Abscisic acid and hypoxic induction of anoxia tolerance in roots of lettuce seedlings

Lettuce (Lactuca sativa L.) seedlings were subjected to anoxic stress after ABA-pretreatment (ABA-PT) or hypoxic-pretreatment (H-PT). The H-PT increased the survivability of the anoxia in roots of the seedlings by 5.2-fold compared to that of non-pretreated (N-PT) seedlings. ABA-PT also increased the survivability at concentrations greater than 1 microM, and the survivability increased with increasing ABA doses. At 100 microM ABA, the survivability was 4.5-fold greater than that of N-PT seedlings. During pretreatment periods, alcohol dehydrogenase (ADH, EC 1.1.1.1) activity in the roots became 3.1- and 3.4-fold greater than that of N-PT seedlings following 100 microM ABA-PT and H-PT seedlings, respectively. After the onset of anoxic stress, ADH activities in all roots increased, but the activities in H-PT and ABA-PT roots remained much greater than that in N-PT roots, and the average ethanol production rate for the initial 6 h was 5.3, 4.0 and 1.4 micromol g(-1) FW h(-1) for H-PT, ABA-PT and N-PT roots, respectively. Roots of the seedlings lost ATP rapidly under anoxic stress; however, the decrease in ATP was much slower in the ABA-PT and H-PT seedlings than in the N-PT seedlings. These results suggest that the ABA-PT and H-PT may maintain ATP levels due to activation of ethanolic fermentation, which may be one of the causes of the increasing anoxia tolerance in the seedling roots. Measurement of endogenous ABA levels, however, showed that ABA levels did not increase during the H-PT, suggesting that the H-PT does not increase tolerance through an increase in ABA levels.     

Induction of alcohol dehydrogenase by plant hormones in alfalfa seedlings

Six-day-old alfalfa (Medicago sativa L.) seedlings were treated with auxin, abscisic acid (ABA), cytokinin and gibberellin to determine the effect of these plant hormones on induction of alcohol dehydrogenase (ADH). The ADH activity was increased at concentrations greater than 1 M for auxin and ABA and 3 M for cytokinin, respectively, and all increases were found within 6 h after treatments. However, ADH activity remained almost unchanged in the seedlings treated with gibberellin. At 100 M doses, the activities in the seedlings were 4.0-, 3.6- and 2.1-fold greater than that of non-treated seedlings for auxin, ABA and cytokinin, respectively.     

Abscisic Acid induces anaerobiosis tolerance in corn

Flooding is a frequently occurring environmental stress that can severely affect plant growth. This study shows that treatment of corn (Zea mays L.) seedlings with abscisic acid (ABA) increases their tolerance to anoxia 10-fold over untreated seedlings and twofold over seedlings treated with water. Corn seedlings stressed anoxically for 1 day showed only 8% survival when planted in vermiculite. Pretreatment of root tips with 100 micromolar ABA or water for 24 hours before the 1 day anoxic stress increased the anoxic survivability of seedlings to 87% and 47%, respectively. Cycloheximide (5 milligrams per liter), added together with ABA, reduced the seedling survival rate, indicating that the induction of anoxic tolerance in corn by ABA was partly a result of the synthesis of new proteins. ABA treatment induced a threefold increase in alcohol dehydrogenase enzyme activity in corn roots. However, after 24 h of anoxia, alcohol dehydrogenase enzyme activity between the ABA-pretreated and non-pretreated corn roots was not significantly different. The results indicated that ABA played an important role in inducing anoxic tolerance in corn and that the induced tolerance was probably mediated by an increase in alcohol dehydrogenase enzyme activity before the anoxic stress.     

Osmotic Stress Increases Alcohol Dehydrogenase Activity in Maize Seedlings

Maize (Zea mays L.) seedlings were exposed to osmotic stress, and alcohol dehydrogenase (ADH) activity and abscisic acid (ABA) concentration were determined. The osmotic stress increased ADH activities in both roots and shoots, whereas the increase was 2-fold greater in roots than the shoots. The stress also increased ABA concentration in both roots and shoots and the increase was greater in the roots than in the shoots.     

