Response to Temperature in a Stand of Pearl Millet (Pennisetum typhoides S. & H. )

Stands of millet were grown in temperature-controlled glasshousesmaintained at mean air temperatures of 19-31 °C and sub-plotswere heated or cooled to examine the effect of soil temperatureon early plant development. Soil temperature influenced all aspects of early vegetativedevelopment: the emergence of seedlings, the initiation, appearanceand final number of leaves and tillers. Results are presentedin terms of both chronological and ‘thermal’ time(the summation of degree days (°C d) above an extrapolatedbase (T_b) determined from the rate/temperature relation). Ratesof the processes examined increased linearly with temperature,but the duration of vegetative phases appeared to be constantbetween 19-30 °C. The rate of all processes can thereforebe described by a specific thermal time () e. g. 26 °C dfor each leaf initiated and a base temperature (T_b) which wassimilar for all the vegetative processes examined. 0 was relativelyconstant over the range of irradiance and saturation deficitexperienced in the experiments. The results are compared to previous data for millet and othertropical species. Key words: Millet, Thermal time, Vegetative development     

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

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

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

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

Effects of Temperature and Water Loss on Terrestrial Locomotor Performance in Land Crabs: Integrating Laboratory and Field Studies

SYNOPSIS. Terrestrial and semi-terrestrial crustaceans are exposedto fluctuations in ambient temperature and conditions that favorevaporative water loss. These environmental stresses alter performancelimits in the laboratory and behavior in the field. The maximalrate of oxygen consumption, maximum aerobic speed, and endurancecapacity are greater at a body temperature (T_b) of 24°Cthan at 15°C or 30°C in the ghost crab, Ocypode quadrata.The total metabolic cost to move at the same relative speedis greater at a T_b of 24°C than at 15°C. Slower aerobickinetics at 15°C result in a smaller relative contributionof oxidative metabolism to total metabolic cost. However, therelative contributions from accelerated glycolysis are similarat both temperatures. When locomotion is intermittent, the totaldistance traveled before fatigue can be similar at Tbs of 15and 24°C but result from different movement and pause durationsat these temperatures. Performance limits of the ghost crabare negatively affected by dehydration and are sensitive torates of water loss. In the laboratory, endurance capacity ofthe fiddler crab, Uca pugilator, is greater at a T_b of 30°Cthan at 25°C. In the field, freely moving fiddler crabswith a T_b of 30°C travel at faster mean preferred speeds,as determined by motion analysis, than crabs at 25°C. Datafor land crabs support and advance general ectothermic modelsfor the effects of temperature and dehydration on locomotorperformance.     

Heat stroke: opioid-mediated mechanisms

Romanovsky, Andrej A., and Clark M. Blatteis. Heatstroke: opioid-mediated mechanisms. J. Appl.Physiol. 81(6): 2565-2570, 1996.In our previousstudy in guinea pigs, intensive and prolonged intraperitoneal heating(IPH) caused heat stroke characterized by high mortality andaccompanied by two paradoxical phenomena: ear skin vasoconstriction ata high body temperature (T_b)(hyperthermia-induced vasoconstriction) and a post-IPHT_b fall at an ambient temperature (T_a) below thermoneutrality(hyperthermia-induced hypothermia). In this study, we tested thehypothesis that the mechanisms of the two phenomena involve endogenousopioid agonists. Experiments were conducted in 24 unanesthetized,lightly restrained guinea pigs, each chronically implanted with anintraperitoneal thermode and intrahypothalamic thermocouple. Thethermoregulatory effects of a wide-spectrum opioid-receptor antagonist,naltrexone (NTX; 50 or 0 µmol/kg sc), were studied in IPH-inducedheat stroke and under normal conditions. IPH was accomplished byperfusing (50 ml/min; 80 min) water (45°C) through the thermode.T_a was maintained at ~24°C.Skin vasodilation occurred at the onset of IPH but later changed tovasoconstriction despite high T_band continuing IPH. IPH-induced hyperthermia (1.8 ± 0.1°C) was followed by a post-IPH T_b fall (5.1 ± 0.7°C; calculated for the survivors only). The 48-h mortality ratewas 50%. NTX prevented the hyperthermia-induced vasoconstriction andattenuated the hyperthermia-induced hypothermia (1.8 ± 0.4°C). None of the NTX-treated animals died. The effects of NTX onT_b regulation under normalconditions were minor. These results indicate that the phenomena ofboth hyperthermia-induced vasoconstriction and hyperthermia-inducedhypothermia are opioid dependent. The latter is speculated to reflectopioid-mediated inhibition of metabolism; the former is thought toresult from opioid-induced hemodynamic alterations. Because bothphenomena did not occur in the NTX-treated survivors, the skinvasoconstriction at high T_b andthe posthyperthermia T_b fall maybe viewed as markers of the severity of heat stroke. It is suggestedthat opioid antagonists may have therapeutic potential in heat-induceddisorders.

