Apoptosis recruits two-pore domain potassium channels used for homeostatic volume regulation

Cell shrinkage is an incipienthallmark of apoptosis and is accompanied by potassium releasethat decreases the concentration of intracellular potassium andregulates apoptotic progression. The plasma membrane K⁺channel recruited during apoptosis has not been characterized despite its importance as a potential therapeutic target. Here weprovide evidence that two-pore domain K⁺ (K_2P)channels underlie K⁺ efflux during apoptotic volumedecreases (AVD) in mouse embryos. These K_2P channels areinhibited by quinine but are not blocked by an array of pharmacologicalagents that antagonize other K⁺ channels. TheK_2P channels are uniquely suited to participate in theearly phases of apoptosis because they are not modulated bycommon intracellular messengers such as calcium, ATP, and arachidonic acid, transmembrane voltage, or the cytoskeleton. A K⁺channel with similar biophysical properties coordinates regulatory volume decreases (RVD) triggered by changing osmotic conditions. Wepropose that K_2P channels are the pathway by whichK⁺ effluxes during AVD and RVD and that apoptosisco-opts mechanisms more routinely employed for homeostatic cell volume regulation.

     

Lamprothamnium, a Euryhaline Charophyte: IV. MEMBRANE POTENTIAL, IONIC FLUXES AND METABOLIC ACTIVITY DURING TURGOR ADJUSTMENT

The early time-course of turgor adjustment following a hyper-or hypo-osomotic shock was examined in the brackish-water charophyteLamprothamnium papulosum. The response to a reduction in turgorwas a five to seven-fold stimulation of the influxes of Cl^–,K⁺ and Na⁺. The distribution of radioactive tracers in the cellsuggested that the ionic composition of the cytoplasm was strictlycontrolled during turgor adjustment. Metabolic activity wasrelatively unaffected by the loss of turgor. high fluxes throughthe cytoplasm, and a cytoplasmic K^– concentration possiblyas high as 280 mol m^–3. Osmotic adjustment to a lower salinity was achieved by largeincreases in the passive effluxes of K⁺ and Cl^– ratherthan by decreases in their influxes. The membrane remained hyperpolarized during hyperosmotic adjustmentbut depolarized after a hypo-osmotic change. This result isdiscussed in relation to changes in the driving forces for ionmovements during osmotic transitions. Key words: Lamprothamnium, Turgor, Osmotic stress     

测定潜流人工湿地根系生物量的新方法

设计了一种新方法研究潜流人工湿地植物根系的分布和生物量。采用自制的圆柱形的不锈钢网柱,安放在潜流湿地的碎石基质中,定期分层取出网柱内的碎石,可观察根系的分布特点;收获网柱内的根,可测定根系的生物量和生长量。网柱的直径20cm,高50cm,网孔直径1．80cm,不锈钢丝粗1．38mm。安装时,使网柱垂直,上端达碎石表面,下端靠近湿地床底。安装好后,装入碎石基质,观察测定时,把基质取出,观察完后,再把基质放回。用该方法,对碎石基质的潜流人工湿地中植物根系的分布和生物量进行了1a的实验测定,认为该方法是测定潜流人工湿地根系生长和分布的有效方法,它易于安装、测定方便、准确。7月和12月份两次测定的湿地根系生物量之和为331．8gm^-2,其中分布于0—5cm的根生物量为174．4gm^-2,5～15cm为142．1gm^-2,15cm以下为15．3gm^-2。种问根系生物量的差异很大,根系生物量最大的是美人蕉,为182．4gm^-2,最小的是水鬼蕉,为1．38gm^-2。根生物量似乎呈不同的季节格局,象草7月份根系生物量较大,而其他种12月份的较大。不同种根系生物量的垂直分布也有显著的差异,具根状茎的芦苇和较粗根的水鬼蕉以直径大于1mm的根为主,它们的根分布较深,而浅层根较少;象草、美人蕉和风车草,直径1mm以内的根占根生物量的80％以上甚至100％,它们的根分布较浅。     

