镉引起小麦苗逆境乙烯的产生及其和镉的吸收分布的关系

溶液培养小麦幼苗转移至含Cd~(2 )的营养液中,根系乙烯产生较快地增加,约在12h达高峰,然后下降;ACC含量亦呈先升后降的趋势。未和Cd~(2 )溶液直接接触的地上部乙烯亦增加,至36h达高峰,此后急剧下降,而ACG和 MAGC含量持续上升。地上部乙烯的增加,主要是由通过根系运往地上部的镉直接作用的结果,不是根部合成ACG运往地上部后再产生的。电镜观察表明,地上部乙烯产生和ACC含量变化的时间进程,可以与镉进入叶细胞内的部位及其对细胞膜和细胞器的影响相联系。     

不同方式干旱胁迫对小麦乙烯释放、ACC和MACC含量的影响

小麦在离体气干时,C_2H_4和ACC先升后降MACC持续增加;在整体土旱条件下,乙烯不增加,ACC和MACG含量也没有明显变化。用PEG溶液进行干旱模拟实验,渗透势在-5×10~5P_a以下的一次性处理能使小麦植株的C_2H_4,ACO和MACC水平增高;逐步降低渗透势,则三者皆不增加。两种反应情况分别与离体气干和整体土旱相似,说明干旱胁迫的方式和强度的不同导致小麦植株发生不同的反应。     

接触二氧化硫后小麦叶片中逆境乙烯的生物合成

AVG和AOA强烈抑制二氧化硫处理小麦叶片中乙烯产生和ACC合成,对MACC的形成也有一定的抑制作用。CoGl_2明显抑制乙烯产生,而ACC大量积累,MACC含量则未因ACC增加而相应增加。DNP和CCCP也抑制乙烯产生,但前者引起ACC大量积累,后者引起ACC含量下降。CHI对乙烯产生和ACC形成均显示强烈的抑制作用,同时也明显抑制MACC形成。这表明小麦叶片接触SO_2引起的逆境乙烯也是循蛋氨酸→SAM→ACC→乙烯途径。     

钙对香蕉采后乙烯释放的抑制

本实验用CaCl_2溶液对香蕉(Musa acuminata cf. 'Dwarf Davendish')组织进行真空浸透处理,研究Ca~(2 )对香蕉采后乙烯释放、EFE活性、ACC水平以及ACC/MACC比值的影响。结果表明,Ca~(2 )处理可抑制香蕉果皮和果肉组织乙烯生成,对抑制果皮的乙烯生成尤为明显。Ca~(2 )处理还可降低内源ACC水平,抑制EFE活性。结果还显示,Ca~(2 )处理对组织中ACC/MACC比值有一定影响。     

外源乙烯对月季(Rosa hybrida)切花花朵开放的影响与乙烯生物合成相关基因表达的关联

以探讨外源乙烯对月季切花花朵开放的影响及其与花瓣内源乙烯生物合成相关基因表达之间的关联为目的. 试材选用外源乙烯对花朵开放进程影响截然相反的两个品种, 其中, Samantha明显被促进, 而Kardinal则明显被抑制. 经外源乙烯处理, 两品种花瓣乙烯生成量、1-氨基环丙烷-1-羧酸(1-aminocyclopropane -1-carboxylate, ACC)合成酶(ACC synthase, ACS)和ACC氧化酶(ACC oxidase, ACO)活性都被诱导升高. 但是, 以上指标两品种间变化有差异, 其中, Samantha主要表现为峰值提前, 即由未经处理对照的盛开期(开花级数4级)提早到初开期(3级); 而Kardinal主要表现为绝对值剧烈升高, 且远高于Samantha. 从花瓣中克隆到3个ACS (Rh-ACS1, Rh-ACS2和Rh-ACS3)和1个ACO(Rh-ACO1)基因的cDNA, 非放射性Northern检测结果表明, Rh-ACS3和Rh-ACO1基因的表达受到乙烯的诱导, 并且其表达变化在两个品种中都与ACS活性和乙烯生成量相一致. 由此推测, 外源乙烯对切花月季品种间花朵开放影响的差异, 可能与花瓣内乙烯生物合成关键酶转录水平上的诱导差异有关, 并且Kardinal可能对外源乙烯更为敏感. 还明确了月季切花3个ACS基因之间的表达存在发育时间和诱导方式上的特异性.     

