ON THE RATE OF OXYGEN CONSUMPTION BY FERTILIZED AND UNFERTILIZED EGGS : IV. CHAETOPTERHS AND ARBACIA PUNCTULATA

1. Unfertilized eggs of Chaetopterus consume about 2.4 mm.³ O₂ per hour per 10 mm.³ eggs at 21°C. 2. In the 1st hour after fertilization, the fertilized eggs consume oxygen at about 53 or 54 per cent of this rate, which is about 1.3 mm.³ O₂ per hour per 10 mm.³ eggs at 21°C. 3. For the first 6 hours after fertilization, at 21°C., the curve of the rate of oxygen consumption is slightly asymmetrically sigmoid. The prefertilization rate is regained between 4½ and 5 hours after fertilization. Soon after 6 hours, ciliary activity begins, and the rate of oxygen consumption rises rapidly. 4. The unfertilized eggs of Arbacia punctulata consume about 0.36–0.5 mm.³ O₂ per hour per 10 mm.³ eggs at 21°C. The absolute determination is difficult as these eggs are highly sensitive to shaking in the manometer vessels, and these difficulties are discussed. 5. The fertilized eggs of Arbacia punctulata consume oxygen at the rate of about 2.0 mm.³ O₂ per hour per 10 mm.³ 21°C. At 1 hour after fertilization the rate is already rising. 6. A comparison of the absolute rates of oxygen consumption, and the changes in rate at fertilization of these and a number of other eggs, together with a theoretical discussion, and a discussion of discrepancies in measurements on the eggs of Arbacia punctulata, is contained in the fifth paper of this series (21).     

Relationship between Respiration and Photosynthesis in Guard Cell and Mesophyll Cell Protoplasts of Commelina communis L

A mass spectrometric method combining ¹⁶O/¹⁸O and ¹²C/¹³C isotopes was used to quantify the unidirectional fluxes of O₂ and CO₂ during a dark to light transition for guard cell protoplasts and mesophyll cell protoplasts of Commelina communis L. In darkness, O₂ uptake and CO₂ evolution were similar on a protein basis. Under light, guard cell protoplasts evolved O₂ (61 micromoles of O₂ per milligram of chlorophyll per hour) almost at the same rate as mesophyll cell protoplasts (73 micromoles of O₂ per milligram of chlorophyll per hour). However, carbon assimilation was totally different. In contrast with mesophyll cell protoplasts, guard cell protoplasts were able to fix CO₂ in darkness at a rate of 27 micromoles of CO₂ per milligram of chlorophyll per hour, which was increased by 50% in light. At the onset of light, a delay observed for guard cell protoplasts between O₂ evolution and CO₂ fixation and a time lag before the rate of saturation suggested a carbon metabolism based on phosphoenolpyruvate carboxylase activity. Under light, CO₂ evolution by guard cell protoplasts was sharply decreased (37%), while O₂ uptake was slowly inhibited (14%). A control of mitochondrial activity by guard cell chloroplasts under light via redox equivalents and ATP transfer in the cytosol is discussed. From this study on protoplasts, we conclude that the energy produced at the chloroplast level under light is not totally used for CO₂ assimilation and may be dissipated for other purposes such as ion uptake.     

Aerobic and anaerobic respiration in the intact spinach chloroplast

Aerobic and anaerobic chloroplastic respiration was monitored by measuring ¹⁴CO₂ evolution from [¹⁴C]glucose in the darkened spinach (Spinacia oleracea) chloroplast and by estimating the conversion of fructose 1,6-bisphosphate to glycerate 3-phosphate in the darkened spinach chloroplast in air with O₂ or in N₂ with nitrite or oxaloacetate as electron acceptors. The pathway of ¹⁴CO₂ evolution from labeled glucose in the absence and presence of the inhibitors iodoacetamide and glycolate 2-phosphate under air or N₂ were those expected from the oxidative pentose phosphate cycle and glycolysis. Of the electron acceptors, O₂ was the best (2.4 nanomoles CO₂ per milligram chlorophyll per hour), followed by nitrite and oxaloacetate. With respect to glycerate 3-phosphate formation from fructose 1,6-bisphosphate, methylene blue increased the aerobic rate from 3.7 to 5.4 micromoles per milligram chlorophyll per hour. A rate of 4.8 micromoles per milligram chlorophyll per hour was observed under N₂ with nitrite and oxaloacetate.     

