Effect of gibberellic acid on starch content of soybean (Glycine max L.) and its correlation with extension growth

This investigation was undertaken to study the effect of GA₃on extension growth of Glycine max L. and on starch contentof its individual internodes at maturity. The effect on hydrolyticactivity of the extract of different internodes was also studied.GA₃ stimulates the extension growth of stem by increasing theelongation of those internodes which are either in the processof elongation or being differentiated at the time of treatment.Starch content decreases with the position of the internode(from base upwards) on the intact plant. Corresponding internodeshave minimum starch content in 100 ppm GA₃-treated plants andmaximum in the controls. Internodes which show the maximum elongationdue to GA₃ treatment, show the least starch content and alsoshow maximum hydrolytic activity during the period of elongation.It is suggested that enhanced extension growth is brought aboutby enhanced mobilization of reserve food by GA₃. (Received November 21, 1967; )     

Characterisation of Non-Uniform Photosynthesis Induced by Abscisic Acid in Leaves Having Different Mesophyll Anatomies

The effects of abscisic acid (ABA) on photosynthesis in leavesof Helianthus annuus L. were compared with those in leaves ofVicia faba L. After the ABA treatment, the response of photosyntheticCO₂ assimilation rate, A, to calculated intercellular partialpressure of CO₂, P_i, (A(p_i) relationship) was markedly depressedin H. annuus. A less marked depression was also observed inV.faba. However, when the abaxial epidermes were removed fromthese leaves, neither the maximum rate nor the CO₂ responseof photosynthetic oxygen evolution was affected by the applicationof ABA. Starch-iodine tests revealed that photosynthesis was not uniformover the leaves of H. annuus treated with ABA. The starch contentwas diffferent in each bundle sheath extension compartment (thesmallest subdivision of mesophyll by veins with bundle sheathextensions, having an area of ca. 0.25 mm² and ca. 50 stomata).In some compartments, no starch was detected. The distributionof open stomata, examined using the silicone rubber impressiontechniques, was similar to the pattern of starch accumulation.In V.faba leaves, which lack bundle sheath extensions, distributionof starch was more homogeneous. These results indicate that the apparent non-stomatal inhibitionof photosynthesis by ABA deduced from the depression of A(pⁱ)relationship is an artifact which can be attributed to the non-uniformdistribution of transpiration and photosynthesis over the leaf.Intercellular gaseous environment in the ABA-treated leavesis discussed in relation to mesophyll anatomy. ¹ Present address: Department of Botany, Duke University, Durham,NC 27706, U.S.A. (Received September 30, 1987; Accepted January 13, 1988)     

Photosynthesis and Light Activation of Ribulose 1,5-bisphosphate Carboxylase in the Presence of Starch

Limitation of photosynthesis and light activation of ribulose,1,5-bisphosphate carboxylase (RuBPCO) were examined in the 5thleaf of seedlings of red clover (Trifolium pratense L. cv. Renova)for 5 d following an increase in photosynthetic photon fluxdensity (PPFD) from 200 to 550µmol quanta m^–2 s^–1.Net photosynthesis and its stimulation at 2.0 kPa O₂ initialactivity of rapidly extracted RuBPCO, standard activity of RuBPCOafter incubation of the extracts in the presence of CO₂, Mg²⁺,and inorganic phosphate and contents of soluble protein, starch,soluble sugars, and various photosynthetic metabolites weredetermined. Photosynthesis decreased and starch content increased.No decrease in photosynthesis was found if, when PPFD was increased,all leaves except the investigated 5th leaf were removed, suggestingthat the decrease in photosynthesis was due to accumulated carbohydrates.The stimulation of photosynthesis at 2.0 kPa O₂ did not decreaseand the ratio of the total foliar steady-state contents of triosephosphate to 3-phosphoglycerate increased suggesting that thedecrease in photosynthesis was not due to limiting inorganicphosphate in chloroplasts. Intercellular CO₂ partial pressureand RuBP content were not decreased. Nevertheless, the ratioof photosynthesis to initial RuBPCO activity decreased, suggestingthat the catalysis per active RuBPCO site was decreased. Theincrease in PPFD in the growth cabinet and the PPFD at whichleaves were preconditioned for 1 h, affected not only initialactivity but also the standard activity of RuBPCO. The resultssuggest that a varying proportion of RuBPCO was bound to membranesand was contained in the insoluble fraction of the extracts.A comparison of photosynthesis with extracted RuBPCO activitysuggested that membrane bound RuBPCO did not contribute to photosyntheticCO₂ fixation and that the binding and release to and from membranesmodulated actual RuBPCO activity in vivo. Key words: Photosynthesis, ribulose 1,5-bisphosphate carboxylase, starch     

