Non-Autotrophic CO2 Fixation and Drought Tolerance in Mosses

Cratoneuron filicinum, a drought-sensitive moss, and Tortularuralis, a drought-tolerant moss, fix CO₂ non-autotrophicallyat a rate of about 1.2 and 2.2 µmol h^–1 g^–1dry wt. respectively. During drying, T. ruralis fixes CO₂ atan undiminished rate until the tissue loses about 60% of theinitial fresh weight. Thereafter, CO₂ fixation rapidly declinesto zero. Dark CO₂ fixation by C.filicinum declines steadilyduring the dehydration period. On rehydration, dark CO₂ fixationis resumed immediately in T. ruralis but not in C.filicinum.When dried T. ruralis is equilibrated with an atmosphere ofnearly 100% relative humidity, its weight increases to about40% of the original fresh weight and dark CO₂ fixation resumesat a rate about 60% of the fresh moss. In C.filicinum thereis only a small increase in weight and little CO₂ fixation inthe dark. The non-autotrophically fixed carbon, in both mossesstudied, is incorporated into amino acids (more than 60% ofthe total, mainly into aspartate, alanine and glutamate) andorganic acids (less than 40% of the total, mainly into malate).It is suggested that on rehydration immediate availability ofNADPH, known to be produced by transhydrogenation from NADHduring dark CO₂ fixation, may be an important factor in therepair of drought-induced cellular damage by reductive biosynthesisof membrane components and other cellular constituents. Key words: Mosses, Dehydration, Rehydration, Dark CO₂ fixation, Amino acids, Organic acids, NADPH, Drought tolerance.     

Stability and Synthesis of Phospholipids during Desiccation and Rehydration of a Desiccation-Tolerant and a Desiccation-Intolerant Moss

The fatty acid composition of the phospholipids from the desiccation-tolerant moss Tortula ruralis (Hedw.) Gaertn, Meyer and Scherb and the desiccation-intolerant moss Cratoneuron filicinum has been determined. No changes in composition occur in either moss as a consequence of rapid drying, but, after slow drying, there is a decline in some unsaturated fatty acids. Upon rehydration of T. ruralis after slow drying, these acids decline further; however, within 105 minutes, they regain the same levels as those in undesiccated controls. A smaller and more transient decline occurs after rapid desiccation. Most phospholipid unsaturated fatty acids decrease during rehydration of C. filicinum, and their levels are not recovered. After both rapid and slow drying of T. ruralis, acetate and glycerol are incorporated into the phospholipid fraction, although de novo synthesis, alone, might not account for the increase in unsaturated fatty acids upon rehydration. Very little acetate or glycerol is incorporated during rehydration of C. filicinum. Loss of unsaturated fatty acids from the phospholipids of T. ruralis does not appear to be associated with increased lipoxygenase activity. Furthermore, there is little correlation between the extent of peroxidation of fatty acids due to desiccation and changes in the phospholipid fraction.     

Respiration in Relation to Adenosine Triphosphate Content during Desiccation and Rehydration of a Desiccation-tolerant and a Desiccation-intolerant Moss

O₂ consumption by the desiccation-tolerant moss Tortula ruralis and the desiccation-intolerant Cratoneuron filicinum increased markedly during the latter stages of desiccation. ATP content of the mosses during desiccation was not correlated with O₂ consumption, but was influenced by the rate at which the mosses lost water. The more rapid the water loss, the more ATP that was present in the dry mosses. The pattern of O₂ consumption on rehydration also was influenced by the previous rate of desiccation. After rapid desiccation of T. ruralis O₂ consumption upon rehydration was considerably elevated, and for up to 24 hours. After very slow desiccation the elevation was small and brief. Normal O₂ consumption did not occur in C. filicinum after rapid desiccation, but did so within a few hours of rehydration after slower speeds of drying. ATP levels in T. ruralis returned to normal within 5 to 10 minutes of rehydration. In C. filicinum, increases in ATP were closely correlated with O₂ consumption. These observations are considered to be related to differential damage caused to mitochondria and to cellular integrity by different speeds of water loss. The desiccation-tolerant moss appears to be able to repair the severe damage imposed by rapid desiccation whereas the desiccation-intolerant moss cannot.     