Metabolic adaptation to flooding stress in upland and lowland rice seedlings

Ability of metabolic adaptation in upland and lowland rice (Oryza sativa L.) seedlings to flooding stress was compared. Flooding stress increased alcohol dehydrogenase (ADH) activity and ethanol concentration in shoots and roots of the upland and lowland rice seedlings. The difference in ADH activity and ethanol concentration in shoots between the upland and lowland rice was not apparent. However, both ADH activity and ethanol concentration in roots of the lowland rice were 2-fold greater than those in roots of the upland rice, suggesting that flooding-induction of ethanolic fermentation in lowland rice roots may be significantly greater than that in the upland rice roots. Since flooding often causes the anaerobic conditions in rooting zone than aerial part of plants and ethanolic fermentation is essential to survive in the anaerobic conditions, the ability of metabolic adaptation in lowland rice seedlings to flooding stress may be greater than that in upland rice seedlings.     

Abscisic acid pretreatment enhances salt tolerance of rice seedlings: Proteomic evidence

Enhanced salt tolerance of rice seedlings by abscisic acid (ABA) pretreatment was observed from phenotypic and physiological analyses. Total proteins from rice roots treated with ABA plus subsequent salt stress were analyzed by using proteomics method. Results showed that, 40 protein spots were uniquely upregulated in the seedlings under the condition of ABA pretreatment plus subsequent salt stress, whereas only 16 under the condition of salt treatment. About 78% (31 spots) of the 40 protein spots were only upregulated in the presence of the subsequent salt stress, indicating that plants might have an economical strategy to prevent energy loss under a false alarm. The results also showed that more enzymes involved in energy metabolism, defense, primary metabolism, etc. were upregulated uniquely in ABA-pretreated rice seedlings, suggesting more abundant energy supply, more active anabolism (nitrogen, nucleotide acid, carbohydrate, etc), and more comprehensive defense systems in ABA-pretreated seedlings than in salt stressed ones.     

Hypoxia induces anoxia tolerance in roots and shoots of lupine seedlings

Lupine seedlings were exposed to 4 kPa partial pressure oxygen (hypoxically pretreated) for 18 hours before treatment with strictly anaerobic conditions (anoxia). Seedlings previously exposed to hypoxia were more tolerant than the controls (not hypoxically pretreated) to anoxic stress in both roots and shoots. Hypoxic pretreatment induced roots and shoots survival in anoxia. Improved viability of roots, following hypoxic pretreatment, was associated with increased activity of ADH. In nonacclimated roots and shots significant increase in LDH activity occurd during the first hours under anoxia but the in vitro activity of LDH was two orders of magnitude lower than that of ADH. The results are discussed in relation to the ability of lupine seedlings to survive anoxia.     

Wounding stress induces alcohol dehydrogenase in maize and lettuce seedlings

To understand the effect of wounding stress on alcohol dehydrogenase(ADH, EC 1.1.1.1) in monocotyledonous and dicotyledonous plants, maize(Zea mays L.) and lettuce (Lactucasativa L.) seedlings were subjected to wounding stress and ADHactivity and abscisic acid (ABA) concentration were determined. In response tothe stress, the ADH activity in seedlings of both species increased rapidly asaresult of increased synthesis of the ADH. At 12 h after thestress,the activities in the wounded lettuce and maize seedlings, respectively,increased to 1.7- and 1.5-fold of that in non-stressed seedlings. Woundingstress also increased the concentration of endogenous ABA during the first 6h in both seedlings. The maximum increased levels of ABA in thelettuce and maize seedlings were 4.9- and 4.7-fold of that in the non-stressedseedlings, respectively.     