     

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

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

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

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

The Potential for Photoinhibition of Pinus sylvestris L. Seedlings Exposed to High Light and Low Soil Temperature

The effect of high light and root chilling on gas exchange,chlorophyll fluorescence, and bulk shoot water potential (_shoot)was examined for Pinus sylvestris seedlings. Transferring plantsfrom low light (200 µmol m^–2s^–1, PAR) anda soil temperature of 15 °C to high light (850 µmolm^–2 s^–1) and 1 °C caused >90% decrease innet photosynthesis and leaf conductance measured at 350 mm³dm^-3 CO₂, and a decrease in the ratio of variable to maximumfluorescence (F_v/F_m) from 0.83 to 0.63. The decrease in Fv/Fmwas, however, only marginally greater than when seedlings weretransferred from low to high light but kept at a soil temperatureof 15 °C. Thus, photoinhibition was a minor component ofthe substantial decrease observed for net photosynthesis at1 °C soil temperature. The decrease in net photosynthesisand _shoot at 1 °C was associated with an increase in calculatedintracellular CO₂ concentration, suggesting that non-stomatalfactors related to water stress were involved in inhibitingcarbon assimilation. Measurements at saturating external CO₂concentration, however, indicate that stomatal closure was thedominant factor limiting net photosynthesis at low soil temperature.This interpretation was confirmed with additional experimentsusing Pinus taeda and Picea engelmannii seedlings. Decreasesin gas-exchange variables at 5 °C soil temperature werenot associated with changes in _shoot Thus, hormonal factors,localized decreases in _needles or changes in xylem flux maymediate the response to moderate root chilling.     

Transverse Relaxation Time of Leaf Water Protons and Membrane Injury in Wheat (Triticum aestivum L.) in Response to High Temperature

The relationship between high temperature stress injury andtemperature dependence of the transverse relaxation time (T₂)of leaf water was examined using NMR in four cultivars of wheatdiffering in their sensitivity to high temperature stress. TheT₂declined with increasing temperature between 25 and 35 °C.A comparison of relative injury based on electrolyte leakageand T₂, between 40 and 50 °C, indicated that while membranepermeability increased with increasing temperature there wasan increase in T₂until 44 and 48 °C in susceptible and tolerantcultivars respectively, followed by a sharp decline. This patternof change in T₂with increasing temperature was consistent whetherthe same or different samples were used for each treatment temperature.Loss of temperature dependence of T₂after heat killing indicatedirreversible changes in T₂, probably due to the loss of membraneintegrity. Heat tolerant varieties, which suffered less membraneinjury, had a higher T₂compared to susceptible varieties. Tolerantvarieties also maintained the T₂of leaf water protons to highertemperatures than did sensitive varieties. This NMR-based, non-invasive,rapid technique could be used to efficiently detect heat injuryin leaf tissues. Copyright 1999 Annals of Botany Company Membrane integrity, transverse relaxation time, high temperature stress, Triticum aestivum L.     

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     

Chilling Damage to Photosynthesis in Young Zea mays: I. EFFECTS OF LIGHT AND TEMPERATURE VARIATION ON PHOTOSYNTHETIC CO2 ASSIMILATION

Carbon dioxide and water vapour exchanges of the second leafof Zea mays in controlled environment cuvettes were measuredin an open gas-exchange system, during and following subjectionto low temperature stress. Photosynthetic CO2 assimilation (Fc)decreased markedly with decrease in leaf temperature so thatFc at 5 °C was c. 7% of Fc at 20 °C. Fc continued todecline if leaf temperature was maintained at 5 °C, andwhen returned to 20 °C the leaf could not regain its previousFc. This chill-induced reduction in the capacity of the leafto assimilate CO2 was proportional to the duration of the chilland increased with water vapour pressure deficit and photonflux density (I_n). Six hours at 5 °C decreased Fc on returnto 20 °C, relative to Fc prior to treatment, by c. 10% indarkness and by c. 50% in a photon flux density approachingfull-sunlight (I_p = 1.5 mmol m^–2 s^–1). The degreeof reduction in Fc following chill treatment showed an almostlinear dependence on both the length and temperature of thechill. Chill treatments resulted in a decrease in both stomataland mesophyll conductances. Examination of the responses ofF_c to light and CO₂ concentration suggested that chill damageto the capacity for CO₂ assimilation resulted from effects onboth the light and CO₂ limited processes within photosynthesis. Key words: Chilling, Photosynthesis, Zea mays, Light-temperature interaction     