A NOTE ON THE RESPIRATION OF ARBACIA EGGS

Methods used in preparing Arbacia eggs for respiration studies, in carrying through the manometric determinations, and in estimating egg quantities have been reexamined. Discrepancies in previous results are almost entirely due to a steady error in measuring egg volume by centrifuging. Volumes so obtained averaged 80 per cent too high. The respiration of unfertilized eggs of Arbacia punctulata at 21°C. is 0.9 c.mm. O₂ per hour per 10 c.mm. of eggs.     

Phycobilisome-thylakoid Topography on Photosynthetically Active Vesicles of Porphyridium cruentum

Conditions are described for isolating functional phycobilisome-thylakoid vesicles from the red alga Porphyridium cruentum. Phycobilisome-thylakoid vesicles were prepared by brief sonication and centrifugation in a medium containing 0.5 molar sucrose, 0.5 molar potassium phosphate, and 0.3 molar sodium citrate (pH 7.0). They required ferricyanide as an oxidant and had O₂ evolution rates (about 450 micromoles O₂ per hour per milligram chlorophyll) higher than whole cells (about 250 micromoles O₂ per hour per milligram chlorophyll). Energy transfer to photosystem II chlorophyll was evident from a high F695 nanometer (−196 C) emission peak. Preparations could be stored for over 24 hours and were considerably more stable than those from the cyanobacterium Anabaena variabilis (Katoh T, E Gantt 1979 Biochim Biophys Acta 546: 383-393). In electron micrographs of negatively stained material, the active thylakoid vesicles were found covered by closely spaced phycobilisomes on their external surface. The phycobilisome number in negatively stained vesicles was 450 per square micrometer, which was in the same range as the 400 per square micrometer observed in surface sections. A cell containing 1.5 × 10⁻⁶ micrograms phycoerythrin and 1.3 × 10⁻⁶ micrograms chlorophyll was found to contain 5 to 7 × 10⁵ phycobilisomes on a thylakoid area of 1.1 to 1.6 × 10³ square micrometers.     

Simulation Model of the Coupling between Nitrification and Denitrification in a Freshwater Sediment

A model was constructed to simulate the results of experiments which investigated nitrification and denitrification in the freshwater sediment of Lake Vilhelmsborg, Denmark (K. Jensen, N. P. Sloth, N. Risgaard-Petersen, S. Rysgaard, and N. P. Revsbech, Appl. Environ. Microbiol. 60:2094-2100, 1994). The model output faithfully represented the profiles of O₂ and NO₃^- and rates of nitrification, denitrification, and O₂ consumption as the O₂ concentration in the overlying water was increased from 10 to 600 μM. The model also accurately predicted the response, to increasing O₂ concentrations, of the integrated (micromoles per square meter per hour) rates of nitrification and denitrification. The simulated rates of denitrification of NO₃^- diffusing from the overlying water (D_w) and of NO₃^- generated by nitrification within the sediment (D_n) corresponded to the experimental rates as the O₂ concentration in the overlying water was altered. The predicted D_w and D_n rates, as NO₃^- concentration in the overlying water was changed, closely resembled those determined experimentally. The model was composed of 41 layers 0.1 mm thick, of which 3 represented the diffusive boundary layer in the water. Large first-order rate constants for nitrification and denitrification were required to completely oxidize all NH₄⁺ diffusing from the lower sediment layers and to remove much of the NO₃^- produced. In addition to the flux of NH₄⁺ from below, the model required a flux of an electron donor, possibly methane. Close coupling between nitrification and denitrification, achieved by allowing denitrification to tolerate some O₂ (~10 μM), was necessary to reproduce the real data. Spatial separation of the two processes (no toleration by denitrification of O₂) resulted in too high NO₃^- concentrations and too low rates of denitrification.     