氧和二氧化碳对莱阳梨果肉切片乙烯生物合成的调节作用

跃变期的莱阳梨果肉切片保温12h期间,降低空气中O_2浓度使乙烯生成减少,ACC含量相应增加,解除处理后,除0％O_2处理外都能恢复相应的乙烯生成速率。CO_2对乙烯生成有促进和抑制双重作用,处理初期表现出促进,O_2浓度低时更显著,随保温时间延长CO_2表现出抑制作用并继续增强。CO_2浓度增高,乙烯生成的抑制增强,ACC含量变化与乙烯减少之间没有很好的相应关系,解除CO_2处理后乙烯生成速率不能恢复。     

高温对两种植物组织乙烯产生的作用

两种喜温程度不同的植物组织对高温的反应不同,35℃开始抑制小麦叶片乙烯产生,而黄豆下胚轴在35～40℃乙烯仍增加,45℃才受到抑制。乙烯生物合成途径中的两个主要步骤对高温的反应也不一样,ACC合成在40℃下还受到促进,ACC转化为乙烯这一步,则是高温钝化的主要位点。小麦叶片经短期40℃处理后回到常温下,经过滞后期出现乙烯剧增现象,表示高温下暂时受损的乙烯形成系统在常温下恢复功能后,可使积存的ACC转化为乙烯。MACC含量在高温逆境下无明显变化。     

乙烯与水浮莲(Pistia stratiotes)种子需光性休眠的关系

水浮莲种子是一种奇特的需光种子。在黑暗中,GA_2或BA均不能代替光照诱导萌发,可是0.1μl/l乙烯却能引起部分种子萌发,在1000μ1/1乙烯的作用下,发芽率可达80％,接近全光照处理的萌发水平(91％发芽率)。ACC也能诱导水浮莲种子的萌发,0.1 mM浓度可获30％发芽率。在较短光照下,ACC对种子萌发有增效作用。在光照前应用ACC,其诱导效应大于两者同时施用。在照光萌发中,种子的内源ACC含量及乙烯释放量均显著增加。CoCl_2和AOA均能抑制光的诱导萌发。推论光打破休眠诱导萌发的作用是与乙烯的生成密切相关。     

含ACC脱氨酶的根际细菌提高植物抗盐性的研究进展

盐胁迫是抑制植物生长的主要非生物因素之一,高浓度的盐分不利于植物体的生长和发育,严重时会导致植物细胞及植物体死亡。已有大量实验结果显示含ACC脱氨酶的根际细菌可以缓解高盐对植物的危害。ACC脱氨酶可以降解乙烯的直接前体1-氨基环丙烷-1-羧酸(ACC),从而降低胁迫乙烯的合成量。胁迫乙烯是阻碍植物生长的主要原因。首先介绍了根际促生细菌的概念,概括了高盐对植物的毒害作用以及乙烯的生物合成和生理效应,着重阐述了含ACC脱氨酶的根际细菌的作用方式及其提高植物耐盐性的生理机制,以期为这类细菌在农业生产中的应用提供理论支撑。     

二氧化硫熏气对小麦叶片中1-氨基环丙烷-1-羧酸、1-(丙二酰氨基)环丙烷-1-羧酸含量的影响及与乙烯产生的关系

在SO_2熏气9h过程中,小麦叶片中乙烯先上升,约6h达高峰,后下降;ACC含量则随熏气时间的延长而上升。停止熏气,乙烯继续下降,ACC含量也明显降低。MACC含量从熏气3h后不断上升,脱离接触后仍继续增加。6-BA预处理对SO_2引起的乙烯和ACC上升有促进作用,但对MACC含量无明显影响。SO_2熏气提高了乙烯形成酶活性。6-BA预处理对SO_2伤害有保护作用。对逆境乙烯的产生与调节作用进行了讨论。     

The Conversion of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid to 1-Aminocyclopropane-1-Carboxylic Acid in Plant Tissues

Since 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), the major conjugate of 1-aminocyclopropane-1-carboxylic acid (ACC) in plant tissues, is a poor ethylene producer, it is generally thought that MACC is a biologically inactive end product of ACC. In the present study we have shown that the capability of watercress (Nasturtium officinale R. Br) stem sections and tobacco (Nicotiana tabacum L.) leaf discs to convert exogenously applied MACC to ACC increased with increasing MACC concentrations (0.2-5 millimolar) and duration (4-48 hours) of the treatment. The MACC-induced ethylene production was inhibited by CoCl₂ but not by aminoethoxyvinylglycin, suggesting that the ACC formed is derived from the MACC applied, and not from the methionine pathway. This was further confirmed by the observation that radioactive MACC released radioactive ACC and ethylene. A cell-free extract, which catalyzes the conversion of MACC to ACC, was prepared from watercress stems which were preincubated with 1 millimolar MACC for 24 hours. Neither fresh tissues nor aged tissues incubated without external MACC exhibited enzymic activity, confirming the view that the enzyme is induced by MACC. The enzyme had a K_m of 0.45 millimolar for MACC and showed maximal activity at pH 8.0 in the presence of 1 millimolar MnSO₄. The present study indicates that high MACC levels in the plant tissue can induce to some extent the capability to convert MACC to ACC.     