Abscisic acid induced stress-like polyamine pattern in wheat seedlings, and its reversal by potassium ions

In 3-day-old wheat ( Triticum aestivum L. cv. Marinat) seedlings, 100 μ M ABA blocked the growth and altered the level of K⁺ in both the shoot and root. The presence of ABA increased the putrescine titer during a 24-h treatment. Increasing the endogenous level of K⁺ by the addition of 10 m M KCl to the ABA-treated seedlings, inhibited the effect of ABA on growth and putrescine level. In both tissues, ABA increased putrescine content at low concentrations (1 μ M ), reaching the maximal effect at 100 μ M . Putrescine increase induced by ABA was inhibited by both α-difluoromethylarginine (DFMA) and α-difluoromethylornithine (DFMO) in shoots while only the inhibitor of arginine decarboxylase was effective in the root. The presence of ABA modulated, in opposite ways, ornithine and arginine decarboxylase activities. These results are discussed in relation to ion balance under stress.     

Low-temperature accumulation of alcohol dehydrogenase-1 mRNA and protein activity in maize and rice seedlings

Low-temperature stress was shown to cause a rapid increase in steady-state levels of alcohol dehydrogenase-1 message (Adh1) and protein activity (ADH1) in maize (Zea mays) (B37N, A188) and rice (Oryza sativa) (Taipei 309, Calmochi 101) seedlings. Maize roots and rice shoots and roots from 7-day seedlings shifted to low temperature (10°C) contained as much as 15-fold more Adh1 mRNA and 8-fold more ADH1 protein activity than the corresponding tissues from untreated seedlings. Time-course studies showed that these tissues accumulated Adh1 mRNA and ADH1 activity severalfold within 4- to 8-hour, levels plateaued within 20 to 24 hours, and remained elevated at 4 days of cold treatment. Within 24 hours of returning cold-stressed seedlings to ambient temperature, Adh1 mRNA and ADH1 activity decreased to pretreatment levels. Histochemical staining of maize and rice tissue imprints showed that ADH activity was enhanced along the lengths of cold-stressed maize primary roots and rice roots, and along the stems and leaves of rice shoots. Our observations suggest that short-term cold stress induces Adh1 gene expression in certain plant tissues, which, reminiscient of the anaerobic response, may reflect a fundamental shift in energy metabolism to ensure tissue survival during the stress period.     

Hypoxic Induction of Anoxia Tolerance in Root Tips of Zea mays

When root tips of fully aerobic, intact maize (Zea mays L.) seedlings are made anaerobic, viability normally is only 24 hours or less at 25°C. We find that viability can be extended to at least 96 hours if seedlings are given a hypoxic pretreatment for 18 hours by sparging the solution with 4% O₂ in nitrogen (v/v) before anoxia. Fully aerobic root tips (sparged with 40% O₂) had very low alcohol dehydrogenase (ADH) activity (per gram root fresh weight), and the level remained low under anoxia. In hypoxically pretreated roots, however, high levels of ADH activity were induced, and activity rose further during the initial 24 hours of anoxia, and then remained high at about 20 times that of controls in 40% O₂. ADH activity in roots in solution sparged with air (21% O₂) was about three times that in 40% O₂. Improved viability of hypoxically pretreated root tips was associated with maintenance of a high energy metabolism (ATP concentration, total adenylates, and adenylate energy charge). Roots that were not pretreated lost 94% of the total adenylates and ATP at 24 hours of anoxia. The relation between induced ADH activity, energy metabolism, and improved anoxia-tolerance in acclimated maize root tips is discussed.     