THE EFFECTS OF OXYGEN,CARBON DIOXIDE,AND PRESSURE ON GROWTH IN CHILOMONAS PARAMECIUM AND TETRAHYMENA GELEII FURGASON

1. The effects of O₂, CO₂, and pressure were studied in two very different species of protozoa, a flagellate, Chilomonas paramecium, grown in acetate-ammonium solution and a ciliate, Tetrahymena geleii, grown in 2 per cent proteose-peptone solution. 2. Chilomonas and Tetrahymena live and reproduce in solutions exposed to a wide range of O₂ concentrations, but Chilomonas is killed at high O₂ tensions in which Tetrahymena grows best. The optimum O₂ concentration for Chilomonas is about 75 mm. pressure but it lives and reproduces in O₂ tensions as low as 0.5 mm. while Tetrahymena fails to grow in concentrations below 10 mm. O₂ pressure. 3. With a constant O₂ tension of 50 mm. pressure, it was found that there is no significant variation in growth in Chilomonas between 50 mm. and 740 mm. total pressure. In Tetrahymena, however, under the same conditions, an optimum total pressure was found at about 500 mm. and growth is comparatively poor at 50 mm. total pressure. 4. Tetrahymena does not live very long in CO₂ tensions over 122 mm., although Chilomonas grows as well at 400 mm. CO₂ as in air at atmospheric pressure (0.2 mm. CO₂). Tetrahymena grows best in an environment minus CO₂, but the optimum for Chilomonas is 100 mm. CO₂ at which pressure an average of 668,600 ± 30,000 organisms per ml. was produced (temperature, 25 ± 1° C.). 5. Chilomonads grown in high CO₂ concentrations (e.g., 122 mm.) produce larger starch granules and more starch than those grown in ordinary air at atmospheric pressure. 6. In solutions exposed to 75 mm. O₂ tension (optimum) and 122 mm. CO₂ plus 540 mm. N₂ pressure, chilomonads contain very little, if any, fat. This phenomenon seems to be due to the action of CO₂ on the mechanisms concerned with fat production. 7. In Tetrahymena exposed to pure O₂, there is very little fat compared to those grown in atmospheric air. This may be due to the greater oxidation of fat in the higher O₂ concentrations. 8. Further evidence is presented in support of the contention that Chilomonas utilizes CO₂ in the production of starch.     

Active CO(2) Transport by the Green Alga Chlamydomonas reinhardtii

Mass spectrometric measurements of dissolved free ¹³CO₂ were used to monitor CO₂ uptake by air grown (low CO₂) cells and protoplasts from the green alga Chlamydomonas reinhardtii. In the presence of 50 micromolar dissolved inorganic carbon and light, protoplasts which had been washed free of external carbonic anhydrase reduced the ¹³CO₂ concentration in the medium to close to zero. Similar results were obtained with low CO₂ cells treated with 50 micromolar acetazolamide. Addition of carbonic anhydrase to protoplasts after the period of rapid CO₂ uptake revealed that the removal of CO₂ from the medium in the light was due to selective and active CO₂ transport rather than uptake of total dissolved inorganic carbon. In the light, low CO₂ cells and protoplasts incubated with carbonic anhydrase took up CO₂ at an apparently low rate which reflected the uptake of total dissolved inorganic carbon. No net CO₂ uptake occurred in the dark. Measurement of chlorophyll a fluorescence yield with low CO₂ cells and washed protoplasts showed that variable fluorescence was mainly influenced by energy quenching which was reciprocally related to photosynthetic activity with its highest value at the CO₂ compensation point. During the linear uptake of CO₂, low CO₂ cells and protoplasts incubated with carbonic anhydrase showed similar rates of net O₂ evolution (102 and 108 micromoles per milligram of chlorophyll per hour, respectively). The rate of net O₂ evolution (83 micromoles per milligram of chlorophyll per hour) with washed protoplasts was 20 to 30% lower during the period of rapid CO₂ uptake and decreased to a still lower value of 46 micromoles per milligram of chlorophyll per hour when most of the free CO₂ had been removed from the medium. The addition of carbonic anhydrase at this point resulted in more than a doubling of the rate of O₂ evolution. These results show low CO₂ cells of Chlamydomonas are able to transport both CO₂ and HCO₃⁻ but CO₂ is preferentially removed from the medium. The external carbonic anhydrase is important in the supply to the cells of free CO₂ from the dehydration of HCO₃⁻.     

