Kinetics of ethanol and acetaldehyde release suggest a role for acetaldehyde production in tolerance of rice seedlings to micro-aerobic conditions

BACKGROUND AND AIMS: This paper examines the basis of the greater tolerance of an indica rice cultivar FR13A to complete submergence compared with relatively intolerant japonica rice CT6241. We study whether this superior tolerance is related to its greater tolerance to O2 shortage and to an ability to run a more favourable rate of alcoholic fermentation during and after O2 deprivation. METHODS Fermentation products were analysed using sensitive laser-based photoacoustics at high time resolution to establish patterns and rates of ethanol and acetaldehyde emission by intact rice seedlings exposed to micro-aerobic (0.05-0.5 % O2) or zero O2 supply, and also during their return to air. Oxygen and CO2 emission or uptake was also quantified. KEY RESULTS: In the dark, no acetaldehyde and ethanol emission was observed until external O2 concentration in a gas phase decreased to 相似文献   

Organ-specific analysis of the anaerobic primary metabolism in rice and wheat seedlings. I: Dark ethanol production is dominated by the shoots

During anaerobiosis in darkness the main route for ATP production in plants is through glycolysis in combination with fermentation. We compared the organ-specific anaerobic fermentation of flooding-tolerant rice (Oryza sativa) and sensitive wheat (Triticum aestivum) seedlings. A sensitive laser-based photoacoustic trace gas detection system was used to monitor emission of ethanol and acetaldehyde by roots and shoots of intact seedlings. Dark-incubated rice seedlings released 3 times more acetaldehyde and 14 times more ethanol than wheat seedlings during anaerobiosis. Ninety percent of acetaldehyde originated from shoots of both species. In comparison to wheat shoots, the high ethanol production of rice shoots correlated with larger amounts of soluble carbohydrates, and higher activities of fermentative enzymes. After 24 h of anaerobiosis in darkness rice shoots still contained 30% of aerated ATP level, which enabled seedlings to survive this period. In contrast, ATP content declined almost to zero in wheat shoots and roots, which were irreversibly damaged after a 24-h anaerobic period. When plants were anaerobically and dark incubated for 4 h and subsequently transferred back to aeration, shoots showed a transient peak of acetaldehyde release indicating prompt re-oxidation of ethanol. Post-anoxic acetaldehyde production was lower in rice seedlings than in wheat. This observation accounts for a more effective acetaldehyde detoxification system in rice. Compared to wheat the greater tolerance of rice seedlings to transient anaerobic periods is explained by a faster fermentation rate of their shoots allowing a sufficient ATP production and an efficient suppression of toxic acetaldehyde formation in the early re-aeration period.Angelika Mustroph and Elena I. Boamfa contributed equally to the paper.     

Relationship between Coleoptile Elongation and Alcoholic Fermentation in Rice Exposed to Anoxia. II. Cultivar Differences

The relationship between coleoptile elongation and survivalvs. alcoholic fermentation of rice under anoxia is examinedusing eight cultivars differing in submergence tolerance. Anoxiawas imposed on either 1 or 4 d aerated seeds either by N₂ flushingsubmerged tissues or by incubating tissues in stagnant deoxygenatedagar at 0·1% w/v; the latter simulated the stagnant conditionsof waterlogged soil. Two cultivars that were most tolerant tosubmergence also had the greatest tolerance to anoxia, whilea submergence intolerant cultivar was also intolerant to anoxia. Coleoptile growth under anoxia was related to rates of ethanolsynthesis (R_E), however differences between growth during anoxiaand survival after anoxia indicated that post-anoxic injurymay also be important in rice seeds exposed to anoxia. The correlationbetween coleoptile growth and R_E measured on a tissue basisusing intact seeds was r² = 0·67 among six varietiesover 0-3 d anoxia. This correlation improved to about r² = 0·85using R_E of (embryos plus coleoptiles) over 0-3 d, or coleoptilesat 3 d after anoxia. Coleoptile growth of individual seeds wasusually poorly correlated to R_E in these cultivars at 2-3 dafter anoxia. When coleoptiles of similar lengths were obtainedfrom different cultivars using 4 d aerated seeds, there weredifferences in R_E and coleoptile growth which were related tocoleoptile growth during 3 or 5 d anoxia, either on a tissue(r² = 0·85) or a fresh weight basis (r² = 0·70-0·97respectively). Results are discussed in relation to factorswhich may limit ethanol synthesis in rice exposed to anoxiaand the importance of growth to the survival of seeds and matureplants during submergence in the natural environment.Copyright1994, 1999 Academic Press Anoxia, ethanol, alcoholic fermentation, Oryza sativa L., rice, submergence     