根际低氧逆境对网纹甜瓜幼苗生长及根系呼吸代谢途径的影响

以耐低氧性具有明显差异的两个网纹甜瓜(Cucumis melo var. raticulalus)品种为试材,研究了根际低氧胁迫下幼苗生长、根系活力及根系呼吸关键酶活性的变化。结果表明,根际低氧胁迫下,两品种幼苗生长均受到明显抑制,而根系活力升高;根系PDC活性两品种均显著提高,品种间无显著差异; MDH活性两品种均显著降低,且耐低氧性弱的‘西域一号’下降幅度较大;根系ADH和LDH活性两品种均显著提高,耐低氧性强的‘东方星光’ADH活性增加的幅度显著高于耐低氧性弱的‘西域一号’,而‘西域一号’LDH活性增加幅度显著高于‘东方星光’。说明‘东方星光’在低氧胁迫下能保持较高的有氧呼吸水平,无氧呼吸的主要途径为乙醇发酵,而‘西域一号’在低氧胁迫下无氧呼吸的主要途径为乳酸发酵。     

Stress-induced accumulation of wheat germ agglutinin and abscisic Acid in roots of wheat seedlings

Wheat germ agglutinin (WGA) levels in roots of 2-day-old wheat seedlings increased up to three-fold when stressed by air-drying. Similar results were obtained when seedling roots were incubated either in 0.5 molar mannitol or 180 grams per liter polyethylene glycol 6000, with a peak level of WGA after 5 hours of stress. Longer periods of osmotic treatment resulted in a gradual decline of WGA in the roots. Since excised wheat roots incorporate more [³⁵S]cysteine into WGA under stress conditions, the observed increase of lectin levels is due to de novo synthesis. Measurement of abscisic acid (ABA) levels in roots of control and stressed seedlings indicated a 10-fold increase upon air-drying. Similarly, a five- and seven-fold increase of ABA content of seedling roots was found after 2 hours of osmotic stress by polyethylene glycol 6000 and mannitol, respectively. Finally, the stress-induced increase of WGA in wheat roots could be inhibited by growing seedlings in the presence of fluridone, an inhibitor of ABA synthesis. These results indicate that roots of water-stressed wheat seedlings (a) contain more WGA as a result of an increased de novo synthesis of this lectin, and (b) exhibit higher ABA levels. The stress-induced increase of lectin accumulation seems to be under control of ABA.     

Ethylene as a possible mediator of light-induced inhibition of root growth

Eliasson, L. and Bollmark, M. 1988. Ethylene as a possible mediator of light-induced inhibition of root growth. - Physiol. Plant. 72: 605–609.
Pea seedlings ( Pisum sativum L. cv. Weibull's Marma) were used to investigate the possible role of ethylene in light-induced inhibition of root elongation. Illumination of the roots with white light inhibited root elongation by 40–50% and increased ethylene production by the roots about 4-fold. Our main approach was to use exogenous 1-aminocyclopropane-1-carboxylic acid (ACC), supplied in the growth solution, to monitor ethylene production of the roots independent of light treatment. Ethylene production of excised root tips increased with increasing ACC concentrations. The rate of ethylene production in dark-grown roots treated with 0.1 μ M ACC was similar to that caused by illumination. Low ACC concentrations (0.01–0.1 μ M ) decreased the rate of root elongation, especially in seedlings grown in the dark, and 0.1 μ M ACC inhibited elongation to about the same extent as light. In light the roots curved and grew partly plagiogravitropically. This effect was also simulated by the 0.1 μ M ACC treatment. At 1 μ M and higher concentrations, ACC inhibited root growth almost completely and caused conspicuous curvatures of the root tips both in light and darkness. Inhibitors of ethylene synthesis and action partially counteracted the inhibition of root elongation caused by light. These observations suggest that the increase in ethylene production caused by light is at least partly responsible for the decreased growth of light-exposed roots.     