Leaf Senescence: Correlated with Increased Levels of Membrane Permeability and Lipid Peroxidation, and Decreased Levels of Superoxide Dismutase and Catalase

The changes in membrane permeability (soluble leakage), lipidperoxidation, and activities of superoxide dismutase (SOD) andcatalase have been studied during in situ senescence of leavesof Nicotiana tabacum L., cv. Wisconsin 38. After full leaf expansionwas reached there was a rapid, almost linear increase in therate of ⁸⁶Rb leakage from the preloaded leaf discs, with leafage. Parallel with this increase in membrane permeability wasa cumulative increase in the level of lipid peroxidation. Atthe same leaf age there were changes in the activities of SODand catalase. SOD activity decreased on the basis of fresh weightbut did not change when measured on the basis of protein contentprobably due to relative stability of SOD during the senescence-associatedgeneral decline in protein content. Catalase activity firstincreased parallel with the chlorophyll content of the leafand then, after full leaf expansion, declined on the basis ofboth fresh weight and protein content. These changes in membranepermeability, lipid peroxidation, and the enzyme activitiescoincide in leaf age with the decline in protein and chlorophyllcontents and in chlorophyll a: b ratio. When the senescenceof the bottom-most leaves was reversed by removing the stemfrom immediately above them, the senescence-associated changesin protein and chlorophyll contents, lipid peroxidation, andthe enzyme activities were also reversed. It is suggested thatleaf senescence may be a consequence of cumulative membranedeterioration due to increasing level of lipid peroxidationprobably controlled by, among other factors, the activitiesof SOD and catalase.     

Inhibition of protein synthesis by products of lipid peroxidation

Effects of lipid peroxidation products on in vivo and in vitro protein synthesis have been studied. Malondialdehyde (MDA), a product, and a routinely used index of lipid peroxidation, inhibits in vivo protein synthesis in the two mosses, Tortula ruralis and Cratoneuron filicinum, and in pea (Pisum sativum) leaf discs. When wheat germ supernatant or poly(A)-rich mRNA of T. ruralis was incubated with MDA its subsequent activity in a cell-free protein-synthesizing system was reduced. When MDA was added directly to the in vitro protein-synthesizing mixture containing moss polyribosomes, the inhibition of amino acid incorporation was small. However, when simultaneous lipid peroxidation was allowed to occur along with in vitro protein synthesis there was a strong inhibition of amino acid incorporation and MDA accumulated in the reaction mixture indicating that products of lipid peroxidation other than, and apparently more toxic than, MDA were involved. It was concluded that lipid peroxidation inhibits protein synthesis probably by releasing toxic products which may react with and inactivate some components of the protein-synthesizing complex.     

The Effects of Rapid and Very Slow Speeds of Drying on the Ultrastructure and Metabolism of the Desiccation-Sensitive Moss Cratoneuron filicium (Hedw.) Spruce

The response of the semi-aquatic moss species Cratoneuron filicinumto desiccation varies with the speed at which it loses water.On rehydration following rapid drying the contents of all cellsare considerably disrupted and they become increasingly disorganizedover a 24 h time period. After very slow drying some cells havethe appearance of those after rapid drying, while others maintaintheir integrity, and the internal organization of mitochondriaand chloroplasts is evident The capacity to resume protein synthesison rehydration is reduced after very slow, slow, and rapid drying:the greater the speed of drying the more it is reduced. Rapidwater loss down to 50% of original fresh weight has no irreversibleeffect on protein synthesis. Respiration does not occur on rehydrationafter rapid drying, although failure to maintain sterile conditionsduring measurement of oxygen consumption can lead to artefactsdue to bacterial contamination. The results are contrasted withthose obtained previously from the desiccation-tolerant mossTortula ruralis, and possible reasons for the differences areoutlined.     

