Affinity of RuBP Carboxylases for Carbon Dioxide and Inhibition of the Enzymes by Oxygen

Ribulose bisphosphate carboxylase (E.C.4.1.1.39) was purifiedfrom leaves of Triticum aestivum, Hordeum vulgare, Spinaceaoleracea, Petroselinum crispum, salad mustard-most likely Brassicanapus, Helianthus annuus, Solanum tuberosum, Beta vulgaris,Lolium perenne, Equisetum arvense, Zea mays, Ginkgo biloba,Pteris aquilina, Salix babylonica, Chamaecyparis lawsonianaand Atrichum undulatum by density gradient centrifugation andgel filtration or by ammonium sulphate fractionation, densitygradient centrifugation, ion-exchange chromatography and gelfiltration. Purified enzymes were freeze-dried and then storedat 0 °C to 4 °C. Portions of each enzyme preparationwere reactivated at 25 °C for 5 h in the presence of 10mM HCO₂ and 20 mM MgCl₂-RuBP carboxylase activities were measuredat four different concentrations of CO₂ at 25 °C and pH8.2 in solutions equilibrated with pure nitrogen or air (21%O₂, 79% N₂). K_m(CO₂), V_max and K₁(O₂) values were computed fromthe results. Significant differences were found in the K_m(CO₂)values for enzymes isolated from different species. Sensitivityof the enzymes to oxygen was less variable.     

Polypeptide Composition of Envelope Membranes Isolated from Chloroplasts of C3, C4, and CAM Plants

Chloroplast envelopes were isolated from chloroplasts purifiedfrom Spinacea oleracea L. (C₃), Panicum miliaceum L. (NAD-malicenzyme-type C₁), Digitaria sanguinalis (L.) Scop. (NADP-malicenzyme-type C₄), Kalanchoe daigremontiana Hamet et Perrier (constitutiveCAM), and from Mesembryanthemum crystallinum L. (inducible CAM)performing either C₃ photosynthesis or Crassulacean acid metabolism(CAM). For each species, methods were developed to isolate chloroplastenvelopes free of thylakoid contamination. The polypeptidesof ribulose bisphosphate (RuBP) carboxylase which has been consistentlyreported in envelope preparations of spinach were not foundin envelope preparations of C₄ mesophyll chloroplasts. Silverstaining of envelope polypeptides resolved electrophoreticallyon sodium dodecylsulfate polyacrylamide gradient slab gels produceda more complex profile than did Coomassie staining which haspreviously been used with C₃ envelope preparations, even thoughsilver reacted poorly with polypeptides corresponding to thesubunits of RuBP carboxylase. All of the plants examined possesseda major polypeptide of 27 to 29 kilodaltons (kD) which was previouslysuggested to be the phosphate translocator in spinach. WithC₃ M. crystallinum, the 29 kD polypeptide stained most intensely.After induction of CAM, a 32 kD polypeptide also stained intensely,giving a profile similar to that obtained with the constitutiveCAM species. A 32 kD polypeptide was also prominent in C₄ envelopepreparations, suggesting that a 32 kD polypeptide may be a translocatorprotein which is required in Crassulacean acid metabolism andC4 photosynthesis, but not in C₃ photosynthesis. (Received April 25, 1983; Accepted July 9, 1983)     

Gas Exchange and Carbohydrate and Nitrogen Concentrations in Leaves of Pascopyrum smithii (C3) and Bouteloua gracilis (C4) at Different Carbon Dioxide Concentrations and Temperatures

