MODE OF NUCLEAR DIVISION IN SYNCHRONOUS CULTURES OF CHLORELLA: COMPARISON OF VARIOUS METHODS OF SYNCHRONIZATION

1. Chlorella ellipsoidea was grown synchronously using variouspossible techniques and the mode of nuclear division in eachcase was followed by staining the nuclei according to FEULGEN.
2. A satisfactory synchrony in respect to nuclear and cellulardivision was obtained by starting the culture from a homogeneouspopulation of young and small cells and by discontinuing theillumination at the stage which was called the L₃-stage. Thestarting young cells were invariably mononuclear and the L₃-cellswere either dinuclear or tetranuclear. When the L₃ were incubatedin the dark, they ripened further, and after passing througha tetranuclear stage (referred to as the L₄) divided into fourmononuclear daughter cells which have been called the D_n-cells.The most clear-cut and repetitive synchronous culture was obtainedwhen the culture (in the light) was started from the D_n-cellsand the illumination was discontinued at the L₃-stage untilthe fully ripened cells divided into four each of D_n-cells.
3. An apparently "synchronous" culture was also obtained by themethod of programmed light-and-dark regimen, in which a randomculture is subjected to a regular alternation of light and darkperiods of adequate durations. In this case, however, the cellsat different stages of culture showed irregular nuclear patterns,and the average "division number" of mother cells was not constant,being subject to change between 4.0 and 4.9.

(Received May 25, 1961; )     

Post-embryonic developmental rates as a function of food type in the cyclopoid copepod, Mesocyclops thermocyclopoides Harada

We studied under laboratory conditions the post-embryonic developmentalrates (from nauplii to adult stage) of Mesocyclops thermocyclopoides,commonly found in the eutrophic and hypertrophic local ponds,in relation to different food types. Nauplii hatched from theeggs collected from laboratory-maintained mass cultures werereared at 25l.5C, using the following test diets: bacteria(Klebsiella aerogenes), cyanobacteria (Microcystis aeruginosa,as single cells and in the form of colonies), green algae (Chlorella,Scenedesmus and Chlorogonium), ciliates (Tetrahymena) and rotifers(Brachionus angularis). The developmental rates were fastest,and the proportion of nauplii reaching the copepodid stage andthat of copepodids reaching the adult stage the highest, withChlorogonium, followed by ciliates and rotifers. Developmentwas incomplete with bacteria and Microcys-tis.Ttie algae Chlorellaand Scenedesmus supported complete post-embryonic developmentonly when cultured in media enriched with beef extract, bactotryptoneand yeast extract. With rotifers as the exclusive food, >70%of the nauplii reached the copepodid stage, and >85% of thecopepodids the adult stage. The ratio (D_c/D_n) of copepodid duration(D_c) and naupliar duration (D_n) was significantly differentfrom 1.0, indicating the absence of isochronal development inM.thermocyclopoides. Our results show that post-embryonic developmentin this species is not possible with certain algal diets, probablybecause of nutritional deficiencies, and that the later stagenauplii are capable of capturing rotifers and utilizing themas food to complete their development to the adult stage.     

Specific inhibitory effect of copper on cellular division in Chlorella

By growing Chlorella ellipsoidea synchronously by the techniqueof TAMIYA et al. with some modifications, it was demonstratedthat cellular division of ripened cells (L₂- and L₃-cells) inthe dark is specifically inhibited—especially stronglyat pH 6.3—by cupric ion present in the medium. The possibleattack site of cupric ion in cellular division of this algais discussed. (Received March 12, 1969; )     

Induction Kinetics of Millisecond-Delayed Luminescence in Intact Bryopsis Chloroplasts

