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Two green macroalgae, Codium decorticatum and Udotea flabellum, differ photosynthetically. Codium had high O(2)-sensitive, and Udotea low O(2)-insensitive, CO(2) compensation points; Codium showed a Warburg effect at seawater dissolved inorganic carbon levels and had photorespiratory CO(2) release, whereas Udotea did not. Seawater dissolved inorganic carbon levels did not saturate photosynthesis. For Codium, but not Udotea, the Warburg effect was increased by ethoxyzolamide, a carbonic anhydrase inhibitor, at high but not low pH. Isolated chloroplasts from both macroalgae showed a Warburg effect that was ethoxyzolamide-insensitive. In both macroalgae, chloroplastic and extrachloroplastic carbonic anhydrase activity was present. P-enolpyruvate carboxykinase (PEPCK) carboxylating activity in Udotea extracts was equivalent to that of ribulose bisphosphate carboxylase, and enzyme activities for C(4) acid metabolism and P-enolpyruvate regeneration were sufficient to operate a limited C(4)-like system. In Udotea, malate and aspartate were early-labeled photosynthetic products that turned over within 60 seconds. Photorespiratory compounds were much less labeled in Udotea. Low dark fixation rates ruled out Crassulacean acid metabolism. A limited C(4)-like system, based on PEPCK, is hypothesized to be the mechanism reducing photorespiration in Udotea. Codium showed no evidence of photosynthetic C(4) acid metabolism. Marine macroalgae, like terrestrial angiosperms, seem to have diverse photosynthetic modes.

Mesophyll cells and bundle sheath strands were isolated rapidly from leaves of the C(4) species Digitaria pentzii Stent. (slenderstem digitgrass) by a chopping and differential filtration technique. Rates of CO(2) fixation in the light by mesophyll and bundle sheath cells without added exogenous substrates were 6.3 and 54.2 micromoles of CO(2) per milligram of chlorophyll per hour, respectively. The addition of pyruvate or phosphoenolpyruvate to the mesophyll cells increased the rates to 15.2 and 824.6 micromoles of CO(2) per milligram of chlorophyll per hour, respectively. The addition of ribose 5-phosphate increased the rate for bundle sheath cells to 106.8 micromoles of CO(2) per milligram of chlorophyll per hour. These rates are comparable to those reported for cells isolated by other methods. The K(m)(HCO(3) (-)) for mesophyll cells was 0.9 mm; for bundle sheath cells it was 1.3 mm at low, and 40 mm at higher HCO(3) (-) concentrations. After 2 hours of photosynthesis by mesophyll cells in (14)CO(2) and phosphoenolpyruvate, 88% of the incorporated (14)C was found in organic acids and 0.8% in carbohydrates; for bundle sheath cells incubated in ribose 5-phosphate and ATP, more than 58% of incorporated (14)C was found in carbohydrates, mainly starch, and 32% in organic acids. These findings, together with the stimulation of CO(2) fixation by phosphoenolpyruvate for mesophyll cells and by ribose 5-phosphate plus ATP for bundle sheath cells, and the location of phosphoenolpyruvate and ribulose bisphosphate carboxylases in mesophyll and bundle sheath cells, respectively, are in accord with the scheme of C(4) photosynthesis which places the Calvin cycle in the bundle sheath and C(4) acid formation in mesophyll cells.Starch and reducing sugars were present in both mesophyll and bundle sheath cells following a period of photosynthesis by whole leaves. However, when isolated cells were exposed to (14)CO(2) in the light, even with appropriate exogenous substrates, only bundle sheath cells accumulated appreciable amounts of labeled carbohydrates. Incubation of mesophyll cells in the light with ATP and either pyruvate and inorganic phosphate, or phosphoenolpyruvate, or 3-phosphoglycerate resulted in large increases in total carbohydrates. The 3-phosphoglycerate treatment produced the greatest increase. These results could not be explained on the basis of increased CO(2) fixation. They suggest that mesophyll cells are able to metabolize exogenously supplied 3-carbon compounds to carbohydrates, despite the apparent inability of these cells to utilize CO(2) for this purpose, and support the view that in the whole leaf 3-phosphoglycerate is transported from bundle sheath to mesophyll cells, where it is reduced to carbohydrate.Sucrose and sucrose-phosphate synthetases and invertase were localized mainly in bundle sheath cells. ADP-Glucose starch synthetase and amylase were present mainly in bundle sheath cells whereas starch phosphorylase was present mainly in mesophyll cells.

