Plants of rape, safflower, s~unflower, flax, and castor bean \\ere grown a t temperatures of 10, 16, 21, and 26.5 "C for the period of seed development. Oil content of sunflower, saffloner, and castor bean was not affected by temperature. Highest oil content in rape and flax was tound a t the lowest temperature and a continual decrease was observed with increases in temperature. Fatty acid composition of the oil from safflomer and castor bean was not affected by a change in te~nperature. I n the other three spccies the amount of the nlore highly unsaturated fatty acids decreased as the temperature was increased. This decrease was accon~panied by a n increase in oleic acid. The levels of saturated fatty acids in all of the species were not affected by changes in temperature.

Photosynthetic 02 production and photorespiratory 02 uptake were measured using isotopic techniques, in the C3 species Hirschfeldia incana Lowe., Helianthus annuus L., and Phaseolus vulgaris L. At high CO2 and normal 02,02 production increased linearly with light intensity. At low 02 or low C02, 02 production was suppressed, indicating that increased concentrations of both 02 and CO2 can stimulate 02 production. At the CO2 compensation point, 02 uptake equaled 02 production over a wide range of 02 concentrations. 02 uptake increased with light intensity and 02 concentration. At low light intensities, 02 uptake was suppressed by increased CO2 concentrations so that 02 uptake at 1,000 microliters per liter CO2 was 28 to 35% of the uptake at the CO2 compensation point. At high light intensities, 02 uptake was stimulated by low concentrations of CO2 and suppressed by higher concentrations of C02. 02 uptake at high light intensity and 1000 microliters per liter CO2 was 75% or more of the rate of 02 uptake at the compensation point. The response of 02 uptake to light intensity extrapolated to zero in darkness, suggesting that 02 uptake via dark respiration may be suppressed in the light. The response of 02 uptake to 02 concentration saturated at about 30% 02 in high light and at a lower 02 concentration in low light. 02 uptake was also observed with the C4 plant Amaranthus edulis, the rate of uptake at the CO2 compensation point was 20% of that observed at the same light intensity with the C3 species, and this rate was not influenced by the CO2 concentration. The results are discussed and interpreted in terms of the ribulose-1,5-bisphosphate oxygenase reaction, the associated metabolism of the photorespiratory pathway, and direct photosynthetic reduction of 02.Both 02 evolution and 02 uptake take place in leaves of C3 and C4 plants in the light (4,8,17,21,23,24,27,28). 02 evolution is derived entirely from the water-splitting reaction of PSII, but three principal 02 uptake processes are presently recognized. These are: the oxygenase reaction of ribulose bisP carboxylase-oxygenase and the associated metabolism of P-glycolate (2,4,5,18,20) Norway) was injected into the system. The system was closed and the gas was circulated over the leaf with a metal bellows pump. Mass 32, mass 36, and mass 40 were monitored continuously with a GD 150/4 mass spectrometer.02 uptake and 02 evolution were calculated using the methods previously described (25,27). CO2 concentration was measured with an IRGA analyzer (UNOR-2, Maihak, Hamburg, Germany) included in the gas circuit, and CO2 concentration during illumination could be controlled by varying the pressure of CO2 on a capillary that bled pure CO2 into the closed system. CO2 uptake, at constant CO2 concentration in the system, was calculated from the rate of CO2 addition. Each measurement was averaged over an 8-to 10-min period of gas exchange after the rate of CO2 uptake had reached a steady rate at each CO2 concentration. The total gas pressure in the small system increa...

