Endogenous Abscisic Acid Promotes Hypocotyl Growth and Affects Endoreduplication during Dark-Induced Growth in Tomato (Solanum lycopersicum L.)

Dark-induced growth (skotomorphogenesis) is primarily characterized by rapid elongation of the hypocotyl. We have studied the role of abscisic acid (ABA) during the development of young tomato (Solanum lycopersicum L.) seedlings. We observed that ABA deficiency caused a reduction in hypocotyl growth at the level of cell elongation and that the growth in ABA-deficient plants could be improved by treatment with exogenous ABA, through which the plants show a concentration dependent response. In addition, ABA accumulated in dark-grown tomato seedlings that grew rapidly, whereas seedlings grown under blue light exhibited low growth rates and accumulated less ABA. We demonstrated that ABA promotes DNA endoreduplication by enhancing the expression of the genes encoding inhibitors of cyclin-dependent kinases SlKRP1 and SlKRP3 and by reducing cytokinin levels. These data were supported by the expression analysis of the genes which encode enzymes involved in ABA and CK metabolism. Our results show that ABA is essential for the process of hypocotyl elongation and that appropriate control of the endogenous level of ABA is required in order to drive the growth of etiolated seedlings.     

亚适宜温光下萘乙酸钠对番茄幼苗生长与生理特性的影响

以番茄“中杂105”为试材,研究亚适宜温光条件下根施10 mg·L^-1萘乙酸钠对番茄幼苗生长与生理特性的影响.结果表明： 亚适宜温光处理番茄幼苗生物量、壮苗指数、根系活力、光合速率、根系和叶片中全氮含量均显著下降,超氧化物歧化酶和过氧化物酶活性升高,过氧化氢酶活性降低,玉米素核苷含量显著下降,而脱落酸含量显著增加.亚适宜温光条件下,与对照相比,根施10 mg·L^-1萘乙酸钠可使番茄幼苗全株干质量、壮苗指数分别提高16.4%、22.9%,并使根、叶中全N含量及光合速率分别增加8.5%、28.5%、37.0%,提高根系活力和保护酶活性,增加吲哚乙酸和玉米素核苷含量,抑制脱落酸含量的增加.亚适宜温光处理下,根施10 mg·L^-1萘乙酸钠可以通过提高番茄幼苗根系活力、保护酶活性和光合速率,调控内源激素水平变化,促进番茄幼苗生长.     

ABA- and ethylene-mediated responses in osmotically stressed tomato are regulated by the TSS2 and TOS1 loci

The study of mutants impaired in the sensitivity or synthesis of abscisic acid (ABA) has become a powerful tool to analyse the interactions occurring between the ABA and ethylene signalling pathways, with potential to change the traditional view of the role of ABA as just being involved in growth inhibition. The tss2 tomato mutant, which is hypersensitive to NaCl and osmotic stress, shows enhanced growth inhibition in the presence of exogenous ABA. The tos1 tomato mutant is also hypersensitive to osmotic stress, but in contrast to tss2, shows decreased sensitivity to ABA. Surprisingly, blocking ethylene signalling suppresses the growth defect of tss2 seedlings on ABA, NaCl, and osmotic stress, but not the osmotic hypersensitivity of tos1. The ethylene production of tss2 seedlings is increased compared with that of control seedlings under osmotic stress. In addition, the tss2 plants are hypersensitive to root growth inhibition by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). This suggests that, in addition to ABA regulation, TSS2 acts as a negative regulator of endogenous ethylene accumulation. As previously shown in Arabidopsis, it is shown here that extensive cross-talk occurs between the ABA and ethylene signalling pathways in tomato and that the TSS2 and TOS1 loci appear as regulators of this cross-talk.     

