h old germinating lettuce (Lactuca salivaL.) seeds were investigated. AOPP causes a significant inhibitionof PAL activity in the seeds (85% inhibition at 10⁴ M). It alsocauses a stimulation of radicle growth at that concentration.The results show that the inhibition of PAL by AOPP may be dueto an irreversible binding of the inhibitor to the enzyme leadingto its inactivation. AOPP also inhibits ethylene biosynthesisin germinating lettuce seeds which could probably explain thestimulation of radicle growth in these seeds. The enzyme shows typical Michaelis-Menten kinetics. The K_m forL-phenylalanine is 4.2 x 10⁵ M. The enzyme does not show anytyrosine ammonia-lyase activity. Various substrate analogs suchas D-phenylalanine, p-fluorophenylalanine, ß-phenyllacticacid, tryptophan and the product of the enzyme reaction, trans-cinnamicacid, inhibit the enzyme competitively. A number of intermediatesand endproducts of the phenylpropanpid pathway, except chlorogenicacid, do not show any inhibition. ¹Scientific contribution number 1423 from the New HampshireAgricultural Experiment Station. (Received May 9, 1986; Accepted September 8, 1986)     

The Effects of Priming and Ageing on Seed Vigour in Tomato

A comparison was made of the effects of seed priming or ageingtreatments on the performance of tomato (Lycopersicon esculentumMill. cv. UC204C) seeds according to a number of indices ofseed vigour. A single lot of tomato seeds was primed in 120mol m^–3 K2HPO4 + 150 mol m^–3 KNO₃ for 5 d at 20?C, or aged at 13% moisture content (dry weight basis) and 50?C for 6 d. Germination percentage (>98%) was unaffectedby priming and reduced to 85% by ageing. X-ray photographs andlongitudinal sections revealed the formation of free space surroundingthe embryo in dry primed seeds, which was not evident in controlor aged seeds. Priming increased the rate of germination atall temperatures above the base temperature (T_b), while ageingdecreased it. T_b was unaffected by priming and only slightlyincreased by ageing. The variation in individual times to germinationwas approximately doubled in both primed and aged seed comparedto the control, based upon the slopes of probit germinationpercentage versus log thermal time curves. Root growth aftergermination tests and seedling growth in both greenhouse andfield tests were not influenced by either priming or ageing.The conductivity test was found to be unreliable as a vigourtest for tomato seeds. The results identify several indiceswhich can be used to quantify seed vigour in tomato. They alsoillustrate that seed priming can enhance seed performance accordingto some criteria, while having no effect or decreasing qualityaccording to other criteria. Seed vigour can apparently be separatedinto various components which can be independently influencedby seed enhancement treatments. Key words: Tomato, seed germination rate, seed priming, seed vigour     

Respiration and germination rates of tomato seeds at suboptimal temperatures and reduced water potentials

Suboptimal temperature (T) affects germination rates (reciprocalof time to radicle emergence) on a thermal time basis; thatis, the T in excess of a base or minimum temperature multipliedby the time to a given per cent germination [t_g) is a constant.Respiration rates are also sensitive to T, and proportionalrelationships are often found between respiration rates andgermination rates. Reduced water potential () delays seed germinationon a hydrotime basis (i.e. the in excess of a base water potentialmultiplied by t_g is a constant). It was tested whether respirationrates prior to radicle emergence vary in proportion to T and as expected from the thermal and hydrotime models. Respirationrates (C0₂ evolution) of cold-tolerant, rapidly germinating(PI 341988) and cold-sensitive, more slowly germinating (T5)tomato [Lycopersicon esculentum Mill.) seeds were evaluatedover a range of T and conditions. For both genotypes, respirationrates until the beginning of radicle emergence were relatedto T on a thermal time basis and increased approximately linearlywith above -2.0 MPa, consistent with the hydrotime model. Respirationrates were uniquely related to germination rates, regardlessof whether germination timing was affected by T, , or genotype.However, germination timing was unaffected when respirationrates were manipulated by varying 0₂ partial pressure. Thus,while both germination and respiration rates vary with T and consistent with thermal and hydrotime models of biologicaltime, respiration rates per se were not the limiting factorin germination timing of tomato seeds. Key words: Lycopersicon esculentum Mill., tomato, germination, respiration, temperature, water potential     

