GROWTH AND REPRODUCTION OF THE SLUG LIMAX VALENTIANUS FIRUSSAC IN EXPERIMENTAL CONDITIONS

Growth and reproduction of batches and isolated Limax valentianus Férussacslugs reared under long-day photoperiods were compared with thosereared under short-day photoperiods combined with higher temperaturesduring the dark period. Weight increase in L. valentianus occurredin three distinct phases: an initial phase of rapid growth (infantilephase), followed by a phase with a smaller increase in weight(juvenile phase) and finally a phase with minimal growth, duringwhich reproduction occurred (adult phase). This phase ended witha weight decrease, due to senescence. Short days associatedwith an increase in temperature during the night reduced thereproductive rate, but did not affect growth. Long days werefavourable for reproduction. Growth rate was fastest in isolatedindividuals reared under long days and warm nights, while reproductionwas greatest in isolated individuals reared under long daysand cool nights. Fertility generally decreased with age, butegg production of slug batches evolved through a maximum, occurringbefore mean life span. High slug density reduced reproductiverate and longevity. (Received 22 December 2000; accepted 10 October 2000)     

Interrelation between Ethylene and Carbon Dioxide in Relation to Respiration and Adenylate Content in the Pre-Germination Period of Cocklebur Seeds

Effects of C₂H₄ and CO₂ on respiration of pre-soaked upper cocklebur(Xanthium pennsylvanicum Wallr.) seeds during a pre-germinationperiod were examined in relation to effects of the two gaseson germination. At 33?C, cocklebur seed germination was greatlystimulated. This high temperature-stimulated germination wasseverely inhibited by C₂H₄, but not by CO₂, although both gasesstimulated germination at 23?C. C₂H₄ promoted seed respirationat 23?C, but its promotive effect decreases with increasingtemperature and disappeared at about 35?C, while CO₂ stimulatedrespiration regardless of temperature. CO₂ augmented the operationof the CN-sensitive, cytochrome path (CP) regardless of temperature,resulting in an increase in the ratio of the CP flux to a CN-resistant,alternative path (AP) flux. On the other hand, C₂H₄ augmentedthe operation of both paths, particularly of the AP, at 23?C,where it promoted germination. However, at 33?C where germinationis suppressed by C₂H₄, C₂H₄ preferentially stimulated respirationvia the AP, thus leading to an extremely high ratio of AP toCP. The inhibitory effect of C₂H₄ on germination at 33?C disappearedcompletely in enriched O₂, under which conditions CP is knownto be augmented. At 23?C, CO₂ and C₂H₄ acted independently incontrolling seed respiration, but they were antagonistic at33?C. The independent action appeared when the AP flux was verylow relative to the CP flux, while the antagonism appeared whenthe AP flux had risen. This differential action of the two gasesat different temperatures was also observed in the ATP level,adenylate pool size and energy charge of the axial tissues.These results suggest that the germination-controlling actionsof both CO₂ and C₂H₄ are fundamentally manifested through themodification of respiratory systems. However, the germination-inhibitingeffect of C₂H₄ at 33 ?C was not removed by inhibitors of AP,and there was little difference in the adenylate compounds betweenthe C₂H₄-treated and non-treated seeds at 33?C. Therefore, thephysiological action of C₂H₄ can not be explained only in termsof regulation of the respiratory system. (Received January 24, 1986; Accepted November 17, 1986)     

Durations of the Photoperiod-sensitive and Photoperiod-insensitive Phases of Development to Flowering in Four Cultivars of Rice (Oryza sativa L.)