Comparative Studies of Leaf Tissue 4: III. EFFECTS OF WALL-DEGRADING ENZYMES AND OSMOTIC STRESS

Commercially available cell wall-degrading enzymes frequentlyused for protoplast isolation inhibited CO₂ fixation and photosyntheticO₂ evolution, and stimulated dark respiration by leaf tissueand isolated mesophyll protoplasts of Nicotiana tabacum L. andAntirrhinum majus L. They also depolarized the membrane potentialof cells of leaf tissue, inhibited uptake of ⁸⁶Rb by tobaccoleaf tissue and isolated mesophyll protoplasts, and stimulated³⁶CI uptake by tobacco leaf tissue. Where studied, these effectswere found to be reversible. The depolarization effect on Antirrhinumleaf cells occurred even when the enzyme preparations had beendenatured, dialysed, or desalted, and the effect was greatestin those fractions of the enzyme preparation which showed thehighest cellulase activity. Plasmolysis of tobacco leaf tissue inhibited photosyntheticO₂ evolution, CO₂ fixation, and ⁸⁶Rb uptake to levels belowthose exhibited by isolated protoplasts in media of the samecomposition and osmolarity. The implications of these resultsfor work with leaf tissue and isolated protoplasts are discussed.     

Active oxygen participation in chlorophyll destruction and lipid peroxidation in SO2-fumigated leaves of spinach

Chlorophyll a and carotenoids of spinach began to be destroyed2 to 3 hr after fumigation with 2 ppm SO₂ under light, whereaschlorophyll b was undamaged during 8 hr of exposure to SO₂.Pheophytin a was not affected by the fumigation. When disks excised from leaves fumigated with SO₂ at 2 ppm for2 hr were illuminated, chlorophyll a and carotenoids were brokendown, while they were not destroyed in darkness. The destructionof these pigments was suppressed under nitrogen. Chlorophylla destruction was inhibited by l,2-dihydroxybenzene-3,5-disulfonate(tiron), hydro-quinone and ascorbate, but not by l,4-diazabicyclo-[2,2,2]-octane(DABCO), methio-nine, histidine, benzoate and formate. Chlorophylla destruction was inhibited by phenazine methosulfate but stimulatedby methyl viologen. Addition of superoxide dismutase (SOD) tothe homogenate of SO₂-fumigated leaves inhibited the chlorophylla destruction. The activity of endogenous SOD was reduced to40% by 2-hr fumigation before the loss of chlorophyll was observed.These results suggest that chlorophyll a destruction by SO₂was due to superoxide radicals (O₂^–). Moreover, malondialdehyde (MDA), a product of lipid peroxidation,was formed in SO₂-fumigated leaves. MDA formation was inhibitedby tiron, hydroquinone and DABCO but not by benzoate and formate.MDA formation was increased by D₂O. These results suggest thatlipid peroxidation in SO₂-fumigated leaves was due to singletoxygen ¹O₂ produced from O_2^–. (Received May 15, 1980; )     

Active oxygen participation in chlorophyll destruction and lipid peroxidation in SO2-fumigated leaves of spinach