Environmental Control of Flowering in Barley (Hordeum vulgare L.). II. Rate of Developement as a Function of Temperature and Photoperiod and its Modification by Low-temperature Vernalization

Plants of six contrasting genotypes of barley were raised fromvernalized (imbibed at 1 °C for 30 d) or non-vernalizedseeds and grown in 12 different controlled environments comprisingfactorial combinations of three photoperiods (10, 13 and 16h d^–1), two day temperatures (18 and 28 °C) and twonight temperatures (5 and 13 °C). Except at longer daysfor Athenais or Arabi Abiad, the 28 °C day temperature wasgenerally supra-optimal and delayed awn emergence. At lowertemperatures and in photoperiods shorter than the critical value,P_C, which delay awn emergence, the time from sowing to awn emergencefor five of the genotypes conformed to the equation 1/f=a +bT{macron}+cPwhere f is the time to awn emergence (d), T{macron} is meandiurnal temperature (°C), P is photoperiod (h d^–1)and a, b and c are genotype-specific constants. In Arabi Abiad,however, significant responses to temperature were not detected.The low temperature pre-treatment of the seeds reduced the subsequenttime to awn emergence in Athenais and the autumn-sown genotypesAger, Arabi Abiad and Gerbel B, especially in longer days, buteither had no effect or tended to delay awn emergence in thespring-sown types Emir and Mona. In the spring-sown types P_Cwas outside the range investigated (i.e. > 16 h d^–1),but in Ager it was approx. 13 h d^–1 and in Gerbel B justover 13 h d^–1. For plants of Arabi Abiad grown from vernalizedseeds P_c was almost 15 h, but     

Yield-density Relationships: the Influence of Resource Availability on Growth and Self-thinning in Populations of Vulpia fasciculata

Monocultures of Vulpia fasciculata were grown over a wide rangeof densities to investigate the influence of crowding and nutrientsupply on growth and self-thinning. For a given time and densityseries the relationship between mean yield per plant (w) andthe density of survivors (N) could be described by the equation w= w_m (1+aN)^–b. where w_m is the yield of an isolated plant, a is the area requiredto achieve a yield of w_m and b describes the effectiveness withwhich resources are taken up from the area. All three parametersincreased with time. Adding nutrients changed not only the rate at which the effectsof crowding occurred but also the intensity of crowding since w_m = C(a^b)^D. where C and D are constants. The addition of nutrients resultedin an increase in the value of C. Such an increase means thata larger weight can be supported by a given area because theresources within that area are greater. During the early phases of growth, populations of V. fasciculataconformed to the –3/2 power law, w = cN^–3/2, butonly at very high densities with a plentiful supply of nutrients.However, once the maximum standing crop had been reached thetrajectory of the thinning line switched to a slope of justless than –1 when weight was ploted against density onlogarithmic scales. The intercept of the –3/2 thinningline was considerably higher (log c = 5.74) than those for mosttrees and forbs but was similar to those of a number of othergrasses. Vulpia fasciculata, dune fescue, yield-density models, self-thinning, density-dependence, nutrient supply     

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)     

Vacuolar H+-ATPase Is Expressed in Response to Gibberellin during Tomato Seed Germination

Completion of germination (radicle emergence) by gibberellin (GA)-deficient (gib-1) mutant tomato (Lycopersicon esculentum Mill.) seeds is dependent upon exogenous GA, because weakening of the endosperm tissue enclosing the radicle tip requires GA. To investigate genes that may be involved in endosperm weakening or embryo growth, differential cDNA display was used to identify mRNAs differentially expressed in gib-1 seeds imbibed in the presence or absence of GA₄₊₇. Among these was a GA-responsive mRNA encoding the 16-kD hydrophobic subunit c of the V₀ membrane sector of vacuolar H⁺-translocating ATPases (V-ATPase), which we termed LVA-P1. LVA-P1 mRNA expression in gib-1 seeds was dependent on GA and was particularly abundant in the micropylar region prior to radicle emergence. Both GA dependence and tissue localization of LVA-P1 mRNA expression were confirmed directly in individual gib-1 seeds using tissue printing. LVA-P1 mRNA was also expressed in wild-type seeds during development and germination, independent of exogenous GA. Specific antisera detected protein subunits A and B of the cytoplasmic V₁ sector of the V-ATPase holoenzyme complex in gib-1 seeds only in the presence of GA, and expression was localized to the micropylar region. The results suggest that V-ATPase plays a role in GA-regulated germination of tomato seeds.     