The induction curve of delayed luminescence emitted from 0.5to 2.5 ms after excitation of dark-adapted intact chloroplastsof the green alga, Bryopsis maxima, showed three transient peaks,L₁, L₂ and L₃ (in order of appearance), at about 0.1, 1 and5 s after theonset of intermittent illumination. Intact chloroplastswere needed for L₂ to appear, whereas L₁ and L₃ were presentin hypotonically treated chloroplasts. L₁ and L₂ are related to the electric field generated acrossthe thylakoid membranesbecause the two peaks parallelled theappearance of the first and second peaks of electrochromic absorptionchanges at 560 nm and they were totally abolished by valinomycinand CCCP. A smaller contribution to the L₁ and L₂ of the protonactivity gradient across the membranes, or of pH changes insideor outside the membranes, was suggested by the partial suppressionof the transient by NH₄CI. L₃ is related to the proton gradient or pH changes because thetransient was inhibited by NH₄CI and CCCP but enhanced by N,N'-dicyclohexylcarbodiimide.In the presenceof valinomycin, which somewhat lowered the peakheight of L₃, the kinetics of delayed luminescence parallelledthat of fluorescence. Electrogenic reactions which occur sequentiallyduring the dark to light transition of the photosynthetic machineryin intact chloroplasts is discussed in connection with transientchanges in delayed luminescence. (Received November 8, 1982; Accepted May 21, 1983)     

Food and suspended sediment influences on the naupliar and copepodid durations of freshwater copepods: comparative studies on Tropodiaptomus and Metadiaptomus

Post-embryonic durations of Tropodiaptomus spectabilis (Kiefer)and Metadiaptomus colonialis(van Douwe) were determined at 20°Cin laboratory factorial experiments involving four algal foodenrichment levels (0, 100, 500 and 2500 µg l^–1 Cof Selenastrum added to 20 µm filtered water from respectivesource-lakes) and three suspended sediment levels (filtered,natural, and 2- to 3-fold sediment-enriched lake water). Foodeffects (30, 75, 225 and 600 (µg ^–1 C of Scenedesmus)were tested alone at 20°C for Metadiaptomus meridianus (vanDouwe). Total naupliar (D_n) and total copepodid (D_c) developmenttimes [summed to give total post-embryonic duration (D_t)] andmetasome lengths at maturity were measured In all taxa, foodsupply maximally affected D_c values 2- to 3-fold, whereas itsmaximal influence on D_n values was relatively slight (generally25%). The measured effect of food supply on D_t, was as strongas the predicted influence of temperature over an appropriateannual range. Food supply influenced size at maturity, and probablythereby fecundity, thus exerting additional demographic influences.Sediment effects were inconsistent, and quantitatively weakerthan food effects Total development of T.spectabilis was 20%raster, and that of M.colonialis 15% slower in sediment-enrichedthan in natural sediment level treatments; contrasting baselinesediment levels (2–3 times higher for the latter species)and different enrichment procedures confound interpretation.Unexpectedly, and inexplicably, development almost invariablyfailed in sediment-free water, implying an apparent dependencyon inorganic particles in these taxa This contrasts with thegenerally adverse influences of high sediment concentrationsupon zooplankton. Minimal male and female D_t values at 20°Cwere comparable and significantly longer in M.colonialis (15.5and 17 7 days) and M meridianus (16.5 and 21.5 days) than inT.spectabilis (11.7 and 12 2 days). These differences in durationare ecologically incongruous in relation to expected r –K life history strategies of genera characteristic of temporaryor semipermanent waters and permanent waters respectively.     