"Living high-training low": effect of moderate-altitude acclimatization with low-altitude training on performance

Levine, Benjamin D., and James Stray-Gundersen."Living high-training low": effect of moderate-altitudeacclimatization with low-altitude training on performance.J. Appl. Physiol. 83(1): 102-112, 1997.The principal objective of this study was to test the hypothesisthat acclimatization to moderate altitude (2,500 m) plus training atlow altitude (1,250 m), "living high-training low," improvessea-level performance in well-trained runners more than an equivalentsea-level or altitude control. Thirty-nine competitive runners (27 men,12 women) completed 1) a 2-wklead-in phase, followed by 2) 4 wkof supervised training at sea level; and3) 4 wk of field training camprandomized to three groups: "high-low"(n = 13), living at moderate altitude(2,500 m) and training at low altitude (1,250 m); "high-high"(n = 13), living and training atmoderate altitude (2,500 m); or "low-low"(n = 13), living and training in amountain environment at sea level (150 m). A 5,000-m time trial was theprimary measure of performance; laboratory outcomes included maximalO₂ uptake(O_{2 max}), anaerobic capacity (accumulated O₂ deficit),maximal steady state (MSS; ventilatory threshold), running economy,velocity at O_{2 max}, and blood compartment volumes. Both altitude groups significantly increased O_{2 max}(5%) in direct proportion to an increase in red cell mass volume(9%; r = 0.37, P < 0.05), neither of which changedin the control. Five-kilometer time was improved by the field trainingcamp only in the high-low group (13.4 ± 10 s), in directproportion to the increase inO_{2 max}(r = 0.65, P < 0.01). Velocity atO_{2 max} andMSS also improved only in the high-low group. Four weeks of livinghigh-training low improves sea-level running performance in trainedrunners due to altitude acclimatization (increase in red cell massvolume and O_{2 max}) and maintenance of sea-level training velocities, mostlikely accounting for the increase in velocity atO_{2 max} and MSS.

     

Physiological changes accompanying the recovery of cell division in "giant" cells of Chlorella vulgaris (EMERSON strain)

A homogeneous population of "giant" cells of the EMERSON strainof Chlorella vulgaris, produced following culture under carefullycontrolled conditions in a glucose medium in the dark, recoversits capacity to undergo cell division when returned to autotrophicconditions. A similar recovery also occurs after a prolongedperiod of culture in the dark. The division of the giant cellsis accompanied, in each case, by marked pigment synthesis anda consequent recovery of photosynthetic capacity. Under autotrophicconditions the recovery of cell division and restoration ofthe full pigment concentration are complete within a 24 hr period.The recovery which takes place in a glucose medium in the darkoccurs only after a period of 10–14 days growth. (Received May 9, 1970; )     

