The higher expression and distribution of 9-cis-epoxycarotenoid dioxygenase1 (AhNCED1) from Arachis hyopgaea L. contribute to tolerance to water stress in a drought-tolerant cultivar

The 9-cis-epoxycarotenoid dioxygenase (NCED) is thought to be the rate-limiting enzyme in the abscisic acid (ABA) biosynthetic pathway. In this study, transient expression of AhNCED1 and ABA distribution were detected in the vascular cambium of a drought-tolerant peanut cultivar (Yueyou 7) under a water stress treatment. It caused increases in ABA content in this region. The synthesis of ABA and AhNCED1 in the leaves of Yueyou 7 took place more quickly than in the control cultivar (Shanyou 523). Furthermore, AhNCED1 mRNA and proteins were induced in Yueyou 7 than in Shanyou 523, coinciding with greater ABA accumulation. During the seedling, blooming, and fruiting stages, AhNCED1 protein expression was higher in Yueyou 7 than in Shanyou 523, and it was induced more quickly when the plants were under water stress. These data suggest that the drought-tolerant cultivar can synthesize and distribute ABA more rapidly than does the control cultivar because of a high level of AhNCED1 expression, which then modulates physiological responses under water stress conditions.     

综合隶属函数法评价花生品种抗旱性与AhNCED1基因表达的关系

利用综合隶属函数法评价不同产地8个花生品种幼苗的抗旱能力, 同时分析各品种花生在模拟干旱处理2小时和12小时后叶片AhNCED1基因表达量的变化, 探讨花生品种抗旱性与叶片AhNCED1基因表达的关系, 建立花生(Arachis hypogaea)幼苗时期通过AhNCED1基因表达变化检测花生抗旱性等级的方法。结果显示, 干旱处理2小时, 各品种叶片AhNCED1基因表达量迅速增加, 与处理前相比差异极显著; 干旱处理12小时, 各品种花生叶片AhNCED1基因表达量均降低, 但仍均高于处理前水平。综合隶属函数值定量反映各品种抗旱性强弱顺序为: 花育24号>福花13号>粤油7号>中花15号>中花16号>航花2号>福花9号>北海1号。干旱处理2小时各品种花生叶片AhNCED1表达量变化大小依次为: 福花13号>花育24号>中花16号>中花15号>航花2号>粤油7号>北海1号>福花9号。其中, 抗旱性强的品种为花育24号和福花13号, 抗旱性弱的品种为福花9号和北海1号, 其余4个品种为中等抗旱。该抗旱性评价结果与这些品种在生产上的表现一致, 干旱胁迫2小时花生品种叶片AhNCED1基因的表达量变化与其抗旱性一致。因此, AhNCED1基因表达量可作为苗期花生品种抗旱性等级的量化指标之一。     

Abscisic acid (ABA) inhibition of lateral root formation involves endogenous ABA biosynthesis in Arachis hypogaea L.

ABA has been found to play a significant role in post-embryonic developmental in peanut seedlings. The results from the current study indicate that in the presence of exogenous 10 μmol l⁻¹ ABA, lateral roots (LRs) number decreased and seedling development was delayed. This effect was eliminated by 25 μmol l⁻¹ naproxen, an inhibitor of ABA biosynthesis. The Arabidopsis mutant deficient in ABA biosynthesis, nced3, displays a phenotype with more and longer LRs. We found that ABA decreased root-branching in peanut in a dose-dependent way. ABA-treated seedlings showed higher endogenous ABA levels than the control and naproxen-treated seedlings. RT-PCR results indicated that the expression of AhNCED1, a key gene in the ABA biosynthetic pathway, was significantly up-regulated by exogenous ABA in peanut. The mRNA levels of AhNCED1 began to increase 2 days after ABA treatment. The results from the current study show that ABA inhibits peanut LR development by increasing endogenous ABA contents.     