Thermal and metabolic responses to cold-water immersion at knee, hip, and shoulder levels

Lee, Dae T., Michael M. Toner, William D. McArdle, IoannisS. Vrabas, and Kent B. Pandolf. Thermal and metabolic responses tocold-water immersion at knee, hip, and shoulder levels.J. Appl. Physiol. 82(5):1523-1530, 1997.To examine the effect of cold-water immersion atdifferent depths on thermal and metabolic responses, eight men (25 yrold, 16% body fat) attempted 12 tests: immersed to the knee (K), hip(H), and shoulder (Sh) in 15 and 25°C water during both rest (R) orleg cycling [35% peak oxygen uptake; (E)] for up to 135 min. At 15°C, rectal (T_re)and esophageal temperatures(T_es) between R and E were notdifferent in Sh and H groups (P > 0.05), whereas both in K group were higher during E than R(P < 0.05). At 25°C,T_re was higher(P < 0.05) during E than R at alldepths, whereas T_es during E washigher than during R in H and K groups.T_re remained at control levels inK-E at 15°C, K-E at 25°C, and in H-E groups at 25°C,whereas T_es remained unchanged inK-E at 15°C, in K-R at 15°C, and in all 25°C conditions (P > 0.05). During R and E, themagnitude of T_re change wasgreater (P < 0.05) than themagnitude of T_es change in Sh andH groups, whereas it was not different in the K group(P > 0.05). Total heat flow wasprogressive with water depth. During R at 15 and 25°C, heatproduction was not increased in K and H groups from control level(P > 0.05) but it did increase in Shgroup (P < 0.05). The increase inheat production during E compared with R was smaller(P < 0.05) in Sh (121 ± 7 W/m² at 15°C and 97 ± 6 W/m² at 25°C) than in H (156 ± 6 and 126 ± 5 W/m²,respectively) and K groups (155 ± 4 and 165 ± 6 W/m², respectively). These datasuggest that T_re andT_es respond differently duringpartial cold-water immersion. In addition, water levels above knee in15°C and above hip in 25°C cause depression of internal temperatures mainly due to insufficient heat production offsetting heatloss even during light exercise.

     

Effects of Water Stress under Contrasting Environmental Conditions on Transpiration and Photosynthesis in Soybean

Continuous and simultaneous measurements of CO₂ exchange andtranspiration rates of whole soybean plants were made undercontrasting, controlled environmental conditions when waterstress was imposed by withholding water. Daytime temperaturesand vapour pressure deficits were 27.5 ° C/12 mbar; 27.5° C/5 mbar; 22.5 ° C/12 mbar, and 22.5 ° C/5 mbar.The experimental conditions were virtually the same as the conditionsunder which the plants had been grown. Under all four treatments photosynthesis and transpiration rateswere closely correlated as water stress increased, but in viewof the evidence for a significant mesophyll resistance to photosynthesisin- both stressed and unstressed plants it is not consideredthat this is due to total stomatal control. At — 0.4 bar soil water potential (_soll) the rates oftranspiration and photosynthesis became independent of the atmosphericconditions and were very similar under all treatments. Thisis attributed to slow movement of water into the root zone fromthe surrounding soil with associated stomatal closure limitingthe rates of water uptake and transpiration. With decreasing _soll, relative water content of the leaf (RWC)fell more rapidly and to lower levels under 27.5 ° C/12mbar conditions than under the other treatments. The least reductionin RWC was under the 22.5 ° C/5 mbar treatment. Increasingsoil water stress had the greatest relative effect on ratesof gaseous exchange under 27.5 ° C/12mbar conditions andleast under 22.5 ° C/5mbar conditions.     

