Inhibitory Effects of Oxygen on the Germination of Oryza sativa L. Seeds

Some workers have reported that the breaking of seed dormancyin rice (O. sativa L.) is usually enhanced by higher oxygentension, whereas others have shown that rice seed dormancy canbe broken by incubation under anaerobic conditions. This articleaims to clarify this paradox. The results show that high oxygentensions inhibit seed germination for a certain period afterharvest in Japonica rice, whereas Indica rice cultivars arenot inhibited by oxygen at any stage. Oxygen inhibition, seed germination, aquatic plants, Japonica rice, Indica rice     

Comparison of Growth Responses of Barnyard Grass (Echinochloa oryzoides) and Rice (Oryza sativa) to Submergence, Ethylene, Carbon Dioxide and Oxygen Shortage

Unlike germination of wheat (Triticum aestivum), millet (Eleucinecoracana), and sorghum (Sorghum caudatum), that of Echinochloaoryzoides (barnyard grass) and Oryza satwa (rice) was not inhibitedby poorly aerated solutions with 11 k Pa oxygen (equilibriumpartial pressure) or less In the dark, seedling shoots of riceincluded a coleoptile, and in Echinochloa, a mesocotyl alsoGrowth in fresh and dry weight of shoots was strongly depressedby poorly aerated solutions in both rice and Echinochloa butthe effects on extension differed in the two species in rice,coleoptile extension was promoted by solutions partly depletedof oxygen, and also by the absence of oxygen The stimulationin partly de-oxygenated solutions resulted from the combinedpromoting effects of small oxygen partial pressures, carbondioxide, ethylene and buoyant tension in contrast, these treatmentsneither promoted nor inhibited elongation by the Echinochloacoleoptile while severely inhibiting extension of the mesocotyl Overall, poorly aerated solutions lengthened the shoot of riceand shortened it in Echinochloa when compared with those submergedin well-aerated solutions These opposite effects were broughtabout by the same gaseous changes, i e oxygen shortage, elevatedethylene and carbon dioxide The effect on Echinochloa was almostentirely restricted to the mesocotyl, coleoptile extension beingremarkably insensitive to large increases in ethylene and carbondioxide, or to extreme oxygen shortage Seedlings of the twospecies thus have contrasting strategies for survival Stress, submergence, ethylene, oxygen shortage, carbon dioxide, adaptation, anaerobiosis, rice (Oryza sativa L), barnyard grass [Echinochloa oryzoides (Ard) Fritseh]     

Life cycles of two limnetic cyclopoid copepods, Cyclops vicinus and Thermocyclops crassus, in two different habitats

The life cycles of Cyclops vicinus and Thermocyclops crassusin two shallow eutrophic habitats, Junsainuma and Naganuma Ponds,Hokkaido, Japan, were investigated. Both ponds exhibited similarseasonal patterns of temperature, oxygen levels and pH duringice-free periods; however, oxygen levels were extremely lowerunder the ice in Naganuma Pond. Cyclops vicinus showed differentlife cycles in the two ponds; in Junsainuma Pond, it reproducedin winter and spring (January-May) and entered diapause duringsummer and autumn (June-October) as copepodite IV stage, whileit reproduced in autumn (October-November) and spring (April-May),and entered diapause in summer (June-September) and winter (Januaryand February) as copepodite V stage in Naganuma Pond. Thermocyclopscrassus entered diapause during winter (December-April) as copepoditeIV and V stages in both ponds, and egg-bearing females appearedonly during the warmseason, from early May to late October,when water temperatures were >10°C. Summer diapause inC.vicinus was suggested to be an adaptation against fish predation,whereas C.vicinus entered winter diapause in Naganuma Pond probablyto avoid low oxygen levels. Thermocyclops crassus entered diapausein both ponds to avoid low water temperature. These resultssuggest that biotic and abiotic factors are important for leadingto specific life cycles of cyclopoid copepods in small waterbodies.     