The Effect of Exogenous ABA on the Resistance to the Chilling Stress in Cucumber Seedlings

In the cucumber seedlings pretreated with ABA under light and dark or additional photosynthetic inhibitor (DCMU) before chilling, the effect and the regulative role of ABA on the chilling resistance of cucumber seedlings were investigated. After the excised cotyledonary discs were floated on 10-6 mol/l ABA solution for 24 h and the seedlings were sprayed by 10-4 mol/1 ABA in light, it has been found that ABA has an effect of the protection against low temperature injury in cucumber seedlings. The results showed that the leakage of electrolytes in cucumber cotyledory discs was decreased. The content of glutathione and the accumulation of MDA content in cotyledon of cucumber seedlings were decreased, and decline of the photosynthesis of the leaves or the quenching of chlorophyll fluorescence were slowed, thus the rate of survival in cucumber seedlings was raised. The effect of these regulation was able to be limited by dark or DCMU.     

外源ABA对黄瓜幼苗抗低温胁迫的作用

在光照下对黄瓜(Cucuntis sativus L.)离体子叶圆片和幼苗分别使用10~(-6)mol/l 与10~(-4)mol/l ABA 处理,有防御低温伤害的作用,表现为降低子叶圆片的电解质渗漏,阻抑幼苗子叶的谷胱甘肽含量的下降和膜脂过氧化产物丙二醛(MDA)的累积,减缓叶片的光合作用的下降和叶绿素荧光的猝灭,提高幼苗的存活率。但这种作用可被黑暗和光合抑制剂(DCMU)所限制。     

外源脱落酸对小麦幼苗抗镉胁迫能力的影响

以小麦(Triticum aestivum L.)为试材,采用水培法研究了100mg/L镉(Cd2+)胁迫条件下施用外源脱落酸(ABA)对小麦幼苗生长及某些生理生化指标的影响。结果表明:(1)100mg/L Cd2+胁迫下,小麦叶片膜脂过氧化产物丙二醛(MDA)含量显著提高,植株生长受到抑制;(2)外源ABA能够明显提高Cd2+胁迫小麦幼苗的根系活力,增加其叶片SOD、CAT和POD活性,促进其脯氨酸积累,降低MDA的含量,并以5.0μmol/L ABA的效果最明显;(3)1.0～5.0μmol/L外源ABA不同程度地缓解Cd2+胁迫对小麦幼苗生长的抑制作用,且5.0μmol/L时效果最明显,其株高、根长、总干重分别比单一Cd2+胁迫处理显著提高6.73%、149%和10.52%,而10.0μmol/LABA反而加重了Cd2+对小麦幼苗生长的伤害。因此,适宜浓度的外源ABA能够通过增加体内保护酶活性和脯氨酸含量来缓解Cd2+胁迫对小麦幼苗生长的抑制作用,增强小麦幼苗的抗Cd2+胁迫能力,并以5.0μmol/L ABA处理效果最好。     

残留地膜对番茄幼苗形态和生理特性的影响

采用盆栽试验的方法,研究了土壤中残留地膜对番茄(Lycopersicon esculentum L.)幼苗形态及生理特性的影响.结果表明,残留地膜使番茄幼苗的株高、茎粗、地上部和根系鲜重、根系活力及叶片氮代谢水平等降低;而且根系的IBA含量降低和ABA含量增加,抑制了根系的生长.同时地膜残留量越大,抑制的效果越显著.这...     

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.     

Abscisic acid root and leaf concentration in relation to biomass partitioning in salinized tomato plants