Developmental Anatomy of the Leaf of L. Ficus religiosa

The leaves of Ficus religiosa show a more or less sigmoid growthpattern, and under the conditions prevailing in Delhi each leafincreases in size in 9 days from about 425 to 4025 mm²(as judgedby the average mature leaf size) after its emergence from thespathe. The leaf is hypostomatic and has paracytic and anomocyticstomata between polygonal epidermal cells. The frequency ofstomata per mm² increases from 33.3 to 400 and the number oflower epidermal cells decreases from about 11 300 to about 3040per mm² with the growth of the leaves while the number of upperepidermal cells decreases from 5600 to 1110. The vasculaturecomprises a single main vein (the mid rib), secondaries, tertiaries,quaternaries, and intermediaries. The number of areoles permm² decreases from 15.5 to 2.7 while the numbers of vein endingsand vein tips per areole show no correlation either with oneanother or with leaf size.     

Mechanism of the exercise hyperkalemia: an alternate hypothesis

Wasserman, Karlman, William W. Stringer, Richard Casaburi,and Yong-Yu Zhang. Mechanism of the exercisehyperkalemia: an alternate hypothesis. J. Appl.Physiol. 83(2): 631-643, 1997.A progressivehyperkalemia is observed as exercise intensity increases. The currentmost popular hypothesis for the hyperkalemia is that theNa⁺-K⁺pump cannot keep pace with the K⁺efflux from muscle during the depolarization-repolarization process ofthe sarcolemmal membrane during muscle contraction. In this report, wepresent data that suggest an alternate hypothesis to those previouslydescribed. Because phosphocreatine (PCr) is a highly dissociated acidand creatine is neutral at cell pH, the concentration of nondiffusibleanions decreases, and an alkaline reaction takes place when PCrhydrolyzes. This creates a state of cation(K⁺) excess andH⁺ depletion in the cell. Toexamine the balance of K⁺ andH⁺ for exercising muscle duringthe early period of exercise when PCr changes most rapidly, catheterswere inserted into the brachial artery and femoral vein (FV) in fivehealthy subjects who performed two 6-min cycle ergometer exercise testsat 40 and 85% of peak oxygen uptake. FV blood was sampled every 5 sduring the first 2 min, then every 30 s for the remaining 4 min ofexercise and the first 3 min of recovery, and then less frequently forthe next 12 min. Arterial sampling was every 30 s during exercise andsimultaneous with FV sampling during recovery. ArterialK⁺ concentration([K⁺]) increase laggedFV [K⁺]increase. The hyperkalemia observed during early exerciseresults from K⁺ release fromskeletal muscle. FV[K⁺] increased by 5 sof the start of exercise and followed the rate ofH⁺ loss from the FV blood for thefirst 30 s of exercise. FV lactate andNa⁺ kinetics differed fromK⁺ kinetics during exercise andrecovery. As predicted from the PCr hydrolysis reaction, the exercisinglimb took up H⁺ and releasedK⁺ at the start of exercise (first30 s) at both exercise intensities, resulting in a FV metabolicalkalosis. K⁺ release wasessentially complete by 3 min, the time at which oxygen uptake (and,presumably, PCr) reached its asymptote. These findings lead us tohypothesize that the early K⁺release by the cell takes place withH⁺ exchange and that the majormechanism for the exercise hyperkalemia is the reduction innondiffusible intracellular anions in the myocyte as PCr hydrolyzes.

     