Chlorophyll a and carotenoids of spinach began to be destroyed2 to 3 hr after fumigation with 2 ppm SO₂ under light, whereaschlorophyll b was undamaged during 8 hr of exposure to SO₂.Pheophytin a was not affected by the fumigation. When disks excised from leaves fumigated with SO₂ at 2 ppm for2 hr were illuminated, chlorophyll a and carotenoids were brokendown, while they were not destroyed in darkness. The destructionof these pigments was suppressed under nitrogen. Chlorophylla destruction was inhibited by l,2-dihydroxybenzene-3,5-disulfonate(tiron), hydro-quinone and ascorbate, but not by l,4-diazabicyclo-[2,2,2]-octane(DABCO), methio-nine, histidine, benzoate and formate. Chlorophylla destruction was inhibited by phenazine methosulfate but stimulatedby methyl viologen. Addition of superoxide dismutase (SOD) tothe homogenate of SO₂-fumigated leaves inhibited the chlorophylla destruction. The activity of endogenous SOD was reduced to40% by 2-hr fumigation before the loss of chlorophyll was observed.These results suggest that chlorophyll a destruction by SO₂was due to superoxide radicals (O₂^–). Moreover, malondialdehyde (MDA), a product of lipid peroxidation,was formed in SO₂-fumigated leaves. MDA formation was inhibitedby tiron, hydroquinone and DABCO but not by benzoate and formate.MDA formation was increased by D₂O. These results suggest thatlipid peroxidation in SO₂-fumigated leaves was due to singletoxygen ¹O₂ produced from O_2^–. (Received May 15, 1980; )     

The Conservation of Polyribosomes in the Moss Tortula ruralis during Total Desiccation

Total desiccation of the moss Tortula ruralis was achieved byplacing it in a dry atmosphere for 90 min. Reintroduction ofthe moss to water resulted in the recovery of its normal morphologicalform within 15–30 s. The sedimentation profile on a sucrosegradient of the ribosomal content of the totally dry moss showsthe presence of distinct polyribosomal peaks. The levels ofthese polyribosomes rise upon rehydration of the moss. The differencebetween the tolerance to water deficit by this moss and by higherplants is outlined.     

Functional characterization of the neuronal-specific K-Cl cotransporter: implications for [K+]o regulation

The neuronal K-Cl cotransporter isoform (KCC2) was functionallyexpressed in human embryonic kidney (HEK-293) cell lines. Two stablytransfected HEK-293 cell lines were prepared: one expressing anepitope-tagged KCC2 (KCC2-22T) and another expressing theunaltered KCC2 (KCC2-9). The KCC2-22T cells produced aglycoprotein of ~150 kDa that was absent from HEK-293 control cells.The ⁸⁶Rb influx in both cell lineswas significantly greater than untransfected control HEK-293 cells. TheKCC2-9 cells displayed a constitutively active⁸⁶Rb influx that could beincreased further by 1 mMN-ethylmaleimide (NEM) but not by cellswelling. Both furosemide [inhibition constant (K_i) ~25µM] and bumetanide (K_i~55 µM) inhibited the NEM-stimulated ⁸⁶Rb influx in the KCC2-9cells. This diuretic-sensitive⁸⁶Rb influx in theKCC2-9 cells, operationally defined as KCC2 mediated, required external Clbut not external Na⁺ and exhibiteda high apparent affinity for externalRb⁺(K⁺)[Michaelis constant(K_m) = 5.2 ± 0.9 (SE) mM; n = 5] but alow apparent affinity for externalCl(K_m >50 mM). Onthe basis of thermodynamic considerations as well as the unique kineticproperties of the KCC2 isoform, it is hypothesized that KCC2 may servea dual function in neurons: 1) themaintenance of low intracellularCl concentration so as toallow Cl influx vialigand-gated Cl channelsand 2) the buffering of externalK⁺ concentration([K⁺]_o) in the brain.

     

Effects of Water Stress on the Respiratory and Nitrogen-fixing Activity of Soybean Root Nodules

