Fruit Number in Relation to Pollen Production and Viability in Groundnut Exposed to Short Episodes of Heat Stress

Hot days and warm nights are important environmental factorslimiting fruit yields of groundnuts in the semi-arid tropics.The objective of the present research was to quantify the effectsof short episodes of heat stress on pollen production and viability,and fruit yield. Plants of cultivar ‘ICGV 86015’were grown at a day/night temperature of 28/22 °C from sowinguntil 9 d after flowering. Cohorts of plants were then exposedto a factorial combination of four day (28, 34, 42 and 48 °C)and two night (22 and 28 °C) temperatures for 6 d. Thereafter,all plants were maintained at 28/22 °C until final harvest9 d later. Number of flowers per plant (FN), the proportionof flowers setting pegs (fruit-set), the number of pegs andpods per plant (reproductive number, RN_t), pollen productionper flower and pollen viability were determined during the 6d stress period. There were strong negative linear relationsbetween day temperature over the range of 28 to 48 °C andFN (slope, -1.1 °C^-1), fruit-set (-2.8% °C^-1), RN_t(-0.90°C^-1), and pollen production (-390 °C^-1) and viability(-1.9% °C^-1). Warmer night temperature (28 vs. 22 °C)had no effect on FN, but reduced fruit-set (31 to 19%), RN_t(8to 5), and pollen production (4389 to 2800) and viability (49to 40%). There were no significant interactions between dayand night temperature. Reduced fruit-set was a consequence offewer pollen grains and reduced pollen viability. The thresholdday temperature for pollen production and viability was 34 °Cand there were strong negative linear relations between bothpollen production and pollen viability and accumulated temperature>34 °C. Copyright 1999 Annals of Botany Company Arachis hypogaea L., fruit-set, groundnut, heat-stress, peanut, pollen viability, pollen production, temperature.     

Theoretical Basis of Protocols for Seed Storage III. Optimum Moisture Contents for Pea Seeds Stored at Different Temperatures

In previous work, we demonstrated that there was an optimummoisture level for seed storage at a given temperature (Vertucciand Roos, 1990), and suggested, using thermodynamic considerations,that the optimum moisture content increased as the storage temperaturedecreased (Vertucci and Roos, 1993b). In this paper, we presentdata from a two year study of aging rates in pea (Pisum sativum)seeds supporting the hypothesis that the optimum moisture contentfor storage varies with temperature. Seed viability and vigourwere monitored during storage under dark or lighted conditionsat relative humidities between 1 and 90%, and temperatures between-5 and 65°C. The optimum moisture content varied from 0·015g H₂O g^-1 d.wt at 65°C to 0·101 g H₂O g^-1 d.wt at15°C under dark conditions and from 0·057 at 35°Cto 0·092 g H₂O g^-1 d.wt at -5°C under lighted conditions.Our results suggest that optimum moisture contents cannot beconsidered independently of temperature. This conclusion hasimportant implications for 'ultra-dry' and cryopreservationtechnologies.Copyright 1994, 1999 Academic Press Seed storage, seed aging, seed longevity, water content, temperature, glass, desiccation damage, ultradry, Pisum sativum L., pea, cryopreservation     

Carbon Exchange Rate of Intact Individual Soya Bean Pods. 2. Ontogeny of Temperature Sensitivity

Diurnal temperature fluctuations induced change in soya bean-pod[Glycine max (L.) Merr.] carbon exchange rate (CER, where positiveCER represents CO₂ evolution). CER appeared to depend linearlyon temperature. Linear regressions of CER on temperature interceptedthe temperature axis at 5°C (i.e. zero CER at 5°C).Slopes of these regressions (i.e. temperature sensitivity) changedover the season. The CER-temperature sensitivity coefficient,K, (calculated from observed values of CER. pod temperatureand temperature intercept) rose from less than 0·02 mgCO₂ h^–1 pod^–1 °C^–1 during early pod-flll,peaked at over 0·04 mg CO₂ h^–1 pod^–1 °C^–1at mid pod-fill, and then declined during late pod-fill andmaturation. Glycine max (L.) Merr., Soya bean, carbon exchange rate, temperature     