Hydrogen peroxide synthesis in isolated spinach chloroplast lamellae : an analysis of the mehler reaction in the presence of NADP reduction and ATP formation

Light-dependent O₂ reduction concomitant with O₂ evolution, ATP formation, and NADP reduction were determined in isolated spinach (Spinacia oleracea L. var. America) chloroplast lamellae fortified with NADP and ferredoxin. These reactions were investigated in the presence or absence of catalase, providing a tool to estimate the reduction of O₂ to H₂O₂ (Mehler reaction) concomitant with NADP reduction. In the presence of 250 micromolar O₂, O₂ photoreduction, simultaneous with NADP photoreduction, was dependent upon light intensity, ferredoxin, Mn²⁺, NADP, and the extent of coupling of phosphorylation to electron flow.

In the presence of an uncoupling concentration of NH₄⁺, saturating light intensity (>500 watts/square meter), saturating ferredoxin (10 micromolarity) rate-limiting to saturating NADP (0.2-0.9 millimolarity), and Mn²⁺ (50-1000 micromolarity), the maxium rates of O₂ reduction were 13-25 micromoles/milligram chlorophyll per hour, while concomitant rates of O₂ evolution and NADP reduction were 69 to 96 and 134 to 192 micromoles/milligram chlorophyll per hour, respectively. Catalase did not affect the rate of NADPH or ATP formation but decreased the NADPH:O₂ ratios from 2.3-2.8 to 1.9-2.1 in the presence of rate-limiting as well as saturating concentrations of NADP.

Photosynthetic electron flow at a rate of 31 micromoles O₂ evolved/milligram chlorophyll per hour was coupled to the synthesis of 91 micromoles ATP/milligram chlorophyll per hour, while the concomitant rate of O₂ reduction was 0.6 micromoles/milligram chlorophyll per hour and was calculated to be associated with an apparent ATP formation of only 2 micromoles/milligram chlorophyll per hour. Thus, electron flow from H₂O to O₂ did not result in ATP formation significantly above that produced during NADP reduction.

     

Effects of CO(2) and O(2) on the Photosynthetic O(2) Evolution of Spirodela polyrrhiza Turions

Net photosynthetic rates of Spirodela polyrrhiza turions, at low O₂ levels, were 6.2 and 38.8 micromoles O₂ per gram fresh weight per hour at 1 millimolar HCO₃⁻ and CO₂ saturation, respectively, and much lower in a regular low-pH growth solution. Air equilibration O₂ concentrations decreased rates considerably, except at CO₂ saturation. The surfacing rate of turions in various inorganic carbon surroundings correlated positively with their photosynthetic rates, but were the same at high and low O₂ levels. The relevance of these findings in relation to environmental conditions conductive to germination of autotrophically growing turions is discussed.     

Stem hypertrophic lenticels and secondary aerenchyma enable oxygen transport to roots of soybean in flooded soil

Background and Aims

Aerenchyma provides a low-resistance O₂ transport pathway that enhances plant survival during soil flooding. When in flooded soil, soybean produces aerenchyma and hypertrophic stem lenticels. The aims of this study were to investigate O₂ dynamics in stem aerenchyma and evaluate O₂ supply via stem lenticels to the roots of soybean during soil flooding.

Methods

Oxygen dynamics in aerenchymatous stems were investigated using Clark-type O₂ microelectrodes, and O₂ transport to roots was evaluated using stable-isotope ¹⁸O₂ as a tracer, for plants with shoots in air and roots in flooded sand or soil. Short-term experiments also assessed venting of CO₂ via the stem lenticels.

