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The effect of oxygen and anaerobiosis on the redox properties of Cyt b559 was investigated in PSII preparations from spinach with different degree of disintegration of the donor side. Comparative studies were performed on intact PSII membranes and PSII membranes that were deprived of the 18-kDa peripheral subunit (0.25 NaCl washed), the 18- and 24-kDa peripheral subunits (1 M NaCl washed), the 18-, 24- and 33-kDa peripheral subunits (1.2 M CaCl2 washed), Cl depleted and after complete depletion of the Mn cluster (Tris washed). In active PSII centers, about 75% of Cyt b559 was found in the high-potential form and the rest in the intermediate potential form. With decomposition of the donor side, the intermediate potential form started to dominate, reaching more than 90% after Tris treatment. The oxygen-dependent conversion of the intermediate potential form of Cyt b559 into the low-potential and high-potential forms was only observed after treatments that directly affect the Mn cluster. In PSII membranes, deprived of all three extrinsic subunits (CaCl2 treatment), 21% of the intermediate potential form was converted into the low-potential form and 14% into the high-potential form by the removal of oxygen. In Tris-washed PSII membranes, completely lacking the Mn cluster, this conversion amounted to 60 and 33%, respectively. In intact PSII membranes, the oxygen-dependent conversion did not occur. The possible physiological role of this oxygen-dependent behavior of the Cyt b559 redox forms during the assembly/photoactivation cycle of PSII is discussed. [ABSTRACT FROM AUTHOR]

Gas production by Chlamydomonas moewusii in the light has been followed by manometric techniques during the adaptation to anaerobiosis. The only detectable gases produced are CO2 and H2 CO2 is produced at a rather constant rate whereas H2 evolution increase with time. This increase of H2 evolution during the adaptation period can be inhibited by cycloheximide and by chloral hydrate, two inhibitors of protein synthesis. If the inhibitors are added to already adapted cells there is no effect on H2 evolution. Adapted cell suspensions are sensitive to oxygen. Incubation under O2 for 10 min inhibits the H2 evolution to 100%. After removal of oxygen the capability to evolve H2 can be restored only by a new adaptation period. This second adaptation to H2 evolution can also be inhibited by cycloheximide. [ABSTRACT FROM AUTHOR]

Respiration was measured under anaerobiosis in the roots of two Senecio species: S. aquaticus Hill, which is flood-tolerant, and S. jacobaea L., which is flood-intolerant. NADH-oxidation under anaerobiosis was measured in roots of S. aquaticus, S. jacobaea and S. vulgaris L., which is also flood-intolerant. protein content of S. aquaticus was about 15% higher under anaerobiosis. At 20°C respiration of the roots of S. aquaticus was 50% inhibited under anaerobiosis, while an almost complete inhibition occurred in the roots of S. jacobaea. The activities of nitrate reductase, glutamate dehydrogenase and lactate dehydrogenase were considerably higher in the roots of S. aquaticus grown under anaerobic conditions. In S. jacobaea glutamate dehydrogenase activity was lower and in S. vulgaris nitrate reductase was lower and glutamate dehydrogenase activity was higher in roots grown under anaerobic conditions. The possible role of these enzymes for metabolism under anaerobic conditions by oxidizing a surplus of NADH is discussed. Since oxidative phosphorylation is 50% inhibited under anaerobiosis, ATP has to be generated in a different way. It is argued that maintenance of the ATP-level may be compensated by way of the enzymes mentioned above, in combination with a modified glucose utilization. [ABSTRACT FROM AUTHOR]

The frequency of glycolytic oscillations in yeast cells is only slightly modified by the consumption rate of either glucose or fructose, but it is reduced to 1/2 to 2/3 if the ketohexose is the only substrate. Phase relations between NADH, adenine nucleotides and sugar phosphates (O-6-P, F-6-P, FDP, DAP) are independent of the hexose fermented. With fructose as a substrate the amplitudes of adenylates and hexose phosphates are distinctly smaller than with glucose. The maximum of G-6-P is higher with glucose and the minimum concentration of FDP is higher with fructose. in the transition to anaerobiosis FDP, adenosine 5'-diphosphate and adenosine 5'-phosphate are extremely high, whereas G-6-P, F-6-P and. ATP concentrations are lower if fructose is the substrate fermented. The results are indicative for different control characteristics of the phosphofructokinase step,. but on their basis it cannot be distinguished between a direct interaction of fructose (or one of its derivatives) on the phosphofructokinase kinetics or the existence of a bypass for fructose which might be able to withdraw a part of the substrate from. the control point at the phospho-fructokinase. [ABSTRACT FROM AUTHOR]