METABOLISM OF GLUCOSE IN THE PROCESS OF "GLUCOSE-BLEACHING" OF CHLORELLA PROTOTHECOIDES

1. As previously demonstrated, normal cells of Chlorella protothecoidesare bleached with degeneration of chloroplasts when they areincubated, under aerobic conditions—either in the lightor in darkness—, in a glucose-containing medium withoutadded nitrogen source ("glucose-bleaching"). It was found inthe present study that under the atmosphere of N₂, neither bleachingnor growth of algal cells occurs in the dark, while in the lighta significant growth of cells takes place with formation ofa certain amount of chlorophyll.
2. Studies on the effects ofvarious inhibitors (ammonium ion,DNP, CMU, -hydroxysulphonates,arsenate, cyanide, azide, andantimycin A) under different conditionsshowed that oxidativephosphorylation is a necessary processfor the occurrence ofthe glucosebleaching as well as the assimilationof glucose(cellular growth). Under light-anaerobic conditionsin the presenceof glucose, assimilation of glucose (cellulargrowth) takesplace being supported by photophosphorylation,but no bleachingoccurs.
3. When the algal cells in the courseof bleaching were transferredto the glucose-free mineral medium,the cell growth ceased immediatelybut the cell bleaching proceededfor several hours before itscessation. The respiratory activity,which was high in the glucose-containingmedium, became loweron transferring the algal cells into theglucose-free medium.The lowered level of respiration was maintained,for more than8 hr after the transfer of cells to the glucose-freemedium.
4. When the cells in the course of bleaching were placed underthe atmosphere of N₂, the cell bleaching ceased almost instantaneously.
5. Based on these observations and other inhibition experiments,it was inferred that a certain intermediate(s) produced by theaerobic respiration of glucose is closely associated with theoccurrence of cell bleaching, and that an O₂-requiring stepmay be involved in the process of chlorophyll degradation.

(Received September 9, 1965; )     

Inhibition of Gibberellic Acid-induced Starch Mobilization by Salicylhydroxamic acid in Avena fatua L. Seed

Inhibition of GA₃-induced endosperm mobilization in Avena fatuaL. by salicylhydroxamic acid (SHAM), a widely used alternativerespiration inhibitor, was studied. SHAM strongly inhibitedthe GA₃-induced release of reducing sugars in the incubationmedium by 3 mm de-embryonated endosperm segments; at 4 mM SHAM,GA₃-induced sugar release was inhibited by 66–79 per cent.Extracts prepared from segments incubated in 0.05 mM GA₃ with2, 5 and 10 mM SHAM showed 30, 53 and 71 per cent lower -amylaseactivity, respectively, compared to the GA₃-alone treatment.Addition of SHAM (0.5–5 mM) during the enzyme assay hadno effect on the activity of -amylase. Thus, the inhibitionof starch mobilization in endosperm by SHAM is due to inhibitionof the production and not the activity of -amylase. The inhibitionof Avena fatua seedling growth by SHAM reported earlier may,in part, be due to its effect on endosperm mobilization. Since (1) Avena fatua seeds have been shown to have little orno SHAM-sensitive respiration, and (2) concentrations of SHAMnecessary for inhibiting endosperm mobilization were significantlyhigher than those generally necessary for inhibiting alternativerespiration, the inhibition of endosperm mobilization by thiscompound does not appear to involve its effect on alternativerespiration. Avena fatua L., wild oat, -amylase, endosperm, gibberellic acid, salicylhydroxamic acid, seed     

Nucleic acid synthesis accompanying the recovery of cell division and chloroplast development in "giant" cells of the Emerson strain of Chlorella

The light-induced recovery of cell division and chloroplastdevelopment in "giant", "bleached", cells of the Emerson strainof Chlorella takes place without any increase in DNA and isrelatively insensitive to mitomycin C and 5-bromouracil. 5-Fluorouracilinhibits cell division only when it is supplied during the earlystages of recovery, perhaps by interfering with that phase ofRNA synthesis which occurs during the first 6 hr of recovery.This early burst of RNA synthesis is more sensitive to chloramphenicolthan is the second phase of RNA synthesis, suggesting that asignificant proportion of it may originate in the chloroplast.Evidence is presented which suggests that 5-fluorouracil interfereswith chloroplast development primarily through an effect onchlorophyll synthesis. The possible significance of these observationsin relation to nuclearchloroplastic interractions is discussed. (Received December 15, 1972; )     