不同浓度NaCl和Na2CO3处理对菊芋幼苗光合及叶绿素荧光的影响

 以砂培菊芋(Helianthus tuberosus)幼苗作为试验材料,分别进行不同浓度NaCl (50、 100、150、200、250 mmol&;#8226;L^－1)和Na₂CO₃ (25、50、 75、100、125 mmol&;#8226;L^－1)胁迫处理,以1/2全营养液作为对照,处理7 d后研究NaCl和Na₂CO₃胁迫处理对菊芋幼苗叶片光合作用及叶绿素动力学 参数的影响。结果表明：1)在NaCl处理下,当浓度小于150 mmol&;#8226;L^－1时,增加了菊芋的叶绿素含量、净光合速率(Net photosynthetic rate, P_n)和气孔导度(Stomatal conductivity, G_s),对荧光参数PSⅡ的电子传递情况( F_m/F_o)、PSⅡ原初光能转换效率(F_v/F_m)、PSⅡ量子效率 (Actual quantum yield of PSⅡ under actinic irradiation,φPSⅡ)和光化学猝灭系数(Photochemical quenching coefficient, qP)和非 光化学猝灭系 数(Non-photochemical quenching coefficient, NPQ)没有显著影响,随着浓度的增加,各项生理指标与对照相比除了NPQ显著 增加,其余均显著降低;2)在Na₂CO₃胁迫处理下,随着Na₂CO₃浓度的增加,与对照相比菊芋幼苗叶绿素含量、P_n、G_s以及叶绿素a荧光诱导动力 学参数F_m/F_o、F_v/F_m、φPSⅡ和qP均显著降低,NPQ显著增加;3)就NaCl和Na₂CO₃相比而言,在相同Na⁺浓度情况下,处于Na₂CO₃胁迫下的菊芋 幼苗的叶绿素含量、P_n、G_s以及叶绿素a荧光诱导动力学参数F_m/F_o、F_v/F_m、φPSⅡ和qP下降幅度和NPQ的增加幅度均显著大于NaCl,这说明 NaCl和Na₂CO₃胁迫均对菊芋幼苗造成不同程度的伤害,但在相同Na⁺浓度情况下,Na₂CO₃的伤害程度大于NaCl。由此说明菊芋对盐的忍耐程度高 于碱。     

Factors Controlling Induction of External Carbonic Anhydrase and Change in K?(CO2) of Photosynthesis in Chlorella regularis

Transfer of algal cells of Chlorella regularis from 3% CO₂ inair into ordinary air in the light increased external carbonicanhydrase (CA) activity as well as photosynthetic affinity forCO₂ by several-fold within 2 h. Since no noticeable differencewas observed in CA activity between intact cells and cell homogenates,CA seemed to be mainly localized on the cell surface. Changesin CA activity and K_?(CO₂) of photosynthesis were not observedin the dark. CA induction was 50%-inhibited by incubation with10 µM DCMU during adaptation of high-CO₂ cells to air,whereas it was considerably suppressed when high-CO₂ cells preincubatedwith DCMU in the light for 6 h or without DCMU in the dark for24 h were used. The change in K_?(CO₂) of photosynthesis wasonly slightly affected by DCMU. Uncoupler like carbonylcyanide-m-chlorophenyl-hydrazone(CCCP) and inhibitors of mitochondrial respiration (KCN plussalicylhydroxamic acid) suppressed CA induction during adaptationof high-CO₂ cells to low CO₂ conditions. These results suggest that photosynthesis is not essential forCA induction in Chlorella regularis when some amounts of photosyntheticproducts are previously stored in the cells and respirationis active. A decrease in K_?(CO₂) of photosynthesis during adaptationfrom high to low CO₂ was mostly independent on photosynthesis.However, light is essential for both phenomena. (Received July 16, 1990; Accepted January 21, 1991)     

SYNCHRONOUS MASS-CULTURE OF CHLORELLA

A new culture apparatus was constructed to obtain large quantitiesof synchronized cells of Chlorella ellipsoidea. Two flat culturechambers made of lucid acrylate resin (each 20 liters in capacity)were placed in a water thermostat together with a bank of 17daylight fluorescent lamps, and the culture was run by the methodstarting from a homogeneous population of D_s-cells accordingto TAMIYA et al. It was demonstrated that with this apparatusone can obtain as much as 200–400 mg (dry weight) eachof algal material at 8 or 9 different stages in one cell cycle.Completely synchronized cell cycles could be repeated as manyas 10 times in one series of experiment, indicating that theapparatus can produce 2–4g (dry weight) each of algalcells of different developmental stages. (Received April 2, 1964; )     

Analysis and Significance of Gravity-induced Asymmetric Growth in the Grass Leaf-sheath Pulvinus