Dark-gown shoots of tubers of the aquatic monocot Potamogeton pectinatus L elongated more strongly in anaerobic than aerobic solutions over 5 days. The response was located in the stem rather than the leaf Anaerobic carbon dioxide (CO2) production was similar to that in aerobic conditions. Approximately half the anaerobic stem extension was attributed to acidification of the submerging medium by respiratory CO2. Sparging with an anaerobic gas mixture of nitrogen and hydrogen to remove dissolved CO2 inhibited stem elongation and prevented acidification of the medium. Similarly supplying CO2 anaerobically promoted stem elongation while acidifying the medium Carbon dioxide was also active on aerobic shoots. The effect of CO2 on anaerobic stem extension could be mimicked with an acidic buffer. Anaerobic stem extension was inhibited by exogenous abscisic acid (ABA), while gibberellic acid and the gabberellin-biosynthesis inhibitor pacIobutrazol proved inactive. Exogenous indoIe-3-acetic acid promoted stem extension in the absence of oxygen. A strong gravitropic response by anaerobic stems of P. pectinatus was inhibited by the auxin-efflux inhibitor naphthylphthalamic acid. [ABSTRACT FROM AUTHOR]

Ethylene production of iris bulbs (Iris hollandica cv. Ideal) was very low. When stored at 30°C, production was 12-20 pmol C2H4 (kg fresh weight)-1 h-1. Higher temperatures (35°C, 40°C) enhanced the ethylene production; a treatment with 40°C for ca 7 days caused a 3 times higher ethylene production than at 30°C. During anaerobic storage (in 100% N2) ethylene production was equal to that of control bulbs. When after a 7 day period of anaerobiosis the N2 was replaced by air, a burstlike ethylene production was observed. Twenty-four h after the replacement, ethylene production was equal to control values again. The effects of this production of ethylene on mitochondrial respiration and flowering were investigated. When mitochondria were isolated immediately after the anaerobic treatment (before the enhanced ethylene production) alternative pathway capacity was not detectable, a situation also occurring in control bulbs. When mitochondria were isolated 24 h after the end of the anaerobiosis (after the ethylene burst) uninhibited respiration did not change significantly, but a capacity of the alternative pathway was observed. The increase in alternative pathway capacity after anaerobiosis was partly inhibited by 2,5-norbornadiene (NBD), an ethylene antagonist. Fermentation occurred during anaerobiosis: ethanol concentrations increased during the treatment and decreased when air was supplied. When bulbs were exposed to ethanol vapour the alternative pathway was induced but only when very high ethanol levels in the bulbs were reached. The amount of ethanol accumulated in the bulbs during a 7 day anaerobic treatment was far too low to explain the observed induction of alternative pathway capacity. Flowering percentages were enhanced after a 24 h treatment with ethylene and after a 7 day anaerobic treatment. NBD significantly inhibited the effect of exogenous ethylene and of anaerobiosis on flowering. Ethanol was not able to induce flowering. The burst-like production of ethylene after anaerobiosis probably is responsible for the effects on respiration and flowering. [ABSTRACT FROM AUTHOR]

Alcohol dehydrogenase (ADH; EC 1.1.1.1) activity was measured in Picea glauca (Moench) Voss cell suspensions under differing conditions of hypoxia. ADH activity increased 4.5 fold after 48 h of induction. When cells were induced under different levels of hypoxia (2,5 and 20% O2) changes in ADH activity were found to increase with lower levels of oxygen. Alanine aminotransferase (AlaAT; EC 2.6.1.2) activity increased under hypoxia in a pattern similar to ADH, however lactate dehydrogenase (LDH; EC 1.1.1.27) activity did not increase under hypoxic conditions. The ability of white spruce cells to accurately regulate heterologous anaerobic promotors was tested by electroporating chimeric ADH reporter genes into protoplasts. While protoplasts were capable of anaerobically regulating a maize ADH reporter construct, constructs with dicotyledonous promoters (pea and Arabidopsis) were not expressed. [ABSTRACT FROM AUTHOR]