Patterns of peroxidative ethane emission from submerged rice seedlings indicate that damage from reactive oxygen species takes place during submergence and is not necessarily a post-anoxic phenomenon

Using ethane as a marker for peroxidative damage to membranes by reactive oxygen species (ROS) we examined the injury of rice seedlings during submergence in the dark. It is often expressed that membrane injury from ROS is a post-submergence phenomenon occurring when oxygen is re-introduced after submergence-induced anoxia. We found that ethane production, from rice seedlings submerged for 24–72 h, was stimulated to 4–37 nl gFW⁻¹, indicating underwater membrane peroxidation. When examined a week later the seedlings were damaged or had died. On de-submergence in air, ethane production rates rose sharply, but fell back to less than 0.1 nl gFW⁻¹ h⁻¹ after 2 h. We compared submergence-susceptible and submergence-tolerant cultivars, submergence starting in the morning (more damage) and in the afternoon (less damage) and investigated different submergence durations. The seedlings showed extensive fatality whenever total ethane emission exceeded about 15 nl gFW⁻¹. Smaller amounts of ethane emission were linked to less extensive injury to leaves. Partial oxygen shortage (O₂ levels <1%) imposed for 2 h in gas phase mixtures also stimulated ethane production. In contrast, seedlings under anaerobic gas phase conditions produced no ethane until re-aerated: then a small peak was observed followed by a low, steady ethane production. We conclude that damage during submergence is not associated with extensive anoxia. Instead, injury is linked to membrane peroxidation in seedlings that are partially oxygen deficient while submerged. On return to air, further peroxidation is suppressed within about 2 h indicating effective control of ROS production not evident during submergence itself.     

Injury to Rice Plants Caused by Complete Submergence; A Contribution by Ethylerie (Ethene)

Complete submergence of rice plants (Oryza sativa L. cv. ‘IR42’)in dilute nutrient solution for 3–6 d almost stopped theaccumulation of dry matter, depressed soluble carbohydrate concentrationby over 75% and promoted chlorosis in fully expanded leaves.Increase in fresh weight by the shoots was not impaired. Extensionby the youngest visible leaf was stimulated. Extension by thenext leaf to appear was retarded by submergence. These growthresponses to submergence were associated with a 1-5-fold increasein the partial pressure of endogenous ethylene (ethene). Applying ethylene (0.3–0.35 Pa) in the gas-phase to non-submergedplants reproduced some, but not all, of these effects of submergence.Thus, greater leaf extension and chlorosis of submerged plantscould be attributable to accumulated ethylene but neither theslow relative growth rate nor the decreased extension of leavesemerging after the start of submergence could be so attributed. Two cultivars (‘FR13A’ and ‘Kurkaruppan’)already known to tolerate submergence, differed little fromsubmergence-intolerant ‘IR42’ in their relativegrowth rate and soluble carbohydrate concentration during submergence.However, their underwater leaf extension was less than in ‘IR42’and chlorosis was much less prevalent, especially in ‘FR13A’.Similarly, ethylene supplied to non-submerged plants was a lesseffective promotor of leaf extension and chlorosis in the twosubmergence tolerant cultivars. Application of 1.0 kPa carbondioxide in the gas-phase prevented the chlorosis response toethylene. The results indicate that accumulated ethylene is a likely causeof fast leaf extension and chlorosis in submergence intolerantforms of rice, particularly when amounts of dissolved carbondioxide are minimal. Key words: Oryza sativa L., aeration, ethylene (ethene), stress-tolerance     

The Sensitivity of Net Photosynthesis in Several Plant Species to Short-term Fumigation with Sulphur Dioxide