The Rate of Photosynthesis in Isolated Chloroplasts

Chloroplasts were isolated using aqueous and nonaqueous procedures.Aqueous chloroplasts lost approximately 50 per cent, of theirsoluble proteins during isolation. Nonaqueous chloroplasts retainedall their soluble enzymes, but lost their ability to performthe light reactions of photosynthesis. It was possible to reconstitutea chloroplast system of higher activity by adding soluble enzymesfrom nonaqueous chloroplasts to protein-deficient aqueous chloroplasts.The properties of the reconstituted chloroplast system wereas follows: 1. The CO₂ fixation rate of the reconstituted chloroplast system( 4 µM./. chlorophyll/hr.) was 3–4 times that ofthe aqueous chloroplasts ( I µM./. chlorophyll/hr.). Thefixation of aqueous chloroplasts isapparently limited in partby lack of soluble enzymes. 2. During light-fixation, the reconstituted chloroplast systemaccumulated PGA. This indicates that the reduction of PGA totriosephosphate is a rate-limiting step in this system. 3. It was possible to increase the CO₂ fixation to 12 µM.CO₂/mg. chlorophyll/ hr. by addition of ATP and TPNH to thesystem, but the reduction of PGA was still rate-limiting. 4. Further increase in the fixation rate was obtained by concentratingthe reaction mixture. Part of the striking differences of theCO₂-fixing capabilities of chloroplasts in vivo and in vitrois caused by dilution effects. Extrapolation of the dilutioneffect to the protein concentration which exists in chloroplastsyields a CO₂ fixation rate of approximately 30 µM./mg.chlorophyll/hr. 5. Inhibitors which are located in vivo outside the chloroplastsaffect the CO₂ fixation in vitro. 6. Under consideration of the examined factors which influencethe CO₂ fixation of isolated chloroplasts, it is possible toraise the fixation from approximately 1 per cent, to at least15 per cent, of the fixation in vivo.     

Growth at elevated CO2 leads to down-regulation of photosynthesis and altered response to high temperature in Quercus suber L. seedlings

The effects of growth at elevated CO₂ on the response to hightemperatures in terms of carbon assimilation (net photosynthesis,stomatal conductance, amount and activity of Rubisco, and concentrationsof total soluble sugars and starch) and of photochemistry (forexample, the efficiency of excitation energy captured by openphotosystem II reaction centres) were studied in cork oak (Quercussuber L.). Plants grown in elevated CO₂ (700 ppm) showed a down-regulationof photosynthesis and had lower amounts and activity of Rubiscothan plants grown at ambient CO₂ (350 ppm), after 14 monthsin the greenhouse. At that time plants were subjected to a heat-shocktreatment (4 h at 45C in a chamber with 80% relative humidityand 800–1000 mol m^–2 s^–1 photon flux density).Growth in a CO₂-enriched atmosphere seems to protect cork oakleaves from the short-term effects of high temperature. ElevatedCO₂ plants had positive net carbon uptake rates during the heatshock treatment whereas plants grown at ambient CO₂ showed negativerates. Moreover, recovery was faster in high CO₂-grown plantswhich, after 30 min at 25C, exhibited higher net carbon uptakerates and lower decreases in photosynthetic capacity (A_max aswell as in the efficiency of excitation energy captured by openphotosystem II reaction centres (F_vJF_m than plants grown atambient CO₂. The stomata of elevated CO₂ plants were also lessresponsive when exposed to high temperature. Key words: Elevated CO₂, temperature, acclimation, photosynthesis, Quercus suber L.     

Behavioral Thermoregulation and the "Final Preferendum" Paradigm

Wider attention to Fry's (1947) "final preferendum" paradigmwould facilitate comparative studies of temperature preference(behavioral thermoregulation) among different animal groups.According to Fry's bipartite definition, the final preferendumis that temperature at which preference and acclimation areequal, and to which an animal in a thermal gradient will finallygravitate regardless of its prior thermal experience (acclimation).This paradigm is helpful in distinguishing between acute thermalpreferenda (measured within 2 hr or less after placing an animalin a thermal gradient), which are influenced by acclimationtemperature, and the species-specific final preferendum (measured24–96 hr after placement in the gradient), which is essentiallyindependent of prior acclimation because reacclimation occursduring the gravitation process. The paradigm does not take intoaccount non-thermal acclimatization influences (e.g., season,photoperiod, age, light intensity, salinity, disease, nutrition,pollutants, biotic interactions) which can also affect temperaturepreference. However, a graph of acutely preferred temperaturesversus acclimation temperatures can be employed to determinean equivalent acclimation temperature for any given acclimatizationstate, as a simple means of quantifying acclimatization statesresulting from interactions of many influences. This paradigm,developed for use with fishes, can also be applied to otherectothermic taxa, although it is most easily employed with aquaticorganisms because of the simplicity of specifying aquatic thermalenvironments in terms of water temperature alone. Methodologiesused in studies of behavioral thermoregulation should take theparadigm into account (especially with respect to length oftests) to enhance the comparative value of data across taxa.     