Reactions of photosystems I and II in spinach chloroplast fragments treated with ethylene glycol

Photochemical reactions of chloroplast fragments isolated fromspinach leaves were measured in the presence of ethylene glycolor were measured after washing with an ethylene glycol-containingmedium. 2,6-Dichlorophenolindophenol (DPIP) photoreduction,oxygen evolution and oxygen uptake (a photosystem I reaction)were investigated in ethylene glycol-treated chloroplast fragments.By washing with ethylene glycol, oxygen evolution was stronglyinhibited, but oxygen uptake was not much affected by ethyleneglycol washing. Chloroplast fragments in 50% ethylene glycolmaintained a high rate of DPIP photoreduction (85% of the controlactivity in an ethylene glycol-less medium). In 67% ethyleneglycol, DPIP photoreduction mediated by photosystem II was eliminatedand only a small rapid reduction mediated by photosystem I wasobserved. Chloroplast fragments inhibited by ethylene glycolphotoreduced DPIP in the presence of p-aminophenol added asan artificial electron donor to photosystem II. The restoredactivity of DPIP photoreduction was inhibited by 3-(3',4'- dichlorophenyl)-1,1-dimethylurea. (Received September 8, 1970; )     

On the Nature of the Soaking Injury of Phaseolus vulgaris Seeds

Phaseolus vulgaris L. seeds are often killed or show signs ofsevere injury after they have been soaked in water for periodsexceeding a very few hours. But all ill effects can be largelyor completely prevented by any one of the following: (a) removingthe testa before or after soaking; (b) thorough or even partialdrying of the soaked seed; (c) draining the seed after cuttingoff its end portion; (d) treatment of the seed with hydrogenperoxide before, during, or after soaking. Air bubbled throughthe soaking water can aggravate the injury. By contrast, injuryfrom soaking can be prevented if oxygen has free access to theinterior of the seeds until they have imbibed about one-thirdof the water required for germination.It is suggested that,despite microbial complications at a later stage, the soakinginjury is caused at a critical early stage of germination bya deficient oxygen supply to the interior of the soaked seed,because during soaking the cavity between the cotyledons isflooded with an excess of water which remains trapped unlessforcibly removed.     

A comparison of net and gross rates of oxygen production as a function of light intensity in some natural plankton populations and in a Synechococcus culture

In vitrorates of gross and net oxygen production were measuredas a function of light intensity in some plankton communitiescollected from Bedford Basin, Nova Scotia, and in a monoclonalculture of Synechococcus. The rate of gross oxygen productionwas measured by a technique in which the stable oxygen isotope,¹⁸O, serves as a photosynthetic tracer Net oxygen productionwas measured by automated Winkler technique. The rate of communityrespiration in the light was then determined by the differencebetween gross and net rates of oxygen production. In the naturalpopulations examined, neither gross nor net oxygen productionrates were significantly inhibited at the highest light intensitymeasured (500–800 µE m^–2 s^–1) In a samplein which the dark respiration rate was small relative to themaximal rate of production [P_max;sensu Platt et al (1980) JMar. Res., 38, 687–701] the rates of ‘light’respiration were 3 times greater. In two other communities,with high rates of dark respiration relative to P_maxthe ratesof ‘light’ respiration were closer to rates of darkrespiration. In the Synechococcus clone, both gross and netoxygen production rates were inhibited at high light intensities.Rates of ‘light’ respiration were found to varyas a function of light intensity. The greatest rates of respirationwere measured in samples incubated at light intensities thatwere just saturating (100 µE m^–2 s^–1). Therates of ¹⁴C production were also measured as a function oflight intensity The photosynthetic quotients, based on ¹⁴C productionrates and gross oxygen production rates, average 1 9     

Methyl Viologen-Dependent Cyclic Electron Transport in Spinach Chloroplasts in the Absence of Oxygen