The Elongation Rate of Wheat Leaves: I. ELONGATION RATES DURING DAY AND NIGHT

A measuring device is described with which it is possible torecord the elongation rate (in mm h^-1) of monocotyledonous leavesduring the whole growing period. By means of inductive displacementtransducers connected to a computer, the elongation rate isdetermined every 10 min during day and night for 3–8 d.A time period of 30 min proved to be suitable for calculatingthe elongation rate at any given moment. Shorter periods emphasizethe experimental error and longer time periods tend to concealsudden changes in the elongation rate. Elongation rate curvesof wheat leaves are presented. They revealed that the elongationrate. Elongation rate curves of wheat leaves are presented.They revealed that the elongation rates during the night periodwere significantly lower than during the day (approximately60–70% of the rates by day). This reduction is not causedby a reduction of the plant temperature. If the night periodwas extended, the elongation rate decreased almost to zero after14 h darkness. The length of this dark period until decreasebegins was dependent on the previous day's light intensity.The elongation rates of the 3rd wheat leaf under the given conditionswere for 5 d about 3 mm h^-1, and during the nights about 2 mmh^-1. During the 7th day, the elongation rate decreased and remainedzero from the 8th day onwards.     

Changes in mRNA of Vigna mungo Cotyledons during Seed Germination

Quantitative and qualitative changes of mRNA in Vigna mungocotyledons during seed germination have been investigated. TotalRNA is higher in dry cotyledons and declines during germination.Poly(A)⁺ RNA also is present at a relatively high level in drycotyledons, increases slightly during the first day of germination,and then decreases. Polysomal RNA is very low in dry cotyledonsbut increases rapidly during the first day of germination, andthen declines. The translational activity of the mRNA in a wheatgerm cell-free system is low on day 0 but increases rapidlyon day 1 of germination. Two-dimensional gel electrophoresisof in vitro translation products reveals that many new peptidesare synthesized on day 1 of germination. Synthesis of most ofthese polypeptides continue throughout 5 days of germination. Change in the mRNA population during germination has been investigatedusing cDNA against poly(A)⁺ RNA from 3-day-old cotyledons. Withtotal RNA of day 3 and 5, the cDNA strongly hybridized withRNA similar in size to 25 S ribosomal RNA, but no specific bandsare detected with samples of day 0 or 1. With poly(A)⁺ RNA ofday 5 or 1, the cDNA tends to hybridize with RNAs of relativelysmall molecular size. Cordycepin and -amanitin prevent the increasein poly (A)⁺ RNA content and the appearance of new mRNAs duringthe first day of germination. ¹Present address: Division of Regulation of Macromolecular Function,Institute for Protein Research, Suita City, Osaka 565, Japan. (Received January 13, 1986; Accepted June 10, 1986)     

Na+/Ca2+ exchange activity in neonatal rabbit ventricular myocytes

Much less is known about the contributions of the Na⁺/Ca²⁺ exchanger (NCX) and sarcoplasmic reticulum (SR) Ca²⁺ pump to cell relaxation in neonatal compared with adult mammalian ventricular myocytes. Based on both biochemical and molecular studies, there is evidence of a much higher density of NCX at birth that subsequently decreases during the next 2 wk of development. It has been hypothesized, therefore, that NCX plays a relatively more important role for cytosolic Ca²⁺ decline in neonates as well as, perhaps, a role in excitation-contraction coupling in reverse mode. We isolated neonatal ventricular myocytes from rabbits in four different age groups: 3, 6, 10, and 20 days of age. Using an amphotericin-perforated patch-clamp technique in fluo-3-loaded myocytes, we measured the caffeine-induced inward NCX current (I_NCX) and the Ca²⁺ transient. We found that the integral of I_NCX, an indicator of SR Ca²⁺ content, was greatest in myocytes from younger age groups when normalized by cell surface area and that it decreased with age. The velocity of Ca²⁺ extrusion by NCX (V_NCX) was linear with [Ca²⁺] and did not indicate saturation kinetics until [Ca²⁺] reached 1–3 µM for each age group. There was a significantly greater time delay between the peaks of I_NCX and the Ca²⁺ transient in myocytes from the youngest age groups. This observation could be related to structural differences in the subsarcolemmal microdomains as a function of age. ontogeny of cardiac excitation-contraction coupling; sodium/calcium exchanger; cytosolic calcium concentration; subsarcolemmal calcium concentration; sarcoplasmic reticulum calcium content     

STUDIES ON THE GROWTH OF FRUIT BODY OF FUNGI: III. OCCURRENCE, FORMATION AND DESTRUCTION OF INDOLE ACETIC ACID IN THE FRUIT BODY OF AGARICUS BISPORUS (LANGE) SING