The negative gravitropic response in the grass leaf-sheath pulvinusis a consequence of cell elongation involving all cells exceptthose of the uppermost region of the upper flank of an horizontallyoriented pulvinus. The lowermost layer of cells elongate maximally,and the regions in between elongate to intermediate extents.The resulting curvatures of a responding pulvinus can be expressedmathematically by relating the angle of curvature () to theoriginal length (L₀) and the maximal length of the lower surface(L₁) and the diameter of the organ (D), using the equation, = (L₁–L₀)/D, where is in radians. The elongation response(S) of any individual cell within the pulvinus can be expressedby the equation, S = 0.5-r cos, where r is the radius of thepulvinus and is in degrees. Microscopic measurement of celllengths in different regions of the pulvinus supports the mathematicalpredictions. Indirect support is also obtained from the useof colchicine, coumarin, dichloro-benzonitrile (DCBN) and isopropylN-chlorophenyl carbamate which exaggerate the inherent asymmetryduring gravitropic response. Coumarin and DCBN also induce thickeningsin the radial walls which appear first in the statenchyma, andlater, in cells located towards the outer periphery of the pulvinus.The distribution patterns of these thickenings suggest thatthe asymmetric growth response of the pulvinus may be due toa differential and radial, centrifugal transport of growth promotorsfrom the central statenchyma region. Gravity perception, grass pulvinus     

Diffusion of Oxyleghaemoglobin

The diffusion of oxyleghaemoglobin, prepared from soybean rootnodules, was measured at 24°C in agar and agarose gels ofvarious strengths, or in 1% agarose containing 0-18% (w/v) bovineserum albumin, to simulate the protein content of the cytoplasmof root nodule cells. Values of D_p, the diffusion coefficient,were unaffected (D_p = 11·8 x 10^-11 m² s^-1; s.e.m. 0·3x 10^-11) until the protein concentration exceeded 6%, abovewhich D_p declined sharply. With 18% bovine serum albumin, theconcentration of total soluble protein calculated to be presentin the cytoplasm of infected cells, where most of the leghaemoglobinis located in vivo, D_p was 5·9 x 10^-11 m² s^-1. Theseresults are discussed in relation to leghaemoglobin-facilitateddelivery of O₂ to the respiring N₂-fixing bacteroids in rootnodule cells.Copyright 1993, 1999 Academic Press Bacteroids, diffusion, Glycine max, N₂ fixation, oxyleghaemoglobin, soybean, root nodules     

Comparison of carbon-specific growth rates and rates of cellular increase of phytoplankton in large limnetic enclosures

Potential carbon-specific growth rates of phytoplankton wereestimated from a series of measurements of photosynthetic radio-carbonuptake over 4- and 24-h exposure periods in the light fieldsof three large limnetic enclosures (‘Lund Tubes’),each providing different limnological and trophic conditions.Photosynthetic behaviour and short-term, chlorophyll-specificcarbon-fixation rates conformed to well-established criteriabut, over 24 h, the net retention represented 23–82% ofthe carbon fixed during the daylight hours. Potential mean growthrates (k'_p, of the photo-autotrophic community were calculatedas the net exponential rates of daily carbon-accumulation relativeto derived, instantaneous estimates of the cell carbon-content.Apparent actual community growth rates (k'_D were calculatedas the sum of the exponential rates of change of each of themajor species present, corrected for probable rates of in situgrazing and sinking, and expressed relative to the fractionof total biomass for which they accounted. The correspondingvalues were only occasionally similar, k'_p generally exceedingK'_D by a factor of between 1 and 30 or 1 and 14, depending uponthe carbon:chlorophyll ratio used. The ratio, K'_p/K'_D was foundto vary inversely both to k'_D and to k_n, the net rate of changein phytoplankton biomass, suggesting that measured carbon fixationrates merely represent a capacity for cellular increase which,owing to other likely limitations upon growth, is seldom realized.Apparent rates of loss of whole cells do not account for theloss of carbon; that the ‘unaccounted’ loss rates(K'_p–K'_D varied in direct proportion to K'_p (i.e., losseswere least when chlorophyll-specific photosynthetic productivitywas itself limited) is best explained by physiological voidingof excess carbon (for instance, by respiration, photorespiration,excretion) prior to the formation of new cells.     