Key Results

The radial distribution of the O₂ partial pressure (pO₂) was stable at 17 kPa in the stem aerenchyma 15 mm below the water level, but rapidly declined to 8 kPa at 200–300 µm inside the stele. Complete submergence of the hypertrophic lenticels at the stem base, with the remainder of the shoot still in air, resulted in gradual declines in pO₂ in stem aerenchyma from 17·5 to 7·6 kPa at 13 mm below the water level, and from 14·7 to 6·1 kPa at 51 mm below the water level. Subsequently, re-exposure of the lenticels to air caused pO₂ to increase again to 14–17 kPa at both positions within 10 min. After introducing ¹⁸O₂ gas via the stem lenticels, significant ¹⁸O₂ enrichment in water extracted from roots after 3 h was confirmed, suggesting that transported O₂ sustained root respiration. In contrast, slight ¹⁸O₂ enrichment was detected 3 h after treatment of stems that lacked aerenchyma and lenticels. Moreover, aerenchyma accelerated venting of CO₂ from submerged tissues to the atmosphere.

Conclusions

Hypertrophic lenticels on the stem of soybean, just above the water surface, are entry points for O₂, and these connect to aerenchyma and enable O₂ transport into roots in flooded soil. Stems that develop aerenchyma thus serve as a ‘snorkel’ that enables O₂ movement from air to the submerged roots.     

Recording the oxygen production of a single Acetabularia cell for a prolonged period

A method for recording the O₂ evolution of an individual Acetabularia cell or cell fragment over a period of weeks is described. The method is based on the polarographic O₂ determination by means of a platinum electrode in a flow-through system. The mean O₂ evolution of a full-grown cell under constant conditions (2 5001m/m², 20 °C) was 3–6 μ1 O₂ per cell perh. Under these conditions the O₂ evolution exhibited a pronounced circadian rhythm with an average period of about 23 h and an amplitude of about 2.3 μ1 O₂ per cell per h. No significant differences were found between nucleate and anucleate cells.     

Photosynthetic and Photorespiratory Characteristics of Mutants of Hordeum vulgare L

The relationship between photosynthesis and photorespiration was determined in normal and 26 mutants of barley (Hordeum vulgare L. var. Himalaya). The rate of apparent photosynthesis ranged from 1 to 30 milligrams of CO₂ per square decimeter per hour. The variation in rate of photosynthesis was due, in some cases, to differences in chlorophyll content, in others to stomatal resistance, and in still others to unknown factors; but no single factor accounted for the variation. Photorespiratory activity, as determined by the ¹⁴CO₂/¹²CO₂ technique, CO₂ evolution into CO₂-free air, and the response of photosynthesis to low and high O₂ concentrations, was positively and significantly correlated with photosynthesis. This supports the idea that the two processes are integrally and tightly coupled. There appears to be no competition between photosynthesis and photorespiration, and the probability of finding plants with high rates of photosynthesis and low rates of photorespiration measured under natural conditions, appears to be very low.     

CO(2) and O(2) Exchange in Two Mosses, Hypnum cupressiforme and Dicranum scoparium

Photosynthetic CO₂ and O₂ exchange was studied in two moss species, Hypnum cupressiforme Hedw. and Dicranum scoparium Hedw. Most experiments were made during steady state of photosynthesis, using ¹⁸O₂ to trace O₂ uptake. In standard experimental conditions (photoperiod 12 h, 135 micromoles photons per square meter per second, 18°C, 330 microliters per liter CO₂, 21% O₂) the net photosynthetic rate was around 40 micromoles CO₂ per gram dry weight per hour in H. cupressiforme and 50 micromoles CO₂ per gram dry weight per hour in D. scoparium. The CO₂ compensation point lay between 45 and 55 microliters per liter CO₂ and the enhancement of net photosynthesis by 3% O₂versus 21% O₂ was 40 to 45%. The ratio of O₂ uptake to net photosynthesis was 0.8 to 0.9 irrespective of the light intensity. The response of net photosynthesis to CO₂ showed a high apparent K_m (CO₂) even in nonsaturating light. On the other hand, O₂ uptake in standard conditions was not far from saturation. It could be enhanced by only 25% by increasing the O₂ concentration (saturating level as low as 30% O₂), and by 65% by decreasing the CO₂ concentration to the compensation point. Although O₂ is a competitive inhibitor of CO₂ uptake it could not replace CO₂ completely as an electron acceptor, and electron flow, expressed as gross O₂ production, was inhibited by both high O₂ and low CO₂ levels. At high CO₂, O₂ uptake was 70% lower than the maximum at the CO₂ compensation point. The remaining activity (30%) can be attributed to dark respiration and the Mehler reaction.     