The effects of exposure of up to 2 h with sulphur dioxide ona range of plant species was observed by measuring changes inthe rate of net photosynthesis under closely controlled environmentalconditions. Ryegrass, Lolium perenne ‘S23’ was thespecies most sensitive to SO₂; significant inhibition was detectedat 200 nl l^–1. Fumigations at 300 nl l^–1 also inhibitedphotosynthesis in field bean (Vicia faba cv. ‘Three FoldWhite’ and ‘Blaze’) and in barley (Hordeumvulgare cv. ‘Sonja’). No effect was detected inwheat (Triticum aestivum cv. ‘Virtue’) at concentrationsup to 600 nl l^–1 SO₂, or in oil-seed rape (Brassica napuscv. ‘Rafal’) except at 800 nl l^–1 SO₂). Recoverycommenced immediately after the fumigation was terminated andwas complete within 2 h when inhibition had not exceeded 20%during the SO₂ treatment. Key words: Sulphur dioxide, short-term fumigation, photosynthesis     

Physiological and Molecular Basis of Susceptibility and Tolerance of Rice Plants to Complete Submergence

Rice plants are much damaged by several days of total submergence.The effect can be a serious problem for rice farmers in therainfed lowlands of Asia, and runs contrary to a widespreadbelief amongst plant biologists that rice is highly tolerantof submergence. This article assesses the characteristics ofthe underwater environment that may damage rice plants, examinesvarious physiological mechanisms of injury, and reviews recentprogress achieved using linkage mapping to locate quantitativetraits loci (QTL) for tolerance inherited from a submergence-tolerantcultivar FR13A. Progress towards identifying the gene(s) involvedthrough physical mapping of a dominant tolerance locus on chromosome9 is also summarized. Available physiological evidence pointsaway from responses to oxygen shortage as being inextricablyinvolved in submergence injury. An imbalance between productionand consumption of assimilates is seen as being especially harmful,and is exacerbated by strongly accelerated leaf extension andleaf senescence that are ethylene-mediated and largely absentfrom FR13A and related cultivars. DNA markers for a major QTLfor tolerance are shown to be potentially useful in breedingprogrammes designed to improve submergence tolerance.     

Relationship between Coleoptile Elongation and Alcoholic Fermentation in Rice Exposed to Anoxia. I. Importance of Treatment Conditions and Different Tissues

The relationship between coleoptile elongation and alcoholicfermentation of rice under anoxia is examined using seeds either:(a) N₂ flushed during submergence, (b) incubated in stagnantdeoxygenated agar at 0·1% w/v to simulate the stagnantconditions of waterlogged soil, or (c) incubated in waterloggedsoil. Coleoptile elongation growth was greater for N₂ flushing> stagnant agar > soil; seed survival was also greatestin this order over 1-5 d. Ethanol concentrations in coleoptiles and intact seeds (cv.IR42) were approximately 300 and 100 mol m^-3 respectively whenseeds were grown 3 d in stagnant agar, however 92% of the ethanolin seeds diffused into the external medium when solutions weremixed for 5-10 s. Coleoptile growth under anoxia was relatedto rates of ethanol synthesis (R_E) in different treatments;there was greater coleoptile growth and R_E for seeds in N₂ flushedsolutions than in stagnant deoxygenated agar. Coleoptile growthof individual seeds was also related to the R_E of each seedat 2-3 d after anoxia (r² = 0·46). Analysis of different tissues was important in evaluating growthand metabolism of coleoptiles. Although the coleoptile onlyaccounted for 0·7% of seed dry weight at 3 d after anoxia,it contained 21% of the ethanol produced by rice seeds. Therewere also three-fold higher rates of R_E on a fresh weight basisin expanding tissues in the base of the coleoptile relativeto the elongated tissues at the apex. Results are discussedin terms of the importance of environmental conditions usedto impose anoxia, quantification of R_E in specific tissues andthe possibility that under stagnant conditions high ethanolconcentrations in tissues may limit R_E and coleoptile growth.Copyright1994, 1999 Academic Press Anoxia, ethanol, alcoholic fermentation, Oryza sativa L., rice, submergence     