Spartina alterniflora Lois. plants were grown under controlled sediment-pH-redox conditions. Uptake of added 15NH4-nitrogen and subsequent photosynthetic activity under different redox conditions in the plant root rhizosphere were measured. Data for total plant nitrogen and 15N concentration indicated that nitrogen allocation was not altered by anaerobic conditions of the sediment. However, average net photosynthesis was reduced by up to 35% for plants under anaerobiosis. The results indicate that anaerobiosis in the root rhizosphere, rather than limiting nitrogen uptake, influences photosynthesis and growth of S. alterniflora under anaerobic conditions. [ABSTRACT FROM AUTHOR]

Nickel and rubidium uptake by oat plants (Avena sativa L. cv. Victory) were examined in relation to solution temperature, solution concentrations, metabolic inhibitors, anaerobic root conditions, transpiration and time. Over a 4-h period, uptake rates for both Ni2+ and Rb* remained constant at 23°C. Decreasing temperatures to 2°C, 20 μM cuncentrations of 2,4-dinitrophenol (DNP), or anaerobic root conditions decreased Ni2+ and Rb+ uptake rates by 97 to 86% in whole plants. Treatment of excised roots with 20 μM DNP decreased Ni2+ uptake by 93%. Nickel and Rb+ uptake rates measured as a function of the external solution concentration followed a typical parabolic curve. Km, (0.012 mM) and Vmax [2.72 μmol (g dry weight)-1 h-1] values for Ni2+ were nearly 7 times lower than those for Rb+ [.09 mM and 19.2 μmol (g dry weight)-1 h-1. In all experiments, Ni2+ and Rb+ showed qualitatively similar uptake patterns, but Rb+ uptake was quantitatively more sensitive than Ni2+ to experimental manipulations. [ABSTRACT FROM AUTHOR]

Three‐week‐old sunflower plants (Helianthus annuus L. cv. Halcón) grown in nutrient solution at two K+ levels (0.3 and 2.5 mM) were used to study the effect of 4 μM abscisic acid (ABA) on the transport of K+ (Rb+) and water to the exuding stream of decapitated plants. Other conditions of the bathing medium of the roots were also assayed, such as presence of 10 mM glucose, aeration and time of ABA application. In the first 2 or 3 h after ABA application, ABA always promoted water and ion fluxes, even under the most unfavorable conditions such as low K+ roots without glucose or under anaerobiosis. The ABA‐promoting effect on ion and water flow was higher with glucose in the medium. Under anaerobiosis the ABA effect disappeared after 3 h. With glucose and aeration the ABA‐promoting effect appeared early and continued for several hours, although the effect decreased with time. If ABA was applied 24 h before excision, the effect was small or even negative. We suggest that ABA acts directly on membranes of certain root cells (endodermal or both endodermal and cortical cells) by increasing their permeability and thus releasing ions. This will decrease cell turgor pressure and, indirectly, the hydraulic conductivity of the whole root. Under conditions of higher hydraulic conductivity, the presence of ions and glucose in the root stimulates the transport of ions into the xylem. and thus increases the osmotic water flow.