Considerable amounts of auxin, mostly IAA, in acid and boundforms, occur in gills, pilei and stipes of the mushroom, Agaricusbisporus. Stipe elongation is not stimulated by applicationof IAA. The juice squeezed from the fruit body has an activity to convertL-tryptophan into IAA. This activity is not lost by heating.The substance(s) responsible for it passes through cellophane,and is insoluble in some organic solvents, such as petroleumether and benzene. The amount of IAA produced depends exactlyon the amount of the extraction residue used for the reaction.Since the activity decreases as thiosulfate is added increasingly,the active principle seems to be some strong oxidizing substance(s). ¹ This paper was read on October 25th, 1958, at the 23rd annualmeeting of the Botanical Society of Japan, held at Fukuoka,Japan. ² This investigation has been aided by a grant from the ROCKEFELLERFoundaion. ³ Present Address: J. W. GIBBS Research Laboratory, Departmentof Botany, Yale University. New Haven, Conn., U.S.A. (Received June 6, 1961; )     

A simple photometric device analysing cuticular transport physiology: surfactant effect on permeability of isolated cuticular membranes of Prunus laurocerasus L.

4-Nitrophenol permeabilities of astomatous cuticular membranesisolated from the upper surface of Prunus laurocerasus L. leaveswere measured applying a newly developed photometric device.Isolated cuticles were mounted between donor and receiver compartmentsof a stainless steel transport chamber. 4-Nitrophenol was appliedas non-dissociated species in citric buffer at pH 3.0 in thedonor compartment and sampled as dissociated species in thereceiver compartment in borate buffer at pH 9.0. Permeances,calculated from steady-state rates of 4-nitrophenol permeation,ranged from 1.73 10^–10 m s^–1 up to 38.410^–10ms^–1. They were in the same order of magnitude comparedto published permeances obtained with a different method usingradiolabelled 4-nitrophenol and isolated cuticles of Citrusaurantium L. In the presence of the surfactant Brij 30, whichis a polydisperse alcohol ethoxylate, cuticular permeabilitiesincreased on average by a factor of 37. Cuticles, initiallyhaving the lowest permeabilities, exhibited the highest increaseof their permeabilities due to the surfactant and vice versa.This increase ofcuticular permeabilities in the presence ofa surfactant is interpreted as a plasticizing effect of thesurfactant molecules on the cuticular wax forming the cuticulartransport barrier. Furthermore, surfactant-induced increasesof cuticular permeabilities were reversible to a large extent.Permeabilities decreased again after the removal of Brij 30reaching final values about 6-times higher compared to the initialpermeabilities. This demonstrates that the surfactant and thepermeating molecule must be present simultaneously in the cuticlein order to enhance cuticular permeation. Possible applicationsof this simple photometric device analysing further aspectsof cuticular transport physiology are finally suggested. Key words: Cuticular transport, leaf surface, permeability, plant cuticle, surfactant     

Water content, hydraulic conductivity, and ice formation in winter stems of Pinus contorta: a TDR case study

Stem water content, ice fraction, and losses in xylem conductivity were monitored from November 1996 to October 1997 in an even-aged stand of Pinus contorta (lodgepole pine) near Potlatch, Idaho, USA. A time domain reflectometry (TDR) probe was used to continuously monitor stem water contents and ice fractions. Stem sapwood water contents measured with TDR were not different from water contents measured gravimetrically. The liquid water content of stems ranged from 0.70 m³ m^-3 to 0.20 m³ m^-3 associated with freezing and thawing of the wood tissue. Ice fraction of the stem varied from 0-75% during the winter suggesting liquid water was always present even at ambient temperatures below -20°C. Shoot xylem tensions decreased through the winter to a minimum of ca. -1.4 MPa in February then increased to -0.4 MPa in May. Shoot xylem tensions decreased during the growing season reaching -1.7 MPa by September. Annually, low shoot water potentials were not correlated to decreases in stem hydraulic conductivity. Xylem conductivity decreased due to cavitation through the winter and was 70% of summer values by March. Decreases in xylem conductivity were correlated to low shoot water potentials and cumulative freezing and thawing events within the xylem. Xylem conductivity increased to pre-winter values by May and no reductions in xylem conductivity were observed during the growing season.     