The durations of the photoperiod-sensitive and photoperiod-insensitivephases of development to panicle emergence were estimated infour contrasting indica cultivars of rice (Oryza sativa L.)in a reciprocal-transfer experiment. Plants were grown in potsin glasshouses maintained at warmer (32/26 C) or cooler (28/20C) day/night temperatures, and the durations from sowing topanicle emergence were determined for plants moved from relativelyshort (11 h) to relatively long (13.5 h) days and vice versaat various times after sowing. Panicle emergence was delayedby long days in all cultivars, but the traditional cvs Carreonand Peta were much more sensitive to photoperiod than the moderncvs IR8 and IR36 The durations of the photoperiod-insensitivepre-inductive phase (equivalent to some definitions of the basicvegetative phase) varied from 14.4 d in cv. Carreon at 32/26C to 42.0 d in cv. IR8 at 28/20 C. In all cultivars this initialphase was of a longer duration in the cool than in the warmregime. The duration of the photoperiod-insensitive post-inductivephase was also consistently greater, but usually only slightso, at cool than relatively warm temperatures; it varied from6.8 d in cv. IR8 at 32/26 C to 272 d in cv. Carreon at 28/20C. As expected, the length of the intervening photoperiod-sensitiveinductive phase was greater in long days, but the effect oftemperature on these durations was not consistent; for example,these durations were longer in warm than in cool temperaturesin cv. 1R8 but, if anything, they were slightly longer in coolthan in warm temperatures in cv. IR36. This difference is compatiblewith previous findings that cv. IR36 has a warmer optimum temperaturefor rate of progress towards panicle emergence than cv. IR8.A subsequent reciprocal-transfer experiment with cv. Peta providedestimates of the durations of the photoperiod-insensitive andphotoperiod-sensitive phases of pre-flowering development whichwere compatible with our earlier estimates. Furthermore, panicleinitiation was found to occur after about 80% of the photoperiod-sensitiveinductive phase had elapsed. We conclude that although the durationof the photoperiod-insensitive pre-inductive phase in rice isgreater than in many other annual crops, genotypic variationin this duration may well be less than was previously deduced.We also conclude that, despite common assumptions to the contrary,photoperiod-sensitivity during rice plant development does notend at panicle initiation. Oryza sativa L., rice, panicle initiation, panicle emergence, photoperiodism, temperature     

Tuberization in Potato at High Temperatures: interaction between Shoot and Root Temperatures

Tuber formation in intact potato plants (Solanum tuberosum L.cv. Sebago) was reduced by high shoot or root temperatures andstrongly inhibited when both were high. When both the shootand root temperatures were high, disbudding strongly promotedtuberization. There was a smaller increase with warm roots andcool shoots, but no response with warm shoots and cool roots.When both the shoots and roots were cool, disbudding reducedtuberization. Exogenous GA₃, effectively substituted for thebuds at high temperatures, completely preventing tuberization.In apical cuttings, removal of the terminal bud, but not theroots, reduced the inhibitory effects of high temperatures ontuberization. The experiment indicates that tuber productionmay be controlled by at least three factors: a promoter, whichis not assimilate, produced by the buds at cool temperatures;an inhibitor, derived from the buds, but dependent on warm roottemperatures for its formation; and a second inhibitor derivedfrom the mature leaves and produced in response to warm shoottemperatures. Solanum tuberosumL, potato, tuberization, temperature, disbudding, gibberellic acid     

Pre- and post-harvest influences on seed dormancy status of an Australian Goodeniaceae species, Goodenia fascicularis

Background and Aims

The period during which seeds develop on the parent plant has been found to affect many seed characteristics, including dormancy, through interactions with the environment. Goodenia fascicularis (Goodeniaceae) seeds were used to investigate whether seeds of an Australian native forb, harvested from different environments and produced at different stages of the reproductive period, differ in dormancy status.

Methods

During the reproductive phase, plants were grown ex situ in warm (39/21 °C) or cool (26/13 °C) conditions, with adequate or limited water availability. The physiological dormancy of resulting seeds was measured in terms of the germination response to warm stratification (34/20 °C, 100 % RH, darkness).

Key Results

Plants in the cool environment were tall and had high above-ground biomass, yet yielded fewer seeds over a shorter, later harvest period when compared with plants in the warm environment. Seeds from the cool environment also had higher viability and greater mass, despite a significant proportion (7 % from the cool-wet environment) containing no obvious embryo. In the warm environment, the reproductive phase was accelerated and plants produced more seeds despite being shorter and having lower above-ground biomass than those in the cool environment. Ten weeks of warm stratification alleviated physiological dormancy in seeds from all treatments resulting in 80–100 % germination. Seeds that developed at warm temperatures were less dormant (i.e. germination percentages were higher) than seeds from the cool environment. Water availability had less effect on plant and seed traits than air temperature, although plants with reduced soil moisture were shorter, had lower biomass and produced fewer, less dormant seeds than plants watered regularly.