We studied the effects of sleep fragmentation on arousal and ventilatory responses to hyperoxic hypercapnia, isocapnic hypoxia, and chemical stimulation of the larynx during sleep in 5 dogs. Sleep fragmentation was induced by repeatedly arousing the dogs with acoustic stimuli throughout 2 to 3 consecutive nights. Responses to respiratory stimuli were then studied during a subsequent daytime sleep. Arterial O2 saturation was measured with an ear oximeter, and sleep stage was determined by electroencephalographic and behavioral criteria. Hypercapnic and hypoxic ventilatory responses were unimpaired by sleep fragmentation. In contrast, alveolar PCO2 levels at arousal increased after sleep fragmentation, from a mean +/- SEM of 52.2 +/- 1.4 mm Hg to 55.6 +/- 1.5 mm Hg (p < 0.05) during slow-wave sleep, and from 57.9 +/- 1.5 mm Hg to 61.3 +/- 2.2 mm Hg (p < 0.05) during rapid-eye movement sleep. Similarly, arterial O2 saturation at arousal decreased after sleep fragmentation from 80.1 +/- 1.0% to 70.2 +/- 2.7% (p < 0.05) during slow-wave sleep, and from 66.3 +/- 3.6% to < 55% (p < 0.05) during rapid-eye-movement sleep. Arousal responses to laryngeal stimulation were also impaired after sleep fragmentation. We conclude that arousal responses to respiratory stimuli are decreased by sleep fragmentation.

The influences of toxic chemicals in man and wildlife are traced from the earliest records. A comprehensive description of wildlife whose populations have suffered from suspected toxic chemical causes is provided. The long-term and long-distance transport of ocean and air currents demonstrate that the impacts of certain pollutants can be delayed, and, once initiated, continued for years past the initiating events. Current toxicological and analytical chemistry approaches to describing and predicting impacts from toxic chemicals are not powerful enough to attack and overcome the problems of the future.

The catalytic degradation of 2-carboxyarabinitol 1-phosphate (CA 1-P), a naturally occurring inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), was investigated by chromatographic and spectroscopic analyses of the reaction products. Carboxy-labeled [(14)C]CA 1-P was incubated with a partially purified tobacco (Nicotiana rustica) chloroplast protein that has been shown previously to catalyze metabolism of CA 1-P to a form incapable of inhibiting Rubisco (ME Salvucci, GP Holbrook, JC Anderson, and G Bowes [1988] FEBS Lett 231: 197-201). In the presence and absence of NADPH, ion-exchange chromatography showed a progressive conversion of [2'-(14)C]CA 1-P to a labeled compound which coeluted with authentic carboxyarabinitol. Parallel assays with unlabeled CA 1-P showed a concomitant decrease in the ability of reaction samples to inhibit Rubisco activity. In separate experiments, a 1:1 stoichiometry was found between the release of inorganic phosphate from [2'-(14)C]CA 1-P and accumulation of the (14)C-labeled product. Liberation of inorganic phosphate was not observed when the tobacco enzyme was incubated with ribulose-1,5-bisphosphate, fructose-1,6-bisphosphate, glucose-1-phosphate, glucose-6-phosphate, or 6-phosphogluconate. Proton nuclear magnetic resonance spectroscopy of the labeled CA 1-P reaction product established its identity as carboxyarabinitol. We therefore propose that light-stimulated degradation of CA 1-P is catalyzed in vivo by a specific phosphatase, 2-carboxyarabinitol 1-phosphatase. Carboxyarabinitol 1-phosphatase activity was detected in the absence of NADPH, but increased threefold when 2 millimolar NADPH was present. Thus, while not required for the reaction, NADPH may play an important role in the regulation of CA 1-P degradation.