Rates of Photosynthesis in Characean Cells: II. PHOTOSYNTHETIC 14CO2 FIXATION AND 14C-BICARBONATE UPTAKE BY CHARACEAN CELLS

Photosynthetic ¹⁴C fixation by Characean cells in solutionsof high pH containing NaH¹⁴CO₃ gave a measure of the abilityof these cells to take up bicarbonate (H¹⁴CO₃^–). Whereascells of Nitella translucens from plants collected and thenstored in the laboratory absorbed bicarbonate at 1–1.5µµmoles cm^–2 sec^–1, rates of 3–8µµmoles cm^–2 sec^–1 were obtained withN. translucens cells from plants grown in the laboratory. Influxesof 5–6 µµmoles cm^–2 sec^–1 wereobtained with Chara australis, 3–8 µµmolescm^–2 sec^–1 with Nitellopsis obtusa, and 1–5µµmoles cm^–2 sec^–1 with Tolypella intricata.It is considered that these influxes represent the activityof a bicarbonate pump, which may be an electrogenic process. In solutions of lower pH, H¹⁴CO₃^– uptake would be maskedby rapid diffusion of ¹⁴CO₂ into the cells: the four Characeanspecies fixed ¹⁴CO₂ at maximum rates of 30–40 µµmolescm^–2 sec^–1 (at 21° C).     

Diurnal fluctuation of light and dark CO2 fixation in peeled and unpeeled leaves of Bryophyllum daigremontiana

Diurnal fluctuation of light and dark CO₂ fixation in peeledand unpeeled leaves of Bryophyllum daigremontiana was examined.A distinct difference in light CO₂ fixation was observed inunpeeled leaves but not in peeled ones. No measurable differencein dark CO₂ fixation was observed in either type. These resultsindicate that the leaves of CAM plants have a high capacityfor CO₂ fixation in the daytime, but it is suppressed by theclosing of the stomata. Also, the rapid depression of CO₂ uptakewhen the illumination was directed at on dark acidified leavescould be prevented by peeling off the epidermis. The net photosyntheticCO₂ uptake in peeled leaves was 77 µmoles/mg chllrophyll/hrin the 3rd leaf and 62 in the 4th leaf. (Received August 7, 1978; )     

Effects of CO2 concentration during growth on subsequent photosynthetic CO2 fixation in Chlorella1

The maximum rate of photosynthetic ¹⁴CO₂ fixation (V_max) aswell as the concentration of CO₂ at which the rate of photosynthetic¹⁴CO₂ fixation attains one-half its maximum velocity (K_m) inChlorella vulgaris 11h cells was strongly dependent on the concentrationof CO₂ continuously provided during the algal growth. The V_max (µmoles ¹⁴CO₂ fixed/ml pcv?min) and K_m (% CO₂)of the algal cells which had been grown in air containing 4%CO₂ (by volume) were ca. 10 and 0.15–0.17, while thosein the cells which had been grown in ordinary air (containing0.04% CO₂) were 7 and 0.05–0.06, respectively. When the concentration of CO₂ in the bubbling gas was loweredfrom 4 to 0.04% during the algal growth, their photosynthetickinetics attained the respective lower steady levels after 5–10hr. On the other hand, when the photosynthetic kinetics weredetermined 24 hr after raising the concentration of CO₂ from0.04 to 4%, the V_max and K_m-values were found to have alreadyattained the respective higher levels. (Received October 15, 1976; )     

Light dependency of the mating process in Closterium acerosum

Sexual cell division and activation of gametangial cells forconjugation in Closterium acerosum were induced by light. L₂₀₀cells conjugated at maximum level under the following conditions;(i) a light intensity higher than 1,000 lux in a 16-hr lightand 8-hr dark regime and (ii) an illumination time longer than12 hr at 3,000 lux. L₂₀₀ cells also conjugated under continuousillumination at 3,000 lux. The action spectrum for the activation of gametangial cellshad peaks around 450, 611 and 665 nm. 3-(4'-Chlorophenyl)-l,l-dimethylurea (CMU) inhibited the accumulationof carbohydrates and sexual cell division at 10^–5 M andthe activation of gametangial cells for conjugation at 10^–4M. (Received August 15, 1977; )     

Elongation of the N-glycans of fowl plague virus hemagglutinin expressed in Spodoptera frugiperda (Sf9) cells by coexpression of human {beta}1,2-N-acetylglucosaminyltransferase I