Conclusions

Goodenia fascicularis seeds are likely to exhibit physiological dormancy regardless of the maternal environment. However, seeds collected from warm, dry environments are likely to be more responsive to warm stratification than seeds from cooler, wetter environments.Key words: Goodenia fascicularis, Goodeniaceae, Australia, physiological dormancy, seeds, temperature, soil moisture, maternal influence, climate     

A bimodal germination response to temperature in cocklebur seeds. II. ATP and adenylate pool

Abstract. The mechanism involved in a bimodal germination-temperature response in pre-soaked cocklebur (Xanthium pennsylvanicum Wallr.) seeds was studied with special reference to adenylate metabolism. Exposure to either low (optimal at 8°C) or high (optimal at 34°C) temperature which was effective in inducing the germination of the seeds brought about the accumulation of ATP in them. The ATP level remained unchanged at temperatures around 23°C. Pretreatment with KCN, stimulating germination even at 23°C, subsequently increased the ATP content, total adenylate pool and energy charge (EC) in the axial tissue prior to germination above those of the untreated controls. The lower the treatment temperature, the greater the inhibitory effect of KCN on ATP formation. An increase in germination following an increasing duration of pre-soaking at 8°C was comparable to increasing both the ATP content and total adenylate pool of axes, but not the EC value. Similarly, changes in germination following an increased exposure duration at 8°C correlated with changes in ATP content rather than EC value in the axes. Unlike the case of chilling, an increase in ATP level in response to 34°C was greater in the early period of water imbibition, during which times its germination-stimulating effect appeared more striking than in the later period, and it occurred without a concomitant rise in EC value because of the increased supply of AMP. Such a supply of AMP was reduced in the presence of benzohydroxamic acid or propyl gallale, inhibitors of an alternative respiratory pathway. It was thus concluded that both low temperature, coupled with warm temperature, and high temperature, by itself, can induce seed germination by increasing the ATP level as well as the total adenylate pool, but not the EC value, in the axial tissue. Further, that increases in both the ATP level and the adenylate pool especially are required for seed germination to proceed, probably depending on the activities of the cytochrome and alternative respiration pathways, respectively.     

Cold-Inhibited Phloem Translocation in Sugar Beet: IV. ANALYSIS OF THE COOLING-INDUCED REPARTITIONING HYPOTHESIS

Systems identification techniques were used to calculate photo-assimilatetransport characteristics in Beta vulgaris and Pisum sativum,before and after the application of localized perturbationsto the transport path. Changes in photo-assimilate partitioningto various monitored sinks were found to be promoted by slowcool (25 ?C to 1 ?C in 40 min), quick cool (25 ?C to 1 ?C in2 min)/quick warm, and apoplastic osmotic treatments of a localizedregion of the source leaf petiole in Beta. Photo-assimilatepartitioning into both intact and surgically modified (embryo-less)ovules of Pisum was also observed to change following quickcool/quick warm treatments applied to a 2.0 cm region of thepeduncle leading to the monitored pod. No changes in transportproperties were observed through the treated petiole regionof Beta during or following the slow cool treatment (i.e. transittime or system gain). High apoplastic osmolality (addition of1 000 mol m^–3 sorbitol) reduced the transit time of tracermovement through the treated petiole of Beta, while enhancingtracer washout from the bathed tissue region. Our modellingtechniques have shown that the physical or physiological basisfor the sink partitioning changes must be due to alterationsdownstream of the treated pathway zone, suggesting the involvementof physical signals transmitted from the treated region. Theseresults support the previously presented cooling-induced repartitioninghypothesis (Grusak and Lucas, 1986) and demonstrate that pathway-originatedstimuli can alter source-sink photo-assimilate partitioning. Key words: Photo-assimilate partitioning, phloem translocation, Beta vulgaris, Pisum sativum     