Interaction of Salinity and Anaerobiosis in Barley and Rice

Barley and rice at the early tillering stage were exposed simultaneouslyto anaerobiosis and high [NaCl]. Barley was grown at 0.5, 70,and 125 mol m^–3 NaCl, and rice at 2, 20, 40, and 80 molm^–3 NaCl. Surprisingly, anaerobiosis only slightly aggravatedthe adverse effects of high [NaCl] on root and shoot growthof both species. For rice and barley grown under aerobic conditions, high [NaCl]increased [Na⁺] and [Cl^–] and decreased [K+] in both rootsand shoots. However, the changes in ion concentrations in theshoots were smaller for rice than for barley. For roots of barley, anaerobiosis decreased [Na⁺], [Cl^–],and [K⁺] at both low and high [NaCl], possibly as a result ofinhibition of active ion accumulation. For barley shoots, anaerobiosisincreased [Na⁺] and [Cl^–], but only at high salinity;in contrast, [K⁺] was reduced by anaerobiosis at both low andhigh [NaCl]. These results indicate that anaerobiosis slightlyincreased the permeability of the barley root system to Na+and Cl^–. For rice, the most important interaction between salinity andanaerobiosis occurred in the shoots, where anaerobiosis increased[Na⁺] and decreased [K⁺], particularly at 40 and 80 mol m^–3NaCl, while there was no interaction between anaerobiosis andsalinity for Cl^– uptake. It is therefore suggested thatanaerobic treatment of rice decreased the selectivity for K⁺over Na⁺ of cation transport to the shoots, at least for plantsgrown at high salinities.     

Responses by Coleoptiles of Intact Rice Seedlings to Anoxia: K+ Net Uptake from the External Solution and Translocation from the Caryopses

This study evaluated the effects of anoxia on K⁺ uptake andtranslocation in 3–4-d-old, intact, rice seedlings (Oryzasativa L. cv. Calrose). Rates of net K⁺ uptake from the mediumover 24 h by coleoptiles of anoxic seedlings were inhibitedby 83–91 %, when compared with rates in aerated seedlings.Similar uptake rates, and degree of inhibition due to anoxia,were found for Rb⁺ when supplied over 1·5–2 h,starting 22 h after imposing anoxia. The Rb⁺ uptake indicatedthat intact coleoptiles take up ions directly from the externalsolution. Monovalent cation (K⁺ and Rb⁺) net uptake from thesolution was inhibited by anoxia to the same degree for thecoleoptiles of intact seedlings and for coleoptiles excised,‘aged’, and supplied with exogenous glucose. Transportof endogenous K⁺ from caryopses to coleoptiles was inhibitedless by anoxia than net K⁺ uptake from the solution, the inhibitionbeing 55 % rather than 87 %. Despite these inhibitions,osmotic pressures of sap (_sap) expressed from coleoptiles ofseedlings exposed to 48 h of anoxia, with or without exogenousK⁺, were 0·66 ± 0·03 MPa; however,the contributions of K⁺ to _sap were 23 and 16 %, respectively.After 24 h of anoxia, the K⁺ concentrations in the basal10 mm of the coleoptiles of seedlings with or without exogenousK⁺, were similar to those in aerated seedlings with exogenousK⁺. In contrast, K⁺ concentrations had decreased in aeratedseedlings without exogenous K⁺, presumably due to ‘dilution’by growth; fresh weight gains of the coleoptile being 3·6-to 4·7-fold greater in aerated than in anoxic seedlings.Deposition rates of K⁺ along the axes of the coleoptiles werecalculated for the anoxic seedlings only, for which we assessedthe elongation zone to be only the basal 4 mm. K⁺ depositionin the basal 6 mm was similar for seedlings with or withoutexogenous K⁺, at 0·6–0·87 µmolg^–1 f. wt h^–1. Deposition rates in zones above6 mm from the base were greater for seedlings with, thanwithout, exogenous K⁺; the latter were sometimes negative. Weconclude that for the coleoptiles of rice seedlings, anoxiainhibits net K⁺ uptake from the external solution to a muchlarger extent than K⁺ translocation from the caryopses. Furthermore,K⁺ concentrations in the elongation zone of the coleoptilesof anoxic seedlings were maintained to a remarkable degree,contributing to maintenance of _sap in cells of these elongatingtissues.     