Pascopyrum smithii (C₃) andBouteloua gracilis (C₄) are importantforage grasses native to the Colorado shortgrass steppe. Thisstudy investigated photosynthetic responses of these grassesto long-term CO₂enrichment and temperature in relation to leafnonstructural carbohydrate (TNC) and [N]. Glasshouse-grown seedlingswere transferred to growth chambers and grown for 49 d at twoCO₂concentrations (380 and 750 µmol mol^-1) at 20 and 35°C, and two additional temperatures (25 and 30 °C) at750 µmol mol^-1CO₂. Leaf CO₂exchange rate (CER) was measuredat a plant's respective growth temperature and at two CO₂concentrationsof approx. 380 and 700 µmol mol^-1. Long-term CO₂enrichmentstimulated CER in both species, although the response was greaterin the C₃,P. smithii . Doubling the [CO₂] from 380 to 750 µmolmol^-1stimulated CER ofP. smithii slightly more in plants grownand measured at 30 °C compared to plants grown at 20, 25or 35 °C. CO₂-enriched plants sometimes exhibited lowerCER when compared to ambient-grown controls measured at thesame [CO₂], indicating photosynthetic acclimation to CO₂growthregime. InP. smithii , such reductions in CER were associatedwith increases in TNC and specific leaf mass, reductions inleaf [N] and, in one instance, a reduction in leaf conductancecompared to controls. InB. gracilis , photosynthetic acclimationwas observed more often, but significant changes in leaf metabolitelevels from growth at different [CO₂] were generally less evident.Temperatures considered optimal for growth (C₃: 20 °C; C₄:35 °C) sometimes led to CO₂-induced accumulations of TNCin both species, with starch accumulating in the leaves of bothspecies, and fructans accumulating only inP. smithii. Photosynthesisof both species is likely to be enhanced in future CO₂-enrichedand warmer environments, although responses will sometimes beattenuated by acclimation. Acclimation; blue grama (Bouteloua gracilis (H.B.K.) Lag ex Steud.); leaf nitrogen concentration; nonstructural carbohydrates; photosynthesis; western wheatgrass (Pascopyrum smithii (Rydb.) Love)     

Humidity Pretreatment Affects the Responses of Stomata and CO2 Assimilation to Vapor Pressure Difference in C3 and C4 Plants

Experiments were carried out to investigate the long-term influenceof humidity on the short-term responses of stomata and CO₂ assimilationto vapor pressure difference in Oryza sativa (rice, C₃ species)and Panicum maximum (green panic, C₄ species). Plants were grownfor four weeks in growth chambers set at 35% and 85% relativehumidity at 25C air temperature, 38+2 Pa CO₂ partial pressureand 1,700µmol m^-2s^-1 photon flux density. Soil was saturatedwith water in both humidity treatments. Low humidity pretreatmentscaused low leaf conductance and low rates of transpiration andCO₂ assimilation in O. sativa, but small changes in stomatalresponses to humidity and in CO₂ assimilation were found inP. maximum. From the short-term gas exchange experiments, itwas noted that the responsiveness of leaf conductance to vaporpressure difference were affected by humidity pretreatmentsin O. sativa, whereas unaffected in P. maximum. In O. sativameasurements of CO₂ assimilation as a function of internal CO₂partial pressure (A-Ci curve) indicated that low humidity pretreatmentsreduced the CO₂ assimilation at high internal CO₂ partial pressure,but the initial slope of the A-Ci curve was unaffected. Furthermore,plant characteristics such as total dry weight and leaf areaof plants subjected to low umidity were lower than plants subjectedto high humidity. The reductions in O. sativa, however, werelarger than in P. maximum. Stomatal frequency from low humiditygrown plant was higher than that from high humidity grown plantsin both species although there is no significant difference.The data indicated that if the short term inhibition of netCO₂ assimilation at a high vapor pressure difference was imposedduring vegetative growth, the photosynthetic biochemistry andthe resultant plant growth were largely depressed in O. sativa,a C₃ species. (Received May 26, 1992; Accepted November 2, 1992)     

Differentiation of Photorespiratory Activity between Mesophyll and Bundle Sheath Cells of C4 Plants II. Peroxisomes of Panicum miliaceum L.