Photoinhibition of Seed Germination in Mediterranean Maritime Plants

Photoinhibition of seed germination was shown for Allium staticiforme,Brassica tournefortii, Cakile maritima and Otanthus maritimus,all plant species inhabiting sandy coasts of the MediterraneanSea. Germination of A. staticiforme was found to be typicallyMediterranean in regard to its temperature range (>0–20°C), while B. tournefortii germinated optimally at intermediatetemperatures (15–25 °C). Light sensitivity was morepronounced in the latter species and 50 % inhibition of seedgermination was obtained with photon flux densities of approximately0.1 and 0.015 mol m^–2 d^–1 in A. staticiforme andB. tournefortii, respectively. However, the slopes of the regressionlines of germination plotted against the logarithm of whitelight flux density are similar in both species. From monthlyexperiments performed under fluctuating conditions of temperatureand light, simulating the elimate of Athens throughout the year,optimal germination response peaked in ‘winter’conditions for A. staticiforme, while a bimodal pattern wasobserved for B. tournefortii (maxima at the warm ends of therainy season). In contrast to the other plants, a fifth speciestested, Crithmum maritimum, showed an absolute light requirement,probably related to the rocky habitats of the species; the optimumgermination period coincided with the rainy season. Pot experimentswith seeds of the five species buried at various depths confirmedthat maximum emergence is favoured by shallow depths (0.5–1cm). It is concluded that seed germination in maritime plantsof the Mediterranean rim is mediated by a photoinhibition mechanismwhich can be considered an adaptation strategy against surfaceseedling establishment at the harsh, sandy or shingle, sea coasthabitats. Allium staticiforme, Brassica tournefortii, Cakile maritima, sea rocket, Crithmum maritimum, rock samphire, Otanthus maritimus, ton-weed, seed germination, light, photoinhibition, phytochrome, seedling emergence     

Global responses of terrestrial productivity to contemporary climatic oscillations

The terrestrial biosphere is subjected to a wide range of natural climatic oscillations. Best known is the El Niño–southern oscillation (ENSO) that exerts globally extensive impacts on crops and natural vegetation. A 50-year time series of ENSO events has been analysed to determine those geographical areas that are reliably impacted by ENSO events. Most areas are impacted by changes in precipitation; however, the Pacific Northwest is warmed by El Niño events. Vegetation gross primary production (GPP) has been simulated for these areas, and tests well against independent satellite observations of the normalized difference vegetation index. Analyses of selected geographical areas indicate that changes in GPP often lead to significant changes in ecosystem structure and dynamics. The Pacific decadal oscillation (PDO) is another climatic oscillation that originates from the Pacific and exerts global impacts that are rather similar to ENSO events. However, the longer period of the PDO provided two phases in the time series with a cool phase from 1951 to 1976 and a warm phase from 1977 to 2002. It was notable that the cool phase of the PDO acted additively with cool ENSO phases to exacerbate drought in the earlier period for the southwest USA. By contrast in India, the cool phase of the PDO appears to reduce the negative impacts of warm ENSO events on crop production.     

Quantal Response of Seed Germination in Brachiaria humidicola, Echinochloa turnerana, Eragrostis tef and Panicum maximum to Photon Dose for the Low Energy Reaction and the High Irradiance Reaction

Various daily photon doses (daily net number of photons perunit area), provided by varying both photon flux density andphotoperiod, were applied to dormant seed populations of fourgraminaceous species tested for germination in alternating-temperatureregimes on filter papers moistened with either water or a solutionof potassium nitrate. In all four species germination was dependentupon daily photon dose, the product of photon flux density andduration, and quantified by linear relations between the probitof percentage germination and the logarithm of the daily photondose determined by probit analysis. Photon flux density andphotoperiod only influenced germination indirectly as factorsof daily photon dose, except in Echinochloa turnerana (Domin)J.M. Black at high daily photon doses where lower germinationwas observed in continuous light than in 8 h d^–1 photoperiod.The low energy reaction, in which increasing dose promotes seedgermination, was observed in Echlnochloa turnerana and Eragrostistef(Zucc.) Trotter but not in the populations of Brachiariahumidicola (Rendle) Schwcickerdt and Panicum maximum Jacq. usedin this study. The high irradiance reaction, in which increasingthe photon dose reduces germination, was, however, observedin all four species. In Eragrostis tef potassium nitrate influencedthe response of seed germination to light, but in the remainingspecies its influence on this relationship was either additive(Panicum maximum) or nil (Brachiaria humidicola and Echinochloaturnerana) in the alternating-temperature regimes used in thisstudy. The implications of the quantal response to photon dosefor devising optimal light regimes to be applied in laboratorytests intended to maximize seed germination are discussed. Key words: Light, seed germination, seed dormancy, grasses     