水稻耐淹涝性状的遗传分析和SSR标记的研究

淹涝胁迫对水稻生产造成了严重影响, 发掘可应用于耐淹涝辅助选择的分子标记(MAS), 将有助于水稻耐淹涝性状的遗传改良。应用耐淹涝材料FR13A和淹涝敏感材料IR39595-503-2-1-2为亲本做正反交获得F₁和F₂代群体。对正反交的F₁群体的耐淹涝性状进行遗传分析, 发现正反交的F₁代群体在耐淹涝性状上没有显著差异, 说明耐淹涝性状是核基因控制。从两次淹涝处理中F₂代群体的分离情况来看, 来源于FR13A的耐淹特性表现出数量-质量性状遗传的特点。当淹涝胁迫压力比较轻时表现为数量性状遗传, 具有微效多基因的作用。当淹涝胁迫压力增大时, 表现为主效基因控制的质量性状。在SSR分析中, 187对SSR引物中有73对引物在两亲本间有明显的差异, 差异率为39%。用这73对差异引物, 对F2群体进行多态筛选, 结果筛选到一个与耐淹涝性状连锁的标记RM219, 验证了耐淹涝性状确实由主效基因Sub1控制, 因此, RM219在水稻耐淹涝育种中具有利用价值。     

Gas Composition in the Internal Air Spaces of Deepwater Rice in Relation to Growth Induced by Submergence

Deepwater rice (Oryza sativa L.) responds to partial submergenceby rapid elongation of the internodes. The elongation of intactplants was measured during 7 days of submergence using angulartransducers. Growth rates began to increase within 3 to 4 hupon submergence and peaked after 3 days; they were higher inthe light than in the dark. The composition of the gas phasein the internodal air spaces was analyzed at different timesafter partial submergence. In the light, the O₂ concentrationsin internal gas compartments of intact plants dropped initially,but recovered largely within 90 min. During longer periods ofsubmergence, the internal O₂ concentration followed a diurnalpattern with O₂ levels being lower during the night than duringthe day. An O₂ gradient was found from the apical parts of theplant near the water surface to the basal parts of the shoot. Concentrations of CO₂ changed with a pattern inverse to thatof the O₂concentrations. The level of ethylene in the internodallacunae increased upon submergence and reached 1µl-liter^–1after 72 h. It was higher at the end of the dark period thanduring the day. The gas exchange of the submerged parts of the plant seems todepend mainly on mass flow of air from the atmosphere to theroot system. Mass flow through this pathway was determined atdifferent pressure gradients and was compared to the intakeof air into plants as established in earlier investigations.A significant decrease in gas flow resistance found during 7days of submergence may constitute a long-term adaptation toflooding. (Received August 30, 1988; Accepted October 25, 1988)     

Submergence tolerance in relation to variable floodwater conditions in rice

Flash floods adversely affect rice productivity in vast areas of rainfed lowlands in South and Southeast Asia and tropical Africa. Tolerant landraces that withstand submergence for 1–2 weeks were identified; however, incorporation of tolerance into modern high-yielding varieties through conventional breeding methods has been slow because of the complexity of both the tolerance phenotype and floodwater conditions, and the ensuing discrepancies encountered upon phenotyping in different environments. Designing an effective phenotyping strategy requires a thorough understanding of the specific floodwater characteristics that most likely affect survival during flooding. We investigated the implications of floodwater temperature and light penetration, caused by artificial shading, seasonal variation, or water turbidity, for seedling survival after submergence. Three field experiments were conducted using rice genotypes contrasting in their tolerance of submergence: FR13A and Kusuma (tolerant); Gangasiuli (intermediate); Sabita, CRK-2-6 and Raghukunwar (elongating/avoiding types); and IR42 (sensitive). We tested the hypotheses that warmer floodwater decreases plant survival and that turbid water augment plant mortality by causing effects similar to those caused by shading, by reducing light penetration. Plants survive better when water is cooler, and survival decreased at about 8% per unit increase in water temperature above 26 °C. Lower intensity of light and warmer temperatures seem to reduce biomass and increase mortality under flooding. An increase in the concentrations of O₂ and CO₂ and a decrease in water pH did not improve survival in clear unshaded water. Turbid floodwater was more damaging to rice as plant mortality increased as the percentage of silt increased, and the effects of water turbidity cannot be explained by the reduction in light penetration alone. Even the most tolerant rice cultivar, FR13A, experienced higher mortality when flooded with turbid floodwater. Correlation studies revealed that cultivars with the capacity to maintain higher biomass, higher chlorophyll, and non-structural carbohydrate concentrations after submergence had higher survival. These findings help to understand the variation observed in submergence tolerance when screening is done under different environments. The study could have implications for designing proper screening strategies and assessing the damage submergence causes across different rice-growing regions.     