The submerged aquatic plant Isoetes howellii Engelmann possesses Crassulacean acid metabolism (CAM) comparable to that known from terrestrial CAM plants. Infrared gas analysis of submerged leaves showed Isoetes was capable of net CO(2) uptake in both light and dark. CO(2) uptake rates were a function of CO(2) levels in the medium. At 2,500 microliters CO(2) per liter (gas phase, equivalent to 1.79 milligrams per liter aqueous phase), Isoetes leaves showed continuous uptake in both the light and dark. At this CO(2) level, photosynthetic rates were light saturated at about 10% full sunlight and were about 3-fold greater than dark CO(2) uptake rates. In the dark, CO(2) uptake rates were also a function of length of time in the night period. Measurements of dark CO(2) uptake showed that, at both 2,500 and 500 microliters CO(2) per liter, rates declined during the night period. At the higher CO(2) level, dark CO(2) uptake rates at 0600 h were 75% less than at 1800 h. At 500 microliters CO(2) per liter, net CO(2) uptake in the dark at 1800 h was replaced by net CO(2) evolution in the dark at 0600 h. At both CO(2) levels, the overnight decline in net CO(2) uptake was marked by periodic bursts of accelerated CO(2) uptake. CO(2) uptake in the light was similar at 1% and 21% O(2), and this held for leaves intact as well as leaves split longitudinally. Estimating the contribution of light versus dark CO(2) uptake to the total carbon gain is complicated by the diurnal flux in CO(2) availability under field conditions.

The Km(CO(2)) values of ribulose 1,5-diphosphate carboxylase in freshly ruptured spinach (Spinacia oleracea L.) chloroplasts and in the purified form isolated from spinach leaves were found to be pH dependent. Raising the pH of the assay solution produced a substantial decrease in the Km(CO(2)) of both enzyme systems. In freshly ruptured chloroplasts at pH 7.2 the Km(CO(2)) was 25 mum, at pH 8 it decreased to 19 mum, and at pH 8.8 a further decrease to 7 mum was found. With the purified enzyme at pH 7.2 the Km(CO(2)) was 147 mum, while the corresponding Km values for pH 8 and 8.8 were 34 and 15 mum CO(2), respectively. The latter figure approximates the physiological Km(CO(2)) of 10 mum estimated for photosynthesizing leaves and intact chloroplasts. The maximum velocity for both enzyme systems at optimum substrate levels was at pH 8, but the highest calculated rate of CO(2) uptake at atmospheric CO(2) levels occurred at pH 8.8. These results support the proposal that the light-induced efflux of protons out of the chloroplast stroma may be a major factor involved with the reported in vivo light activation of ribulose 1,5-diphosphate carboxylase.

Previous reports indicate that apnea is induced by high frequency ventilation (HFV) in anesthetized animals. We have studied conscious dogs ventilated with HFV during sleep and wakefulness to determine if this apnea is state related. Eucapnic apnea or very low breathing frequencies were observed during quiet wakefulness, quiet sleep and tonic REM sleep. However, spontaneous breathing at nearly normal rates was invariably seen during phasic REM sleep. We conclude that HFV as administered induces apnea or near apnea in conscious animals and that the inhibitory pathways causing this apnea are probably disabled during phasic REM sleep.

The ability to detect added inspiratory flow-resistive loads during wakefulness was examined in 5 men with laboratory-documented obstructive sleep apnea. The patients were eucapnic, and standard measurements of lung volumes and flow rates were within the normal range. The patients breathed through a circuit, to which each of 5 flow resistances of 0.12 to 5.5 cm H2O/L/s was added at 20- to 30-s intervals for 1 inspiration, following a cue. Each resistance was presented 10 times in random sequence, and the percentage of trials in which each load was detected by the patient was calculated. The threshold level of load detection, defined as the change in resistance that could be detected 50% of the time, was higher in the patients (2.37 +/- 0.41 cmH2O/L/s, mean +/- SE) than in 9 healthy subjects (0.65 +/- 0.08; p less than 0.001), and this difference persisted when the threshold load was corrected for background resistance (1.05 +/- 0.11 versus 0.45 +/- 0.07; p less than 0.001). In addition, the ventilatory response to hypercapnia was less in the patients (1.82 +/- 0.22 L/min/mm Hg) than in the normal subjects (3.87 +/- 0.40; p less than 0.005), and there was a significant negative correlation (r = 0.97; p less than 0.001) between the load detection threshold and the ventilatory response to CO2. The results add to the developing concept that subtle defects in respiratory control can be demonstrated even during wakefulness in eucapnic patients with obstructive sleep apnea.