Cyanide-sensitive and Cyanide-resistant Respiration in the Germination of Cocklebur Seeds

Interrelation between the CN-sensitive cytochrome path and the CN-resistant, benzohydroxamic acid (BHM)-sensitive, or n-propylgallate (nPG)-sensitive alternative path in seed respiration during germination was examined using the nondormant upper and lower seeds of Xanthium pensylvanicum Wallr. The operation of both paths was required not only for normal germination of the lower seed but also for KCN- or NaN₃-induced germination of both. From the sensitivity to BHM of the germination response, it became obvious that the alternative path exerts its physiological activity as soon as it develops during the early period of water imbibition. Pretreatments with KCN and NaN₃ for promoting germination, strikingly decreased only the engagement of the cytochrome path in the subsequent respiration without affecting that of the alternative path. Nevertheless, no germination occurred without the operation of the cytochrome path. This suggested that excess operation of the cytochrome path is detrimental to germination, being maximal following the BHM-sensitive phase.     

Mimicking a semi-arid tropical environment achieves dormancy alleviation for seeds of Australian native Goodeniaceae and Asteraceae

Background and Aims: Seed physiological dormancy (PD) limits the use and conservationof some of Queensland's (Qld) native forb species. It was hypothesisedthat optimum dormancy-alleviating treatments would reflect environmentalconditions that seeds experience in situ, and this premise wastested for PD seeds of four species native to south-west Qld. Methods: High temperatures and increased rainfall during summer are characteristicof this semi-arid tropical environment. Ex situ treatments weredesigned to mimic conditions that seeds dispersed in springexperience during the summer months before germinating in coolerautumn temperatures. Seeds received between 4 and 20 weeks ofa dry after-ripening (DAR), warm stratification or dry/wet cyclingtreatment (DAR interspersed with short periods of warm stratification),in darkness, before being transferred to germination test conditions.In addition, natural dormancy alleviation of one of the Goodeniaceaespecies was investigated in situ. Key Results: Dry/wet cycling resulted in higher levels of germination ofActinobole uliginosum (Asteraceae), Goodenia cycloptera andVelleia glabrata (Goodeniaceae) when compared with constantDAR or stratification, while Goodenia fascicularis (Goodeniaceae)responded better to short durations of warm stratification.Long durations of DAR partially alleviated PD of A. uliginosum;however, stratification induced and maintained dormancy of thisspecies. Modifications to the dry/wet cycling treatment andgermination test conditions based on data collected in situenabled germination of G. cycloptera and V. glabrata to be furtherimproved. Conclusions: Treatments designed using temperature, relative humidity andrainfall data for the period between natural seed dispersaland germination can successfully alleviate PD. Differences betweenthe four species in conditions that resulted in maximum germinationindicate that, in addition to responding to broad-scale climatepatterns, species may be adapted to particular microsites and/orseasonal conditions.     

Nitrate Nutrition and Temperature Effects on Wheat: Soluble Components of Leaves and Carbon Fluxes to Amino Acids and Sucrose