Salinization is one of the most important causes of crop productivity reduction in many areas of the world. Mechanisms that control leaf growth and shoot development under the osmotic phase of salinity are still obscure, and opinions differ regarding the Abscisic acid (ABA) role in regulation of biomass allocation under salt stress. ABA concentration in roots and leaves was analyzed in a genotype of processing tomato under two increasing levels of salinity stress for five weeks: 100 mM NaCl (S10) and 150 mM NaCl (S15), to study the effect of ABA changes on leaf gas exchange and dry matter partitioning of this crop under salinity conditions. In S15, salinization decreased dry matter by 78% and induced significant increases of Na⁺ and Cl⁻ in both leaves and roots. Dry matter allocated in different parts of plant was significantly different in salt-stressed treatments, as salinization increased root/shoot ratio 2-fold in S15 and 3-fold in S15 compared to the control. Total leaf water potential (Ψ_w) decreased from an average value of approximately −1.0 MPa, measured on control plants and S10, to −1.17 MPa in S15. In S15, photosynthesis was reduced by 23% and stomatal conductance decreased by 61%. Moreover, salinity induced ABA accumulation both in tomato leaves and roots of the more stressed treatment (S15), where ABA level was higher in roots than in leaves (550 and 312 ng g⁻¹ fresh weight, respectively). Our results suggest that the dynamics of ABA and ion accumulation in tomato leaves significantly affected both growth and gas exchange-related parameters in tomato. In particular, ABA appeared to be involved in the tomato salinity response and could play an important role in dry matter partitioning between roots and shoots of tomato plants subjected to salt stress.     

Overexpression of a rice defense-related F-box protein gene OsDRF1 in tobacco improves disease resistance through potentiation of defense gene expression

F-box proteins play important roles in plant growth/development and responses to environmental stimuli through targeting substrates into degradation machinery. A rice defense-related F-box protein gene, OsDRF1, was cloned and identified during a course of study aimed at elucidating the molecular basis of induced immunity in rice. OsDRF1 encodes a protein of 328 amino acids, containing a highly conserved F-box domain. Expression of OsDRF1 was induced upon treatment with benzothiadiazole (BTH), a chemical inducer of defense responses in rice. Moreover, in BTH-treated rice seedlings, expression of OsDRF1 was further induced by infection with Magnaporthe grisea, the rice blast fungus, compared with those in water-treated seedlings. OsDRF1 was also upregulated in rice seedlings after treatment with ABA. Overexpression of OsDRF1 in transgenic tobacco resulted in enhanced disease resistance against tomato mosaic virus (ToMV) and Pseudomonas syringae pv. tabaci and strengthened expression of defense-related genes after salicylic acid treatment or ToMV infection. Root elongation of the OsDRF1-overexpressing transgenic seedlings was significantly inhibited by ABA, indicating that overexpression of OsDRF1 resulted in increased ABA sensitivity. The results suggest that OsDRF1 plays a role in disease resistance via upregulating defense-related gene expression and that OsDRF1 may also be involved in the response to ABA.     

Carotenoid composition and down regulation of photosystem II in three conifer species during the winter

Seedlings and coppice shoots of Betula pubescens Ehrh. were grown under controlled conditions designed to simulate the annual growth cycle, and a water stress was introduced during the short day (SD). Alleviation of hud dormancy after increasing periods at chilling temperatures was tested under long day (LD) conditions. Abscisic acid (ABA) was analysed in leaf and bud samples by gas chromatography-mass spectrometry using [²H₄]ABA as the internal standard. Elongation growth of coppice shoots was faster than that of seedlings under both LD and SD conditions, while the final growth cessation occurred in a similar manner and was not affected by water stress, which significantly reduced growth rate in both plant types. Bud dormancy gradually decreased with increasing length of chilling, starting from the basal parts of the plant axis. Water stress did not retard hudhurst. but rather improved it in the chilled coppice shoots and in the non-chilled and partially chilled seedlings. Water content of buds was higher in coppice shoots than in seedlings, but after exposure to SD. it gradually decreased to 45% in both plant types and was not affected by water stress or chilling. The ABA level in both leaves and buds increased during SD treatment and was" enhanced by water stress. No clear differences in bud ABA level were found between the seedlings and coppice shoots under SD conditions, although coppice shoots had less ABA during the preceding LD conditions. There was, in general, no clear effect of chilling on bud ABA level. Budbursl in chilled, single-node cuttings was inhibited by external ABA treatment, which raised the internal ABA levels 10 to 150 times above normal. The observed correlation between ABA level and water content in buds during induction of dormancy under SD and water stress conditions indicates a possible role for ABA in the regulation of dormancy.     