Incubation under water in a 30 C/14-hour or 12 C/10-hour photoperiod caused the CO(2) compensation points of 10 aquatic macrophytes to decrease below 25 or increase above 50 microliters CO(2) per liter, respectively. Submerged and aerial leaves of two amphibious angiosperms (Myriophyllum brasiliense and Proserpinaca palustris) maintained high compensation points when incubated in air but, when the submerged or aerial leaves of Proserpinaca were incubated under water, the compensation points dropped as low as 10. This suggests that, in addition to temperature and photoperiod, some factor associated with submergence regulates the compensation point of aquatic plants. In the high-compensation point plants, photorespiration, as a percentage of net photosynthesis, was equivalent to that in terrestrial C(3) plants. For Hydrilla verticillata, the decreasing CO(2) compensation points (110, 40, and 10) were associated with reduced photorespiration, as indicated by decreased O(2) inhibition, decreased rates of CO(2) evolution into CO(2)-free air, and increased net photosynthetic rates.The decrease in the CO(2) compensation points of Hydrilla, Egeria densa, and Cabomba caroliniana was accompanied by an increase in the activity of phosphoenolpyruvate, but not of ribulose bisphosphate, carboxylase. In Hydrilla, several C(4) enzymes also increased in activity to the following levels (micromoles per gram fresh weight per hour): pyruvate Pi dikinase (35), pyrophosphatase (716), adenylate kinase (525), NAD and NADP malate dehydrogenase (6565 and 30), NAD and NADP malic enzymes (239 and 44), and aspartate and alanine aminotransferases (357 and 85), whereas glycolate oxidase (6) and phosphoglycolate and phosphoglycerate phosphatases (76 and 32) showed no change. Glycolate dehydrogenase and phosphoenolpyruvate carboxykinase were undetectable. The reduced photorespiration in these plants may be due to increased CO(2) fixation via a C(4) acid pathway. However, for three Myriophyllum species, some other mechanism appears operative, as phosphoenolpyruvate carboxylase was not increased in the low compensation point state, and ribulose bisphosphate carboxylase remained the predominant carboxylation enzyme.

Growth at an elevated CO(2) concentration resulted in an enhanced capacity for soybean (Glycine max L. Merr. cv Bragg) leaflet photosynthesis. Plants were grown from seed in outdoor controlled-environment chambers under natural solar irradiance. Photosynthetic rates, measured during the seed filling stage, were up to 150% greater with leaflets grown at 660 compared to 330 microliters of CO(2) per liter when measured across a range of intercellular CO(2) concentrations and irradiance. Soybean plants grown at elevated CO(2) concentrations had heavier pod weights per plant, 44% heavier with 660 compared to 330 microliters of CO(2) per liter grown plants, and also greater specific leaf weights. Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) activity showed no response (mean activity of 96 micromoles of CO(2) per square meter per second expressed on a leaflet area basis) to short-term ( approximately 1 hour) exposures to a range of CO(2) concentrations (110-880 microliters per liter), nor was a response of activity (mean activity of 1.01 micromoles of CO(2) per minute per milligram of protein) to growth CO(2) concentration (160-990 microliters per liter) observed. The amount of rubisco protein was constant, as growth CO(2) concentration was varied, and averaged 55% of the total leaflet soluble protein. Although CO(2) is required for activation of rubisco, results indicated that within the range of CO(2) concentrations used (110-990 microliters per liter), rubisco activity in soybean leaflets, in the light, was not regulated by CO(2).