Amounts of some metabolites and the incorporation of ¹⁴CO₂ intophotosynthetic products were measured in the third leaf of wheat,grown with two rates of nitrate supply at two temperatures,to analyse the effects of environmental conditions on the fluxesof carbon. Ribulose bisphosphate and 3-phosphoglyceric acidcontent per unit area were greater under nitrate deficiencyand decreased with leafage, but did not differ consistentlywith temperature. Sucrose content of young leaves was largerin cool than in warm conditions and with low nitrate, and decreasedwith age to similar values in all treatments. Starch accumulatedwith leaf age, slightly more in cool than warm conditions, andwith nitrate deficiency. Glutamate (plus glutamine), aspartate(plus asparagine), glycine and serine content of leaves weregreatest with added nitrate in cool temperature; changes withleaf age and conditions are discussed. The ¹⁴C content of assimilationproducts after exposure to ¹⁴CO₂ (for up to 10 min at 20 ?C)under steady-state conditions was slightly greater in plantsgrown in the warm than in the cool temperature and with additionalnitrate. Additional nitrate increased the proportion of ¹⁴Cin, and flux of carbon to, amino acids, particularly serineand glycine, and decreased it in sugar phosphates and sucrose.Cool growth temperatures increased the proportion of ¹⁴C inamino acids (pre-dominantly glycine and serine) and decreasedthat in sucrose. Changes in the balance of carbon fluxes betweenamino acids and carbohydrates are discussed in relation to glycolatepathway metabolism and alternative routes of amino acid synthesis. Key words: Wheat, temperature, nitrate supply, carbon flux, sucrose, amino acids     

Dormancy in Dioscorea: Range, Duration and Timing of High-Temperature Treatment in Germination Inhibition of D. tokoro Seeds

The effects of temperature on induction and release of high-temperatureinhibition in seed germination of Dioscorea tokoro Makino, amonocotyledonous summer perennial of the temperate zone of EastAsia, were investigated. Germination was increasingly inhibitedwith elevation of temperature over 23°C and lengtheningof its duration. The low temperature limit for germination inhibitiondecreased with lengthening of the duration of high temperature.The most sensitive phase for high temperature was 1–2days after the start of imbibition at 20°C. The germination inhibition by high temperature was reversedby chilling at 5°C, which is the optimum temperature forbreaking the natural dormancy (primary dormancy) of this seed.This showed that the high-temperature inhibition of germinationdoes not cause mortal damage but only secondary dormancy (induceddormancy). Seeds from a cold climate (Miyagi Pref.) responded rather quicklyto both high temperature and chilling compared to seeds froma warm climate (Kagoshima Pref.). The responsiveness to hightemperature and chilling of D. tokoro seed may affect the germinationtime under natural conditions. (Received October 22, 1982; Accepted January 14, 1983)     

Kinetics of creatine kinase in an experimental model of low phosphocreatine and ATP in the normoxic heart

To study the dependence of the forward flux of creatine kinase(CK) on its substrates and products we designed an acute normoxic modelof steady-state depletion of phosphocreatine (PCr) and adenylate in theisovolumic acetate-perfused rat heart. Various concentrations of PCrand ATP were induced by prior perfusion with 2 deoxy-D-glucose in the presenceof insulin. The apparent rate constant(k_f) and theforward CK flux were measured under metabolic and contractile steadystate by progressive saturation-transfer³¹P nuclear magnetic resonance(NMR). At high adenylate content CK flux was constant for a twofoldreduction in PCr concentration ([PCr]); CK flux was 6.3 ± 0.6 mM/s (vs. 6.5 ± 0.2 mM/s in control) because of adoubling of k_f.Although, at the lowest ATP concentration and [PCr], CKflux was reduced by 50%, it nevertheless always remained higher thanATP synthesis estimated by parallel oxygen consumption measurement.NMR-measured flux was compared with the flux computed under thehypothesis of CK equilibrium. CK flux could not be fully predicted bythe concentrations of CK metabolites. This is discussed in terms ofmetabolite and CK isozyme compartmentation.

     

The temperature dimension of the seed germination niche in fen wetlands

The seed germination niche partly determines adaptation, ecological breadth and geographic range in plant species. In temperate wetlands, environmental temperature is the chief regulator of germination timing, but the ecological significance of high and low temperatures during dormancy break and germination is still poorly understood. Our aim was to characterize the temperature dimension of the germination niche in mountain base-rich fens, determining (1) the effect of different temperatures on dormancy break and germination, and (2) whether different germination strategies may be identified at the species level. We conducted laboratory germination experiments with seeds of 15 species from these habitats, collected in 18 fen sites in the Cantabrian Mountains (Spain) for two consecutive years. In all the species, the seeds were totally or conditionally dormant at dispersal and stratification produced a significant increase of germination. In most cases, there was not an obligatory requirement for cold temperatures during dormancy break, since warm stratification promoted germination as well. Although the optimal germination thermoperiod was generally high (30/20 °C), most species could also germinate at lower temperatures after cold-stratification. We also identified a group of species associated to cold-water springs that germinated only at low temperatures. Our results demonstrate that dormancy break in mountain base-rich fens does not obligatorily depend on cold temperatures during overwintering. Furthermore, germination at cool temperatures may be more widespread in wetland habitats than previously thought. The existence of two distinctive germination strategies, ‘warm’ and ‘cool’, can potentially give rise to divergent species responses to climate change.     