The methyl viologen (MV)-dependent, linear electron flow fromPS II to PS I was severely blocked in intact or broken, uncoupledchloroplasts when oxygen was removed from the suspension medium,as revealed by measurements of chlorophyll fluorescence andthe rate of photoreduction of MV. Kinetics of the reductionof pre-oxidized P700 by a saturating light pulse showed thatreduced MV in the absence of oxygen re-reduces P700⁺ via theintersystem electron transport chain. Since the re-reductionof P700⁺ was inhibited by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone,the MV-mediated cyclic electron flow, in contrast to the phenazinemethosulphate-catalyzed one, involves the plastoquinone pool.However, 2-n-heptyl-4-hydro-xyquinoline-N-oxide, 2-n-nonyl-4-hydroxyquinoline-N-oxideand antimycin A did not inhibit the MV-mediated flow. Thus,the inhibition of the linear electron flow in chloroplasts underanaerobic conditions suggested the overreduction of the plastoquinonepool as a result of the MV-mediated cyclic flow (Received February 13, 1990; Accepted March 31, 1990)     

Differential effects of oxygen on N2 fixation and C2H2 reduction by Anabaena cylindrica

Both nitrogen fixation and acetylene reduction by intact cellsof Anabaena cylindrica were inhibited by oxygen, but nitrogenfixation was invariably less sensitive than acetylene reduction.The C₂H₂/N₂ ratio ranged from 6 to 8 in the absence of oxygen,and it decreased with increase in partial pressure of oxygento 2 at a pO₂ of 0.3 atm. (Received June 5, 1979; )     

Changes in Light-Induced Electron Transfer Through Cytochrome b-563 Depending on the Oxidation-Reduction Conditions in Intact Cells of the Cyanobacterium Synechocystis PCC 6714

Flash-induced redox changes of cytochrome b-563 were studiedin intact cells of the cyanobacterium Synechocystis PCC 6714.The redox reactions of this cytochrome depended on the redoxstate of the electron transport system, as determined by a balancebetween the influx of electron from substrates and the effluxto molecular oxygen. Under aerobic conditions, flash-inducedchanges in cytbchrome b-563 were almost insignificant in thephotoheterotrophic cells grown in the presence of DCMU (0.1mM) and glucose (60 mM), whereas a rapid reduction of the cytochrome,followed by a re-oxidation, was clearly observed when the respiratoryoxidase was inhibited by KCN (1 mM). Under anaerobic conditions,when cytochrome b-563 was fully reduced in the dark, a prominentoxidation of the cytochrome was observed after a flash; thesubsequent re-reduction was very slow. The oxidation of cytochromeb-563 was inhibited by the addition of 2-heptyl-4-hydroxyquinolineN-oxide (HQNO). These results suggest that electron transferin the cytochrome bf complex occurs by a modified Q-cycle mechanism,the reaction sequence of which depends on the redox states ofcytochrome b-563 and plastoquinone. Flash-induced oxidationand reduction of cytochrome b-563 in cells grown under photoautotrophicconditions were less prominent, but the patterns of the reactionswere consistent with the suggested interpretation. (Received May 9, 1988; Accepted August 15, 1988)     

The Physiology and Nitrogen-fixing Capability of Aquatically and Terrestrially Grown Neptunia plena: The Importance of Nodule Oxygen Supply

The aquatic legume Neptunia plena (L.) Benth. was grown in non-aeratedwater culture or vermiculite. Growth, nodulation, nitrogen fixationand nodule physiology were investigated. Over an 80-d period,plants grew and fixed nitrogen and carbon equally well in bothrooting media, although distribution of growth between plantparts varied. Total nodule dry weights and volumes were similarbut vermiculite-grown plants had three times as many (smaller)nodules than those grown in water. Oxygen diffusion resistanceof nodules exposed to 21% oxygen and 10% acetylene did not differsignificantly. Both treatments showed similar declines in rootrespiration and acetylene reduction activity (approx. 10%) whenroot systems were exposed to stepped decreases and increasesin rhizosphere oxygen concentration. However, nitrogenase activityof aquatically grown plants was irreversibly inhibited by rapidexposure of nodules to ambient air, whereas vermiculite-grownplants were unaffected. Aeration of water-cultured N. plenareduced stem length (but not mass) and number of nodules perplant. The concentration of nitrogen fixation by 163%. PossibleO₂ transport pathways from the shoot atmosphere to roots andnodules are discussed. Aquatic legume, diffusion resistance, Neptunia plena, nitrogen fixation, oxygen, root nodules     