Spodoptera frugiperda (Sf9)-cells differ markedly in their proteinglycosylation capacities from vertebrate cells in that theyare not able to generate complex type oligosaccharide side chains.In order to improve the oligosaccha ride processing propertiesof these cells we have used baculovirus vectors for expressionof human (ß1,2-N-acetylglucosaminyltransferase I (hGNT-I),the enzyme catalysing the crucial step in the pathway leadingto complex type N-glycans in vertebrate cells. One vector (Bac/GNT)was designed to express unmodified GNT-I protein, the secondvector (Bac/tagGNT) to express GNT-I protein with a tag epitopefused to its N-terminus. In Sf9-cells infected with Bac/tagGNT-virusa protein of about 50 kDa representing hGNT-I was detected withan antiserum directed against the tag epitope. HGNT-I activitywas increased at least threefold in lysates of infected cellswhen N-acetylglucosamine (GlcNAc)-free ovalbumine was used assubstrate. To monitor hGNT-I activity in intact Sf9-cells, theglycosylation of coexpressed fowl plague virus hemagglutinin(HA) was investigated employing a galactosylation assay andchromatographic analysis of isolated HA N-glycans. Coexpressionof hGNT-I resulted in an at least fourfold increase of HA carryingterminal GlcNAc-residues. The only structure detectable in thisfraction was GlcNAcMan₃GlcNAc₂. These results show that hGNT-Iis functionally active in Sf9-cells and that the N-glycans ofproteins expressed in the baculovirus/insect cell system areelongated by coexpression of glycosyltransferases of vertebrateorigin. Complete complex type oligosaccharide side chains werenot observed when hGNT-I was overexpressed, thus supportingthe concept that Sf9-cells do not contain glycosyltransferasesacting after hGNT-I. ß1,2-N-acetylglucosaminyltransferase I baculovirus expression of recombinant protiens N-glycosylation in Sf9-cells     

Alkalization of the Medium by Unicellular Green Algae during Uptake Dissolved Inorganic Carbon

When Chlorella vulgaris 11h, Chlorella vulgaris C-l, Chlamydomonasreinhardtii, Chlamydomonas moewusii, Scenedesmus obliquus, orDunaliella tertiolecta were illuminated in with 0.5 mM NaHCO₃,the pH of the medium increased in a few minutes from 6 to about9 or 10. The alkalization, which was accompanied by O₂ evolution,was dependent on light, external dissolved inorganic carbon(DIC) as HCO^-₃, and algae grown or adapted to a low, air-levelCO₂ in order to develop a DIC concentrating mechanism. Therewas little pH increase by algae without a DIC concentratingprocess from growth on 3% CO₂ in air. Photosynthetic O₂ evolutionwithout alkalization occurred using either internal DIC or externalCO₂ at acidic pH. The PH increase stopped between pH 9 to 10,but the alkalization would restart upon re-acidification betweenpH 6 and 8. Alkalization was suppressed by the carbonic anhydraseinhibitors, acetazolamide, ethoxyzolamide or carbon oxysulfide.The pH increase appeared to be the consequence of the externalconversion of HCO^–₃ into CO₂ plus OH^– during photosynthesisby cells with a high affinity for CO₂ uptake. Cells grown onhigh CO₂ to suppress the DIC pump, when given low levels ofHCO^–₃ in the light, acidified the medium from pH 10 to7. Air adapted Scenedesmus cells with a HCO^–₃ pump, aswell as a CO₂ pump, alkalized the medium very rapidly in thelight to a pH of over 10, as well as slower in the dark or inthe light with DCMU or without external DIC and O₂ evolution.Alkalization of the medium during photosynthetic DIC uptakeby algae has been considered to be part of the global carboncycle for converting H₂CO₃ to HCO^–₃ and for the formationof carbonate salts by calcareous algae from the alkaline conversionof bicarbonate to carbonate. These processes seem to be a consequenceof the algal CO₂ concentrating process. ¹Present address: Department of Biology, Faculty of Science,Niigata University, Niigata, 950-21 Japan.     