Relationship between Plant Weight and Growing Period for Vegetable Crops in the United Kingdom

A generalized equation is derived that relates total dry matterproduction to time from emergence for crops grown in the fieldwith adequate water and nutrients. It is: w+K₁lnw+W₀=K₂t where w is the plant dry weight in t ha^–1, t is time indays after emergence, K₂ and K₁ are constants and W₀ equals–(w₀+K₁lnw₀) where w₀ is the value of w at the start ofthe growing period. The increases in the dry matter of 18 different types of vegetablecrop were measured at intervals during growth in the field.In every case the data fitted the equation very satisfactorilywith K₁ set equal to 1 t ha^–1. The fitted values of K₂were similar for many crops; those of W₀ varied considerablybut were always similar to the values calculated from the individualseed weight and the plant population. Good fits were also obtainedwhen time in days was replaced with cumulative evaporation froman open water surface. It is concluded that the growth-time curves of many differentvegetable crops can be described by the same simple equationand that the variation between curves can be largely attributedto differences in seed weight and plant population.     

Differential Effects of Day and Night Temperature on Development to Flowering in Rice

There are conflicting reports with regard to difference in effectsof day temperature (T_D) and night temperatures (T_N) on plantdevelopment. The objective of this study is to determine whetherthere are different effects ofT_DandT_Non development from sowingto flowering in rice (Oryza sativaL.). Plants of 24 rice cultivars were grown in naturally-lightedgrowth chambers at five diurnally constant (22, 24, 26, 28 and32 °C) and four diurnally fluctuating temperatures (26 /22,30 /22, 22 /26 and 22 /30 °C forT_D/T_Nwith 12hd^-1each) witha constant photoperiod of 12hd^-1. The treatments were selectedto enable the separation of effects ofT_DandT_Non developmentrate (DR). The response of DR to constant temperatures was typically nonlinear.This nonlinearity could not explain the difference in floweringdates between fluctuating temperatures with the same mean dailyvalue but oppositeT_D/T_Ndifferences. Differential effects ofT_DandT_NonDR to flowering were detected in all but one cultivar. In mostcases,T_Dexerted a greater influence thanT_N, in contrast withmany previous reports based on the assumption of a linearitybetween DR and temperature. The data were further analysed bya nonlinear model which separated effects ofT_DandT_N. The estimatedvalue for the optimumT_Nwas generally 25 –29 °C, about2 –4 °C lower than the estimated optimumT_Din mostcultivars. The effects ofT_DandT_Non DR were found to be interactivein some cultivars. These results form a new basis for modellingflowering dates in rice. Oryza sativa; rice; flowering; development; day and night temperature; thermoperiodicity     

Metabolism of C1 unit precursors in Neurospora: Effects of media supplements on labelling of nucleic acids and protein

Mycclia of Neurospora crassa wild type (FE SC no. 853), harvestedduring the exponential phase of growth on defined minimal mediaincorporated glycine-2-¹⁴C, serine-3-¹⁴C and formate-¹⁴C intoproteins, DNA and RNA. Supplementing the growth medium with1 mM glycine increased the flow of glycine and formate carboninto these products. In contrast, this supplement decreasedthe incorporation of serine-¹⁴C. When such cultures were preincubatedfor 30 min with adenine, formaldehyde, formate or L-methionine,labelling of the nucleic acids and protein fractions by glycine-2-¹⁴Cwas altered. It is concluded that glycine increases the turnoverof C₁ units in Neurospora, resulting in greater contributionsof the C-2 in nucleic acid and protein synthesis. (Received May 14, 1977; )     

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