The influence of temperature and light on the upper limit of Microcystis aeruginosa production in a hypertrophic reservoir

Primary production was measured for 7 years, using the in situ¹⁴C-method in hypertrophic Hartbeespoort Dam, South Africa,to examine the influence of light and water temperature on theupper limit of Microcystis aeruginosa production. Water temperaturesvaried from 11 to >25°C and chlorophyll concentrationsreached 6500 mg m^–3. The maximum volumetric rate of production(A_max) was 12->8800 mg C m^–3 h^–1 with areal productions(A) of 69->3300 mg C m^–2 h^–1 for euphotic zonedepths of <0.5–8.4 m. The intrinsic parameters of phytoplanktonproduction (, A_max/B, I_k) indicated that the phytoplankton populationwas adapted to high light levels. Both A_max/B and I_k were correlatedwith temperature. Under optimal conditions, , the theoreticalupper limit of A, was calculated to be 2.8 g Cm^–2 h^–1,while the measured rate was 2.5 g Cm^–2 h^–1. Measuredareal rates exceeding were overestimated due to methodologicalproblems when working with Microcystis scums. Light and watertemperature interacted to yield high production rates: watertemperature through its direct effect on photosynthetic ratesand indirectly in the formation of diurnal mixed layers; lightindirectly through water temperature and directly through itsattenuation and induction of light-adapted physiology in Microcystis.     

Factors controlling primary production in a hypertrophic lake (Hartbeespoort Dam, South Africa)

The physical factors controlling algal primary production weredemonstrated from data collected for a hypertrophic lake. A_maxranged between 12.4 and 5916 mg C m^–3 h^–1. Arealrates (A) varied between 46.9 and 3381 mg C m^–2 h^–1.The factors permitting and controlling production were subjectivelyseparated into two categories. In category 1, nutrients (N +P), which were in overabundance, permitted large standing cropsof Microcystis aeruginosa to develop (>1000 µg chla 1^–1). Wind patterns determined the dramatic spatialand temporal changes in algal standing crop which could dropto 2.7 µg chl a 1^–1. In category 2 were the factorswhich affected the rate processes. The buoyancy mechanism ofMicrocystis usually kept the alga in the euphotic zone. A powerrelationship (r = 0.92, n = 54) between A and A_max/_min showedthat with increasing phytoplankton vertical stratification,A_max was increasingly important in the integral. The saturationparameter I_K and photosynthetic capacity were temperature dependent.Variations of A were significantly related to changes in watercolumn stability (g cm cm^–2) because both axes of thephotosynthesis depth-profile were affected by stability changes.     

Temperature-dependent consumption and gut-residence time in the opossum shrimp Mysis relicta

Maximum daily consumption was estimated for Mysis relicta fedad libitum rations of Daphnia pulex at 4,10,15 and 18°C.Gut-residence time was also evaluated for M.relicta fed clado-ceranprey at 4, 10 and 157deg;C. Mean daily consumption (g dry weightof Daphnia g^–1 dry weight of Mysis day^–1) rangedfrom 6% at 4%C to 12% at 10°. At 18°C, Mysis feedingrate declined to 9% day1. Mean, weight-adjusted consumptionrates exhibited a ‘dome-shaped’ response in relationto water temperature. Consumption rate was highest at 10°Cand lowest at 4°C. Estimated Q₁₀ was more sensitive from4 to 10°C (Q₁₀= 3) than from 10 to 15°C (Q₁₀=1.2). Gut-residencetime for Mysis was inversely related to water temperature, implyingthat evacuation rate increases linearly with water temperature.Feeding and gut-evacuation rates become disassociated at watertemperatures >10°C. As water temperature increased above1°C, relative evacuation rate increased, whereas feedingrate declined. It is postulated that at higher water temperatures,disassociated feeding and gut-evacuation rates reduce the scopefor growth of vertically migrating Mysis and impose a physiologicalconstraint that isolates Mysis from warm, epilimnetic waterduring thermal stratification. ¹Present address: Center for Aquatic Ecology, Illinois NaturalHistory Survey, Sam Parr Biological Station, 6401 Meacham Road,Kinmundy, IL 62854, USA     