Arousal from sleep is an important component of any co-ordinated response to an external stimulus. Respiratory stimuli imposed during sleep are capable of eliciting arousal responses as well as the classic ventilatory responses Considerable survival advantage may result as a consequence of intact arousal mechanisms. Developmental studies of arousal responses to respiratory stimuli are lacking. Arousal responses to chemoreceptor stimuli have been examined in adult tracheotomized dogs, both before and following bilateral surgical denervation of the carotid bodies. Prior to denervation of the carotid bodies arousal in response to isocapnic progressive hypoxia occurred at an arterial oxygen saturation (SaO2) of 83% during slow-wave sleep and 70% in rapid-eye-movement sleep. Airway occlusion induced arousal from Slow-wave-sleep at SaO2 of 88% and from rapid-eye-movement sleep at SaO2 of 84%. Following denervation of the carotid bodies, arousal failed to occur in response to either progressive hypoxia or airway occlusion despite desaturation to 60% in Slow-wave sleep and 50% in rapid-eye-movement-sleep, at which level experiments were arbitrarily terminated. The effect of sleep fragmentation on arousal responses of sleeping dogs to chemoreceptor stimuli has also been studied. A marked impairment of both hypoxic and hypercapnic arousal was produced by sleep fragmentation. The consequences of interfering with arousal mechanisms in experimental animals indicates the considerable potential for similar dysfunction in man to contribute to the pathophysiology of the clinical syndromes of obstructive sleep apnoea and sudden infant death.(ABSTRACT TRUNCATED AT 250 WORDS)

By using commercially available units, an electrometer and an IBM personal computer, it was relatively inexpensive and simple to assemble a system which permits gamma-ray-emitting radionuclide activities to be measured in an ionization chamber with an uncertainty of +/- 0.5% and a reproducibility of +/- 0.05%.

Net photosynthesis in the submersed angiosperms Myriophyllum spicatum L. and Hydrilla verticillata (L.f.) Royal was inhibited by 21% O2, but the degree of inhibition was greater for plants in the high than in the low photorespiratory state. Increasing the CO2 concentration from 50 through 2,500 μl l(-1) decreased the O2 inhibition of the high-photorespiration plants in a competitive manner, but it had no effect on the O2 inhibition of plants in the low photorespiratory state. Carbonic-anhydrase activity increased by almost threefold with the induction of the low photorespiratory state. Ethoxyzolamide, an inhibitor of carbonic anhydrase, reduced the net photosynthesis of low-photorespiration Myriophyllum and Hydrilla plants by 40%, but their dark respiration was unaffected. This ethoxyzolamide inhibition of net photosynthesis exhibited a competitive response to CO2 concentration, resulting in a decrease in the apparent affinity of photosynthesis for CO2. The net photosynthesis of plants in the high photorespiratory state was inhibited only slightly by ethoxyzolamide, and this inhibition was independent of the CO2 level. Ethoxyzolamide treatment caused an increase in the O2 inhibition of net photosynthesis of plants in the low photorespiratory state. Ethoxyzolamide increased the low CO2 compensation points of low-photorespiration Myriophyllum and Hydrilla, but the values for the high-photorespiration plants were unchanged. In comparison, the CO2 compensation points of the terrestrial plants Sorghum bicolor (C4), Moricandia arvensis (C3-C4 intermediate) and Nicotiana tabacum (C3) were unaltered by ethoxyzolamide treatment. These data indicate that the low photorespiratory state in Myriophyllum and Hydrilla is repressed by ethoxyzolamide treatment, thus implicating carbonic anhydrase as a component of the photorespiration-reducing mechanism in these plants. The competitive interaction of CO2 with ethoxyzolamide provides evidence that the low photorespiratory state in submersed angiosperms is the result of some type or types of CO2 concentrating mechanism. In Myriophyllum it may be via bicarbonate utilization, but in Hydrilla it probably takes the form of an inducible C4-type system.