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) supports adhesion and migration of mesenchymal stem cells and tenocytes

AIM: To establish the potential of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) as a material for tendon repair. METHODS: The biocompatibility of PHBHHx with both rat tenocytes (rT) and human mesenchymal stem cells (hMSC) was explored by monitoring adhesive characteristics on films of varying weight/volume ratios coupled to a culture atmosphere of either 21% O2 (air) or 2% O2 (physiological normoxia). The diameter and stiffness of PHBHHx films was established using optical coherence tomography and mechanical testing, respectively. RESULTS: Film thickness correlated directly with weight/volume PHBHHx (r2 = 0.9473) ranging from 0.1 mm (0.8% weight/volume) to 0.19 mm (2.4% weight/volume). Film stiffness on the other hand displayed a biphasic response which increased rapidly at values 1.6% weight/volume. Optimal cell attachment of rT required films of ≥ 1.6% and ≥ 2.0% weight/volume PHBHHx in 2% O2 and 21% O2 respectively. A qualitative adhesion increase was noted for hMSC in films ≥ 1.2% weight/volume, becoming significant at 2% weight/volume in 2% O2. An increase in cell adhesion was also noted with ≥ 2% weight/volume PHBHHx in 21% O2. Cell migration into films was not observed. CONCLUSION: This evaluation demonstrates that PHBHHx is a suitable polymer for future cell/polymer replacement strategies in tendon repair.     

Growth of Photoheterotrophic Cells of Peanut (Arachis hypogaea L.) in Still Nutrient Medium

Cell suspension cultures were established from the callus proliferation of leaf explants of 10- to 12-day-old seedlings of the peanut (Arachis hypogaea L. var. TMV-3). The cells could be cultivated in both agitated and still media, the latter promoting more of chlorophyll (Chl) synthesis. High Chl content (210-240 micrograms Chl per gram fresh weight), yield of free and pipetable cells, presence of all the pigments in the same ratio as that of the leaf tissue, and high rates of O₂ evolution (140-170 micromoles O₂ per milligram Chl per hour) were some of the desirable features of the still-grown cell cultures. However, considerable variations with regard to the above characters were observed between the cell cultures of different varieties of the peanut.

O₂ evolution by the cultured cells was dependent on exogenous supply of HCO₃⁻. A well-developed photosynthetic apparatus as evidenced from photosystem I and photosystem II activities of the isolated chloroplasts and variable fluorescence measurements with the cell cultures was further documented by electron microscopic evidence of distinct granal stackings in chloroplasts and sodium dodecyl sulfate-polyacrylamide gel separation of thylakoid membranes into P700 Chl a protein complex and light-harvesting Chl a/b complex. Evidence is presented for the relative increase in the Chl associated with P700 Chl a protein complex in contrast to the light-harvesting Chl a/b complex in the cultured cells as compared to intact leaf.

     

Use of a laser-driven photoacoustic detection system for measurement of ethylene production in cymbidium flowers

A laser-based photoacoustic method was used for determination of ethylene (C₂H₄) production of emasculated orchid (Cymbidium) flowers in a flow-through system. The laser photoacoustic equipment consisted of a line-tuneable CO₂ laser in conjunction with a single-pass resonant acoustic cell. The minimum detection limit of the system for C₂H₄ in air was 0.03 nanoliter per liter. C₂H₄ production of intact Cymbidium (cv Mary Pinchess `Del Rey') flowers was very low (0.015 nanoliter per gram per hour) and showed an increase within 3 hours following emasculation (removal of pollinia plus anthercap). Production peaked (0.14 nanoliter per gram per hour) 8 hours after emasculation and decreased thereafter. Production again increased 45 hours after emasculation. Coloration of the labellum appeared shortly after the first peak; wilting of the petals and sepals appeared during the second rise in ethylene production. The use of the laser photoacoustic technique in plant physiological studies is discussed.     

