Relationships between Photosynthesis and Light Intensity in the Tomato

Curves were fitted to the rates of CO₂ uptake (P) of singleleaves of tomato against light intensity (I). It was shown thatan asymptotic curve of the form P = a–bp^I gave a consistentlybetter fit to the observed data than the rectangular hyperbola.Saturating rates of photosynthesis, estimated as the asymptoteof the curve, showed marked changes with leaf age, being maximalat or shortly after the start of the experiment, in small rapidlyexpanding leaves, and falling continuously thereafter. Photochemicalefficiency, measured as the slope of the curve at zero lightintensity, gave no discernable trends with time except in visiblysenescent leaves, when the value decreased appreciably.     

Determination of a Critical Nitrogen Dilution Curve for Winter Oilseed Rape

Several controlled environmental and field experiments werecarried out to define the critical nitrogen dilution curve forwinter oilseed rape, cultivar Goeland. This curve is describedby the following power equation:N=4.48 W^-0.25,whereNis the totalnitrogen concentration in the shoot biomass andWthe shoot biomass.This curve has been validated over the range of shoot dry matterof 0.88 to 6.3 t ha^-1. For lower shoot biomasses this equationoverestimated the critical nitrogen concentration; we proposea constant value of 4.63 (Nis expressed in reduced N, whichis a more stable N fraction in the shoot at these stages ofdevelopment). These results have been validated in several pedoclimaticconditions in France on a single variety in 1994 and 1995. Thehigher position of this curve relative to the C₃species referencecurve (Greenwoodet al.,Annals of Botany67: 181–190, 1990)can be explained by the experimental conditions obtained byGreenwoodet al. (1990); therefore, all their rape data are ratherclose to the critical curve that we propose. The differencesfound between wheat and winter oilseed rape critical N dilutioncurves correspond to their respective leaf:stem dry matter ratioand the specific leaf loss phenomenon occuring in rape. Winteroilseed rape has a higher capacity of N accumulation in itsshoot than wheat for the same aerial dry matter. The proportionof nitrate in shoots rises with the nitrogen nutrition index(N.N.I.) and is more important for rapeseed than for wheat forthe same N.N.I. This difference is especially high at the beginningof flowering when the shade provided by the canopy of rapeseedflowers decreases nitrate reductase activity.Copyright 1998Annals of Botany Company Winter oilseed rape;Brassica napusL.; plant N concentration; nitrate; reduced N; shoot biomass; critical nitrogen concentration; dilution curve; N productivity.     

Experimental and Analytical Studies of Pteridophytes XXXVI. Further Experiments on the Developmental Potentialities of Leaf Primordia in Dryopteris aristata Druce

The curve of growth in area of Pelargonium leaves against timeis strongly asymmetrical, and cannot be fitted by the usuallogistic curve. It is shown that the Gompertz curve providesan excellent fit, and the significance of its parameters isdiscussed.     

Photosynthesis and primary production of Microcystis aeruginosa Kutz. in Lake Kasumigaura

Seasonal changes in the photosynthesis and primary productionof Microcystis aeruginosa Kütz. were investigated in LakeKasumigaura during 1981–1982. Microcystis always showeda light-saturated photosynthesis-light curve. Both P_max andthe initial slope of the photosynthesis-light curve of Microcystisin early summer were very high, so it was concluded that Microcystisutilized both low and high light intensities efficiently. TheP_max of Microcystis was found to be a function of the watertemperature except in August and September. The linear regressionon the temperature-P_max relationship discontinued at 11°C,where the P_max value dropped; Microcystis did not photosynthesizebelow 4°C. The initial slope of the curve was also descendingbelow 11°C. It is suggested that Microcystis changes itsphysiological properties below 11°C. The highest value ofgross production calculated for M. aeruginosa was 5.4 gC m^–2d^–1 in July; the annual gross production was estimatedto be 300 gC m^–2year^–1 (i.e., 40% of the total primaryproduction in this lake).     