不同花生品种响应干旱胁迫后叶片内ABA与AhNCEDl的分布

以粤油7号和汕优523两个不同抗旱性品种为材料,研究响应干旱胁迫后叶片ABA（abscisicacid,脱落酸）和AhNCEDl（Arachishypogaeanine-cis-epoxycarotenoiddioxygenase）的分布以及含量变化。结果表明,两种花生品种响应干旱胁迫后叶片的维管组织中ABA分布增强且含量增加,AhNCEDl蛋白分布也增强;且在水分胁迫初期粤油7号花生AhNCEDl蛋白分布强于汕优523,其体内ABA分布水平也高于汕优523;经ABA生物合成抑制剂N印roxen处理后,两种花生叶片ABA分布减弱,但粤油7号叶片维管组织ABA分布水平仍高于汕优523。结果表明维管组织是干旱胁迫下花生叶片中ABA和AhNCEDl分布的主要区域,且粤油7号花生抗旱性强可能与其体内AhNCEDl和ABA的分布量较高有关。     

Involvement of G1-to-S transition and AhAUX-dependent auxin transport in abscisic acid-induced inhibition of lateral root primodia initiation in Arachis hypogaea L

Previous study indicated that increasing endogenous abscisic acid (ABA) level could inhibit the lateral root (LR) formation of peanuts. In this study, we investigated the mechanisms by which ABA regulated lateral root primordia (LRP) initiation in peanuts (Arachis hypogaea L). Results suggested that ABA inhibited LRP initiation through blocking G1-to-S transition in seedlings and mature roots: e.g. 5.8% increase in the proportion of G1 phase and 18% decrease in the proportion of S phase after ABA treatment for 6 days. Further study of the expression of the cell cycle marker gene for G2-to-M transition in peanut roots suggested that AhCYCB1 expression was regulated by ABA. We also investigated the cooperative regulation of LRP initiation by ABA and indole-3-acetic acid (IAA). ABA treatment greatly reduced the effects of endogenous IAA on mature roots. The expression of the IAA polar transport gene AhAUX1 appeared to be regulated by ABA since ABA inhibited auxin-mediated LRP initiation by suppressing AhAUX-dependent auxin transport in peanut roots. We further examined the effect of ABA on the expression of DR5::GUS and AtAUX1 in the model plant Arabidopsis. The results of Arabidopsis were consistent with that of the peanut.     

Molecular cloning and characterization of a dehydration-inducible cDNA encoding a putative 9-cis-epoxycarotenoid dioxygenase in Arachis hygogaea L.

A rate-limiting step in abscisic acid (ABA) biosynthesis in plants is catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED). Here we present the cloning, characterization of a cDNA from dehydrated peanut (Arachis hygogaea L.) leaves that encodes a putative NCED. The 2486-bp full-length cDNA (designated as AhNCED1), obtained by rapid amplification of cDNA ends (RACE), has an open reading frame of 601 amino acid residues and encodes a protein with a calculated molecular weight of 66.86 kDa and an isoelectric point of 8.39. Sequence analysis shows that the deduced amino acid sequence of AhNCED1 shares high identity with the reported NCED protein sequences. There is a 30-amino-acid chloroplast-targeting peptide at the N-terminus of the AhNCED1 protein predicted by iPSORT algorithm. Semi-quantification by duplex RT-PCR reveals that the expression of AhNCED1 is up-regulated by dehydration and that rehydration represses its expression. The organ specific expression pattern of AhNCED1 has been examined, which indicates its dominant expression in leaves and stems. Molecular analysis of the drought-inducible gene of peanut may be useful to investigate the response of agricultural crops to drought stress.     