Seedlings of pond pine (Pinus serotina Michx.), sand pine [P. clausa (Engelm.) Sarg.], and loblolly pine (P. taeda L., wet‐site and drought‐hardy seed sources) were grown in hydroponic solution culture using a non‐circulating, continuously flowing design under anaerobic or aerobic conditions to determine whether flooding tolerance was correlated with enhanced internal root aeration. Transport of atmospheric O2 from the shoot to the root of anaerobically grown loblolly and pond pine seedlings was demonstrated via rhizosphere oxidation, using both reduced indigo‐carmine solution and a polarographic, ensheathing Pt‐electrode. Stem and root collar lenticels were the major sites of atmospheric O2 entry for submerged roots in these seedlings. No O2 leakage was detected from roots of aerobically grown pine seedlings. Longitudinal and radial pathways for gaseous diffusion via intercellular air spaces in the pericycle and between ray parenchyma cells, respectively, were demonstrated histo‐logically in anaerobically grown loblolly and pond pines. Rhizosphere oxidation, and lenticel and aerenchyma development in roots of flood‐intolerant sand pine seedlings grown in anaerobic solutions were minimal. Only 15 days of anaerobic growth conditions were necessary to increase internal root porosities of loblolly and pond pine seedlings – although not to the extent found in seedlings treated for 30 or 75 days. Histological results indicated that root tissue in the secondary stage of growth was capable of forming intercellular air spaces, demonstrating a degree of internal plasticity – at least in the more flood‐tolerant loblolly and pond pine seedlings. [ABSTRACT FROM AUTHOR]

Fifteen or 30 days of anaerobic growth conditions significantly reduced shoot and root nitrogen, potassium, phosphorus, iron and manganese concentrations in seedlings of pond pine (Pinus serotina Michx.), sand pine [P. clausa (Engelm.) Sarg.] and drought‐hardy and wet‐site loblolly pine (P. taeda L.) grown in a culture system using non‐circulating, continuously flowing solution. Calcium and shoot magnesium levels were least affected by anaerobic growth conditions – largely reflecting the passive nature of their uptake. Shoot and root nutrient content (mg nutrient pot‐1) followed similar trends, with wet‐site loblolly and pond pine seedlings least affected by anaerobic solution culture. Shoot biomass of wet‐site loblolly and pond pine seedlings was not affected by anaerobiosis, suggesting an increase in shoot nutrient utilization efficiency. Root biomass was significantly reduced by 15 or 30 days of anaerobiosis, with sand pine exhibiting the largest reduction in root dry weight (57%). These results suggest that anaerobiosis interferes with net nutrient acquisition, even under the high nutrient conditions provided by solution culture. Sand pine suffered the largest reductions in shoot and root biomass and nutrient concentrations, showing earlier symptoms of waterlogging injury and nutrient stress than drought‐hardy loblolly pine seedlings. Whether net nutrient acquisition decreased because of the reduction in root surface area available for absorption and/or reduced uptake efficiency cannot be ascertained from these data. [ABSTRACT FROM AUTHOR]

The induction of secondary dormancy in caryopses of genetically pure dormant lines of Avena fatua L. is described. Seeds harvested from mature plants were after-ripened under controlled conditions (26°C, 25% relative humidity) until fully non-dormant. Secondary dormancy was then induced into these caryopses by incubation on moist filter papers in an aspirated nitrogen atmosphere at 20°C over periods from 3 h to 14 days. These caryopses failed to germinate when returned to an aerobic environment. The dose-response curves for gibberellic acid, sodium azide, sodium nitrite, sodium nitrate and ethanol show that all of these treatments can overcome the induced secondary dormancy. Drying increased the sensitivity of secondary dormant caryopses to these treatments. These treatments overcame secondary dormancy at all times, indicating the presence of only one of the two known blocks to germination that exist during primary dormancy. Similarities between primary and secondary dormancy in A. fatua are discussed. [ABSTRACT FROM AUTHOR]

Dormant embryos of Pyrus malus L. cv. Golden delicious, isolated from the fruits at harvest time or after a few months storage at 10 to 15°C. were kept under anaerobic conditions in order to eliminate primary dormancy. Germination tests were then carried out at different temperatures, using three modes of culture depending on the nature of the contact between the embryo and the medium. In CM the distal part of the two cotyledons was immersed in the medium. In RM only the embryonic axis was immersed. In C/2M the embryo was placed flat on the medium, the radicle and the external surface of one cotyledon being in contact with it. Results showed that primary dormancy was released progressively depending on the duration of the anaerobic treatment. After a treatment of 11 or 13 days the last symptoms of primary dormancy were only apparent when germination tests were carried out at high temperatures (26-30°C) or in CM mode of culture. When the embryos were kept at 4°C during 3 months inside the fruits, subsequent germination was inhibited at high temperature and in CM mode of culture. When the embryos were kept under anaerobic conditions (7 days) after the chilling treatment inside the fruits, germination was no longer inhibited. It is concluded that the inhibition of germination at high temperature and in CM mode of culture is due to the persistence of traces of primary dormancy. Therefore, these conditions do not seem to induce secondary dormancy in apple embryos. After elimination of primary dormancy by anaerobiosis. only application of (±) abscisic acid (3.8 and 19μM) inhibited germination. These results support the idea that ABA is an important factor in the induction of dormancy. However, the question remains whether this secondary embryo dormancy has the same characteristics as the original primary dormancy. [ABSTRACT FROM AUTHOR]