Intracellular pH and Proton-Transport in Barley Root Cells under Salt Stress: in Vivo 31P-NMR Study

Salt stress-induced changes of intracellular pH and in levelsof phosphorous compounds were monitored in intact root tipsof barley seedlings (Hordeum vulgare cv. Akashin-riki) by invivo ³¹P-nuclear magnetic resonance (NMR) spectroscopy. Vacuolaralkalization was observed after treatment with both 300 and500 mM NaCl. Much of the observed apparent alkalization of thecytoplasm was eliminated when the effect of Na⁺ ions on thetitration curve was considered. Within 1 h after the initiationof salt stress, levels of glucose-6-phosphate and UDP-glucosedecreased markedly, and such decreases might lead directly orindirectly to cell death. Simultaneous measurements of the externaland intracellular pH revealed the promotion of external acidificationand internal alkalization during salt stress. Possible mechanismsof Na⁺/H⁺ antiport at the tonoplast and the role of proton-pumpin the plasma membrane are discussed. ³Present address: Shijonawate Gakuen Women's Junior College,Daito, Osaka, 574 Japan.     

Conductometric Method for Detecting Ion Efflux during a Single Action Potential of Chara

A simple device was developed to detect net ion efflux duringa single action potential of Chara as an increase in the electricconductance of the bathing solution. The device showed a sufficientlyhigh sensitivity and rapid response to the increase in the electricconductance. Net efflux of monovalent ions was estimated as65–660 pmol cm^–2 impluse^–1 (average 220 pmolcm^–2 impulse^–1). (Received June 28, 1985; Accepted November 13, 1985)     

The Effect of pH on the Binding of Calcium to Pea Epicotyl Cell Walls and its Implications for the Control of Cell Extension

Cell walls were prepared from the epicotyls of dark-grown pea(Pisum sativum L.) seedlings. The walls were found to bind externally-added⁴⁵Ca²⁺, with a binding constant of 4 ? 10^–4 mol dm^–3and a maximum capacity of 1.5 ? 10^–8 g-ions of Ca²⁺ perg fresh weight of epicotyl. The binding capacity decreased asthe pH of the medium was decreased below 6.0, suggesting thatthe calcium was bound by an anionic group with an apparent pKof 4.7. More than half the calcium binding was due to polygalacturonicacid in the wall, since up to 60% of the calcium binding capacitywas removed by pre-incubation of the cell walls with polygalacturonase(E.C.3.2.1.15). Only small decreases in calcium binding wereseen following pre-incubation with protease, nucleases, phospholipaseand hemicellulase. These results indicate that calcium willbe displaced from the cell wall at hydrogen ion concentrationswhich are known to occur in the wall during wall extension.They are consistent with a mechanism by which calcium inhibitswall extension by forming ionic bridges between polygalacturonicacid molecules, and also with the hypothesis that calcium andhydrogen ions exert opposing influences on cell wall extensionby competing for the same binding sites on the polygalacturonicacid. Key words: Pea epicotyl, Cell wall, Calcium, pH     