Ribulose bisphosphate carboxylase/oxygenase (RuBPCase) from several plants had substantially greater activity in extracts from lightexposed leaves than dark leaves, even when the extracts were incubated in vitro with saturating HCO(3) (-) and Mg(2+) concentrations. This occurred in Glycine max, Lycopersicon esculentum, Nicotiana tabacum, Panicum bisulcatum, and P. hylaeicum (C(3)); P. maximum (C(4) phosphoenolpyruvate carboxykinase); P. milioides (C(3)/C(4)); and Bromelia pinguin and Ananas comosus (Crassulacean acid metabolism). Little or no difference between light and dark leaf extracts of RuBPCase was observed in Triticum aestivum (C(3)); P. miliaceum (C(4) NAD malic enzyme); Zea mays and Sorghum bicolor (C(4) NADP malic enzyme); Moricandia arvensis (C(3)/C(4)); and Hydrilla verticillata (submersed aquatic macrophyte). It is concluded that, in many plants, especially Crassulacean acid metabolism and C(3) species, a large fraction of ribulose-1,5-bisphosphate carboxylase/oxygenase in the dark is in an inactivatable state that cannot respond to CO(2) and Mg(2+) activation, but which can be converted to an activatable state upon exposure of the leaf to light.

The CO(2) compensation point of the submersed aquatic macrophyte Hydrilla verticillata varied from high (above 50 microliters per liter) to low (10 to 25 microliters per liter) values, depending on the growth conditions. Plants from the lake in winter or after incubation in an 11 C/9-hour photoperiod had high values, whereas summer plants or those incubated in a 27 C/14-hour photoperiod had low values. The plants with low CO(2) compensation points exhibited dark (14)CO(2) fixation rates that were up to 30% of the light fixation rates. This fixation reduced respiratory CO(2) loss, but did not result in a net uptake of CO(2) at night. The low compensation point plants also showed diurnal fluctuations in titratable acid, such as occur in Crassulacean acid metabolism plants. However, dark fixation and diurnal acid fluctuations were negligible in Hydrilla plants with high CO(2) compensation points.Exposure of the low compensation point plants to 20 micromolar (14)CO(2) resulted in 60% of the (14)C being incorporated into malate and aspartate, with only 16% in sugar phosphates. At a high CO(2) level, the C(4) acid label was decreased. A pulse-chase study indicated that the (14)C in malate, but not aspartate, decreased after a long (270-second) chase period; thus, the C(4) acid turnover was much slower than in C(4) plants.Phosphoenolpyruvate carboxylase activity was high (330 micromoles per milligram chlorophyll per hour), as compared to ribulose bisphosphate carboxylase (20 to 25), in the plants with low compensation points. These plants also had a pyruvate, Pi dikinase activity in the leaves of 41 micromoles per milligram chlorophyll per hour, which suggests they are not C(3) plants. NAD- and NADP(+)-malate dehydrogenase activities were 6136 and 24.5 micromoles per milligram chlorophyll per hour, respectively. Of the three decarboxylating enzymes assayed, the activities of NAD- and NADP(+)-malic enzyme were 104.2 and 23.7 micromoles per milligram chlorophyll per hour, while phosphoenolpyruvate carboxykinase was only 0.2.Low compensation point Hydrilla plants fix some CO(2) into C(4) acids, which can be decarboxylated for later refixation, presumably into the Calvin cycle. Refixation would be advantageous in summer lake environments where the CO(2) levels are high at night but low during the day. Hydrilla does not fit any of the present photosynthetic categories, and may have to be placed into a new group, together with other submersed aquatic macrophytes that have environmentally variable CO(2) compensation points.

We studied the independent effects of bilateral carotid body denervation and bilateral cold blockade of the vagus nerves on the arousal response to airway occlusion during sleep. Dogs breathed through a cuffed endotracheal tube inserted via a chronic tracheostomy, and airway occlusion was imposed at end-expiration and maintained until the moment of arousal. Arterial O2 saturation (SaO2) was measured with an ear oximeter, and sleep stage was determined by electroencephalographic and behavioral criteria. Mean +/- SE SaO2 values at arousal were 88.7 +/- 2.7% during slow-wave sleep, and 84.9 +/- 3.5% during rapid-eye-movement sleep (0.05 less than p less than 0.1). After carotid body denervation (2 dogs), arousal SaO2 values were less than 60% during slow-wave sleep and less than 50% during rapid-eye-movement sleep, at which time airway occlusion was arbitrarily terminated. In a few studies after denervation, when airway occlusion was maintained beyond these values, the dogs occasionally failed to arouse at all, and resuscitation was required. Bilateral cold blockade of the vagus nerves (2 dogs) resulted in no significant change in SaO2 at arousal. We concluded that the arousal response to airway occlusion is mediated primarily by the carotid bodies.