Germination and Storage of Pollen of Phytolacca dodecandra L. (endod)

The effect of sucrose, H₂BO₃, KNO₃, Ca(NO₂)₂.4H₂O and MgSO₄.7H₂O on pollen germination of Phytolacca dodecandra L. (endod)in a liquid medium was investigated. Sucrose and H₃BO₃ werecritical to pollen germination. A concentration of 10% sucroseand 161.8 µm H₂BO₃ gave over 70% germination. The germinationof pollen was not enhanced by Ca(NO₃)₂.4H₂O, KNO₃ and MgSO₄.7H₂O.Endod pollen was dehydrated over CaCl₂ and stored in gelatincapsules in cryogenic vials at –175 °C, 1±1°C and 24±2 °C. The pollen moisture content atcollection was approx. 7.8% (f. wt basis) and dehydration overCaCl₂ reduced it to about 1.4%. Pollen stored at 1±1°C and –175 °C maintained viability for over 6months. Pollen stored at room temperature lost viability within4 weeks of storage. Pollination with cryopreserved pollen resultedin normal fruit set. Phytolacca dodecandra, endod, pollen germination, pollen storage     

The Carbon Economy of Rubus chamaemorus L. II. Respiration

Respiratory activity and seasonal changes in carbohydrate contentof the storage organs of Rubus chamaemorus L. have been investigated.Leaf dark respiration rate increases in a non-linear mannerfrom 0·7 mg CO₂ evolved dm^–2 h^–1 at 0 °Cto 4·6 rng CO₂ evolved dm^–2 hh^–1 at 30 °C.Root and rhizome respiration rates increase from 1 µ1O₂ uptake g^–1 fresh weight h^–1 at 0.7 ° C to10 µ10, uptake g^–1 f. wt h^–1 at 20 °C.Rhizome carbohydrate reserves decline from a September peakof 33 per cent alcohol insoluble d. wt to 16 per cent in May. The circumpolar distribution of R. chamaemorus is discussedin relation to the evidence presented here and in the precedingpaper of the series.     

The Effect of Temperature and Light on Gas Exchange and Acid Accumulation in the C3-CAM Plant Clusia minor L

Gas exchange and organic acid accumulation of the C₃-CAM intermediateClusia minor L. were investigated in response to various day/nighttemperatures and two light regimes (low and high PAR). For bothlight levels equal day/night temperatures between 20°C and30°C caused a typical C₃ gas exchange pattern with all CO₂uptake occurring during daylight hours. A day/ night temperatureof 15°C caused a negative CO₂ balance over a 24 h periodfor low-PAR-grown plants while high-PAR-grown plants showeda CAM gas exchange pattern with most CO₂ uptake taking placeduring the dark period. However, there was always a considerablenight-time accumulation of malic acid which increased when thenight-time temperature was lowered and had its maximum (54 mmolm^–2) at day/night temperature of 30/15°C. A significantamount of malic acid accumulation (23 mmol m^–2) in low-PAR-grownplants was observed only at 30/15°C. Recycling of respiratoryCO₂ in terms of malic acid accumulation reached between 2·0and 21·5 mmol m_–2 for high-PAR-grown plants whilethere was no significant recycling for low-PAR-grown plants.Both low and high-PAR-grown plants showed considerable night-timeaccumulation of citric acid. Indeed under several temperatureregimes low-PAR-grown plants showed day/night changes in citricacid levels whereas malic acid levels remained approximatelyconstant or slightly decreased. It is hypothesized that lowand high-PAR-grown plants have different requirements for citrate.In high-PAR-grown plants, the breakdown of citrate preventsphotoinhibition by increasing internal CO₂ levels, whereas inlow-PAR-grown plants the night-time accumulation of citric acidmay function as an energy and carbon saving mechanism. Key words: C. minor, C₃, CAM, citric acid, light intensity     

Respiratory Efflux in Relation to Temperature of Simulated Swards of Perennial Ryegrass with Contrasting Soluble Carbohydrate Contents