The effects of food deprivation, prey density and volume on clearance rates and ingestion rates of Diacyclops thomasi

The ingestion rates of the copepod, Diacyclops thomasi, on thesoft-bodied rotifer, Synchaeta pectinata, increased 10-fold(0.07–0.77 Synchaeta h^–1) over the range 50–250prey l^–1. The saturating functional response curve appearedsigmoid but was statistically indistinguishable from a parabola.The response curve was more linear and 10 times lower over thesame range of density when Diacyclops was offered Kerarellacochleans, a species having a stiffened lorica. Diacyclops maximizedits ingestion rate on Synchaeta as a function of the availablegut space. Predation effort, measured as clearance rates, waslinked tentatively to changes in swimming speed of Diacyclopsand was a function of hunger level. Diacyclops, which were starvedfor varying periods of time, increased their ingestion rateson Synchaeta up to a maximum (-3.0 h^–1) after 7–10h of food deprivation. The gut passage time of Diacyclops wasestimated to be 7–8 h. Therefore, ingestion rates (andclearance rates) appeared to be strongly correlated to the volumeof food in the gut.     

Are Seasonal Dormancy Patterns in Arabidopsis thaliana Regulated by Changes in Seed Sensitivity to Light, Nitrate and Gibberellin?

Imbibed seeds of Arabidopsis thaliana (L.) Heynh., passed annuallythrough a pattern of changes in dormancy. Dormancy was brokenin summer and re-induced in autumn-winter. A second small germinationflush occurred in early spring. The role of sensitivity to light,nitrate and gibberellins (GAs) in regulating annual dormancypatterns and germination was studied with the use of GA-deficient(gal-2) and wild-type seeds. Dark-incubated seeds were exposedto a natural temperature regime for periods up to 18 monthsand at regular intervals germination capacity of portions ofseeds was tested at laboratory conditions. Germination datafitted as logistic dose response curves showed that sensitivityto light varied with the seasons in both genotypes. From interpretationof curve parameters, it is proposed that the observed sensitivitychanges involve alterations in the number of receptors, in thebinding characteristics of the receptors and/or in the responsechain initiated by ligand-receptor interaction. In this responsechain GA biosynthesis is stimulated (wild type) and sensitivityto GAs is enhanced (wild type, gal -2). GA sensitivity is alsodirectly influenced by temperature, thus without the interferenceof light. However, the significance of direct regulation ofGA requirement seemed to diminish with prolonged incubationoutdoors, whereas reversible changes in light sensitivity remainedclear. Therefore, we propose that seasonal dormancy patternsare mainly regulated by changes in sensitivity to light. GAsensitivity contributes to this pattern but is not primarilycontrolling dormancy. The GA requirement for germination isobvious as gal-2 seeds did not germinate at any time of theyear when deprived of applied GAs. However, GA biosynthesisis not required for dormancy control, as a dormancy patternwas also observed in the absence of the capacity to synthesizeGAs. Nitrate or sensitivity to nitrate did not contribute tothe regulation of dormancy and germination of this species.Copyright1994, 1999 Academic Press Arabidopsis thaliana (L.) Heynh., curve fitting, dormancy, fluence response curve, germination, gibberellin, gibberellin dose response curve, hormone mutant, light, mouse-ear-cress, nitrate, phytochrome, receptor, seasonal dormancy pattern, sensitivity     

Light Dependency of Carboxylation Efficiency and Ribulose-1, 5-Bisphosphate Carboxylase Activation in Trifolium subterraneum L. Leaves