Seventy-five per cent of the N₂-fixing activity (measured asthe reduction of C₂H₂ to C₂H₄) and 50 per cent of the respiratoryactivity of detached soybean root nodules was lost when thewater potential () of the nodules was lowered from approximately–1 ? 105 Pa (turgid nodules) to –9 ? 105 Pa (moderatelystressed nodules). Severely stressed nodules ( = –1.8? 10⁶ Pa) showed almost total loss of N₂-fixing activity andup to 80 per cent loss of respiratory activity. Increasing theoxygen partial pressure (PO₂) from 10⁴ to 10⁵ Pa completelyrestored both N₂-fixation and respiration in moderately stressednodules, but only partial recovery was possible in severelystressed nodules. The activity of the stressed nodules was verylow at low PO₂ (5 ? 10³ and 10⁴ Pa). The C₂H₂-reducing activityof nodule slices, nodule breis, and bacteroids from turgid andmoderately stressed nodules was almost identical but some activitywas lost in the breis and bacteroids from severely stressednodules. Calculations showed that at low PO₂ (10⁴ and 2 ? 10⁴Pa), the rate of O₂ diffusion into severely stressed noduleswas ten times lower than that for turgid nodules, but only fourtimes lower at a higher PO₂ (4 ? 10⁴ Pa). Carbon monoxide inhibitionof C₂H₂ reduction was slower in stressed nodules than in turgidnodules. The results are discussed in view of the possible developmentof a physical barrier to gaseous diffusion and/or the possiblealtered affinity of the nodule leghaemoglobin for O₂ in thewater-stressed nodules.     

The mechanism supplying acetyl-CoA for terpene biosynthesis in sweet potato with black rot: Incorporation of acetate-2-14C, pyruvate-3-14C and citrate-2,4-14C into ipomeamarone

Silica gel thin layer chromatography showed that acetate-2-¹⁴C,pyruvate-3-¹⁴C and citrate-2,4-¹⁴C were incorporated into ipomeamaronein sweet potato root tissues infected by Ceratocystis fimbriata.Rates of incorporation of ¹⁴C, from these 3 substances, intothe CHCl³-CH₃OH-soluble lipid fraction and ipomeamarone wereof the followingder: acetate > pyruvate > citrate ¹This paper constitutes Part 82 of the Phytopathological Chemistryof Sweet Potato with Black Rot and Injury (Received December 11, 1969; )     

Evidence for Involvement of the Superoxide Radical in the Conversion of 1-Aminocyclopropane-1-Carboxylic Acid to Ethylene by Pea Microsomal Membranes

Electron spin resonance (ESR) spectroscopy has provided evidencefor involvement of the superoxide anion (O₂^–) radicalin the conversion of l-aminocyclopropane-l carboxylic acid (ACC)to ethylene by microsomal membranes from etiolated pea seedlings.Formation of ethylene from ACC by the membrane system is oxygen-dependent,heat denaturable, inhibited by the radical scavenger n-propylgallate and sensitive to superoxide dismutase (SOD) and catalase.Addition of 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron)to the reaction mixture results in formation of the Tiron semiquinone(Tiron radical) ESR signal derived from O₂^–, and alsoinhibits ethylene production. The radical signal is oxygen-dependentand inhibited by SOD and catalase, but is formed both in thepresence and absence of ACC. Heat denaturation of the microsomalenzyme system completely blocks formation of the radical signal.The data collectively suggest that O₂^– generated by amembrane-bound enzyme facilitates the conversion of ACC to ethylene. (Received September 8, 1981; Accepted January 19, 1982)     

Reactive oxygen species as causative agents in the ichthyotoxicity of the red tide dinoflagellate Cochlodinium polykrikoides

The underlying toxic mechanisms of the red tide dinoflagellate,Cochlodinium polykrikoides, were studied with respect to thereactive oxygen species-mediated toxic effect. Cochlodiniumpolykrikoides generates superoxide anion (O₂^–) and hydrogenperoxide (H₂O₂), as measured by the cytochrome c reduction methodand scopoletin–peroxidase method, respectively. The capabilityof C.polykrikoides to generate these oxygen radicals was relatedto the growth phase: the highest rate in the exponential phaseand a gradual decrease in the stationary phase. Other phytoplankton,such as Eutreptiella gymnastica, Heterosigma akashiwo, Prorocentrummicans, Gymnodinium sanguineum and Alexandrium tamarense, alsoproduce H₂O₂; the rate of H₂O₂ generation by these species waslower than that of C.polykrikoides. The exposure of liposomalsamples to intact or ruptured individuals of C.polykrikoidesresulted in severe membrane damage, such as liposomal lipidperoxidation. Cochlodinium polykrikoides-induced lipid peroxidationwas significantly reduced by oxygen radical scavengers, superoxidedismutase, benzoquinone, catalase and mannitol. In addition,lipid peroxidation of gill tissue of flatfish exposed to C.polykrikoidesincreased with increasing algal cell density. These resultssuggest that reactive oxygen species generated from C.polykrikoidesare responsible for oxidative damage leading to fish kills.     