Relations between MAPK phosphorylation and ABA level in <Emphasis Type="Italic">Malus sieversii</Emphasis> under water stress

A correlation between protein kinase phosphorylation and ABA level was studied in Malus sieversii (Ledeb.) Roem. seedlings under water stress. The seedlings were treated with PEG 6000 for imitation of water stress, and the MAPK activity and ABA content in each treatment were then determined. We demonstrated that the increase in the activities of the total protein kinase (TPK) and mitogen-activated protein kinase (MAPK) after treatment with 20% PEG 6000 appeared to result in a high level of ABA. MAPK activity accounted for 76.8% of TPK activity. The activity peaks of TPK and MAPK preceded the highest level of ABA accumulation. It is interesting that the ABA level in roots and leaves of seedlings pretreated with 2 × 10⁻² mM exogenous ABA for 20 min following treatment by 20% PEG 6000 was much higher than that of seedlings treated with exogenous ABA only. We analyzed the influence of MAPK inhibitor ITU (5-iodotubercidin) on ABA accumulation in the seedlings of M. sieversii under water stress and showed that 1 μM ITU significantly decreased the ABA level induced by a water loss. However, the phosphoesterase inhibitor PAO (phenylarisine oxide) enhanced ABA accumulation, indicating that the phosphorylated MAPK was correlated to ABA synthesis. Together, these results suggest that MAPK phosphorylation played an important role in ABA accumulation under water stress, and MAPK might mediate the signal transduction of ABA synthesis.     

Suppression Subtractive Hybridization Analysis of Genes Regulated by Application of Exogenous Abscisic Acid in Pepper Plant (Capsicum annuum L.) Leaves under Chilling Stress

Low temperature is one of the major factors limiting pepper (Capsicum annuum L.) production during winter and early spring in non-tropical regions. Application of exogenous abscisic acid (ABA) effectively alleviates the symptoms of chilling injury, such as wilting and formation of necrotic lesions on pepper leaves; however, the underlying molecular mechanism is not understood. The aim of this study was to identify genes that are differentially up- or downregulated in ABA-pretreated hot pepper seedlings incubated at 6°C for 48 h, using a suppression subtractive hybridization (SSH) method. A total of 235 high-quality ESTs were isolated, clustered and assembled into a collection of 73 unigenes including 18 contigs and 55 singletons. A total of 37 unigenes (50.68%) showed similarities to genes with known functions in the non-redundant database; the other 36 unigenes (49.32%) showed low similarities or unknown functions. Gene ontology analysis revealed that the 37 unigenes could be classified into nine functional categories. The expression profiles of 18 selected genes were analyzed using quantitative RT-PCR; the expression levels of 10 of these genes were at least two-fold higher in the ABA-pretreated seedlings under chilling stress than water-pretreated (control) plants under chilling stress. In contrast, the other eight genes were downregulated in ABA-pretreated seedlings under chilling stress, with expression levels that were one-third or less of the levels observed in control seedlings under chilling stress. These results suggest that ABA can positively and negatively regulate genes in pepper plants under chilling stress.     

Exogenous Catalase and Ascorbate Modify the Effects of Abscisic Acid (ABA) on Root Hydraulic Properties in Phaseolus vulgaris L. Plants

Abscisic acid (ABA) modifies the hydraulic properties of roots by increasing root water flux (J_v). The role of reactive oxygen species (ROS) in this ABA-induced process was evaluated. At the same time, some antioxidant enzyme activities in root tissues were measured. Phaseolus vulgaris plants were grown hydroponically, and different concentrations of ABA in combination with catalase enzyme or ascorbate were added to the nutrient solution. Catalase treatment had no effect by itself (no ABA) and had little or only a small stimulatory effect at ABA concentrations of 1, 50, and 100 μM, but it partially inhibited the ABA effect at 5 μM. Ascorbate by itself doubled J_v and root hydraulic conductance over the control value. In the presence of ABA, ascorbate partially or, at 100 μM, completely inhibited that ABA stimulation of J_v. These results are discussed in relationship to the possibility that ABA signaling in the roots involves ROS.     