Peroxisomes were isolated by sucrose density gradient centrifugationfrom mesophyll and bundle sheath protoplasts of a C₄ plant,Panicum miliaceum L. The equilibrium density in the gradientwas 1.25 for bundle sheath peroxisomes and 1.23 for mesophyllperoxisomes, the former density being similar to that of peroxisomesof wheat mesophyll protoplasts. Photorespiratory and other microbody enzymes were assayed forthe peroxisomes of P. miliaceum to detect possible differentiationat an enzyme level. The specific activities of photorespiratoryenzymes, except for hydroxypyruvate reductase, in bundle sheathperoxisomes were 40–60% of those in wheat peroxisomes,when compared on a protein basis, and only 20–30% in mesophyllperoxisomes. However, peroxisomes from both cell types containedsignificant levels of all the enzymes involved in the photorespiratoryglycolate pathway, when compared with castor bean glyoxysomes.The activity of hydroxypyruvate reductase in the peroxisomesof P. miliaceum was comparable to or higher than that in wheatperoxisomes. Two ß-oxidation enzymes and urate oxidasewere detected in the peroxisomes in a similar level to thatin wheat peroxisomes. These results suggest that the peroxisomes of mesophyll andbundle sheath cells of P. miliaceum are essentially similarto those of C₃ plants, and that they cannot be differentiatedexcept for a difference in equilibrium density in a sucrosegradient. (Received December 24, 1984; Accepted April 9, 1985)     

Exposure of Leaves of Cucumis sativus L. to Low Temperatures in the Light Causes Uncoupling of Thylakoids I. Studies with Isolated Thylakoids

Chilling of leaves of cucumber (Cucumis sativus L.) at 5?C inmoderate light for 5 h caused almost complete suppression ofphotosynthetic oxygen evolution in the leaves. Comparison ofelectron transport activities determined in the presence andabsence of an uncoupler, methylamine, indicated that thylakoidsprepared from such treated leaves were uncoupled without anysignificant changes in the capacity for electron transport.Immunoblotting revealed that the amount of coupling factor 1(CF₁) associated with membranes was reduced by the chillingtreatment in the light. Thylakoids prepared from leaves thathad been chilled in moderate light for 5 h and then re-warmedfor 1 h were coupled and capable of synthesising ATP. However,the capacity of leaf photosynthesis was not restored by therewarming. These results indicate that the thylakoids are uncoupledby the dissociation of some CF₁ complexes from the thylakoidmembranes during the chilling treatment of leaves in the lightand that thylakoids are recoupled by reassociation of CF₁ duringthe subsequent rewarming of the treated leaves at 25?C. It alsoappears that chilling in the light causes irreversible damageto reaction(s) other than those involved in electron transportand photophosphorylation. ¹ Present address: Department of Biological Science, Facultyof Science, Himeji Institute of Technology, Kamigori, Ako-gun,Hyogo, 678-12 Japan (Received July 1, 1991; Accepted October 4, 1991)     

Effects of Low Temperature, Light and O2 on Chilling-sensitive and -resistant Strains in Chlorella ellipsoidea

A low-temperature sensitive strain, Chlorella ellipsoidea Gerneck(IAM C-102), lost its chilling sensitivity during preservation.Cells of the original strain (low-temperature sensitive) andthe variant (low-temperature resistant) were both synchronouslygrown under a 14-hr light-10-hr dark regime. In the originalstrain, cells at the D-L stage (transient phase) were most sensitiveto a low temperature, whereas the variant cells were not damagedat any stage. During low-temperature treatment, the viability of D-L cellsin the sensitive strain decreased after a lag period of 1 hr.The O₂-uptake activity (respiration) showed the same behavioras the viability, whereas the O₂-evolution activity (photosynthesis)decreased from the start of chilling. In the resistant strain,only O₂ evolution decreased. The decreased activity was restoredwhen the chilled cells were incubated at 25°C. This restorationwas inhibited by oligomycin. Lowering the light intensity or eliminating O2 diminished thechilling injury of the sensitive strain. The results indicatethat the chilling injury of Chlorella results from the combinedeffects of low temperature, light and O₂. (Received September 26, 1980; Accepted March 23, 1981)     