The effect of photosynthetic photon flux density (PPFD) on carboxylationefficiency, estimated as the initial slope (IS) of net CO₂ assimilationrate versus intercellular CO₂ partial pressure response curve,as well as on ribulose-1, 5-bisphosphate carboxylase (Rubisco)activation was measured in Trifolium subterraneum L. leavesunder field conditions. The relationship between IS and PPFDfits a logarithmic curve. Rubisco activation accounts for theIS increase only up to a PPFD of 550 µmol photons m^-2s^-1. Further IS increase, between 550 and 1000 µmol photonsm^-2 s^-1, could be related to a higher ribulose fcwphosphate(RuBP) availability. The slow, but sustained IS increase above1000 µmol photons m^-2 s^-1 could be explained by the mesophyllCO₂ diffusion barriers associated with the high chlorophylland protein content in field developed leaves. Key words: Photosynthesis, initial slope, ribulose-1, 5-bissphosphate carboxylase activation, light response, Trifolium subterraneum L     

Leaf Thickness and Water Deficit in Plants: A Tool for Field Studies

B?rquez, A. 1987. Leaf thickness and water deficit in plants:a tool for field studies.—J. exp. Bot. 38: 109–114. A technique for estimating plant water deficits using a relativelyinexpensive micrometer to measure leaf thickness was developed.A strong correlation was found between leaf thickness and relativewater content (RWC) in Brassica napus, Mirabilis jalapa, Phaseolusvulgaris and Impatiens parviflora. Although leaf thickness ata given RWC varied between plants, it increased linearly withleaf RWC, the rate of change being similar in leaves of plantsof the same age and species. Due to this relationship, the constructionof a pressure-volume curve makes possible the estimation ofleaf water potential. In this case a calibration curve is neededfor each population studied or, for the highest accuracy, foreach individual. The technique is particularly useful in fieldconditions where other techniques are not reliable because ofdifficulties in controlling temperature and where non-destructivemeasurements are required. Key words: Leaf thickness, relative water content, water potential     

苦参碱对棉铃虫幼虫神经细胞钠通道的影响

用全细胞膜片钳技术研究了生物碱类植物杀虫剂苦参碱对棉铃虫Helicoverpa armigera幼虫离体培养中枢神经细胞钠离子通道门控过程的影响。结果表明： 苦参碱对棉铃虫幼虫神经细胞所表达的TTX （tetradotoxin, 河豚毒素)敏感钠通道具有浓度依赖性阻滞作用,1,10和100 μmol/L的苦参碱作用5 min后,分别使钠电流峰值较给药前下降（12.49±1.67）%、（18.79±2.16）%和（43.15±8.17）% (n=8, P<0.05)。苦参碱使钠电流的电流 电压关系曲线上移,但并不改变其激活电压、峰电压和电流电压关系曲线的形状。苦参碱对钠通道的阻滞作用可能是其具有某些毒理效应的离子基础。     

Effect of Wind on the Transpiration of Young Trees

The effects of wind on the transpiration rates of four plantspecies, Pinus sylvestris L., Quercus robur L., Fagus sylvaticaL. and Sorbus aucuparia L., were studied in a controlled environmentwind tunnel. Transpiration declined with increasing wind speedin a manner consistent with predictions of the Penman-Monteithequation. The stomatal resistance declined with increasing windspeed in two species and increased in one, but this effect wassmaller than reported in other studies. In all cases the magnitudeof the stomatal response was over-shadowed by the decliningleaf to air vapour pressure difference. Pinus sylvestris L., Quercus robur L., Fagus sylvatica L., Sorbus aucuparia L., wind, transpiration, cooling curve technique, stomatal resistance, aerodynamic resistance, Penman-Monteith equation     

Biomass Accumulation and Main Stem Elongation of Durum Wheat Grown under Mediterranean Conditions