Effects of temperature and CO2 concentration on photosynthetic CO2 fixation by Chlorella

The rates of photosynthetic ¹⁴CO₂ fixation by Chlorella vulgarisllh, grown under high CO₂, were determined between 4 to 37°Cwith air containing from 300 to 13,000 ppm ¹⁴CO₂. When the CO₂level was increased, both the rate of photosynthesis and theoptimum temperature for maximum photosynthesis increased. Themaximum photosynthetic rate was reached at 12°C with 300ppm ^l4CO₂. Among the photosynthetic products fromed at 300 ppm ¹⁴CO₂, glycolatedecreased greatly when the temperature was raised from 20 to30°C. At 3,000 ppm ¹⁴CO₂ an insignificant amount of glycolatewas formed at all temperatures, whereas ¹⁴C-incorporation intothe insoluble fraction, sucrose, and the lipid fraction wassignificantly higher than at 300 ppm ¹⁴CO₂. The ¹⁴C in sucrosewas greatly increased and the radioactivity in the insolublefraction decreased when the temperature was raised from 28 to36°C. (Received April 8, 1980; )     

ABA Increases the Desiccation Tolerance of Photosynthesis in the Afromontane Understorey Moss Atrichum androgynum

The effect of pretreatment with abscisic acid (ABA) on the physiologyof the moss Atrichum androgynum during a desiccation–rehydrationcycle was examined. During rehydration following desiccationfor 16 h, net CO₂fixation recovered much more slowly than photosystemII (PSII) activity, conditions conducive to the formation ofreactive oxygen species (ROS) in the photosynthetic apparatus.Pretreatment with ABA increased the rate of recovery of photosynthesisand PSII activity, and also doubled non-photochemical quenching(NPQ). Increased NPQ activity will reduce ROS formation, andmay explain in part how ABA hardens the moss to desiccation.In ABA-pretreated, but not untreated mosses, desiccation significantlyincreased the concentration of soluble sugars. Sugar accumulationmay promote vitrification of the cytoplasm and protect membranesduring desiccation. Starch concentrations in freshly collectedA. androgynum were only approx. 40 mg g^-1dry mass; they roseslightly during desiccation but were only slightly affectedby ABA pretreatment. ABA did not reduce chlorophyll breakdownduring desiccation. Copyright 2001 Annals of Botany Company Moss, desiccation, abscisic acid, photosynthesis, chlorophyll fluorescence     

Photosynthetic and Photorespiratory Enzymes in Widely Divergent Plant Species with Special Reference to the Moss Ceratodon purpureus: Properties of Ribulose Bisphosphate Carboxylase/ Oxygenase, Phosphoenolpyruvate Carboxylase and Glycolate Oxidase