Chlorophyll Deficiency Caused by a Specific Blockage of the C5-Pathway in Seedlings of Virescent Mutant Rice

Temperature-sensitive mutants of rice, designated virescent(v₁, v₂ and v₃), develop chlorophyll-deficient leaves at a restrictivetemperature (20°C) but develop nearly normal green leavesat a permissive temperature (30°C). Analysis of the chlorophyllbiosynthetic pathway in the virescent mutants indicated thatthe chlorophyll deficiency at the restrictive temperature wasdue to specific blockage of the C₅-pathway. Northern analysissuggested that the chlorophyll deficiency in the virescent mutantswas caused by specific inhibition of the expression of chloroplasttRNA^Glu. (Received October 22, 1993; Accepted January 25, 1994)     

A Comparison of the Growth of the C4 Grass Spartina anglica with the C3 Grass Lolium perenne at Different Temperatures

Dunn, R., Thomas, S. M., Keys, A. J. and Long, S. P. 1987. Acomparison of the growth of the C₄ grass Spartina anglica withthe C₃ grass Lolium perenne at different temperatures.—J.exp. Bot. 38: 433–441. S. anglica is one of the few C₄ species which occurs naturallyin cool temperate zones. It is known to attain photosyntheticrates which equal or exceed those of C₃ grasses over the temperaturerange typical of the spring and summer in cool temperate climates.This study examines whether S. anglica can also attain comparablegrowth rates at these temperatures. Seedlings of S. anglicaand L. perenne cv. S23 were grown in controlled environmentsat 10,15,20 and 25 °C. Quantitative growth analysis wasconducted by taking frequent harvests to determine the progressionsof leaf area and plant weight of individual plants with time.Quadratic regressions were found to describe these progressionswell. Instantaneous derived growth parameters were calculatedfrom the fitted regressions. Both absolute and relative growthrates of S. anglica were significantly lower than for L. perenne,this being largely attributable to a lower ratio of leaf areaproduction per unit of plant dry weight. Although the amountof dry matter invested into leaves was similar, the leaf areaper unit of leaf dry weight was lower in S. anglica. In comparisonto L. perenne, the rate of dry matter accumulation per unitof leaf area (ULR) was higher in S. anglica at 25 °C andinitially equal at 10 °C. Prolonged exposure to 10 °Csteadily reduced ULR in S. anglica which approached zero at80 d. Although growth in S. anglica is reduced more by low temperaturethan it is in L. perenne, by comparison to other C₄ speciesthe assimilatory capacity of S. anglica is more tolerant oflow temperature exposure. Key words: C4 photosynthesis, temperature, quantitative growth analysis     

Acid-Base Regulation and Temperature in Selected Invertebrates as a Function of Temperature

The pH of the hemolymph of selected invertebrates decreasesas their body temperature increases. The magnitude of this change(pH/°C) is very similar to the change of the pH of waterwith temperature (pN/°C) and suggests that these invertebrates,like poikilothermous vertebrates, regulate the pH of their extracellularfluid so that its degree of alkalinity relative to the pH ofwater remains constant. The degree of alkalinity (pH_blood-pN)varies between species, but seems to be fixed for any givenspecies. In Limulus pH-pN was essentially the same for in vivosamples, measured after the whole animal had been acclimatedto different temperatures, as it was for in vitro samples inwhich the hemolymph was cooled or warmed anaerobically, suggestingthat the CO₂ content of the extracellular fluid is constantas the temperature changes. The P_CO2 of the hemolymph is invariablylower in animals breathing water than in those breathing air.In the invertebrates, as in the vertebrates, manipulation ofP_CO2 and HCO₃- is probably the major mechanism in the regulationof the relative alkalinity of the extracellular fluid.     