Detecting and exploiting genetic variation in biomass accumulationis of great importance for increasing wheat yield when the harvestindex is close to its upper limit. This study was undertakento analyse the pattern of biomass accumulation and main stemelongation in 25 durum wheat (Triticum turgidum L. ‘Durum’)genotypes. Field experiments were conducted over 2 years intwo environments contrasting in the amount of available water,in northeastern Spain. Plants were sampled at the main stagesof Zadoks' scale, and dry weight per plant, crop dry weight(CDW) and main stem length were measured at each stage. Measurementsfor growth traits and thermal time from sowing fitted betterto an asymmetric logistic peak curve than to the Richards logisticmodel. Four biological variables were computed from the curve.Differences among curves describing changes in biomass werefound to be greater between irrigated and rainfed sites thanbetween years. Drought stress had less effect on main stem elongationthan on biomass accumulation. Average dry weight per plant andCDW were reduced by drought by 42 and 38%, respectively, duemainly to similar reductions in the mean rate of growth of thetwo variables. In contrast, cycle length from sowing to themaximum values of dry weight per plant and CDW was only slightlymodified by drought. Copyright 2001 Annals of Botany Company Triticum turgidum L. ‘Durum’, durum wheat, biomass, crop dry weight, stem length, rate of growth, modelling, growth analysis, logistic peak curve     

Effect of chronically elevated CO2 on CA1 neuronal excitability

To study the effect of chronically elevated CO₂ on the excitability and function of neurons, we exposed mice to 7.5–8% CO₂ for 2 wk (starting at 2 days of age) and examined the properties of freshly dissociated hippocampal neurons. Neurons from control mice (CON) and from mice exposed to chronically elevated CO₂ had similar resting membrane potentials and input resistances. CO₂-exposed neurons, however, had a lower rheobase and a higher Na⁺ current density (580 ± 73 pA/pF; n = 27 neurons studied) than did CON neurons (280 ± 51 pA/pF, n = 34; P < 0.01). In addition, the conductance-voltage curve was shifted in a more negative direction in CO₂-exposed than in CON neurons (midpoint of the curve was –46 ± 3 mV for CO₂ exposed and –34 ± 3 mV for CON, P < 0.01), while the steady-state inactivation curve was shifted in a more positive direction in CO₂-exposed than in CON neurons (midpoint of the curve was –59 ± 2 mV for CO₂ exposed and –68 ± 3 mV for CON, P < 0.01). The time constant for deactivation at –100 mV was much smaller in CO₂-exposed than in CON neurons (0.8 ± 0.1 ms for CO₂ exposed and 1.9 ± 0.3 ms for CON, P < 0.01). Immunoblotting for Na⁺ channel proteins (subtypes I, II, and III) was performed on the hippocampus. Our data indicate that Na⁺ channel subtype I, rather than subtype II or III, was significantly increased (43%, n = 4; P < 0.05) in the hippocampi of CO₂-exposed mice. We conclude that in mice exposed to elevated CO₂, 1) increased neuronal excitability is due to alterations in Na⁺ current and Na⁺ channel characteristics, and 2) the upregulation of Na⁺ channel subtype I contributes, at least in part, to the increase in Na⁺ current density. sodium ion channels; oxygen deprivation     

An empirical model of primary productivity (14C) using mesocosm data along a nutrient gradient

The two parameters of the hyperbolic tangent equation, P_m and, were estimated from in situ vertical profiles of primary productionusing mesocosm data along a nutrient gradient. The parameters,derived from 4-h (around noon) ¹⁴C incubations, were used togetherwith the photosynthesis-light curve and hourly solar radiationdata to calculate daily primary production rates (P_d). Approximately40% of the daily production occurred in the 4 h around noon.Considering parameter uncertainty, there was no indication ofan increase in variation in production with increased nutrientloading, nor did biomass-specific P-I parameters increase. Annualproduction ranged from 82 to 901 g C m^–2 year^–1and was highest in the highest nutrient treatment tank. Dailyproductivity ranged from 0.02 to 9.1 g C m^–2 day^–1and was significantly correlated, in all treatments, with acomposite parameter BI₀/k (where B is phytoplankton biomass;I₀ is daily radiation and k is the extinction coefficient).Linear regressions of P_d against BI₀/k indicated that much ofthe variability (86%) in productivity was explained by lightavailability and phytoplankton biomass. Two approaches for predictingproductivity were compared: (i) predicting production directlyfrom environmental variables (i.e. BI₀/k) and (ii) predictingthe parameters of the P-I curve from environmental variablesand using these to calculate daily production.     