Rintamäki, E. and Aro, E.-M. 1985. Photosynthetic and photorespiratoryenzymes in widely divergent plant species with special referenceto the moss Ceratodon purpureus: Properties of ribulose bisphosphatecarboxylase/oxygenase, phosphoenolpyruvate carboxylase and glycolateoxidase.—J. exp. Bot. 36: 1677–1684. Km(CO₂) values and maximal velocities of ribulose bisphosphatecarboxylase/oxygenase (E.C. 4.1.1.39 [EC] ) were determined for sixplant species growing in the wild, consisting of a moss, a fernand four angiosperms. The maximum velocities of the RuBP carboxylasesvaried from 0.13 to 0.;62 µmol CO₂ fixed min^–1 mg^–1soluble protein and the Km(CO₂) values from 15 to 22 mmol m^–3CO₂. The highest Km(CO₂) values found were for the moss, Ceratodonpurpureus, and the grass, Deschampsia flexuosa. These plantsalso had the highest ratios of the activities of RuBP carboxylaseto RuBP oxygenase. Glycolate oxidase (E.C. 1.1.3.1 [EC] ) activitieswere slightly lower in D.flexuosa, but not in C. purpureus,than for typical C₃ species. Phosphoenolpyruvate carboxylase(E.C. 4.1.1.31 [EC] ) was not involved in the photosynthetic carboxylationby these two plants. However, another grass, Phragmites australis,was intermediate in PEP carboxylase activity between C₃ andC₄ plants The properties of RuBP carboxylase/oxygenase are discussedin relation to the activities of PEP carboxylase and glycolateoxidase and to the internal CO₂ concentration. Key words: RuBP carboxylase, oxygenase, Km(CO₂), moss     

The Role of Superoxide Dismutase in Regulating the Light Emission of Luminescent Fungi

Luminescent fungi spontaneously emit light during certain stagesof their life cycles. Most of them are luminous during a partof their mycelial stage, but not many of them are luminous whenthey form fruiting bodies. In the case of Panellus stipticus,both the mycelium and the fruiting body can be luminous, andthe emission of light takes place when its luciferin is aerobicallyoxidized in the presence of the superoxide anion (O₂) and acationic surfactant. It is highly likely that the luminescencereactions of all kinds of luminous fungi are basically the sameas that of P. stipticus. In order to determine the factor thatmakes a fungus luminous or non-luminous, we studied the relationsbetween the light emission of fungi at various growth stagesand the contents of luciferin, its precursor, superoxide dismutase(SOD), and catalase, on six species of luminescent fungi: Armillariellamellea, Mycena citricolor, Mycena lux-coeli, Omphlotus olearious,Panellus stipticus, and Pleurotus japonicus. The analysis ofthe data suggested that the fungi generally contain the componentsnecessary for light emission, but also contain very large amountsof SOD which destroy O₂^–. If an appreciable amount ofSOD is distributed at the site of light emission, the luminescencereaction is prevented. For the reaction to take place, it isessential that the SOD activity at the site is sufficientlylow or inhibited, despite the high content of SOD in the wholetissue. Thus, the level of SOD activity at the site of lightemission appears to be a limiting factor in regulating the luminescenceof fungi. Key words: Bioluminescence, chemiluminescence, luminous fungi, superoxide ion, superoxide dismutase     

Colocalization of glycolytic enzyme activity and KATP channels in basolateral membrane of Necturus enterocytes

⁸⁶Rb fluxes throughATP-regulated K⁺(K_ATP) channels in membranevesicles derived from basolateral membranes ofNecturus small intestinal epithelialcells as well as the activity of single K_ATP channels reconstituted intoplanar phospholipid bilayers are inhibited by the presence of ADPplus phosphoenolpyruvate in the solution bathingthe inner surface of these channels. This inhibition can be preventedby pretreatment of the membranes with 2,3-butanedione, an irreversibleinhibitor of pyruvate kinase (PK) and reversed by the addition of2-deoxyglucose plus hexokinase. The results of additional studiesindicate that PK activity appears to be tightly associated with thismembrane fraction. These results, together with considerations of thepossible ratio ofNa⁺-K⁺pumps to K_ATP channels in thebasolateral membrane, raise the possibility that "cross talk"between those channels and pumps (i.e., the "pump-leakparallelism") may be mediated by local, functionallycompartmentalized ATP-to-ADP ratios that differ from those in the bulk cytoplasm.