The Regulation of Photosynthesis in Leaves of Field-Grown Spring Wheat (Triticum aestivum L., cv Albis) at Different Levels of Ozone in Ambient Air

Wheat (Triticum aestivum L. cv Albis) was grown in open-top chambers in the field and fumigated daily with charcoal-filtered air (0.015 microliters per liter O₃), nonfiltered air (0.03 microliters per liter O₃), and air enriched with either 0.07 or 0.10 microliters per liter ozone (seasonal 8 hour/day [9 am-5 pm] mean ozone concentration from June 1 until July 10, 1987). Photosynthetic ¹⁴CO₂ uptake was measured in situ. Net photosynthesis, dark respiration, and CO₂ compensation concentration at 2 and 21% O₂ were measured in the laboratory. Leaf segments were freeze-clamped in situ for the determination of the steady state levels of ribulose 1,5-bisphosphate, 3-phosphoglycerate, triose-phosphate, ATP, ADP, AMP, and activity of ribulose, 1,5-bisphosphate carboxylase/oxygenase. Photosynthesis of flag leaves was highest in filtered air and decreased in response to increasing mean ozone concentration. CO₂ compensation concentration and the ratio of dark respiration to net photosynthesis increased with ozone concentration. The decrease in photosynthesis was associated with a decrease in chlorophyll, soluble protein, ribulose bisphosphate carboxylase/oxygenase activity, ribulose bisphosphate, and adenylates. No decrease was found for triose-phosphate and 3-phosphoglycerate. The ratio of ATP to ADP and of triosephosphate to 3-phosphoglycerate were increased suggesting that photosynthesis was limited by pentose phosphate reductive cycle activity. No limitation occurred due to decreased access of CO₂ to photosynthetic cells since the decrease in stomatal conductance with increasing ozone concentration did not account for the decrease in photosynthesis. Ozonestressed leaves showed an increased degree of activation of ribulose bisphosphate carboxylase/oxygenase and a decreased ratio of ribulose bisphosphate to initial activity of ribulose bisphosphate carboxylase/oxygenase. Nevertheless, it is suggested that photosynthesis in ozone stressed leaves is limited by ribulose bisphosphate carboxylation possibly due to an effect of ozone on the catalysis by ribulose bisphosphate carboxylase/oxygenase.     

MEASUREMENTS OF THE METABOLISM OF TWO PROTOZOANS

1. The respiration of Amoeba proteus was measured. 10 c. mm. of cells were found to use about 1.6 mm.³ of oxygen per hour at 20°C. The respiratory quotient was found to be nearly unity. 2. No anaerobic metabolism was found for Amoeba. 3. The respiration of Blepharisma was found to be from 3 to 7 mm.³ oxygen per hour for 10 mm.³ cells. The respiratory quotient was about 1. 4. Blepharisma was shown to have a definite anaerobic metabolism. 80 mm.³ cells caused the evolution of 12.5 mm.³ carbon dioxide per hour at 20°C. in the presence of bicarbonate.     

Activity of root systems of six plant species at different stages of development

Summary A number of data on root performance of six different crop species during development were measured. The plants wre cultivated in nutrient solution. Normal plant requirements were in the range of 4 mg O₂ per g dry root per hour, 0.2–4μg K per cm² total root surface per hour,² 0.2–2μg NO₃ per om² total root surface per hour. An attempt was made to establish a ratio between forced water entry and total root surface as a measure of functional root surface. The indication is that the relative surface of permeable root remains dominant during the phase of exponential growth and declines thereafter. The data collected are considered to be representative of normal requirements. They compare well with results published in the literature.