An in vivo assay method for nitrate reduction is proposed,based on the use of endogenous nitrate rather than on the accumulation of nitrite. Loss of endogenous nitrate and accumulation of nitrite were studied in barley (Hordeum vulgare L. cv. Gars Clipper ex Napier) leaves. Leaf sections were incubated in the dark in a gaseous environment of air or N2. Nitrate disappeared under both conditions, the highest loss being observed in tissue under anaerobiosis. Nitrite accumulated only in leaf sections under anaerobiosis, but the amount of nitrite accumulated was much lower than the amount of nitrate lost A comparative study of the capacity of barley leaf sections to use endogenous nitrate and accumulate nitrite showed that both activities were dependent on temperature in a manner characteristic of enzymatic reactions. Disappearance of endogenous nitrate increased with increasing levels of nitrate in the tissue. [ABSTRACT FROM AUTHOR]

Induction and release of secondary dormancy in genetically pure dormant (AN‐51, Mont 73) and non‐dormant (CS‐40, SH‐430) lines of wild oat (Avena fatua L.) were studied. These lines differed with regard to the optimal period of anaerobiosis necessary for induction of dormancy, and/or the degree (% of seeds acquiring dormancy) and duration of the dormancy induced. Secondary dormancy could be induced more effectively in the after‐ripened seeds of dormant lines than in the non‐dormant lines, where only a short‐term dormancy could be induced (in 5–7 week‐old‐seeds). Higher anaerobiosis temperatures were more effective in inducing dormancy in all lines studied. Thus, as with primary dormancy, wild oat biotypes exhibit genetic variability in their secondary dormancy behaviour and factors like temperature can modify the expression of this trait. The germination stimulants kinetin, isopentenyl adenine, sodium azide, potassium nitrate, ethanol and substituted phthalimides, which break primary dormancy in wild oats, stimulated germination of secondarily dormant seeds (line AN‐51). Since these chemicals are structurally diverse, primary and secondary dormancies appear to be similar in part in their regulation. Salicylhydroxamic acid, an inhibitor of cyanide‐insensitive (alternative) respiration, did not inhibit: 1, spontaneous release of secondary dormancy in the line SH‐430; and 2, stimulation of germination of secondarily dormant AN‐51 seeds by various chemicals (except azide), suggesting that this respiratory pathway is not necessary for the release of induced dormancy. [ABSTRACT FROM AUTHOR]

Solution culture experiments were designed to investigate the plant water relations of 3 Pyrus species subjected to root anaerobiosis. Root anaerobiosis induced partial stomatal closure prior to alterations in leaf water potential (ψLW) or root osmotic potential (ψRπ). In contrast, stomatal closure was accompanied by a decline in root hydraulic conductivity (Lp). Anoxia markedly reduced ψLW for Pyrus communis L. and eventually led to wilting and defoliation. Pyrus betulaefolia Bunge and Pyrus calleryana Decne, however, were less affected by root anaerobiosis. To delineate if the increased root resistance was in the radial or longitudinal direction, 10-4 M cistrans abscisic acid (ABA) was added to detopped root systems of P. communis in solution culture after steady-state rates of Lp were established. A consistent 25 to 30% promotion of Lp was observed 1.5 h after the addition of ABA for aerobically treated plants. ABA did not influence Lp when applied to roots previously deprived of O2 for 4 days. Additional evidence against the limiting resistance being in the radial direction was obtained when water fluxes were compared through intact P. communis roots, roots with all feeder roots detached., and stems without root systems. Severing feeder roots from anaerobically treated plants did not increase water flux to rates observed for aerobically treated plants. Resistance progressed basipetally to eventually encompass the stem itself. These results can only be explained by occlusion of the xylem vessels. [ABSTRACT FROM AUTHOR]