Ectopic expression of a tomato 9-cis-epoxycarotenoid dioxygenase gene causes over-production of abscisic acid

The tomato mutant notabilis has a wilty phenotype as a result of abscisic acid (ABA) deficiency. The wild-type allele of notabilis, LeNCED1, encodes a putative 9-cis-epoxycarotenoid dioxygenase (NCED) with a potential regulatory role in ABA biosynthesis. We have created transgenic tobacco plants in which expression of the LeNCED1 coding region is under tetracycline-inducible control. When leaf explants from these plants were treated with tetracycline, NCED mRNA was induced and bulk leaf ABA content increased by up to 10-fold. Transgenic tomato plants were also produced containing the LeNCED1 coding region under the control of one of two strong constitutive promoters, either the doubly enhanced CaMV 35S promoter or the chimaeric 'Super-Promoter'. Many of these plants were wilty, suggesting co-suppression of endogenous gene activity; however three transformants displayed a common, heritable phenotype that could be due to enhanced ABA biosynthesis, showing increased guttation and seed dormancy. Progeny from two of these transformants were further characterized, and it was shown that they also exhibited reduced stomatal conductance, increased NCED mRNA and elevated seed ABA content. Progeny of one transformant had significantly higher bulk leaf ABA content compared to the wild type. The increased seed dormancy was reversed by addition of the carotenoid biosynthesis inhibitor norflurazon. These data provide strong evidence that NCED is indeed a key regulatory enzyme in ABA biosynthesis in leaves, and demonstrate for the first time that plant ABA content can be increased through manipulating NCED.     

亚适温条件下缺铁和硝酸盐胁迫对番茄幼苗生长及铁吸收的影响

研究亚适温(昼/夜18 ℃/12 ℃)条件下缺铁和硝酸盐胁迫对番茄幼苗生长及铁吸收的影响.结果表明: 与适温对照相比,亚适温条件下番茄幼苗生长受到明显的抑制,株高、叶面积显著变小,干物质积累下降;亚适温下缺铁对番茄幼苗生长的影响比适温下缺铁的影响大.亚适温条件下,缺铁、硝酸盐胁迫及二者同时胁迫的番茄幼苗株高与无胁迫处理差异不显著,但幼苗叶面积明显变小,电解质渗漏率、根系活力和三价铁还原酶活性明显增加,叶绿素含量降低;根总长、根表面积、根体积及根尖数明显减小;幼苗根、茎、叶中铁含量明显降低.亚适温下硝酸盐胁迫以及缺铁与硝酸盐二者同时胁迫加重了番茄幼苗干物质积累的减少、电解质渗漏率的增加,以及减少了对铁离子的吸收.Fe²⁺对K⁺和Ca²⁺吸收具有拮抗作用,不同器官中的表现有所差异;降低营养液中的Fe²⁺浓度可使番茄幼苗的缺铁症状更加严重.     

Abscisic acid-induced hydrogen peroxide is required for anthocyanin accumulation in leaves of rice seedlings