Fully light-intercepting simulated swards of S24 perennial ryegrasswere exposed to contrasting environmental conditions in a growthroom for 4 days. Half experienced 20 h days of 120 Wm^–2(400–700. nm) and 5 °C, and came to have a WSC (watersoluble carbohydrate) content of 235 mg g^–1 and half 4h days of 20 Wm^–2 and 25 °C leading to a WSC of 25mg g^–1. Their rates of CO₂ efflux were monitored at anumber of temperatures during an 8 h dark period; half experiencedincreasing (5–30 °C) and half decreasing (30–5°C) temperatures. The ‘high’ WSC swards hadrespiration rates of 3.7 mg CO₂ g^–1 (d. wt) h^–1at 15 °C, and the ‘low’ swards 0.8 mg CO₂ g^–1h^–1. The order in which the temperatures were experiencedwas immaterial. Even the ‘low’ WSC swards showedno evidence of a respiratory decline during the dark periodthat could be attributed to substrate shortage. The relationshipbetween temperature and CO₂ efflux was best represented by logisticcurves. Even so, a Q₁₀ of 2 fitted the data reasonably well,at least up to 20 °C, and has practical advantages wheninterpolating estimated between measured values of respirationin the construction of a carbon balance sheet. Lohum perenne L., ryegrass, respiration, temperature, Q₁₀, soluble carbohydrate content, simulated sward     

Concurrent Rates of N2 Fixation, Nitrate and Ammonium Uptake by White Clover in Response to Growth at Different Root Temperatures

Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown for 71 d in flowing nutrient solutions containingN as 10 mmol m_–3 NH₄NO₃, under artificial illumination,with shoots at 20/15°C day/night temperatures and root temperaturereduced decrementally from 20 to 5°C. Root temperatureswere then changed to 3, 7, 9, 11, 13, 17 or 25°C, and theacquisition of N by N₂ fixation, NH₄+ and NO₃^– uptakewas measured over 14 d. Shoot specific growth rates (d. wt)doubled with increasing temperature between 7 and 17°C,whilst root specific growth rates showed little response; shoot:root ratios increased with root temperature, and over time at11°C. Net uptake of total N per plant (N₂ fixation + NH₄++ NO₃^–) over 14 d increased three-fold between 3 and 17°C.The proportion contributed by N₂ fixation decreased with increasingtemperature from 51% at 5°C to 18% at 25°C. Uptake ofNH₄+ as a proportion of NH₄+ + NO₃^– uptake over 14 d variedlittle (55–62%) with root temperature between 3 and 25°C,although it increased with time at most temperatures. Mean ratesof total N uptake per unit shoot f. wt over 14 d changed littlebetween 9 and 25°C, but decreased progressively with temperaturebelow 9°C, due to the decline in the rates of NH₄+ and NO₃^–uptake, even though N₂ fixation increased. The results suggestthat N₂ fixation in the presence of sustained low concentrationsof NH₄+ and NO₄^– is less sensitive to low root temperaturethan are either NH₄+ or NO₃^– uptake systems. White clover, Trifolium repens L. cv. Huia, root temperature, nitrogen fixation, ammonium, nitrate     

Evidence for Essential Maintenance Respiration of Leaves of Xanthium Strumarium at High Temperature

Mesophyll resistance to photosynthetic carboxylation (r'_m) wasused as a criterion for leaf integrity. It was measured, at25 °C, in the light, before and after periods of high temperature(3 h at 38 °C) in the dark. During the high temperatureperiods, respiration (R_D) of attached leaves of Xanthium strumariumwas suppressed from 27%-36% by either low [O₂] (1.04% or 0.21%v.v.) or high [CO₂] (840 µl 1^–1) in the ambientair. Neither treatment affected rates of R_D or photo-respirationduring the second period at 25 °C. There was no significant increase of r'_m when R_D was not suppressedduring the high temperature treatment. When R_D was suppressedat high temperatures, r'_m increased from about 3s cm^–1before, to about 26 s cm^–1 after the high temperaturetreatment. The increase depended upon the degree of suppression. It is concluded that increased R_D at high temperature in Xanthiumleaves is partly the result of an increase of energy demandingmaintenance. The subsequent rate of carbon dioxide fixationis reduced when this increase of maintenance-induced respirationis inhibited.     