Polyamine Content and Action in Roots of Zea mays L. in Relation to Aerenchyma Development

Roots of Zea mays L. developed more aerenchyma (cortical gas-filledspace) when partially deficient in oxygen (3 kPa) than whensupplied with air (20·8 kPa oxygen) in association withfaster production of ethylene (ethene). The possibility wastested that the additional ethylene production resulted fromdecreases in spermidine (spd) and spermine (spm) which share,with ethylene, a common precursor, S-adenosylmethionine. However,no decreases in spd and spm were seen in root tissue up to 4d-old. Removing oxygen completely also had little effect onspd and spm, but strongly suppressed both ethylene productionand aerenchyma formation. Partial oxygen shortage (3 kPa) increased the concentrationof putrescine (put), the precursor of spd and spm. This increasewas not a response to the extra ethylene formed by such rootssince ethylene treatment did no reproduce the effect. Applicationof inhibitors of put biosynthesis, difluoromethylarginine anddifluoromethylornithine, led to increased aerenchyma formation.Exogenous put inhibited the development of aerenchyma whilestimulating rather than inhibiting ethylene production, whentested in either air or 3 kPa oxygen. Thus, put appears to limitaerenchyma formation by suppressing ethylene action rather thanits production.Copyright 1993, 1999 Academic Press Ethylene, ethene, roots, aerenchyma, polyamines, oxygen shortage, anaerobiosis, environmental stress, Zea mays     

Inhibition of nitrogenase activity and nodule oxygen permeability by water deficit

Short-term effects of water deficit on nitrogenase activitywere investigated with hydroponically grown soybean plants (Glycinemax L. Merr. cv. Biloxi) by adding polyethylene glycol (PEG)to the hydroponic solution and measuring nitrogenase activity,nodule respiration, and permeability to oxygen diffusion (P_o).These experiments showed a rapid decrease in acetylene reductionactivity (ARA) and nodule respiration. A consequence of thedecreased respiration rate was that P_o calculated by Fick'sLaw also decreased. However, these results following PEG treatmentwere in direct conflict with a previous report of stabilityin P_o determined by using an alternative technique. To resolvethis conflict, an hypothesis describing a sequence of responsesto the initial PEG treatment is presented. An important findingof this study was that the response to water deficit inducedby PEG occurred in two stages. The first stage of decreasednodule activity was O₂-limited and could be reversed by exposingthe nodules to elevated pO₂. The second stage which developedafter 24 h of exposure to PEG resulted in substantial loss innodule activity and this activity could not be recovered withincreased pO₂. Severe water deficit treatments disrupt noduleactivity to such a degree that O₂ is no longer the major limitation. Key words: Glycine max, N₂ fixation, soybean, oxygen permeability, water deficit     

Effect of Oxygen on Photosynthetic 14CO2 Fixation in Chroomonas sp. (Cryptophyta) III: Effect of Oxygen on Photosynthetic Carbon Metabolism

Photosynthetic carbon metabolism was studied with Chroomonassp. cells in which the rate of photosynthesis was inhibitedunder both an anaerobic condition and high concentrations ofoxygen. The time course of ¹⁴C-incorporation into photosyntheticproducts showed that 3-phosphoglycerate was the initial productof photosynthetic CO₂ fixation in Chroomonas sp. cells. During5-min photosynthesis, a considerable amount of ¹⁴C was incorporatedinto the insoluble fraction (mostly cryptomonad starch), andoxygen predominantly affected ¹⁴C-incorporation into this fraction.Although ¹⁴C-incorporation into intermediates of the photorespiratorypathway increased with increasing O₂ concentration, the amountswere much less than expected from the degree of oxygen inhibition.It is noteworthy that ¹⁴C-dihydroxyacetone phosphate accumulatedduring photosynthesis only under the anaerobic condition, whereasthe levels of the other phosphate esters were scarcely affectedby the oxygen concentration. Ribulose-1,5-bisphosphate carboxylase from Chroomonas sp. wascompetitively inhibited by oxygen, and its K_m(CO₂) value wassimilar to those of terrestrial C₃ plant enzymes. (Received November 19, 1984; Accepted May 20, 1985)     