The role of hydrogen peroxide (H(2)O(2)) in abscisic acid (ABA)-induced anthocyanin accumulation in detached and intact leaves of rice seedlings was investigated. Treatment with ABA resulted in an accumulation of anthocyanins in detached rice leaves. Dimethylthiourea, a chemical trap for H(2)O(2), was observed to be effective in inhibiting ABA-induced accumulation of anthocyanins. Inhibitors of NADPH oxidase (diphenyleneiodonium chloride and imidazole), phosphatidylinositol 3-kinase (wortmannin and LY 294002), and a donor of nitric oxide (N-tert-butyl-alpha-phenylnitrone), which have previously been shown to prevent ABA-induced H(2)O(2) accumulation in detached rice leaves, inhibited ABA-induced anthocyanin increase. Exogenous application of H(2)O(2), however, was found to increase the anthocyanin content of detached rice leaves. In terms of H(2)O(2) accumulation, intact (attached) leaves of rice seedlings of cultivar Taichung Native 1 (TN1) are ABA sensitive and those of cultivar Tainung 67 (TNG67) are ABA insensitive. Upon treatment with ABA, H(2)O(2) and anthocyanins accumulated in leaves of TN1 seedlings but not in leaves of TNG67. Our results, obtained from detached and intact leaves of rice seedlings, suggest that H(2)O(2) is involved in ABA-induced anthocyanin accumulation in this species.     

Production of Polyamines Is Enhanced by Endogenous Abscisic Acid in Maize Seedlings Subjected to Salt Stress

It is known that salt stress and exogenously applied abscisic acid （ABA） can enhance the polyamine content in plants and that salt stress itself can lead to an increase in endogenous ABA production. In the present study, the relationships between salt-induced ABA and polyamine accumulation were inves- tigated using ABA-deficient mutant （vp5/vp5） maize （Zea mays L.） seedlings and ABA and polyamine biosynthesis inhibitors. The results show that reduced endogenous ABA levels, as a result of either the mutation or by using a chemical inhibitor （sodium tungstate）, also reduced the accumulation of polyamines in salt-stressed leaves of maize seedlings. The polyamine synthesis inhibitors D-arginine and α- difluoromethylornithine also reduced the polyamine content of the leaves of maize seedling under salt stress. Both ABA and polyamine enhanced the dry weight accumulation of salt-stressed seedlings and also increased the activities of the two dominant tonoplast membrane enzymes, H^＋-ATPase and H^＋-PPase, when plants were under salt stress. The results suggest that salt stress induces an increase in endogenous ABA levels, which then enhances polyamine synthesis. Such responses may increase a plant＇s tolerance to salt.     

干旱胁迫下氮素营养与根信号在气孔运动调控中的协同作用

干旱胁迫下根系与地上部分之间的信息传递可使植物叶片及时感知土壤水势变化,从而使植物在没有真正受到干旱伤害时即可做出主动、快速的抗旱应答反应,而在这一过程中,脱落酸（abscisic acid,ABA）和pH起着关键的作用。本研究表明。干旱胁迫下鸭趾草（Commelina communis L．）、番茄（Lycopersicon esculentum Mill．）和向日葵（Helianthus annuus L．）木质部汁液中pH的变化很不相同,且该pH变化和木质部汁液中硝态氮离子浓度的变化没有直接的关系;然而,饲喂实验表明,无论对于何种植物,蒸腾流中硝态氮离子浓度的增加都可有效地增加气孔对ABA的敏感度;分根实验进一步表明,土壤中硝态氮营养的增加可明显提高气孔对根信号的敏感度。以上结果说明,氮素营养可以和根信号相互作用共同操纵气孔运动。     

Effect of ethylene perception inhibitor on growth, water relations, and abscisic acid content in wheat plants under water deficit

The effects of treatment with 1-methylcyclopropene (1-MCP, the inhibitor of ethylene receptors) of 7-day-old wheat (Triticum durum Desf., cv. Bezenchukskaya 139) seedlings on growth characteristics, water relations, and the content of phytohormones during three days after watering cessation were studied. In treated seedlings, a decrease in the water content in the substrate resulted in a decrease in stomatal conductance in the leaves by one day earlier than in untreated seedlings. This could be related to the more rapid and substantial accumulation of ABA in treated plants. There was no clear relationship between changes in the content of cytokinins and water relations under the influence of 1-MCP under drought conditions. The role of ethylene and ABA in the regulation of growth and water relations in plants suffering from water deficit is discussed.