Esophageal temperature threshold for sweating decreases before ovulation in premenopausal women

The purpose ofthis study was to test the hypothesis that regulated body temperatureis decreased in the preovulatory phase in eumenorrheic women. Six womenwere studied in both the preovulatory phase (Preov-2;days 9-12), which was 1-2days before predicted ovulation when 17-estradiol(E₂) was estimated to peak, andin the follicular phase (F; days2-6). The subjects walked on a treadmill (~225W · m²)in a warm chamber (ambient temperature = 30°C; dew-pointtemperature = 11.5°C) while heavily clothed.E₂, esophageal temperature(T_es), local skin temperatures,and local sweating rate were measured. The estimate of when theE₂ surge would occur was correctfor four of six subjects. In these four subjects,E₂ increased(P  0.05) from 42.0 ± 24.5 pg/mlduring F to 123.2 ± 31.3 pg/ml during Preov-2. RestingT_es was 37.02 ± 0.20°Cduring F and 36.76 ± 0.28°C during Preov-2(P  0.05). TheT_es threshold for sweating wasdecreased (P  0.05) from 36.88 ± 0.27°C during F to 36.64 ± 0.35°C during Preov-2. Both meanskin and mean body temperatures were decreased during rest in Preov-2group. The hypothesis that regulated body temperature is decreasedduring the preovulatory phase is supported.

     

The Influence of Stress Conditions on Chlorophyll Content of Two Range Grasses with Contrasting Photosynthetic Pathways

The influence of various treatments and temperature regimeson total chlorophylls and on the chlorophyll a:b ratio of westernwheatgrass and blue grama plants was investigated at differenttime intervals during the 120-day growth period. Western wheatgrass,a C₃ species, accumulated greater amounts of chlorophyll thandid blue grama plants, a C₄ species. Maximum concentrations(mg gd wt^–1) of chlorophylls in western wheatgrass andin blue grama were recorded at the lower (13/7°C) and higher(30/18°C) temperature regimes. Nitrogen fertilizer alonedecreased the chlorophyll content in both species. The chlorophylla:b ratio in blue grama ranged from an average of 2·00under irrigated plus fertilized conditions to 3·00 undercontrol and fertilized conditions. On the other hand, the chlorophylla:b ratio in western wheatgrass remained constant at 3·00throughout the growing season under various treatments and temperatureregimes.     

Carbon Exchange Rate of Intact Individual Soya Bean Pods. 1. Response to Step Changes in Light and Temperature

Carbon exchange rates (CER) of individual intact field-grownsoya bean [Glycine max (L.) Merr.] pods were measured continuouslywith a mobile gas analysis laboratory. Conditions in pod chamberssimulated those experienced normally by pods except for experimentalmodification of incident radiation or pod temperature. Undernormal conditions, CER (where positive CER represents CO₂ evolution)fluctuated diurnally with a morning rise followed by a slowafternoon and evening decline which was similar among pods whichwere measured simultaneously. The frequency of measurementspermitted detection of rapid CER responses to step changes inlight and pod temperature. CER rapidly decreased and increasedwhen the chamber was alternately exposed to full sunlight andcomplete darkness, respectively. CER responded similarly tosteps up [from ambient to elevated (+ 10°C) temperature]and steps down (from elevated to ambient temperature), respectively.Thus, a temperature sensitive process which regulated pod CERwas located within the pod. CER ranged from less than 0·1to more than 1·2 mg CO₂ h^–1 pod^–1 over theperiod of rapid dry-matter accumulation. Glycine max (L.) Merr., Soya bean, carbon exchange rate, light, temperature     

Growth and development of Neocalanus flemingeri/plumchrus in the northern Gulf of Alaska: validation of the artificial-cohort method in cold waters