Carbon isotope discrimination in photosynthetic bark

We developed and tested a theoretical model describing carbon isotope discrimination during photosynthesis in tree bark. Bark photosynthesis reduces losses of respired CO₂ from the underlying stem. As a consequence, the isotopic composition of source CO₂ and the CO₂ concentration around the chloroplasts are quite different from those of photosynthesizing leaves. We found three lines of evidence that bark photosynthesis discriminates against ¹³C. First, in bark of Populus tremuloides, the '¹³C of CO₂ efflux increased from -24.2‰ in darkness to -15.8‰ in the light. In Pinus monticola, the '¹³C of CO₂ efflux increased from -27.7‰ in darkness to -10.2‰ in the light. Observed increases in '¹³C were generally in good agreement with predictions from the theoretical model. Second, we found that '¹³C of dark-respired CO₂ decreased following 2-3 h of illumination (P<0.01 for Populus tremuloides, P<0.001 for Pinus monticola). These decreases suggest that refixed photosynthate rapidly mixes into the respiratory substrate pool. Third, a field experiment demonstrated that bark photosynthesis influenced whole-tissue '¹³C. Long-term light exclusion caused a localized increase in the '¹³C of whole bark and current-year wood in branches of P. monticola (P<0.001 and P<0.0001, respectively). Thus bark photosynthesis was shown to discriminate against ¹³C and create a pool of photosynthate isotopically lighter than the dark respiratory pool in all three experiments. Failure to account for discrimination during bark photosynthesis could interfere with interpretation of the '¹³C in woody tissues or in woody-tissue respiration.     

Polyamine Content in Relation to Embryo Growth and Dedifferentiation in Barley (Hordeum vulgare L.)

Putrescine, spermidine, and spermine content were analysed inzygotic embryos of barley (Hordeum vulgare L.). Changes in polyaminecontent were observed during zygotic embryo growth. In two cultivars,‘Bomi’ and ‘Golden Promise’, the totalpolyamine content in the embryos was 2.6–2.9 nmol mg^–1fresh weight 10 d after anthesis, the highest content observed.It dropped to 1.3 nmol mg^–1 fresh weight 14 d after anthesis.This drop was caused by decreases in all three polyamine concentrations.From 14 to 35 d after anthesis the putrescine content continuedto decrease while the spermidine and spermine content increased,thus the total polyamine content remained constant until 35d after anthesis. The mutant ‘Ris? 1508’ showeda constant polyamine content around 1.3 nmol mg^–1 freshweight from 14 to 35 d after anthesis. The polyamine patternwas conserved in all three lines throughout the period of investigationshowing a spermidine content higher than putrescine contentwhich was, in turn, higher or equal to the spermine content.The polyamine content measured as nmol µg^–1 proteindecreased from 14 to 21 d post anthesis in all three lines,because the protein content (µg mg^–1 fresh weight)increased during the period. In dedifferentiating zygotic embryoscultured in vitro the putrescine content (nmol mg^–1 freshweight) rose by a factor of nine and the spermidine contentdoubled within the first week of cultivation, whereas sperminecontent did not change. For embryoderived calli a repeated patternof change in polyamine content was observed throughout the subculturingperiod. Key words: Polyamines, Hordeum vulgare L., embryo development     

Cytosolic potassium controls CFTR deactivation in human sweat duct

Absorptive epithelial cells must admit large quantities of salt (NaCl) during the transport process. How these cells avoid swelling to protect functional integrity in the face of massive salt influx is a fundamental, unresolved problem. A special preparation of the human sweat duct provides critical insights into this crucial issue. We now show that negative feedback control of apical salt influx by regulating the cystic fibrosis transmembrane conductance regulator (CFTR) Cl^– channel activity is key to this protection. As part of this control process, we report a new physiological role of K⁺ in intracellular signaling and provide the first direct evidence of acute in vivo regulation of CFTR dephosphorylation activity. We show that cytosolic K⁺ concentration ([K⁺]_c) declines as a function of increasing cellular NaCl content at the onset of absorptive activity. Declining [K⁺]_c cause parallel deactivation of CFTR by dephosphorylation, thereby limiting apical influx of Cl^– (and its co-ion Na⁺) until [K⁺]_c is stabilized. We surmise that [K⁺]_c stabilizes when Na⁺ influx decreases to a level equal to its efflux through the basolateral Na⁺-K⁺ pump thereby preventing disruptive changes in cell volume. electrolytes; phosphatases; protein kinase A; cystic fibrosis transmembrane conductance regulator; epithelial Na⁺ channel     

Effects of organ culture on arterial gene expression and hypoxic relaxation: role of the ryanodine receptor