An association between the use of parenteral corticosteroids in acute asthma and the development of an acute myopathy was first reported in 1977. We report 2 further cases that contribute significantly to our knowledge of this rare complication of the treatment of acute asthma. These cases demonstrate that the acute myopathy is not just a complication of the use of parenteral hydrocortisone in patients requiring ventilatory support during an episode of acute asthma. The acute myopathy can occur with several parenteral corticosteroids, may be severe (with rhabdomyolysis and myoglobinuria), and may have protracted morbidity. Prospective follow-up allowed demonstration of histopathology, electrophysiology, and also the contribution of various pharmacologic agents. Careful analysis of the evidence strongly implicates corticosteroids as the causative agent.

The effects of DDT (2,2-bis-(p-chlorophenyl)-1, 1, 1-trichloroethane) on the growth of seven marine phytoplankters, representative of five algal divisions, were studied. At a concentration of 80 parts per billion (0.23 mum) DDT, growth of Dunaliella tertiolecta was unaffected, and there was slight, if any, influence on the development of Cyclotella nana, Thalassiosira fluviatilis, Amphidinium carteri, Coccolithus huxleyi, and Porphyridium sp. Skeletonema costatum exhibited a 9 day lag before cell division commenced, the rate of growth subsequently being the same as in the control (no DDT). A further inoculation of this culture of S. costatum into 80 parts per billion DDT gave another 9-day lag before initiation of normal growth.The ability of marine phytoplankton to metabolize DDT varied. DDE (2,2-bis-(p-chlorophenyl)-1, 1-dichloroethylene) was the only significant hexane-soluble metabolite detected. It occurred in cells of S. costatum, C. nana, T. fluviatilis and D. tertiolecta. Maximum degree of conversion was 7.5% and was based on the total DDT found in the cell-water system of 9-day D. tertiolecta cultures. The total amount of DDT recovered from cultures in 2- to 3-week experiments ranged from 63.5% for T. fluviatilis to 90.7% for S. costatum. The amount of DDT found associated with the cells, collected by centrifugation, in the cell-water system ranged from 70.8 to 99.5%.Chloroplast particles were isolated from a "resistant" species, D. tertiolecta. Noncyclic electron flow, as measured by ferricyanide reduction, was inhibited by DDT and DDE, and could explain growth inhibition in other phytoplankters. Fifty percent inhibition occurred at 20 mum DDT. Sensitivity of phytoplankton to toxic hydrophobic chlorinated hydrocarbons may be dependent upon penetration of the molecules to active sites within membranes.

An electrometric system for determination of carbonic anhydrase activity was constructed. Enzyme activity was assayed in homogenates of marine macroscopic Chlorophyta, Rhodophyta, and Phaeophyta. Plants surveyed included Ulva expansa (Setchell) Setchell and Gardner, Codium fragile (Suringar) Hariot, Enteromorpha sp., Chaetomorpha torta (Farlow) McClatchie (Chlorophyta); Laurencia papillosa (Greville). Plocamium coccineum var. pacificum (Kylin) Dawson, Pterocladia capillacea (Gmelin) Bornet and Thuret. Gigartina armata J. Agardh (Rhodophyta); Eisenia arborea Areschoug and Macrocystis pyrifera (Linnaeus) C. A. Agardh (Phaeophyta). Activity was present in all algae; in the Phaeophyta this could be demonstrated only after dialysis. p-Chloromercuriphenylsulfonic acid (10(-4)m) decreased activity in 1 species, Plocamium; this inhibition could be almost completely overcome with the addition of 10(-3)m dithiothreitol. In 2 green and 2 red algae assayed for sensitivity to acetazolamide (Diamox), inhibition was complete at 10(-4)m concentration of inhibitor. Dithiothreitol at a concentration of 10(-3)m did not enhance activity in any of the homogenates, and was not necessary for enzyme expression.