In situ growth and development of Neocalanus flemingeri/plumchrusstage C1–C4 copepodites were estimated by both the artificial-cohortand the single-stage incubation methods in March, April andMay of 2001–2005 at 5–6°C. Results from thesetwo methods were comparable and consistent. In the field, C1–C4stage durations ranged from 7 to >100 days, dependent ontemperature and chlorophyll a (Chl a) concentration. Averagestage durations were 12.4–14.1 days, yielding an averageof 56 days to reach C5, but under optimal conditions stage durationswere closer to 10 days, shortening the time to reach C5 (fromC1) to 46 days. Generally, growth rates decreased with increasingstage, ranging from 0.28 day^–1 to close to zero but weretypically between 0.20 and 0.05 day^–1, averaging 0.110± 0.006 day^–1 (mean ± SE) for single-stageand 0.107 ± 0.005 day^–1 (mean ± SE) forartificial-cohort methods. Growth was well described by equationsof Michaelis–Menten form, with maximum growth rates (G_max)of 0.17–0.18 day^–1 and half saturation Chl a concentrations(K_chl) of 0.45–0.46 mg m^–3 for combined C1–3,while G_max dropped to 0.08–0.09 day^–1 but K_chl remainedat 0.38–0.93 mg m^–3 for C4. In this study, in situgrowth of N. flemingeri/plumchrus was frequently food limitedto some degree, particularly during March. A comparison withglobal models of copepod growth rates suggests that these modelsstill require considerable refinement. We suggest that the artificial-cohortmethod is the most practical approach to generating the multispeciesdata required to address these deficiencies.     

Acclimation of NO-3 fluxes to low root temperature by Brassica napus in relation to NO-3 supply

Acclimation of NO^–₃ transport fluxes (influx, efflux)in roots of oilseed rape (Brassica napus L. cv. Bien venu) andtheir sensitivity to growth at low root temperature was studiedin relation to external NO^–₃ supply, defined by constantconcentrations ranging from sub- to supra-optimal with respectto plant growth rate. Plants were grown from seed in flowingnutrient solutions containing 250 mmol m^–3 NO^–₃at 17°C for 20d, and solution temperature in half the cultureunits was then lowered decrementally over 3 d to 7°C. Threedays later plants were supplied with NO^–₃ at 1, 10, 100or 1000 mmol m^–3 maintained for 18 d. Dry matter productionwas decreased more by low root zone temperature than low [NO^–₃]_e. Root specific growth rates were inversely related to [NO^–₃]_eand shoot:root ratios increased with time at [NO^–₃]_e between10–1000 mmol m^–3. Net uptake of NO^–₃ at 17°Cwas twice that at 7°C, and at both temperatures it doubledwith increasing [NO^–₃]_e between 1–10 mmol m^–3with further small increases at higher [NO^–₃]_e. Mean unitabsorption rates of NO^–₃ between 0–6 d and 6–14d were linearly related (r² of 0.79–0.99) to log₁₀[NO].Steady-state Q₁₀ (7–17°C) for uptake between 0–6d were 0.91, 1.62, 1.27, and 1.10, respectively, at [NO^–₃]_eof 1, 10, 100, and 1000 mmol m^–3, compared with correspondingvalues of 0.98, 1.38, 1.68, and 1.89 between 6–14 d. Thedata indicated that net uptake rates at 7 and 17°C divergedover time at high [NO^–₃]_e. Short-term uptake rates from1 mol m^–3 NO^–₃ measured at 17°C were higherin plants grown with roots at 7°C than at 17°C; for7°C plants there was a strong inverse linear relationship(r²=0.94) between uptake rate and treatment log₁₀ [NO^–₃]_ewhilst rates in 17°C plants were independent of prior [NO^–₃]_e. Rates of NO^–₃ influx and efflux under different steady-stateconditions of NO^–₃ supply and root temperature were calculatedfrom dilution of ¹⁵N added to culture solutions. Efflux wassubstantial relative to net uptake in all treatments, and wasinversely related to [NO^–₃]_e at 17°C but not at 7°C.Ratios of influx: efflux ranged from 1.6–2.9 at 17°Cand 1.3–1.8 at 7°C, indicating the proportionatelygreater impact of efflux at low root temperature. Ratios ofefflux: net uptake were 0.53–1.56 at 17°C and 1.21–3.58at 7°C. The apparent sensitivities of influx and effluxto steady-state root temperature varied with [NO^–₃]_e.Both fluxes were higher at 17°C than 7°C in the presenceof 100–1000 mmol m^–3 NO^–₃ but the trend wasreversed at 1–10 mmol m^–3 NO. Concentrations oftotal N measured in xylem exudate were at least 2-fold higherat 7°C compared with 17°C, attributable mainly to higherconcentrations of NO^–₃ glutamine and proline. The resultsare discussed in terms of acclimatory and other responses shownby the NO^–₃ transport system under conditions of limitingNO^–₃ supply and low root temperature. Key words: Brassica napus, nitrate supply, efflux, influx, root temperature, xylem exudate     