Statistical Studies Using AIC Method to Decide the Question of "Break" or "Straight" in Arrhenius Plots of Water Proton NMR Relaxation Times in Chilling-Sensitive Vigna and Insensitive Pisum Seedlings

The question of "break" or "straight" in Arrhenius plots forthe temperature dependency of NMR relaxation times (T₁) of waterprotons in etiolated intact seedlings for chilling-sensitivetwo Vigna species and chilling-insensitive Pisum was statisticallystudied using the Akaike's Information Criterion (AIC), a versatileprocedure for statistical model identification. Among sevenmodels, the most appropriate was based on the following assumptions:individual k (preparation numbers) two-half lines connectingat the break point (TCB) and imposing no restrictions for thegradient and the break point (Model 7). The worst two modelswere one straight line or one TCB (Model 1 or 4). Thus, thedata obtained from replicated preparations should not be treatedas a whole but as individual in each sample case. Break pointsdetermined with Model 7 ranged around 11-5°C for V. radiataand 17-10°C for V. mungo. The implication of the occurrenceof "break" for Pisum clearly differed from Vigna judging bythe model fitness based on the AIC values. The question of "break"or "straight" in Arrhenius plots is therefore fairly dependenton the validity of the model selection in the statistical analysis,and the AIC method is a useful procedure for the resolutionof the problem of the "use" or "misuse" of Arrhenius plots inplant physiology. (Received November 2, 1988; Accepted January 17, 1989)     

THE ROLE OF RESPIRATION AND PHOTOSYNTHESIS IN THE CHLOROPLAST REGENERATION IN THE "GLUCOSE-BLEACHED" CELLS OF CHLORELLA PROTOTHECOIDES

1. As previously demonstrated, entirely chlorophyll-less cellsof Chlorella protothecoides are obtained when the alga is grownin a medium rich in glucose and poor in nitrogen source (urea).These cells, which are referred to as "glucose-bleached" cells,have neither discernible chloroplast structures nor photosyntheticactivity. When the "glucose-bleached" cells are incubated, inthe light, in a nitrogen-enriched mineral medium without addedglucose, they turn green, after an induction period, with regenerationof chloroplasts and development of the capacity for performingnormal photosynthesis. In the present study, changes in respiratoryactivity of algal cells during the process of greening (chloroplastregeneration) were followed, and the effects of various inhibitorsof respiration and photosynthesis on the greening process wereexamined. 2. The glucose-bleached cells showed a very low activity ofrespiration, and the activity increased markedly during an earlyphase of chloroplast regeneration, showing, however, a decreaseduring the subsequent phase of greening. 3. Some antimetabolites which inhibited the cell respiration,were found to suppress also the greening of cells. 2,4-Dinitrophenoland azide, potent inhibitors of oxidative phosphorylation, acceleratedconsiderably both the respiration and greening of algal cells.CMU inhibited completely photosynthesis of the greening cells,but suppressed only slightly the greening process. 4. Based on these results it was concluded that the primaryrole of respiration in the chloroplast regeneration in the glucose-bleachedcells is to produce oxidized carbon compounds (and perhaps reducedforms of NAD and NADP) for various biosynthetic reactions. Itwas further suggested that ATP may be supplied for the chloroplastregeneration by a certain means different from the oxidativephosphorylation or photophosphorylation. The activities of photosyntheticphosphorylation and CO₂-fixation developing in the greeningcells do not appear to play any essential role in the chloroplastregeneration. (Received December 27, 1965; )     