Growth and Partitioning in Pascopyrum smithii (C3) and Bouteloua gracilis(C4) as Influenced by Carbon Dioxide and Temperature

This study investigated how CO₂and temperature affect dry weight(d.wt) accumulation, total nonstructural carbohydrate (TNC)concentration, and partitioning of C and N among organs of twoimportant grasses of the shortgrass steppe,Pascopyrum smithiiRydb. (C₃) andBouteloua gracilis(H.B.K.) Lag. ex Steud. (C₄).Treatment combinations comprised two temperatures (20 and 35°C)at two concentrations of CO₂(380 and 750 µmol mol^-1),and two additional temperatures of 25 and 30°C at 750 µmolmol^-1CO₂. Plants were maintained under favourable nutrient andsoil moisture and harvested following 21, 35, and 49d of treatment.CO₂-induced growth enhancements were greatest at temperaturesconsidered favourable for growth of these grasses. Comparedto growth at 380 µmol mol^-1CO₂, final d.wt of CO₂-enrichedP.smithiiincreased 84% at 20°C, but only 4% at 35°C. Finald.wt ofB. graciliswas unaffected by CO₂at 20°C, but wasenhanced by 28% at 35°C. Root:shoot ratios remained relativelyconstant across CO₂levels, but increased inP. smithiiwith reductionin temperature. These partitioning results were adequately explainedby the theory of balanced root and shoot activity. Favourablegrowth temperatures led to CO₂-induced accumulations of TNCin leaves of both species, and in stems ofP. smithii, whichgenerally reflected responses of above-ground d.wt partitioningto CO₂. However, CO₂-induced decreases in plant tissue N concentrationswere more evident forP. smithii. Roots of CO₂-enrichedP. smithiihadgreater total N content at 20°C, an allocation of N below-groundthat may be an especially important adaptation for C₃plants.Tissue N contents ofB. graciliswere unaffected by CO₂. Resultssuggest CO₂enrichment may lead to reduced N requirements forgrowth in C₃plants and lower shoot N concentration, especiallyat favourable growth temperatures. Acclimation to CO₂; blue grama; Bouteloua gracilis ; carbohydrate; climate change; global change; grass; growth; growth temperature optima; nitrogen; N uptake; Pascopyrum smithii; western wheatgrass     

Heat-Stability of Iron-Sulfur Centers and P-700 in Photosystem I Reaction Center Complexes Isolated from the Thermophilic Cyanobacterium Synechococcus elongatus

Stabilities of iron-sulfur centers and reaction center chlorophyllP-700 in Photosystem I reaction center complex (CP1-a), isolatedby sodium dodecyl sulfate treatment from the thermophilic cyanobacteriumSynechococcus elongatus, were studied by EPR and optical spectroscopy.P-700 was destroyed by treatment at temperatures above 80?Cfor 5 minutes with a half inactivation temperature of 93?C.The three iron-sulfur centers F_A, F_B and F_X showed similar thermalstabilities and were half inactivated at about 70?C. Thus, theisolated Photosystem I reaction center complexes of S. elongatusare still highly resistant to heat. (Received May 9, 1990; Accepted June 25, 1990)     

Photosynthetic efficiency of Panicum hians and Panicum milioides in relation to C3 and C4 plants

Panicum hians and Panicum milioides were found to have characteristicsintermediate to those of C₃ and C₄ species with respect to CO₂compensation point, percentage inhibition of photosynthesisby O₂ at various O₂/CO₂ solubility ratios, and water use efficiency.C₄ species have a higher carboxylation efficiency than eitherthe intermediate or C₃ species. During photosynthesis, evenunder 2.5% O₂, C₄ species have a higher affinity for intercellularCO₂ (Km 1.6 µM) apparently due to the initial carboxylationthrough PEP carboxylase. Under low O₂ the intermediate and C₃species had a similar affinity for intercellular CO₂ duringphotosynthesis (Km 5–7 µM) consistent with carboxylationof atmospheric CO₂ through RuDP carboxylase. There were considerablevariation in photosynthesis/unit leaf area at saturating CO₂levels in the species examined which in part is due to differencesin RuDP carboxylase /unit leaf area. The highest rates of photosynthesis/unitleaf area under CO₂-saturating conditions were with the C₃ specieswhich had a correspondingly high level of RuDP carboxylase/unitleaf area. Possibilities for the greater efficiency of P. hiansand P. milioides in comparison to C₃ species in utilizing lowlevels of CO₂ in the presence of atmospheric O₂ are discussed. ¹ This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and theUniversity of Wisconsin Research Committee with funds from theWisconsin Alumni Research Foundation. (Received June 25, 1977; )     