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilatesto filling seeds of soybean (Glycine max L. Merr.), resultingin higher seed growth rates. The plant growth substance ABAhas been implicated in the regulation of assimilate transferwithin filling soybean seeds. Thus, we hypothesized that anincreased concentration of endogenous ABA in seeds may enhancesucrose accumulation and seed growth rate of soybeans exposedto short-day photoperiods. Plants of cv. Hood 75 were grownin a greenhouse under an 8-h short-day photoperiod (SD) until11 d after anthesis (DAA) of the first flower, when half ofthe plants were transferred to a night-interruption (NI) treatment(3 h of low-intensity light inserted into the middle of thedark period). Plants remaining in SD throughout seed developmenthad seed growth rates 43% higher than that of plants shiftedto NI (7·6 mg seed^–1 d^–1 vs. 5·3 mgseed^–1 d^–1). On a tissue-water basis, the concentrationof ABA in SD seeds increased rapidly from 7.6 µmol l^–1at 11 DAA to 65·2 µmol l^–1 at 18 DAA, butthen declined to 6·6 µmol l^–1 by 39 DAA.In contrast, the concentration of ABA increased more slowlyin NI seeds, reaching only 47·4 µmol l^–1by 18 DAA, peaking at 57·0 µmol l^–1 on 25DAA, and declining to 10·2 µmol l^–1 by 39DAA. The concentration of sucrose in SD embryos peaked at 73·5mmol l^–1 on 25 DAA and remained relatively constant forthe remainder of the seed-filling period. In NI, the concentrationof sucrose reached only 38·3 mmol 1^–1 by 25 DAA,and peaked at 61·5 µmol l^–1 on 32 DAA. Thusin both SD and NI, sucrose accumulated in embryos only afterthe peak in ABA concentration, suggesting that ABA may havestimulated sucrose movement to the seeds. The earlier accumulationof ABA and sucrose in SD suggests that ABA may have increasedassimilate availability during the critical cell-division period,thus regulating cotyledon cell number and subsequent seed growthrate for the remainder of the seed-filling period. Glycine max L. Merr. cv. Hood 75, soybean, assimilate partitioning, abscisic acid, photoperiod, source-sink     

Physiological Changes in Phaseolus vulgaris in Response to Long-term Ozone Exposure

The effects of ozone on Phaseolus vulgaris cv. Lit were investigatedusing open-top chambers (OTCs) ventilated with charcoal andPurafil filtered air (CF treatments), ambient air (NF treatments)and ambient air to which low, medium or high concentrationsof ozone were added (NFL, NFM and NFH). Ozone additions of 8,16 and 23 nl l^–1 were made during phase 1 of the experiment(0–44 d after emergence, DAE), and additions of 15, 30and 47 nl l^–1 were made during phase 2 (45–99 DAE).Ozone was added to the chambers between 1100 and 1800 h GMT,for 3 or 4 consecutive days each week. The seasonal 7-h meanozone concentrations were 8, 21, 27, 33 and 38 nl l^–1in the CF, NF, NFL, NFM and NFH treatments, respectively. No visible symptoms of ozone injury or significant physiologicalchanges were detected in P. vulgaris during phase I of the experiment.In phase 2, the photosynthesis (Pn) and stomatal conductance(gs) of NFH-plants were inhibited by 73% and 86%, respectively,during ozone exposure, and recovered to pre-exposure valueson the following day. These observations were made prior tothe appearance, 60 DAE, of bronze lesions on the leaves of NFH-plants.The photosynthetic capacity and gs of NFH-leaves decreased asthe severity of ozone injury increased. Rates of weight lossfrom excised leaves also increased with increasing ozone injury.Microscopic investigations of the bronzed regions revealed extensivecellular breakdown, including tonoplast and chloroplast enveloperupture, and the aggregation of the cytoplasmic contents towardsone end of the cell. Severely damaged leaves abscised from the plants, resultingin premature canopy senescence in the NFM and NFH treatments.This, coupled with the lower photosynthetic capacity of existingleaves led to 25 % lower yield in the NFH than the NF treatment(P < 0.05). Phaseolus vulgaris, green bean, ozone, symptom development, photosynthesis, cell ultrastructure     