Effect of Oxygen on Photosynthetic 14CO2 Fixation in Chroomonas sp. (Cryptophyta) III: Effect of Oxygen on Photosynthetic Carbon Metabolism

Photosynthetic carbon metabolism was studied with Chroomonassp. cells in which the rate of photosynthesis was inhibitedunder both an anaerobic condition and high concentrations ofoxygen. The time course of ¹⁴C-incorporation into photosyntheticproducts showed that 3-phosphoglycerate was the initial productof photosynthetic CO₂ fixation in Chroomonas sp. cells. During5-min photosynthesis, a considerable amount of ¹⁴C was incorporatedinto the insoluble fraction (mostly cryptomonad starch), andoxygen predominantly affected ¹⁴C-incorporation into this fraction.Although ¹⁴C-incorporation into intermediates of the photorespiratorypathway increased with increasing O₂ concentration, the amountswere much less than expected from the degree of oxygen inhibition.It is noteworthy that ¹⁴C-dihydroxyacetone phosphate accumulatedduring photosynthesis only under the anaerobic condition, whereasthe levels of the other phosphate esters were scarcely affectedby the oxygen concentration. Ribulose-1,5-bisphosphate carboxylase from Chroomonas sp. wascompetitively inhibited by oxygen, and its K_m(CO₂) value wassimilar to those of terrestrial C₃ plant enzymes. (Received November 19, 1984; Accepted May 20, 1985)     

Studies on the Relation Between Net Photosynthesis and Nitrogenase-linked Respiration in Subterranean Clover

The relation between the rate of nitrogenase-linked respirationand net photosynthesis, and the effect of defoliation on thisrelation, was studied in plants of subterranean clover (Trifoliumsubterraneum L. cv. Seaton Park). Nitrogenase-linked respirationwas estimated as the difference between the rate of nodulatedroot respiration at 21% O₂ and at 3% O₂. The level to which the rate of nitrogenase-linked respirationfell several hours after defoliation was directly proportionalto the decline in the rate of net photosynthesis. Approximately9% of net photosynthesis was always expended in nitrogenaseactivity, irrespective of whether or not the plants were defoliated.This proportion was maintained during the first 3 d of regrowth. To determine whether the decline in nitrogenase-linked respirationafter defoliation was due solely to the decline in the rateof photosynthesis, a further experiment was conducted in whichthe pre-defoliation rate of net photosynthesis was restoredimmediately (with supplementary light) or within 5 min (supplementarylight and CO₂) after defoliation. Restoring the rate of netphotosynthesis did not prevent the post-defoliation declinein nitrogenase-linked respiration. However, when photosynthesiswas reduced to zero by the imposition of darkness, and the rateof nitrogenase-linked respiration allowed to decline to a steadyrate after 3 h, a rapid recovery in the rate of nodulated rootrespiration began within 2 h of returning the plants to thelight. It was hypothesized that a ‘shoot factor’,which was affected by defoliation, could override the apparentrelation between nitrogenase-linked respiration and the rateof current photosynthesis. Key words: Defoliation, N₂ fixation, photosynthesis, nitrogenase-linked respiration, subterranean clover     

The Influence of the Rht1 and Rht2 Alleles on the Deposition and Use of Stem Reserves in Wheat