Chronic hormone replacement therapy alters thermoregulatory and vasomotor function in postmenopausal women

Brooks, E. M., A. L. Morgan, J. M. Pierzga, S. L. Wladkowski, J. T. O'Gorman, J. A. Derr, and W. L. Kenney. Chronic hormone replacement therapy alters thermoregulatory and vasomotor function in postmenopausal women. J. Appl.Physiol. 83(2): 477-484, 1997.This investigationexamined effects of chronic (2 yr) hormone replacement therapy (HRT),both estrogen replacement therapy (ERT) and estrogen plus progesteronetherapy (E+P), on core temperature and skin blood flow responses ofpostmenopausal women. Twenty-five postmenopausal women [9 not onHRT (NO), 8 on ERT, 8 on E+P] exercised on a cycle ergometer for1 h at an ambient temperature of 36°C. Cutaneous vascularconductance (CVC) was monitored by laser-Doppler flowmetry, and forearmvascular conductance (FVC) was measured by using venous occlusionplethysmography. Iontophoresis of bretylium tosylate was performedbefore exercise to block local vasoconstrictor (VC) activity at oneskin site on the forearm. Rectal temperature (T_re) was ~0.5°C lower forthe ERT group (P < 0.01) comparedwith E+P and NO groups at rest and throughout exercise. FVC: mean body temperature (T_b) and CVC:T_b curves were shifted~0.5°C leftward for the ERT group(P < 0.0001). Baseline CVC wassignificantly higher in the ERT group(P < 0.05), but there was nointeraction between bretylium treatment and groups once exercise wasinitiated. These results suggest that1) chronic ERT likely acts centrally to decrease T_re,2) ERT lowers theT_re at which heat-loss effector mechanisms are initiated, primarily by actions on active cutaneous vasodilation, and 3) addition ofexogenous progestins in HRT effectively blocks these effects.

     

The Arrhenius Equation as a Model for Explaining Plant Responses to Temperature and Water Stresses

The Arrhenius equation describes the response of biologicalprocesses to temperature. This study was conducted to examinethe applicability of the Arrhenius equation to whole plant processesand to explore the application of the Arrhenius equation asa basis for characterizing plant responses to water stress.Rates of growth of leaf area and shoot dry mass of spring wheatseedlings were measured at combinations of five soil water potentials(–0.03, –0.06, –0.10, –0.17 and –0.25MPa) and seven root temperatures (12, 14, 17, 22, 27, 29 and32 C). A non-linear least square procedure was used to fitthe modified Arrhenius equation to experimental observations.Adequate distribution of experimental observations with respectto temperature reduces the uncertainties in parameter evaluations.The standard error of the estimate of optimum temperature forleaf area growth increased from 1.4 C to 6.3 C when one ofthe data points was omitted. The optimum temperature and theenthalpy of denaturalization of enzyme systems were independentof soil water potential. A linear relation was found betweenthe rate constant and the activation energy: The Arrhenius equation was modified using this linear relation,leaving the activation energy as the only parameter affectedby water stress. The activation energy increased linearly assoil water potential decreased, with slopes of –27.18 10₃ and –28.09 10₂ K MPa^–1 for the rates ofgrowth of leaf area and shoot dry mass, respectively. Theseslopes could be used as indicators of the sensitivity of plantprocesses to water stress. Temperature, water, plants, Arrhenius equation     

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     

Reanalysis of Vernalization Data of Wheat and Carrot

Vernalization is an important determinant of the growth, development,and yield of biennial and perennial crops. Accurate simulationof its response to temperature is thus an important componentof successful crop systems modelling. Vernalization has a lowoptimum temperature compared to other temperature responsesof plants, and thus may be difficult to treat using expressionsthat are appropriate for other plant processes. This paper examinesthe application of a simple equation that has been used forother processes. It reads as v=V_max(T_max-T_{Tmax- Topt} ) (T_Topt)^{T_optTmax-T_opt}, where v is thedaily rate of vernalization progress at temperature T, T_optandT_maxare the optimum and maximum temperatures for vernalization,respectively, andV_max is the maximum daily rate of vernalization(the inverse of the minimum number of days required to completevernalization), which occurs at T_opt. The model was appliedto published vernalization data for wheat and carrot. The fitsto data were good (adjusted R²for wheat of 0.94, for carrot0.98), with estimatedT_opt and T_maxbeing 5.7±0.5 and 21.3±1.4°C, respectively, for wheat ‘Norin 27’ and 6.6±0.2and 14.1±0.3 °C for carrot ‘ Chantenay RedCored’. The estimated parameters, in particular the highT_maxfor wheat, were close to those reported using differentanalytical approaches. It was suggested that the function wouldbe useful for summarizing vernalization data, and that its usewould avoid the abrupt changes that are inevitable when differentlinear relationships are used for part of the overall response.It was also suggested the high T_maxshould be taken into accountwhen interpreting data obtained with wheat grown under warmconditions. Copyright 1999 Annals of Botany Company Plant, vernalization, temperature response, modelling, wheat (Triticum aestivum L.), carrot (Daucus carota L.).     