Seed Dormancy in Acer pseudoplatanus L.: the Role of the Covering Structures

The present studies with Acer pseudoplatanus L. suggest thatthe covering structures play an important and multiple rolein the dormancy of the fruit. Whole fruits and seeds with thetesta intact required a period of chilling at 5 °C beforedormancy was broken whereas bare embryos germinated immediatelyat 20 °C without pretreatment. This suggested that dormancywas coat-imposed and that the testa was responsible for thiseffect. Germination of dormant seeds was inhibited by lightwhereas the non-dormant bare embryos showed little response.Studies on the manner in which the testa imposed dormancy onthe embryo indicated that restriction on oxygen uptake, wateruptake, mechanical restriction to embryo enlargement, and thepresence of germination inhibitors in the testa were not limitingfactors at this stage of dormancy. Results from leaching experimentssuggest that dormancy was the result of the restriction by thetesta of the outward diffusion of a germination inhibitor(s)present in the embryo. In seeds that had nearly completed theirstratification requirements, the covering structures seemedto act in a manner other than by preventing the leaching ofan inhibitor from the embryo. At this point the physical propertiesof the covering structures seem to determine any further delaysin germination by the mechanical restriction of embryo enlargementby the testa and by restriction of oxygen uptake by the pericarp.     

The Aeration of Catharanthus roseus L. G. Don Suspension Cultures in Airlift Bioreactors: The Inhibitory Effect at High Aeration Rates on Culture Growth

An investigation was carried out to examine the effect of aerationon the growth of Catharanthus roseus suspension cultures inairlift bioreactors. A high aeration rate (0·86 v.v.m.)was found to inhibit the growth of cultures. Venting culturesat a high rate with low oxygen content gas mixtures was equallyinhibitory to culture growth, showing that high aeration wasnot inhibitory as a result of oxygen toxicity. The dissolvedcarbon dioxide tension was found to be lower in cultures operatedat high aeration than those operated at low aeration. Supplyingexogenous CO₂ to cultures at high aeration restored the CO₂tension to values normally encountered at a low aeration rate,and was found to alleviate the inhibitory effects at high aeration.However, further increasing the CO₂ supply to cultures was foundto be severely inhibitory to growth. Therefore, the growth ofC. roseus cultures is very sensitive to dissolved CO₂ concentration,growth being inhibited at values either higher or lower thanan optimum. Key words: Aeration, carbon dioxide, Catharanthus roseus suspension culture     

Analysis of Rapid Light-Induced Potential Change in Cells of Chara corallina

Perfused Chara cells were used to measure the rapid light-inducedpotential change (rapid LPC) caused by activation of a K⁺ channelin the plasma membrane through photosynthesis in the presenceof various photosynthetic inhibitors. The rapid LPC was inhibitedby DCMU but recovered on addition of phenazinemethosulfate (PMS)in the presence of DCMU. Carbonylcyanide m-chlorophenylhydrazone(CCCP) stimulated the rapid LPC. DCCD partially inhibited therapid LPC with a partial inhibition of oxygen evolution. Itis concluded that both cyclic and noncyclic electron flows arecoupled with the rapid LPC. To understand the mechanism of K⁺ channel activation by photosyntheticelectron flow, the rapid LPC was measured under continuous internalperfusion. It was suggested that a diffusible substance wasnot released from chloroplasts, since vigorous continuous perfusiondid not inhibit the rapid LPC. The suggestion that the rapid LPC is caused by changes in surfacecharge density of chloroplasts was supported by the fact thatthe rapid LPC was inhibited by increasing the ionic strengthof the perfusion medium. (Received February 28, 1986; Accepted April 30, 1986)     