Effect of Elevated CO2 on Stomatal Density and Distribution in a C4 Grass and a C3 Forb under Field Conditions

Two common tallgrass prairie species, Andropogon gerardii, thedominant C₄ grass in this North American grassland, and Salviapitcheri, a C₃ forb, were exposed to ambient and elevated (twiceambient) CO₂ within open-top chambers throughout the 1993 growingseason. After full canopy development, stomatal density on abaxialand adaxial surfaces, guard cell length and specific leaf mass(SLM; mg cm^-2) were determined for plants in the chambers aswell as in adjacent unchambered plots. Record high rainfallamounts during the 1993 growing season minimized water stressin these plants (leaf xylem pressure potential was usually >-1·5 MPa in A. gerardii) and also minimized differencesin water status among treatments. In A. gerardii, stomatal densitywas significantly higher (190 ± 7 mm^-2; mean ±s.e.) in plants grown outside of the chambers compared to plantsthat developed inside the ambient CO₂ chambers (161 ±5 mm^-2). Thus, there was a significant 'chamber effect' on stomataldensity. At elevated levels of CO₂, stomatal density was evenlower (P < 0·05; 121 ± 5 mm^-2). Most stomatawere on abaxial leaf surfaces in this grass, but the ratio ofadaxial to abaxial stomatal density was greater at elevatedlevels of CO₂. In S. pitcheri, stomatal density was also significantlylower when plants were grown in the open-top chambers (235 ±10 mm^-2 outside vs. 140 ± 6 mm^-2 in the ambient CO₂ chamber).However, stomatal density was greater at elevated CO₂ (218 ±12 mm^-2) compared to plants from the ambient CO₂ chamber. Theratio of stomata on adaxial vs. abaxial surfaces did not varysignificantly in this herb. Guard cell lengths were not significantlyaffected by growth in the chambers or by elevated CO₂ for eitherspecies. Growth within the chambers resulted in lower SLM inS. pitcheri, but CO₂ concentration had no effect. In A. gerardii,SLM was lower at elevated CO₂. These results indicate that stomataland leaf responses to elevated CO₂ are species specific, andreinforce the need to assess chamber effects along with treatmenteffects (CO₂) when using open-top chambers.Copyright 1994, 1999Academic Press Andropogon gerardii, elevated CO₂, Salvia pitcheri, stomatal density, tallgrass prairie     

Effects of Chilling on the Ultrastructure and Net Photosynthesis of Pellia epiphylla

Thalli of Pellia epiphylla were collected frozen from natureand chilled artificially for varying lengths of time at –22°C. The survival and recovery of this material was comparedwith that of the non-chilled material by performing CO₂ exchangeexperiments. Electron microscopy was done from the chilled andhardened thalli, and clear differences were observed in theultrastructure of these materials. The vacuoles of the hardenedtissue contained fine granular material but those of the chilledtissue had large electrondense particles embedded in finer granularsubstance. Oil bodies had greatly changed. In the cytoplasmthere were abundant lipid-like bodies resembling oil globulesof oil bodies and particularly in the vacuoles there were oily-lookingflecks. Chloroplasts had large starch grains and the lamellarsystem was somewhat disorganized. Net photosynthesis was highestwith material stored for the longest time at –22 °C. Pellia epiphylla, ultrastructure, net photosynthesis, chilling     

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.     