Thermoregulatory responses to variations of photoperiod and ambient temperature in the male lesser mouse lemur: a primitive or an advanced adaptive character?

The lesser mouse lemur, a small Malagasy primate, is exposed to strong seasonal variations in ambient temperature and food availability in its natural habitat. To face these environmental constraints, this nocturnal primate exhibits biological seasonal rhythms that are photoperiodically driven. To determine the role of daylength on thermoregulatory responses to changes in ambient temperature, evaporative water loss (EWL), body temperature (T _b) and oxygen consumption, measured as resting metabolic rate (RMR), were measured in response to ambient temperatures ranging from 5 °C to 35 °C, in eight males exposed to either short (10L:14D) or long (14L:10D) daylengths in controlled captive conditions. In both photoperiods, EWL, T _b and RMR were significantly modified by ambient temperatures. Exposure to ambient temperatures below 25 °C was associated with a decrease in T _b and an increase in RMR, whereas EWL remained constant. Heat exposure caused an increase in T _b and heat loss through evaporative pathways. Thermoregulatory responses to changes in ambient temperature significantly differed according to daylength. Daily variations in T _b and EWL were characterized by high values during the night. During the diurnal rest, lower values were found and a phase of heterothermia occurred in the early morning followed by a spontaneous rewarming. The amplitude of T _b decrease with or without the occurrence of torpor (T _b < 33 °C) was dependent on both ambient temperature and photoperiod. This would support the hypothesis of advanced thermoregulatory processes in mouse lemurs in response to selective environmental pressure, the major external cue being photoperiodic variations. Accepted: 4 August 1998     

Base water potential of Picea abies as a characteristic of the soil water status

Variation in base water potential (Ψ_b, a daily maximum level of plant water potential, which is presumed to correspond to the condition of equilibrium between the soil and plant water potentials) was examined in shoots of Norway spruce trees growing in well-drained and waterlogged soils. The influence of soil water content, air temperature, and vapour pressure deficit of the atmosphere on Ψ_b was studied using the pressure chamber technique. Maximum daily water potentials were not always observable before dawn; some were registered up to two hours later. This tendency being characteristic of trees growing under stress (shade, waterlogging) conditions, increased with declining soil water availability. In trees growing in well-drained soil, Ψ_b depended asymptotically on the available soil water storage (R²=0.73), while the values were slightly influenced by vapour pressure deficit of the atmosphere as well. In trees growing in waterlogged soil, Ψ_b was independent of the soil water storage, but sensitive to the vapour pressure deficit.     

Body temperatures in free-flying pigeons

We examined the relationship between body temperature (T_b) of free flying pigeons and ambient water vapor pressure and temperature. Core or near core T_b of pigeons were measured using thermistors inserted into the cloaca and connected to small transmitters mounted on the tail feathers of free flying tippler pigeons (Columba livia). Wet and dry bulb temperatures were measured using modified transmitters mounted onto free-flying pigeons. These allowed calculation of relative humidity and hence water vapor pressure at flight altitudes. Mean T_b during flight was 42.0 ± 1.3 °C (n = 16). Paired comparisons of a subset of this data indicated that average in-flight T_b increased significantly by 1.2 ± 0.7 °C (n = 7) over that of birds at rest (t = −4.22, P < 0.05, n = 7) within the first 15 min of takeoff. In addition, there was a small but significant increase in T_b with increasing ambient air (T_a) when individuals on replicate flights (n = 35) were considered. Inclusion of water vapor pressure into the regression model did not improve the correlation between body temperature and ambient conditions. Flight T_b also increased a small (0.5 °C) but significant amount (t = 2.827, P < 0.05, n = 8) from the beginning to the end of a flight. The small response of T_b to changing flight conditions presumably reflects the efficiency of convection as a heat loss mechanism during sustained regular flight. The increase in T_b on landing that occurred in some birds was a probable consequence of a sudden reduction in convective heat loss. Accepted: 2 February 1999