The metabolism of sucrose to long chain fatty acids in the endosperm of developing castor bean (Ricinus communis L.) seeds requires a combination of cytosolic and proplastid enzymes. The total activity and the subcellular distribution of the intermediate enzymic steps responsible for the conversion of sucrose to pyruvate have been determined. Hexose phosphate synthesis from sucrose occurs in the cytosol along with the first oxidative step in the pentose phosphate pathway, glucose-6-phosphate dehydrogenase. The proplastids contain the necessary complement of glycolytic enzymes to account for the in vivo rates of acetate synthesis from glucose 6-phosphate. These organelUes also contain the majority of the cellular 6-phosphogluconate dehydrogenase, transketolase, and transaldolase activities.The consequence of these enzyme distributions is that glucose 6-phosphate or 6-phosphogluconate produced in the cytosol must be transported into the proplastids where conversion to pyruvate occurs. The unique segregation of the two oxidative steps in the pentose phosphate pathway may be required to meet the metabolic needs of these fatstoring seeds. Compartmentation of glucose-6-phosphate dehydrogenase in the cytosol and 6-phosphogluconate dehydrogenase in the proplastids is discussed in light of the NADPH requirements for fatty acid synthesis in these subceflular locations.In photosynthetic tissues (9) and germinating seeds (1) some aspects of metabolism are regulated by means of subcellular compartmentation. Similarly, developing seeds show metabolic control by compartmentation. In the endosperm of developing castor bean seeds, oleic acid is synthesized from acetyl-CoA in proplastids (6,20). Phosphofructokinase and pyruvate kinase (5), the key enzymes of glycolysis as well as the pyruvate dehydrogenase complex (13) are also present in this organelle, suggesting that there is a particulate pathway for the conversion of hexose-P to long chain fatty acids (LFA).2 Furthermore, Yamada and his co-workers (11,18,19) have demonstrated the incorporation of sucrose, hexose, glucose 1-P, glucose 6-P, pyruvate, and acetate into fatty acids by purified proplastids. They suggest that sucrose synthase and UDPG synthase are involved in the initial conversion of sucrose to hexose-P within the organelle. The objectives of the research reported here were: to determine the level of the enzymes of the glycolytic and pentose phosphate pathway present in the cytosol and proplastid fraction; to determine which enzyme activities were adequate to account for the in vivo rate of long chain fatty acid biosynthesis; to determine the relationship between the pentose-P and glycolytic pathways in the supply of NADPH and carbon intermediates. MATERIALS AND METHODSPreparation of Proplastids. Thirty to 40-day-old developing castor bean seeds (Ricinus communis L., Baker 296 Dwarf Inbred) were harvested from plants grown in the greenhouse. The endosperm was extracted and homogenized as described previously (13) and cell debris was removed by centrifugati...

Mass spectrometry has been used to confirm the presence of an active transport system for CO2 in Synechococcus UTEX 625. Cells were incubated at pH 8.0 in 100 micromolar KHCO3 in the absence of Na+ (to prevent . Upon illumination the ceUls rapidly removed almost all the free CO2 from the medium. Addition of carbonic anhydrase revealed that the CO2 depletion resulted from a selective uptake of CO2. rather than a total uptake of all inorganic carbon species. CO2 transport stopped rapidly (<3 seconds) when the light was turned off. lodoacetamide (3.3 millimolar) completely inhibited CO2 fixation but had little effect on CO2 transport. In iodoacetamide poisoned cells, transport of CO2 occurred against a concentration gradient of about 18,000 to 1. Transport of CO2 was completely inhibited by 10 micromolar diethylstilbestrol, a membrane-bound ATPase inhibitor. Studies with DCMU and PSI light indicated that CO2 transport was driven by ATP produced by cyclic or pseudocyclic photophosphorylation. Low concentrations of Na+ (<100 microequivalents per liter), but not of K+, stimulated CO2 transport as much as 2.4-fold. Unlike Na+-dependent HC03-transport, the transport of CO2 was not inhibited by high concentrations (30 milliequivalents per liter) of Li'. During illumination, the CO2 concentration in the medium remained far below its equilibrium value for periods up to 15 minutes. This could only happen if CO2 transport was continuously occurring at a rapid rate, since the continuing dehydration of HC03-to CO2 would rapidly raise the CO2 concentration to its equilibrium value if transport ceased. Measurement of the rate of dissolved inorganic carbon accumulation under these conditions indicated that at least part of the continuing CO2 transport was balanced by HCO3-efflux.Photosynthesis by cyanobacteria can occur when the CO2 concentration in the extracellular medium is so low that CO2 fixation via Rubisco2 could not occur were it not for the presence of 'CO2-concentrating' mechanisms (1,2,9,13,16,19,21,25,28 (1,2,9,18,29). For a given DIC concentration, the rate of DIC accumulation was faster under the nonequilibrium conditions (high CO,/HCO3-) than under equilibrium conditions (high HCO3-/C0.), thus indicating a lower Kmn for CO2 transport than for HCO3 transport (1. 2, 9, 29).Miller and Canvin (17) provided further evidence for a CO,-transport capacity, distinct from the HCO3-transport capacity, when they made use of the observation that HCO-transport in rapidly growing cells of Synechococcus UTEX 625 is inhibited by the absence of Na+ in the extracellular medium (8,17,22). Cells that were incubated in the absence of Na + were stimulated to accumulate normal levels of intracellular DIC by the addition of CA (17). It was postulated that, in the absence of the CA, the rate of supply of CO2 to the CO,-transport system was limited by the rate of HCO3-dehydration to CO2 in the extracellular medium. The DIC transport occurring in the presence of CA was not inhibited by the addition of Li+, whereas the Na+-dependent...