Resource competition between two rotifer species (Brachionus rubens and B.calyciflorus): an experimental test of a mechanistic model

A mechanistic model of competition on a single resource wastested experimentally with two freshwater rotifers, Brachionusrubens and B.calyciflorus, both grown on the alga Chlorellapyrenoidosa. Using open culture systems for each species wemeasured: (i) the resource-saturated exponential growth rate,µ_max, and (ii) the relationship between specific growthrate, µ, at steady-state and the residual algal concentrationover a range of system turnover rates, or dilution rates, D.The µ_max of B.calyciflorus was {small tilde}60% higherthan B. rubens. These results were then used to construct agraphical model for predicting the victor in interspecific competitionbetween the two rotifers. Since the two resource-dependent growthrates crossed, one species, B.calyciflorus, was predicted tobe the victor at a high D while B. rubens was predicted as thevictor at low D. Finally, the outcome of competition was determinedfor two turnover rates. As predicted by the graphical competitionmodels, B.calyciflorus was the dominant species at rapid D (0.029h^–1) and B.rubens was dominant at slow D (0.0044 h^–1).These studies support recent conclusions that mechanistic competitionmodels may be applied to predict dominant species from a prioriinformation on growth potential and resource levels, which isnot possible with traditional Lotka-Volterra models.     

Radial Hydraulic Conductivity of Individual Root Tissues of Opuntia ficus-indica (L.) Miller as Soil Moisture Varies

The constraints on water uptake imposed by individual root tissueswere examined forOpuntia ficus-indicaunder wet, drying, andrewetted soil conditions. Root hydraulic conductivity (L_P) andaxial conductance (K_h) were measured for intact root segmentsfrom the distal region with an endodermis and from midroot witha periderm;L_Pwas then measured for each segment with successivetissues removed by dissection. Radial conductivity (L_R) wascalculated fromL_PandK_hfor the intact segment and for the individualtissues by considering the tissue conductivities in series.Under wet conditions,L_Rfor intact distal root segments was lowestfor the cortex; at midroot, where cortical cells are dead,L_Rforthe cortex was higher and no single tissue was the predominantlimiter ofL_R.L_Rfor the endodermis and the periderm were similarunder wet conditions. During 30d of soil drying,L_Rfor the distalcortex increased almost three-fold due to the death of corticalcells, whereasL_Rfor the midroot cortex was unaffected;L_Rforthe endodermis and the periderm decreased by 40 and 90%, respectively,during drying. For both root regions under wet conditions, thevascular cylinder had the highestL_R, which decreased by 50–70%during 30d of soil drying. After 3d of rewetting, new lateralroots emerged, increasingL_Rfor the tissues outside the vascularcylinder as well as increasing uptake of an apoplastic tracerinto the xylem of both the roots and the shoot. The averageL_Rforintact root segments was similar under wet and rewetted conditions,but the conductivity of the tissues outside the vascular cylinderincreased after rewetting, as did the contribution of the apoplasticpathway to water uptake. Opuntia ficus-indica; prickly pear; root hydraulic conductivity; endodermis; periderm; apoplast; lateral root emergence     

Form of inorganic carbon utilized for photosynthesis in Chlorella vulgaris 11 h cells

The rate of photosynthetic ¹⁴CO₂ fixation in Chlorella vulgaris11h cells in the presence of 0.55 mM NaH¹⁴CO₃ at pH 8.0 (20?C)was greatly enhanced by the addition of carbonic anhydrase (CA).However, when air containing 400 ppm ¹⁴CO₂ was bubbled throughthe algal suspension, the rate of ¹⁴CO₂ fixation immediatelyafter the start of the bubbling was suppressed by CA. Theseeffects of CA were observed in cells which had been grown inair containing 2% CO₂ (high-CO₂ cells) as well as those grownin ordinary air (containing 0.04% CO₂, low-CO₂ cells). We thereforeconcluded that, irrespective of the CO₂ concentration givento the algal cells during growth, the active species of inorganiccarbon absorbed by Chlorella cells is free CO₂ and they cannotutilize bicarbonate. The effects observed in the high-CO₂ cellswere much more pronounced than those in the high-CO₂ cells.This difference was accounted for by the difference in the affinityfor CO₂ in photosynthesis between the high- and low-CO₂ cells. (Received May 19, 1978; )