Low Temperature Effects on Early Vegetative Growth, Leaf Gas Exchange and Water Potential of Chilling-sensitive and Chilling-tolerant Crop Species

Two chilling-sensitive (Phaseolus vulgaris L., Zea mays L.)and two chilling-tolerant (Pisum sativum L., Spinacia oleraceaL.) species were raised in growth chambers under warm (28/18°Cday/night cycle) and cool (18/12°C) temperature regimes.Growth analysis techniques were used to evaluate leaf area andbiomass partitioning during early autotrophic growth. Plantsacclimated to both temperatures were measured for leaf gas exchangeand water potential (     

The Interactive Effects of Phytochrome, Nitrate and Thiourea on the Germination Response to Alternating Temperatures in Seeds of Ranunculus sceleratus L.: A Quantal Approach

Probert, R. J., Gajjar, K. H. and Haslam, I. K. 1987. The interactiveeffects of phytochrome, nitrate and thiourea on the germinationresponse to alternating temperatures in seeds of Ranunculussceleratus L.: A quantal approach.—J. exp. Bot. 38: 1012–1025. The interactive effects of phytochrome, potassium nitrate andthiourea on the germination response to alternating temperaturesin achenes (seeds) of Ranunculus sceleratus L. were studied.Using thermogradient bars, high levels of germination were recordedover a broad range of alternating temperatures providing seedsreceived daily irradiations. Reduced germination in temperaturecycles with a relatively long warm phase was related to thelevel of the active form of phytochrome (Pfr). Dose-responseexperiments to red light (R) and temperature shifts showed thatthe actions of Pfr and alternating temperatures were interdependent.Maximum germination was recorded when intermittent pulses ofR were combined with daily 4 h temperature shifts from 16°Cto 26°C. Whilst probit analysis showed that potassium nitrateand thiourea both increased population sensitivity to temperatureshifts, thiourea was a more potent stimulant. Although the effectof both chemicals was dependent on phytochrome photo-equilibriumthe threshold level of Pfr required for thiourea action wasclearly much lower than that required for nitrate action. Thioureapotentiated a response to daily temperature shifts even whenPfr was at a low, normally inhibitory level. These results indicatedifferent mechanisms of action for potassium nitrate and thioureain relation to phytochrome controlled seed germination. Key words: Phytochrome, nitrate, thiourea, alternating temperatures, germination     

Photoinhibition of Seed Germination in the Maritime Plant Matthiola tricuspidata

The three-horned stock, Matthiola tricuspidata (L.) R. Br. isa widespread annual plant of the Mediterranean sandy shores.Its seeds are dark germinating and negatively photosensitive,in accordance with our previous findings for a number of othermaritime plants. Full germination was obtained at a wide rangeof temperatures (5-25 °C) in the dark. Inhibition of germinationunder light of various spectral qualities could be generallycorrelated, negatively and positively, respectively, with phytochromephotostationary state (ø) and relative cycling rate ofphytochrome (H). The inhibition of germination by white (fluorescent),blue and far-red light, applied either continuously or intermittently,consistently showed a linear dependence upon the logarithm ofthe flux density of the irradiation. The resulting photoinhibitioncurves had parallel slopes and, compared to those of other maritimeplants, they were shifted to higher flux densities, Continuousblue or far-red irradiations, both establishing a similar øvalue (0·26), resulted in statistically similar regressioncurves, thus favouring the hypothesis that phytochrome is thesingle photoreceptor in the photoinhibition of seed germination.Copyright1994, 1999 Academic Press Matthiola tricuspidata (L.) R. Br., three-horned stock, seed germination, light, photoinhibition, phytochrome