Re-examining the role of ABA as the primary long-distance signal produced by water-stressed roots

The role of ABA as the primary long-distance signal produced by water-stressed roots and transported to stomata continues to be challenged. We have recently reported that expression of ABA biosynthetic genes in roots only increases in the later stage of water stress. Our results support the hypothesis that in early water stress, increased levels of ABA in xylem sap are due to leaf biosynthesis and translocation to roots and from there to xylem. If so, other xylem-borne chemicals may be the primary stress signal(s) inducing ABA biosynthesis in leaves. We found that apart from ABA, sulfate was the only xylem-borne chemical that consistently showed higher concentrations from early to later water stress. We also found increased expression of a sulfate transporter gene in roots from early water stress onwards. Moreover, using bioassays we found an interactive effect of ABA and sulfate in decreasing maize transpiration rate, as compared to ABA alone. While ABA is undoubtedly the key mediator of water stress responses such as stomatal closure, it may not be the primary signal produced by roots perceiving water stress.Key words: abscisic acid, ABA biosynthesis, corn, drought, maize, malate, pH, stomatal conductance, sulfate, Zea mays     

Abscisic acid mediates hydrogen peroxide production in peanut induced by water stress

Peanut plants exposed to water stress induced by polyethylene glycol (PEG) accumulated abscisic acid (ABA) and hydrogen peroxide (H₂O₂), the increase being significant at 12 and 24 h after addition, respectively. To address the question whether the increase in H₂O₂ production was related to ABA accumulation, the peanut leaves were pretreated with ABA biosynthesis inhibitor (sodium tungstate) and then exposed to water stress. Under these conditions, a decrease of ABA and H₂O₂ content were found after 12 h. The addition of 100 μM ABA restored H₂O₂ content reaching values similar to those under water stress at 12 h. We concluded that ABA accumulation is the first signal that triggers the H₂O₂ generation in peanut during first 12 h but its subsequent production is partially ABA-independent.     

水分胁迫下湖北海棠根系脂氧合酶活性与ABA积累的关系

采用无细胞体系（ｃｅｌｌ－ｆｒｅｅ ｓｙｓｔｓｍ）及非离体根,研究了湖北海棠（Ｍａｌｕｓ ｈｕｐｅｈｅｎｓｉｓ（Ｐａｍｐａｎ．）Ｒｅｈｄ．）实生幼苗根中脂氧合酶（ＬＯＸ）活性和脱落酸（ＡＢＡ）生物合成及胁迫诱导ＡＢＡ积累的关系。结果表明,水分胁迫（３０％ＰＥＧ处理或０．６ｍｏｌ／Ｌ甘露醇处理）及盐胁迫（０．２ｍｏｌ／ＬＮａＣｌ）诱导ＡＢＡ积累的同时,ＬＯＸ活性也上升,两者呈一致关系。ＬＯＸ专一抑制     

水分胁迫下湖北海棠根系脂氧合酶活性与ABA积累的关系

The relationship between lipoxygenase (LOX) activity and ABA accumulation was studied in the roots of Malus hupehensis (Pampan. Rehd.) seedling using both intact young roots and cell-free system. The result showed that LOX activity and ABA content increased simultaneously after treatment of 30% PEG 6000, 0.6 mol/L mannitol, and 0.2 mol/L NaCl, respectively. NDGA (nordihydroguaiaretic acid), an inhibitor of LOX, inhibited simultaneously both the activity of LOX and the enhancement of ABA level under the stresses. Likewise adding soybean LOX to root cell-free system led to the increase of ABA content. The results suggested that LOX may be a key enzyme in ABA biosynthesis under water stress.     

Long Distance Transport of Abscisic Acid in NaCI-Treated Intact Plants of Lupinus albus