PHOTOCHEMICAL REDUCTION AND OXIDATION OF MENADIONE (VITAMIN K3) IN CHLOROPLASTS

1. Menadione (vitamin K³) was found to be completely reduced byilluminated spinach chloroplasts under highly anaerobic conditionand in the presence of ethylenediamine tetraacetate (EDTA) inthe reaction mixture. This photoreductive reaction is sensitivetoward heat-treatment and inhibited by 2?10^-3M hydroxylamine.
2. In the presence of oxygen, the reduced form of menadione israpidly photooxidized by chloroplasts. This photooxidative activityalso is suppressed by heat-treatment but not inhibited by hydroxylamine.
3. Dyes which are inefficient as HILL oxidants such as thionineand methylene blue were found to be readily reduced by illuminatedchloroplasts, if the experimental conditions were appropriateto prevent the reoxidation of the photoreduced dyes; i.e., exhaustiveremoval of oxygen and the addition of EDTA in the reaction mixture.Menadione was found to accelerate the HILL reaction with thesedyes as oxidant under such experimental conditions.
4. In thepresence of molecular oxygen in the reaction mixture,menadionewas found to inhibit the HILL reaction with 2,6–dichlorophenolindophenol as oxidant, while the reaction rate was little influencedin high anaerobiosis.
5. These findings are explained by theintermediary oxidation and(photo-) reduction of menadione asan intermediary hydrogencarrier, and by the trends toward rapidphotooxidation of reducedmenadione.

(Received July 2, 1960; )     

牛蒡L1-2组分对桔全爪螨的毒性和几种代谢酶的作用

【目的】探讨杀螨植物牛蒡Arctium lappa L.提取物中主要杀螨成分L1-2的杀螨作用机理。【方法】采用叶片浸渍法处理桔全爪螨Panonychus citri雌成螨后,测定了静止期、兴奋期、痉挛期、麻痹期、复苏和死亡期5个中毒阶段试虫体内几种代谢酶的活性。【结果】L1-2组分在静止期和复苏期对羧酸酯酶（carboxylesterase, CarE）具有一定的抑制作用,在其他时期均激活CarE活性。除了静止期外,在其他时期均能激活乙酰胆碱酯酶（acetylcholinesterase , AChE）和谷胱甘肽转移酶（glutathione S-transferases, GSTs）的活性,在痉挛期和麻痹期活性增强,随后在麻痹期和复苏期降低。【结论】L1-2组分对CarE的抑制与其毒杀活性有关,而中毒试虫的复苏可能与AChE和GSTs有关。该组分可在较长时期内影响桔全爪螨的神经传导及消化和生殖系统,具有潜在的应用研究价值。     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis I. Anatomy and Respiration in Triticum aestivum L.

Anatomical changes in roots of wheat seedlings (Triticum aestivumL. cv. Hatri) following oxygen deficiency in the rooting mediumwere investigated. The response of the plant to stress was testedat a very early developmental stage when the first adventitiousroots had just emerged. In order to analyze the adaptation ofdifferent roots, respiration rates of the roots 1–3 and4–n were compared with the respiration rates of the totalroot system. Oxygen deficiency was induced either by flushingnutrient solution with nitrogen or flooding of sand. In contrast to plants grown in well aerated media, both stressvariants led to a significant increase of the intercellularspace of the root cortex in seminal and first adventitious roots.Radial cell enlargement of cortical cells near the root tip,cell wall thickenings in flooded sand cultures and an increasein phloroglucinol-stainable substances were found to be furtherindicators of low oxygen supply. The roots 4–n which were promoted in growth under hypoxiashowed higher respiration rates; hence the total root respirationwas not restricted. Triticum aestivum L. cv. Hatri, wheat, roots, anatomy, anaerobiosis, stress, root respiration, intercellular space