A field experiment was undertaken with a set of near-isogenicspring wheat lines (cv. Triple Dirk) to determine the influenceof the Rht₁ and Rht₂ alleles on the deposition of carbon inthe stem, and the subsequent use of these reserves during graingrowth. The amount of dry matter stored and mobilized was estimatedby the measurement of changes in masses of stem from frequentharvests. Deposition or absolute reserve was defined as thesum of the increments in mass in each segment of the large culmbetween the time that the segment ceased extending and the timethat it reached maximum mass. The incorporation of the Rht₁and Rht₂ alleles into a Triple Dirk background reduced the absoluteamount of stored carbon in the stem by 35 and 39%, respectively.This was a consequence of the 21% reduction of stem height inRht₁ and Rht₂ lines. Use or mobilization of reserve was definedas the sum of the decrements in mass in each segment of thelarge culm between maximum and maturity. The alleles did notconfer an ability to mobilize more of the stored stem reservesin absolute terms, although the efficiency of use of stem reserves(i.e. use as a proportion of deposition) was higher in Rht₁than in rht or Rht₂ . The possible contribution of stored carbonin the stem to final grain yield was estimated to be 22, 18and 14% in the rht, Rht₁ and Rht₂ lines. In these estimates,the loss of mass was adjusted by 33% to allow for respiration.It was concluded that the larger stem reserves in rht wheatsare of no real advantage under favourable environmental conditions,and may in fact be a disadvantage if the accumulation of thatextra dry matter results in a reduction of sink size.Copyright1993, 1999 Academic Press Triticum aestivum L., Rht genes, stem reserves, deposition, mobilization, grain growth     

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)     

The Response of the C3-CAM Tree, Clusia rosea, to Light and Water Stress: II. INTERNAL CO2 CONCENTRATION AND WATER USE EFFICIENCY

Gas exchange in Clusia rosea has been measured under variousconditions of water status, light and leaf-air vapour pressuredeficit (_w, mbar bar^–1) which produce daytime (C₃), night-time(CAM) or 24 h uptake of CO₂. At high light levels, at a _w of6.6, well-watered plants utilized C₃ photosynthesis while CAMand 24 h uptake occurred under lower light levels and with lowto normal water availability and differing _w (13.5 and 3.4,respectively). CO₂ uptake was highest, stomatal conductanceto water vapour (gH₂o) lowest, and water use efficiency (WUE)highest in plants using C₃ photosynthesis. This latter factis contrary to the accepted view that CAM is most water useefficient, i.e. it optimizes CO₂ uptake with minimal water loss.It is suggested that the low CO₂ uptake in CAM photosynthesismay be related not only to the higher _w but also to the factthat Clusia species accumulate citrate which may originate fromß-carboxylation of fatty acids (i.e. an internal sourceof CO₂) and does not contribute to night-time external CO₂ assimilation.Curves of assimilation (A) versus internal partial pressureof CO₂ (A/c₁) for the three photosynthetic types, under atmosphericconditions, did not produce a single trend. The trends whichwere produced represent the supply function for the interaction,under differing modes of photosynthesis, of the two major enzymesystems involved in CAM. Key words: Clusia rosea, Crassulacean acid metabolism, C₃ photosynthesis, internal CO₂ concentration, 24 h carbon dioxide uptake, water use efficiency.     

Seasonal and diurnal changes in photosynthesis and carbon partitioning in Vitis vinifera leaves in vines withand without fruit

In Vitis vinifera L. cv. Chardonnay maintained in a greenhouse,the maximum rate of photosynthesis, the measured rates of denovo sucrose and starch synthesis and the total leaf sucroseand starch contents were relatively constant throughout theperiod from April to July although the partitioning of newlyfixed carbon was modified in favour of sucrose synthesis half-waythrough the growing period. In these experimental conditions,no significant differences in these parameters were observedin plants from which the fruit had been removed in comparisonto the controls. In field-grown vines, photosynthesis rose toa maximum in the early morning consistent with the increasein ambient irradiance and then subsequently progressively decreased.This occurred every day. On clear days the mid-morning depressionin the rate of CO₂ assimilation was closely linked to decreasein stomatal conductance, but there was no correlation betweenthese parameters on days when the sun was overcast. There wasno correlation between leaf sucrose content and the depressionin photosynthesis. The calculated rate of non-cyclic electronflow did not decline in parallel with the mid-morning depression and the quantum efficiency of photosystem II was constantfor the whole of the period when the CO₂ assimilation was decreasing.The mid-morning depression of photosynthetic CO₂ assimilationwas related to both stomatal and non-stomatal effects. In neithersituation did it have any measurable feedback effect on theelectron transport rate or on the carbo hydrate contents ofthe leaves. Key words: Vitis vinifera L., source-sink interactions, sucrose, starch, photosynthesis