Cryopreservation of horse-chestnut (Aesculus hippocastanum L. ) somatic embryos using three different freezing methods

Cryopreservation of somatic embryos of Aesculus hippocastanum L. cultured on nutritive media containing abscisic acid (ABA) at concentrations of 0.75 μM, 7.5 μM and 75.0 μM was evaluated for three cooling methods: (i) slow freezing with cryoprotectants, (ii) fast freezing with cryoprotectants, and (iii) fast freezing with desiccation techniques. The ‘cryoprotectant’ freezing techniques included the embryo pretreatment on ABA containing medium for 4 days, followed by cryoprotective treatment in liquid medium containing 0.5 M dimethylsulfoxide, 0.5 M glycerol, 1.0 M sucrose, and cooled at slow, and rapid rates. Embryos pretreated on a medium containing 0.75 μM ABA, and cooled to −35 °C at 1°C /min, held for 30 min at this transfer temperature and then immersed in liquid nitrogen (LN) had the best embryo recovery (43%). The ‘desiccation’ method involved an air drying step of similar ABA-pretreated, non-cryoprotected embryos followed by rapid cooling. Embryos precultured on 0.75 μM ABA, then subjected to a 4 h period of air desiccation (water content reduction to 13%) showed about the same level of survival (46%) as found with the ‘cryoprotectant’ slow freezing technique. The air-dry ‘desiccation’ method is easier to apply than the more complicated ‘cryoprotectant’ method. This revised version was published online in June 2006 with corrections to the Cover Date.     

Implication of ABA and proline on cell membrane injury of water deficit stressed barley seedlings

The aim of this work was to examine the ability of ABA and proline to counteract the deleterious effect of water deficit stress on cell membrane injuries. Six-day-old seedlings of two barley genotypes (cv. Aramir, line R567) were treated with ABA (2·10⁻⁴ M) or proline (0.1 M) for 24 h, and then subjected to osmotic stress for 24h, by immersing their roots in polyethylene glycol (PEG 6000) solution of osmotic potential of −1.0 MPa and −1.5 MPa or by submerging the leaf pieces in PEG solution of osmotic potential of −1.6 MPa. Pretreatment of plants with ABA and proline caused an increase of free proline level in the leaves. Plants treated with ABA exhibited a lower membrane injury index under water stress conditions than those untreated even when no effect of this hormone on RWC in the leaves of stressed plants was observed. Pretreatment of plants with proline prevented to some extent membrane damage in leaves of the stressed seedlings, but only in the case when stress was imposed to roots. Improvement in water status of leaves was also observed in seedlings pretreatment with proline. The protective effect of both ABA and proline was more pronounced in line R567 that exhibited higher membrane injury under water deficit stress conditions.     

The effects of exogenous ABA applied to maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) roots on plant responses to chilling stress

This work aimed to discuss the effects of exogenous abscisic acid (ABA) on the root growth regulation of maize seedlings under chilling stress. The roots of the maize cultivar Zhengdan 958 were irrigated with ABA (10^?7, 10^?6, 10^?5 and 10^?4 M) at the third true leaf stage under chilling duration (0, 2, 4, 6, and 8 days). The biomass, the phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) enzyme activities, total phenolic and flavonoid contents, the ferric reducing ability of plasma (FRAP) antioxidant capacity, and 2,2-azinobis (3-ethlbenzothiazo-line-6-sulfonic acid) diammonium salt radical (ABTS^·+) scavenging capacity of the roots of maize seedlings were measured after the treatment. The results showed that appropriate concentrations of exogenous ABA effectively enhanced root biomass, increased PAL and PPO enzyme activities, and significantly increased total phenolic contents and flavonoid contents. Moreover, the ABA markedly improved the FRAP antioxidant capacity and ABTS^·+ scavenging capacity under low-temperature stress. These results indicate that ABA-treated maize seedlings are resistant to chilling stress and that the optimum concentration of ABA is 10^?5 M. Exogenous applications of ABA have a concentration effect in alleviating chilling stress, in which low concentrations have a promoting effect and high concentrations have an inhibiting effect.