上海地区三带喙库蚊春季首次出现、季节分布及其与气象条件的关系

根据1982～1992年和2001～2002年上海奉贤地区每年3月～6月灯诱捕蚊的现场调查数据,采取相关对比分析、统计分析、天气图分析法,探讨三带喙库蚊春季首次出现、季节分布及其与气象条件的关系。结果表明,三带喙库蚊季节分布按蚊虫密度变化划分为首次出现期、季节增多期和混合发生期三个时期。三带喙库蚊春季首次出现的温度条件是：首现日当天和前1天的日平均气温均≥11.0℃,其2天的日平均气温累加值≥25.5℃,或首现日当天、前2天和后1天任意连续3天的日平均气温均≥11.0℃,其3天的日平均气温累加值≥34.0℃,结果三带喙库蚊春季首现日和首现日温度日期的差异在1～2天内(91.7%)。三带喙库蚊季节增多期其逐候蚊虫密度（Y₁）与平均气温（X₁）呈显著的正相关,用一元回归方程表示为：Y₁=-9.3534+0.7217X₁;至候平均气温≥18℃（平均始日为5月3日）进入三带喙库蚊混合发生期。总体上三带喙库蚊蚊虫密度季节分布与平均气温、“S”系风向变化存在密切关系。首次出现期至季节增多期三带喙库蚊突增日与锋面天气活动存在着较大的关联,候平均气温≥18℃是三带喙库蚊大量发生和进入峰期重要的温度指标。上述结果提示上海地区三带喙库蚊春季和初夏随气流北迁降落的可能性相当大。     

A Temperature Effect on the Expression of Genotypic Differences in Flowering Induction in Antirrhinum majus

Three inbred lines of Antirrhinum majus and the F₁ generationsof crosses between them were scored for flowering time in ninegreenhouse and garden experiments. The inbreds fell into twogroups, the difference between which showed a marked interactionwith environments. The two lines (An 105, An 106) which weresimilar were earlier flowering than the third line (An 101)in those environments which produced generally early flowering,but were later than An 101 when the environmental conditionsled to late flowering. In all cases the F₁ generations wereat least as early as the earlier parent. Cabinet experiments identified temperature as the importantenvironmental factor when day length was kept constant at 16h. At 25°C, An 105 and An 106 were earlier than An 101 whileat 12°C, at which temperature the average flowering timewas much later, An 101 was earlier. The F₁ generations werelike An 105 and An 106 at 25°C but showed heterosis at 12°C. The differences in flowering time between genotypes were inall cases established by the time the first reproductive budsbecame visible (budding time). Thus a temperature differencewell outside the range of vernalizing temperatures is havinga striking effect on the phenotypic expression of genotypicdifferences determining the transition from vegetative to floweringdevelopment.     

Transnodal Transport of 14C in Nitella flexilis: II. TANDEM CELLS WITH APPLIED PRESSURE GRADIENTS

Using carefully standardized test conditions and tandem pairsof cells of Nitella flexilis, the influx of ¹⁴C (added as H¹⁴CO₃^–and transnodal transport were studied under various pressuregradients applied across the node up to P=± 2·5bar. When mannitol was used as the osmoticum, influx was foundto increase only when the mannitol solution was around the cellproximal to the feed. ¹⁴C was transported across the node tothe distal cell, probably as ¹⁴C-photosynthate products, evenagainst a pressure gradient of 2 bars or more, as was ³⁶Cl^–and ³²P. The % transported in general decreased with increasingP, whether assisted or opposed by added pressure. It was unchangedby the presence of mannitol at the node and was essentiallythe same whether the pressure gradient was produced by directpressure or by use of the osmoticum. Transnodal transport of¹⁴C products is almost certainly via plasmodesmata and appearsto be largely by an active mechanism. In absolute amounts itis the same whether the pressure gradient assists or opposesflow. Valving is evident at the node, increasing the resistanceto transport as the pressure gradient increases whether ¹⁴C(asHCO₃^–), ⁴²K⁺ (as KCl), ³⁶Cl^– (as NaCl) or ³²P (asNa₃PO₄) are used to detect it. The mechanism of movement ofK⁺ across the node differs from that of photosynthate products. Key words: Node, plasmodesmata, pressure gradients, active transport