Effect of Root Zone Temperature on the Mineral Composition of Xylem Sap and Plasma Membrane K+-Mg++-ATPase Activity of Grafted-Cucumber and -Figleaf Gourd Root Systems

Cucumber (Cucumis sativus L.) seedlings were grafted onto cucumber-(CG) or figleaf gourd- (FG, Cucurbita ficifolia Bouché)seedlings in order to determine the effect of solution temperature(12, 22, and 32°C) on the mineral composition of xylem sapand the plasma membrane K⁺-Mg⁺⁺-ATPase activities of the roots.Low solution temperature (12°C) lowered the concentrationof NO^–₃ and H₂PO^–₄ in xylem sap of CG plants butnot of FG plants. Concentrations of K⁺, Ca⁺⁺ and Mg⁺⁺ in xylemsap were less affected than anions by solution temperature.The plasma membrane of FG plants grown in 12°C solutiontemperature showed the highest K⁺- Mg⁺⁺-ATPase activity at allATP concentrations up to 3 mM and at low reaction temperatureup to 12°C, indicating resistance of figleaf gourd to lowroot temperature. (Received December 27, 1994; Accepted March 10, 1995)     

Transnodal Transport of 14C in Nitella flexilis: I. TANDEM CELLS WITHOUT APPLIED PRESSURE GRADIENTS

Using NaH¹⁴CO₃ (0·01-0·03 mol m^–3) fed to5·0 mm of Nitella flexilis in artificial pond water at22–25°C, we have found that uptake in 5 min or in1 h varies with the streaming rate of the fed cell and is reducedby anoxia over the uptake position. We have also found thatthe %¹⁴C transported across the node between two internodalcells in tandem is highly sensitive to the streaming rate ineach cell, to the physiological state of the cells (summer versuswinter), to the method of feeding (5 min versus 1 h) and tocovering the node, particularly with winter cells or summercells preconditioned for 3 h in the dark and run in the dark.Transnodal transport by plasmodesmata is sensitive to anoxiaand seems to be at least partly active. Key words: Node, plasmodesmata, anoxia, active transport, influx     

Joint field experiments for comparisons of measuring methods of photosynthetic production

During the 1st GAP Workshop at Konstanz in April 1982 comparativemeasurements of phytoplankton primary production by severaltechniques were conducted simultaneously at an offshore stationin Lake Konstanz and an experimental algal pond. Suspended glassbottle exposure techniques using ¹⁴C and ¹³C uptake gave P_z(mg C m^–3 h^–1) values which varied considerablynear-surface, but estimates of areal rates for the euphoticzone P_cu(mg C m^–3 h^–1) which were reasonably close.In the lake, P_z, from a vertical tube exposure (with ¹⁴C uptake)was greater than rates derived for integrated bottle samples.The oxygen bottle method permitted a good estimate of compensationdepth, corresponding to in situ growth studies. There were difficultiesin direct comparison between O₂ and carbon methods. Correlationbetween them for P_z was good in the lake but poor in the pond,both for suspended bottle and vertical tube methods. This seriesdemonstrates that despite reasonable overall estimates, comparativelyminor methodological differences in experimental technique cancause large variation. ⁺ Coordinator of the group for comparative measurements of photosyntheticproduction at the GAP Workshop, Konstanz, April 1982. ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP) First International Workshop heldat the Limnological Institute, University of Konstanz, in April1982.