Organ culturespecifically inhibits vasorelaxation to acute hypoxia andpreferentially decreases specific voltage-dependent K⁺channel expression over other K⁺ and Ca²⁺channel subtypes. To isolate further potential oxygen-sensing mechanisms correlated with altered gene expression, we performed differential display analysis on RNA isolated from control and culturedcoronary arterial rings. We hypothesize that organ culture results inaltered gene expression important for vascular smooth musclecontractility important to the mechanism of hypoxia-induced relaxation.Our results indicate a milieu of changes suggesting both up- anddownregulation of several genes. The altered expression pattern of twopositive clones was verified by Northern analysis. Subsequent screeningof a porcine cDNA library indicated homology to the ryanodine receptor(RyR). RT-PCR using specific primers to the three subtypes of RyR showsan upregulation of RyR2 and RyR3 after organ culture. Additionally, thecaffeine- and/or ryanodine-sensitive intracellular Ca²⁺store was significantly more responsive to caffeine activation afterorgan culture. Our data indicate that organ culture increases expression of specific RyR subtypes and inhibits hypoxicvasorelaxation. Importantly, ryanodine blunted hypoxic relaxation incontrol coronary arteries, suggesting that upregulated RyR might play anovel role in altered intracellular Ca²⁺ handling during hypoxia.

     

Response of Wheat Seedlings to Low O2 Concentrations in Nutrient Solution: II. K +/Na+ SELECTIVITY OF ROOT TISSUES9

This paper reports the effects of low O₂ concentration (0–01,0–055, and 0.115mol m^–3) in nutrient solutions onK⁺/Na⁺ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O₂ uptake,K⁺ uptake and K⁺/Na⁺ selectivity were all more pronounced and/oroccurred at higher external O₂ concentrations in the apex (0–2mm) than in the expanding tissues (2–4 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (4–12 mm). Selectivity for K⁺ over Na⁺ in roots and shoots was particularlysensitive to O₂ deficiency. For example, in apical tissues (0–2mm) K ⁺ /Na⁺ selectivity was already reduced at 0.115 mol m^–3O₂, yet at this O₂ concentration there was no effect on eithergrowth or (K⁺/Na⁺) uptake. Upon transfer from 0.01 to 0.26 mol m^–3 O₂, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K⁺ + Na⁺) concentrations and K⁺/^Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K⁺ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K⁺/Na⁺ selectivity, expanded and expanding tissues     

Effects of Gamma-Irradiation on the Activity of Tonoplast H+-ATPase from Potato Tubers (Solanum tuberosum L.)

Tonoplast vesicles were prepared from potato tubers (Solariumtuberosum L.) on a step gradient (0% and 6%, w/w) of dextranT-70 to clarify the mechanism by which the tonoplast H⁺-ATPaseis inactivated by gamma-irradiation. H⁺-ATPase activity andH⁺ -pumping were examined after irradiation of tubers (in vivoirradiation) and of isolated tonoplast vesicles (in vitro irradiation)at doses up to 1.0 kGy. Both in vivo irradiation and in vitroirradiation resulted in significant decreases in ATPase andH⁺-pumping activities. The ATPase and H⁺-pumping activities12 h after irradiation were much lower than those 2 h afterirradiation. Solubilized H⁺-ATPase was inactivated, in a dose-dependentmanner, by irradiation (enzyme irradiation) to a greater extentthan was observed after in vitro irradiation or in vivo irradiation.The activity of ATPase 12 h after enzyme irradiation was almostthe same as it was 2 h after enzyme irradiation. The free fattyacid content of vacuolar membranes was increased by in vivoirradiation and by in vitro irradiation with an accompanyingdecrease in tonoplast H⁺-ATPase activity. Lipids from irradiatedtonoplasts had a considerable inhibitory effect on the activityof solubilized H⁺-ATPase. This result suggests that the directinactivation of H⁺-ATPase in potato tonoplast by gamma-irradiationis augmented by the effects of deterioration of membrane lipidsthat is induced by the irradiation. (Received December 21, 1994; Accepted May 16, 1994)