The electromotive force of the Chara membrane during the hyperpolarizing response

The hyperpolarizing response of the Chara internodal cell wasstudied by applying the voltage clamp and constant current techniques.By assuming the membrane as an electromotive force (emf) inseries with a resistance r (which is the sum of a series resistancer_s and the membrane resistance r_m), it was shown that the hyperpolarizingresponse was brought about not only by the increase in membraneresistance but by the increase in membrane emf. The time dependentcurrent-voltage (I–V_m) curve obtained under the voltageclamp during the hyperpolarizing response showed a negativeresistance. The hyperpolarizing response is also an excitation,since it is a transition process of the membrane across a negativeresistance region. (Received July 22, 1974; )     

ACTION POTENTIAL OF NITELLA INTERNODES

The ionic current during a non-propagating action potentialis analysed from the voltage clamp experiments. The shape ofthe action potential of the Nitella internode can be reconstructedfrom the data of the voltage clamp experiments. The N-shapedcurrent-voltage characteristics (I-V curve) of the Nitella membraneis not constant with time as it is in the tunnel diode, butdecays with time, converging finally into a delayed rectificationcurve. The temporal locus of the potential at which each I-Vcurve crosses the voltage axis coincides almost exactly withthe action potential. The membrane resistance which is calculatedfrom the slope of the I-V curve at each intersection with thevoltage axis also changes in parallel to the action potential.Such correlations are found in the Nitella not only in the pondwater, but also in high Na, high Ca or high Mg medium, wherethe shape of the action potential is modified in various ways.It is highly probable that the action potential is a locus ofthe change of the membrane potential so that the net membranecurrent may be maintained at zero after the transient modificationof the membrane structure by stimulation. (Received June 30, 1966; )     

Characterization of the Germination Responses to Temperature of Lettuce (Lactuca sativa L.) Achenes

Germination tests were done on 23 cultivars of lettuce (Lactucasativa L.) comprising a variety of different morphological formsselected for cultivation at various seasons. Significant differences at the upper limit of temperature tolerancewere found between different cultivars: maximum temperaturesfor 50 per cent germination ranged from 23 to 32 °C, andsusceptibility to the induction of secondary dormancy by hightemperatures varied widely from one cultivar to another. Nocorrelations were established between germination responsesand heading type, achene colour or growing season The germination responses of all cultivars at temperatures fromjust above 0 to 20 °C were closely similar and results froma large number of experiments were used to produce a standardgermination reference curve foti culvars of L. sativa. Departfuresrom this curve were found to arise predominantly from variationsin seed quality or test conditions rather than from the genotypeof the cultivar. Detailed comparisons of germination at all possible combinationsof alternate and constant day/night temperatures are presentedfor two cultivars. One with relatively high tolerance to high-temperatureinducedinhibition, the other with low tolerance. The results are discussed in relation to the original distributionof the species as a wild plant and its history of cultivationby man. Lactuca sativa L., Lettuce, achene germination, temperature response     

Estimation of the photosynthesis/irradiance (P/I) curve parameters from light and dark bottle experiments