Plants of Lupinus albus were grown for 51 d under control (1.1mol m^–3 NaCl) and saline (40 mol m^–3 NaCl) conditions.Plants were harvested and changes of carbon, nitrogen and abscisicacid (ABA) contents of individual organs were determined 41d and 51 d after germination. In the period between the twoharvests xylem and phloem saps were collected and respirationand photosynthesis of individual organs were measured. Usingflows of carbon, C/ABA ratios and increments of ABA flows ofABA in phloem and xylem and rates of biosynthesis and degradationof ABA were calculated. Both under control and saline conditionsnet biosynthesis occurred in the root, the basal strata of leavesand in the inflorescence. Metabolic degradation of ABA tookplace in the stem internodes and apical leaf strata. Salt stress increased xylem transport of ABA up to 10-fold andphloem transport to the root up to 5-fold relative to that ofthe controls. A considerable amount of ABA in the xylem saporiginated from biosynthesis in the roots, i.e. 55% in salt-treatedand smaller than 28% in control plants. The remaining part ofABA in the xylem sap originated from the shoot: it was translocatedin the phloem from fully differentiated leaves towards the rootand from there it was recirculated back to the aerial partsof the plant. The data suggest that ABA may serve as a hormonalstress signal from the root system. Key words: Lupinus albus, salt stress, abscisic acid, long distance transport     

How the roots contribute to the ability of Phaseolus vulgaris L. to cope with chilling-induced water stress

Intact plants and stem-girdled plants of Phaseolus vulgaris grown hydroponically were exposed to 5 degrees C for up to 4 d; stem girdling was used to inhibit the phloem transport from the leaves to the roots. After initial water stress, stomatal closure and an amelioration of root water transport properties allowed the plants to rehydrate and regain turgor. Chilling augmented the concentration of abscisic acid (ABA) content in leaves, roots and xylem sap. In intact plants stomatal closure and leaf ABA accumulation were preceded by a slight alkalinization of xylem sap, but they occurred earlier than any increase in xylem ABA concentration could be detected. Stem girdling did not affect the influence of chilling on plant water relations and leaf ABA content, but it reduced slightly the alkalinization of xylem sap and, principally, prevented the massive ABA accumulation in root tissues and the associated transport in the xylem that was observed in non-girdled plants. When the plants were defoliated just prior to chilling or after 10 h at 5 degrees C, root and xylem sap ABA concentration remained unchanged throughout the whole stress period. When the plants were chilled under conditions preventing the occurrence of leaf water deficit (i.e. at 100% relative humidity), there were no significant variations in endogenous ABA levels. The increase in root hydraulic conductance in chilled plants was a response neither to root ABA accretion, nor to some leaf-borne chemical signal transported downwards in the phloem, nor to low temperature per se, as indicated by the results of the experiments with defoliated or girdled plants and with plants chilled at 100% relative humidity. It was concluded that the root system contributed substantially to the bean's ability to cope with chilling-induced water stress, but not in an ABA-dependent manner.     

Cloning,characterization and functional analysis of the role MhNCED3, a gene encoding 9-cis-epoxycarotenoid dioxygenase in Malus hupehensis Rehd., plays in plant tolerance to osmotic and Cd2+ stresses

Aims

Abscisic acid (ABA) plays an important role in the stress tolerance of seedlings and 9-cis-epoxycarotenoid dioxygenase (NCED) is considered to be the rate-limiting enzyme involved in ABA biosynthesis. However, the genes encoding NCED in M. hupehensis Rehd. have not been reported.

Methods

In this study, a gene encoding NCED, MhNCED3, was isolated from the roots of M. hupehensis Rehd. Its functions were investigated in M. hupehensis Rehd. seedlings and transgenic Arabidopsis lines under various abiotic stresses.

Results

The expression of MhNCED3 in M. hupehensis Rehd. roots was differentially induced by dehydration, chilling, salt and cadmium stresses and ABA biosynthesis was highly correlated with MhNCED3 expression. Ectopic expression of MhNCED3 successfully complemented the phenotypic defects of the 129B08/nced3 mutant. Furthermore, overexpression of MhNCED3, when it was transformed into the wild type (WT) seedling resulted in enhanced tolerance to osmotic and cadmium stresses compared to the normal WT seedling. The transgenic lines displayed higher rates of seed germination, improved growth and developmental status, reduced water loss/oxidative damage, lowered apoptosis rates and increased ABA accumulation. Furthermore, the higher antioxidant enzyme activities detected in the transgenic lines were probably responsible for the decrease in oxidative damage and apoptosis rates.