ABSTRACIAn open ps exchange system was used to monitor the nonsteady state and steady state changes in nitrogenase activity (H2 evolution in N2:02 and Ar:02) and respiration (CO2 evolution) in attached, excised, and sliced nodules of soybean (Glycine max L. Menf.) exposed to extenal P02 of 5 to 100%. In attached nodules, increases in external P02 in steps of 10 or 20% resulted in sharp declines in the rates of H2 and CO2 evolution. Recovery been proposed (18). Evidence for a distinct barrier to gas diffusion in the nodule cortex has been obtained experimentally by direct measurements of P02 in the outer and central tissues of soybean nodules (2 1).The exact nature of the diffusion barrier and the manner in which it is regulated are unknown, but it has been suggested that the nodules of many symbiotic associations increase their diffusion resistance to O2 entry when they are exposed to an atmosphere containing 10% C2H2, or one in which N2 is replaced by Ar (25). This increase in diffusion resistance is apparent as a decline in nodule respiration rate, with a concomitant decline in C2H2 reduction or H2 production rate, during the first 30 min of exposure to C2H2 or Ar. The presence or absence of an C2H2-or Ar-induced decline has been correlated with the optimum P02 for N2 fixation within a specific legume-Rhizobium association and, by inference, with the speed with which the diffusion barrier is regulated in that association (25). It has also been suggested that the regulation of the diffusion resistance of the nodule requires physical changes in the diffusion barrier (4), and this may limit the speed with which the nodule responds to changes in its gaseous environment.The aims of this study were (a) to determine whether the gas exchange characteristics of soybean nodules following changes in external P02 are consistent with the presence of a variable diffusion barrier in the nodule cortex, and (b) if so, to identify experimental conditions which could be used to vary this diffusion barrier. An open circuit gas exchange system was used to monitor continuously changes in respiration (CO2 evolution) and nitrogenase activity (H2 evolution in N2:02 and Ar:02) as the P02 surrounding the nodules was varied. Nonsteady state measurements of CO2 production and H2 evolution were used to determine the speed with which the nodules adjust to changes in rhizosphere O2 concentration. Steady