Energy charge, [(ATP + &frag12; ADP)/(ATP +ADP + AMP)], was measured in Echinochloa crus-galli (L.) Beauv. var. oryzicola seeds germinated in an aerobic or anaerobic environment. Within 24 h after the seeds were imbibed, total nucleotides increased and energy charge values went from 0.6 to at least 0.8 in both air and N2. Upon transfer from air to N2, the energy charge initially decreased, but subsequently (within 24 h) increased to at least 0.8. Total nucleotides also increased after an initial decline when transferred from air to N2. Emergence of the coleoptile and radicle were also examined at oxygen levels ranging from 21% to less than 0,005%. At all O2 levels, the time for 50% emergence of coleoptiles was less than for radicle emergence. This was most evident when the O2 concentration was 1% or less. These data indicate that one of the adaptations that allows E. crus-galli var. oryzicola to germinate and grow under anaerobic conditions is its ability to maintain a high level of energy, In its natural environment, this would permit coleoptile growth and penetration of the shoot into a more aerobic zone. [ABSTRACT FROM AUTHOR]

The usefulness of the nitrate‐free in vivo nitrate reductase assay for the study of nitrate pools in wheat leaves was investigated. Leaf sections from 7‐day‐old wheat seedlings, exposed 24 h before harvest to 1.5, 3.0 or 5.0 mM KNO3 were used. After 2 to 4 h of incubation nitrite production ceased, reaching a plateau. The time required to reach the plateau and the level of the plateau increased with increasing endogenous nitrate content. At nitrite plateau the amount of nitrate left in the tissue was independent of the original nitrate content in the tissue. Addition of nitrate at plateau caused resumed nitrite production. It is concluded that nitrate was the limiting factor in nitrite production. Oxygen inhibited nitrate reduction and stimulated further assimilation of nitrite. A considerable initial leakage of nitrate from tissue to the assay medium, followed by a slower continuous leakage, was observed throughout the incubation. N2‐flushing or inclusion of Triton X‐100 in the assay medium increased nitrite production by making more nitrate available for reduction. These treatments also increased the leakage of nitrate. At plateau levels the amount of nitrate left in the tissue was dependent on the oxygen tension in the assay medium. Under low oxygen tension nearly all nitrate in the tissue was available for reduction. Nitrite production at plateau is not a useful index for a metabolic nitrate pool and nitrate left in the tissue is not a useful index for a nitrate storage pool because both parameters are highly dependent on the oxygen tension in the assay medium. Further, in view of the considerable leakage, the nitrate‐free in vivo nitrate reductase assay cannot be used to detect two separate nitrate pools in wheat leaves. [ABSTRACT FROM AUTHOR]

A method for growing Fusarium oxysporum, a mycelial fungus, and a technique for its use in mineral uptake studies have been described. Some general characteristics of the uptake process were determined. The fungus, grown for 54 hours, was found to take up as much K as 15 to 20 meq/100 g dry weight in 2 to 4 hours from a solution of 5 meq/l KCl. Approximately 3 to 5 meq of this uptake was readily removed by a CaCl2 rinse. The uptake was only slightly sensitive to pH over the range of 4 to 9. Below pH 4 uptake dropped rapidly. The age of the culture appeared to be the dominant factor in determining the rate of uptake. In contrast to other fungi, the presence of glucose during uptake was detrimental to K uptake. Conditions unfavorable for metabolic activity as low temperature, anaerobiosis, or the presence of DNP markedly reduced the uptake rate. Although the fungus took up Na from single salt solutions nearly as well K, the latter ion was much preferred in mixtures of the two ions. The organism showed no significant metabolic uptake of Ca or Cl. During uptake from KCl solutions, the organic acid content increased. The increase, chiefly in succinic acid and to a lesser extent in acetic and citric acids, amounted to about half the K uptake. The remainder of the K taken up was correlated with a roughly equivalent efflux of cellular Mg. [ABSTRACT FROM AUTHOR]