Conclusions

Overall, MhNCED3 played a significant role in enhancing plant tolerance to abiotic stresses through the regulation of endogenous ABA biosynthesis.     

Production of a major stilbene phytoalexin, resveratrol in peanut (Arachis hypogaea) and peanut products: a mini review

As a major stilbene phytoalexin, resveratrol is produced or elicited in several plant species as a part of defense systems protecting plants against diseases. Resveratrol can be present in both the trans- and cis-isomeric forms, and only the trans-form increases the life expectancy and lowers the risk of cardiovascular diseases as the most bioactive form. In addition to the usages for diet and industry, peanut plant (Arachis hypogaea) and peanuts are getting higher attention due to their containment of resveratrol in the kernels and other parts of peanut plant, such as leaves, roots, and peanut shell. Recently, natural resveratrol derived from peanuts has also become a promising nutraceutical agent, promoting human health. Resveratrol has also been detected in peanut products including peanut butters, roasted peanuts, and boiled peanuts. Although, smaller and immature peanuts contain higher levels of resveratrol than mature peanuts, resveratrol in peanuts can also be preserved by cooking or manufacturing processes. Moreover, the amount of resveratrol in peanut plants and peanuts has been found to increase by external stimuli including microbial infection, wounding, UV light irradiation, ultrasonication, yeast extract treatment and by plant stress hormones. In addition, molecular level analysis has confirmed that four resveratrol synthase (RS) genes (RS1, RS2, RS3 and RS4) which catalyze synthesis of resveratrol have been identified in peanuts, and up-regulation of the genes is positively correlated to the increased contents of resveratrol. In this review, we summarize the natural biosynthesis of resveratrol in peanuts and peanut plants, as well as the occurrence of this natural phytoalexin in various peanut products. A brief knowledge on the biosynthetic pathway of resveratrol synthesis has been described. This review also deals on highlighting the effect of various external stimuli (biotic and abiotic stresses) in order to achieve the maximum induction and/or elicitation of resveratrol in peanuts and peanut plants.     

Regulation by ABA of osmotic-stress-induced changes in protein synthesis in tomato roots

Polypeptide synthesis and accumulation were examined in the roots of tomato seedlings exposed to a polyethylene glycol‐imposed water deficit stress. In these roots, the synthesis of a number of polypeptides was induced, while that of several others was enhanced or repressed. To examine the role played by abscisic acid (ABA) in co‐ordinating the accumulation of these proteins, water‐deficit‐stress‐responsive polypeptide synthesis was investigated in the roots of the ABA‐deficient mutant flacca. In the roots of this mutant, the ability to accumulate a complete set of water‐deficit‐stress‐responsive polypeptides was impaired, indicating that ABA is required for their synthesis. The role of ABA was further examined by exposing the roots of both genotypes to exogenous ABA, which, with one exception, elicited the accumulation of all water‐deficit‐stress‐responsive proteins. Polyethylene glycol‐induced polypeptide accumulation was accompanied by a 1·6‐fold increase in the level of endogenous ABA in the roots of wild‐type plants and a 5‐fold increase in the roots of flc. Thus, although the absolute level was lower than that of the wild‐type, flc has the capacity to accumulate ABA in its roots. When fluridone was used to prevent the biosynthesis of ABA, the accumulation of several water‐deficit‐stress‐responsive polypeptides was reduced further. The synthesis of polypeptides was also examined in the roots of salt‐treated seedlings. Salt altered the accumulation of several polypeptides, all of which were previously observed in water‐deficit‐stressed roots, indicating that their synthesis was the result of the osmotic component of the salt stress. However, the accumulation of these polypeptides was not impaired in flc roots, indicating that the role played by ABA in regulating their accumulation in salt‐and polyethylene glycol‐treated roots differs. As such, salt‐ and water‐deficit‐stress‐induced changes in gene expression may be effected by different mechanisms, at least at the level of polypeptide accumulation.