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 reinhardtli. In the presence of 50 micromolar dissolved inorganic carbon and light, protoplasts which had been washed free of extemal carbonic anhydrase reduced the 13CO2 concentration in the medium to close to zero. Similar resuits 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. demonstrated for these organisms (2, 4, 9, 15). In the case of cyanobacteria, both HCO3-and CO2 are substrates for active transport (2,3,6,7,14,15) with CO2 being selectively and preferentially used by the cells (2,6,16). In Chlamydomonas, HC03-is actively transported (4, 25, 29), but CO2 uptake has been considered to be passive (18,20). Carbon dioxide, however, is taken up from the medium faster than HCO3-by Chlamydomonas (13,28,29) and several authors (13,29) have considered the possibility of active CO2 transport.Studies on the DIC transport mechanism of green algae are complicated by their cellular compartmentation. Recently, it was shown that isolated chloroplasts of low C02 Chlamydomonas reinhardtii were able to accumulate DIC (19) and a model was presented where the only active DIC transport mechanism was located on the chloroplast envelope (18,19). In that model the plasma membrane was suggested to be only a diffusion barrier for CO2 generated by external carbonic anhydrase. In contrast, by comparison of the apparent affinities for DIC of whole cells and purified chloroplasts, Suiltemeyer et al. (26) came to the conclusion that active transport by the chloroplast alone may not be responsible for the photosynthetic characteristics of whole cells.Another difficulty in examining the DIC species taken up by whole cells is the presence of an external carbonic anhydrase (10) which catalyzes the rapid equilibrium between CO2 and HCO3-, thus making a direct discrimination between CO2 and HCO3-uptake impossible (7, 13). However, using inhibitors for external carbonic anhydrase or the cell-wall less mutant CW-15, some authors came to the conclusion that CO2 and not HCO3-(13) or that both C02 and HCO3- (29) were actively transported.Confusion about which DIC species is actively taken up from the medium may also be caused by methods which only measure total rates of transport rather than transport of CO2 or HC03-individually. Using MS, which measures free dissolved gases in liquid, several authors presented direct eviGreen algae and cyanobacteria possess a high apparent affinity for DIC3 when grown at low DIC concentrations (low CO2 cells: 2,5,9,17), and DIC accumulation has been '

At low concentrations of dissolved inorganic carbon (DIC) at pH 8.0 the rates of DIC transport and fixation by Synechococcus feopoliensis were markedly stimulated by the addition of Na+. Carbonic anhydrase (CA) addition gave similar results. The Na+-stimulated photosynthesis was inhibited by Lit whereas the CA-stimulated photosynthesis was not. The addition of a high DIC con~ntration (1 mM) overcame the need for either Na+ or CA. We suggest that Na+ stimulated HCOs transport whereas CA stimulated CO, transport (by increasing the supply rate of CO,, to the cells). SynechococcusInorganic carbon uptake Photosynthesis Na+-dependent HCOr, transport CO, transport

The assimilation of nitrate, nitrite and ammonia in barley, wheat, corn and bean leaves was studied using (15)N-labelled molecules and either leaf chamber experiments with the uptake of the nitrogen species in the transpiration stream, or vacuum-infiltration experiments. The assimilation of (15)NO3 (-) into amino nitrogen was strictly dependent on light and ceased abruptly when the light was extinguished. If the leaves were exposed to air, CO2-free air or N2 there was no effect on the rate of NO3 (-) assimilation over 0.5 h. After 1.25 h of CO2-free air, NO3 (-) assimilation into amino acids was sharply reduced. Resupply of air at this time stimulated NO3 (-) assimilation and restored it to the rate observed in leaves exposed to air only. There was no recovery by tissue pretreated for 1.25 h in N2 and subsequently resupplied with air. Incorporation of (15)NO2 (-) was also markedly dependent on light with little reduction occurring in the dark. Incorporation of (15)NH4 (+) into amino acids was stimulated 5 fold by light but considerable incorporation occurred in the dark. The presence of 100 mM NO3 (-) had no effect on the rate of incorporation of (15)NO2 (-) or (15)NH4 (+). Nitrite at 1 mM had no effect on (15)NO3 (-) incorporation but at 10 mM inhibited it completely after 0.5 h. Ammonia at 1 mM had no effect on (15)NO3 (-) or (15)NO2 (-) incorporation and while 10 mM inhibited incorporation for 0.5 h this inhibition did not persist.