Light and dark bottle experiments, carried out in three systemsin the Netherlands, were used to estimate the parameters ofmodels relating the oxygen production rate to incident lightintensity. The maximum production rate (P_M) and the light saturationconstant (I_S) were estimated using both gross and nett oxygenproduction data. In the latter case, the community oxygen consumptionrate (R_ox was also estimated. Eight models were compared withrespect to goodness of fit, as has been accomplished previouslyby Jassby and Platt (Limnol. Oceanogr., 21, 540–547, 1976)and many others. This study, however, emphasizes the problemof parameter correlation and the consequential usefulness ofthese type of experiments to identify the P/I curve parameters.The results show that at a 90% level of confidence, the modelscannot be distinguished with respect to goodness of fit. However,the models do show distinct differences in parameter correlation.Parameter correlation was shown to be related to the shape ofthe curve. P/I curves with high convexity were shown to be lesssensitive for parameter correlation. In particular, models showinglow convexity suffer from over-paraineterisation, which meansthat on the basis of the observed production rates it is difficultto discriminate between the parameters. Also, alternative modelformulations, using P_M and the initial slope (), were investigated.These formulations produced less parameter correlation. However,for models with low convexity, showing high parameter correlationanyway, the reduction is limited. The use of nett oxygen productiondata does not show a significant difference in fit at a 90%confidence level. However, measured R_ox from dark bottle experimentstends to be higher than the values found by estimating R_ox fromnett oxygen production.     

GTP和GDP类似物对棉铃虫神经细胞高电压敏感钙通道的调节作用

以Ba²⁺为载流子,采用全细胞膜片钳法,研究了在电极液中分别加入G蛋白稳定 激活剂GTPγS（GTP类似物）和抑制剂GDPβS（GDP类似物）对棉铃虫Helicoverpaarmigera 3龄幼虫神经细胞高电压敏感钙通道的调节作用。Ba²⁺电流记录时间为20 min。对照组 和实验组的Ba²+电流在记录的初期均出现电流的增加现象,随后电流衰减,即“rundown ”。对照组峰电流在第20 min时降为初始值的(72.09±12.80)%。电极内液中加入2 mmol/L GTPγS可缓解电流的衰减现象,在第20 min时,峰电流为初始值的(95.99±7.93)%,明显大 于对照组的峰电流(P<0.01),而且电流 电压（I-V）关系曲线向正电压方向移动。相反 ,电极内液加入2 mmol/L GDPβS则导致峰电流衰减更加严重,第20 min时,峰电流仅为初始水 平的(41.95±9.32)%,显著小于对照组（P<0.01）,但未见电流 电压（I-V）关系曲 线的明显漂移。结果表明,棉铃虫神经细胞钙通道活动受G蛋白激活剂GTPγS和G蛋白抑制剂GDPβS的影响,提示G蛋白活动水平的改变调节钙通道的电流幅值和电压依赖性。     

Overwintering of Microcystis aeruginosa Kutz. in a shallow lake

The standing crop and photosynthetic activity of Microcystisaeruginosa Kütz. in both the plankton and sediment wereinvestigated from November 1979 to May 1982 in Lake Kasumigaura,Japan. The number of planktonic colonies of this species decreasedfrom early autumn to early spring, but increased in the sedimentduring late summer and autumn. The overwintering colonies inthe sediment were –100–1000 times greater per unitarea than those in lake water. No photoinhibition of photosynthesiscould be observed in overwintering Microcystis. The values ofthe initial slopes of photosynthesis-light (P-I) curves weresimilar to those of the summer population, although the maximumphotosynthetic rate (P_max) measured at 20°C was lower thanthat of the summer planktonic population. In winter the valuesof initial slope of the P-I curve, and the ratio of phycobilinto chlorophyll a sorted from sediment were higher than in coloniesfrom the plankton.     

稻田节肢动物群落的多样性及对褐飞虱的控制功能

对江苏江浦及安徽安庆两地五种类型稻田的节肢动物群落生物多样性研究表明,以对褐飞虱Nilaparvata lugens具有抗性的粳稻田多样性指数最高。稻田蜘蛛亚群落与褐飞虱种群数量变化间存在明显的相关性,11年中64%的年份表现为显著相关。利用天敌功能指数EF=（E+P）^E/P、数值反应的方法研究了稻田蜘蛛功能团与褐飞虱种群间的生存、繁殖和数量关系,结果表明,初始EF值与褐飞虱对水稻的危害率及褐飞虱种群的未来最大饱和容量K值间呈显著相关。本文讨论了利用初始EF值来预测天敌对害虫的功能作用及生物防治与化学防治协调的可能性。