Responses of the antioxidative enzymes in Malaysian rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) cultivars under submergence condition

The potential involvement of activated oxygen species by submergence stress was studied in two Malaysian rice cultivars, MR219-4 and MR219-9, and cultivar FR13A that is known to be tolerant to submergence. Seedlings of these three rice cultivars were subjected to different submergence periods (4, 8, and 12 days). Under 8 days of complete submergence, FR13A cultivar showed higher lipid peroxidation in terms of malondialdehyde level and activities of antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) when compared to the MR219-4 and MR219-9 cultivars. MR219-9 showed higher SOD, APX, and GR activities after 12 days of submergence. The levels of SOD activity indicated that detoxification of O₂^·− to H₂O₂ was maintained at a stable level throughout the submergence stress until up to 8 days and increased rapidly at 12 days of submergence. The results indicated that tolerance to submergence in rice is associated until 8 days submergence for MR219-4 and FR13A cultivars. These findings suggested that tolerance to submergence stress in rice might be proven by increased the capacity of antioxidative system. In addition, CAT activity has much higher affinity for scavenges H₂O₂ than APX. Therefore, ascorbate glutathione cycle might be more efficient to scavenge H₂O₂.     

Metabolic origin of acetaldehyde emitted by poplar (Populus tremula x (P. alba) trees

The metabolic origin and emission by the leaves of the tropospheric trace gas acetaldehyde were examined in 4-month-old poplar trees (Populus tremula x P. alba) cultivated under controlled environmental conditions in a greenhouse. Treatments which resulted in increased ethanol concentration of the xylem sap caused significantly enhanced rates of acetaldehyde and ethanol emission by the leaves. Leaves fed [¹⁴C]-ethanol via the transpiration stream emitted [^<14C]-acetaldehyde. These findings suggest that acetaldehyde in the leaves is synthesized by a metabolic pathway that operates in the opposite direction of alcoholic fermentation and results in oxidation of ethanol. Enzymatic studies showed that this pathway is mediated either by alcohol dehydrogenase (ADH; EC 1.1.1.1) or catalase (CAT; EC 1.11.1.6), both constitutively present in the leaves of poplar trees. Labelling experiments with [¹⁴C]-glucose indicated that the ethanol delivered to the leaves by the transpiration stream is produced in anaerobic zones of submersed roots by alcoholic fermentation. Anoxic conditions in the rhizosphere caused by flooding of the root system resulted in an activation of alcoholic fermentation and led to significantly increased ethanol concentrations in the xylem sap. These results support the hypothesis that acetaldehyde emitted by the leaves of trees is derived from xylem transported ethanol which is synthesized during alcoholic fermentation in the roots.Keywords: Acetaldehyde, emission, ethanol, anaerobiosis, Populus tremula x P. alba      

Anoxic Seed Germination of Erythrina caffra: Ethanol Fermentation and Response to Metabolic Inhibitors

Erythrina caffra seeds were shown to be true anaerobic germinators.They exhibit a Pasteur effect, high alcohol dehydrogenase activityand produce high levels of ethanol under anoxia, in which situationgermination starts to be suppressed by as little as 0.1% externallyapplied ethanol. Toxic levels of ethanol production appear tobe prevented by a decrease in the rate of ethanol accumulation.Carbon monoxide does not inhibit germination. Cyanide, SHAM,iodoacetate, pyrazole, and 4-methylpyrazole are more inhibitoryto anoxic than aerobic germination whereas azide, arsenate,and fluoride inhibit both. Azide, pyrazole, 4-methylpyrazoleand a low concentration of cyanide and SHAM tend to stimulateethanol production in air. At 10 mol m^–3, 4-methylpyrazolestimulates anaerobic ethanol production. At higher concentrationsthis compound and all other inhibitors used suppress anaerobicethanol production initially. Inhibition of ethanol productionby 10 mol m^–3 cyanide is paralleled by an accumulationof acetaldehyde. Azide and cyanide appear to exert their inhibitoryeffect at different loci. Key words: Erythrina caffra, anoxic germination, fermentation, metabolic inhibitors