Autoinhibition of Ethylene Production in Citrus Peel Discs : SUPPRESSION OF 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHESIS

Wound ethylene formation induced in flavede tissue of citrus fruit (Citrus paradisi MacFad. cv. Ruby Red) by slicing was almost completely inhibited by exogenous ethylene. The inhibition lasted for at least 6 hours after removal of exogenous ethylene and was then gradually relieved. The extent of inhibition was dependent upon the concentration of ethylene (1 to 10 microliters/liter) and the duration of treatment. The increase in wound ethylene production in control discs was paralleled by an increase in 1-aminocyclopropane-1-carboxylic acid (AAC) content, whereas in ethylene-treated discs there was little increase in ACC content. Application of ACC completely restored ethylene production in ethylene-pretreated discs, indicating that the conversion of ACC to ethylene is not impaired by the presence of ethylene. Thus, autoinhibition of ethylene synthesis was exerted by reducing the availability of ACC. Ethylene treatment resulted in a decrease in extractable ACC synthase activity, but this decrease was too small to account for the marked inhibition of ACC formation. The data indicate that autoinhibition of ethylene production in citrus flavede discs results from suppression of ACC formation through repression of the synthesis of ACC synthase and inhibition of its activity.     

The effect of water stress on 1-(malonylamino)cyclopropane-1-carboxylic acid concentration in plant tissues

Since the discovery of1-(malonylamino)cyclopropane-1-carboxylic acid (MACC)as a major metabolite of both endogenous andexogenously applied 1-aminocyclopropane-1-carboxylicacid (ACC), it has become evident that the formationof MACC from ACC can act to regulate ethyleneproduction in certain tissues. Hence it was suggestedthat MACC could serve as an indicator of water-stresshistory in plant tissues. The accurate quantificationof MACC in plant tissues is essential forunderstanding the role of MACC in the regulation ofethylene biosynthesis.Hoffman et al. [15] described a method for themeasurement of MACC in which MACC was hydrolysed byHCl to ACC, which was then assayed by chemicaloxidation to form ethylene. Attempts have been made byothers to raise monoclonal antibodies to MACC so thatan immunoassay could be developed in order to gain adeeper understanding of stress-induced ethyleneproduction but no further publications have beenforthcoming.Here a method employing GC-MS is compared with theindirect assay for MACC, which is based uponhydrolysis of MACC to ACC and conversion of ACC byhypochlorite reagent to ethylene which is subsequentlyquantified by GC.     

Changes in 1-(malonylamino)cyclopropane-1-carboxylic acid content in wilted wheat leaves in relation to their ethylene production rates and 1-aminocyclopropane-1-carboxylic acid content

In excised wheat (Triticum aestivum L.) leaves, water-deficit stress resulted in a rapid increase, followed by a decrease, in ethylene production rates and in the levels of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene. However, the level of N-malonyl-ACC (MACC), the major metabolite of ACC, increased gradually, then leveled off. This increase in MACC was much greater than the decrease in ACC level. The MACC levels were positively correlated with severity of water stress. Once established, the MACC levels did not decrease even after the stressed tissues were rehydrated. Administration of labeled ACC and MACC showed that the conjugation of ACC to MACC was essentially irreversible. Repeated wilting treatments following the first wilting and rehydration cycle resulted in no further increase in ethylene production and in the levels of ACC and MACC. However, when benzyladenine was supplied during the preceding rehydration process, subsequent wilting treatment resulted in a rise in MACC level and a rapid rise followed by a decline in ethylene production rates and in the level of ACC. The magnitude of these increases was, however, smaller in these rewilted tissues than that observed in the first wilting treatment. Since MACC accumulates with water stress and is not appreciably metabolized, the MACC level is a good indicator of the stress history in the detached leaves used.     

Accumulation of 1-(malonylamino)cyclopropane-1-carboxylic acid in ethylene-synthesizing tobacco leaves

During the hypersensitive reaction of Samsun NN tobacco to tobacco mosaic virus (TMV) the inoculated leaves synthesize large quantities of ethylene. At the same time, 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), a conjugate of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) accumulates. Smaller amounts of MACC are formed concomitant with ethylene synthesis during the normal development of tobacco leaves. The conjugate appears neither to be hydrolysed to liberate ACC, nor to be transported to other plant parts. Its accumulation thus reflects the history of the operation of the pathway of ethylene synthesis in the leaf. In floating leaf discs exogenously applied ACC was converted only slowly to both ethylene and MACC. More ethylene and less MACC were produced in darkness than in light, suggesting that environmental conditions may influence the ratio at which ACC in converted to either ethylene or MACC.     

Transport and Metabolism of 1-Aminocyclopropane-1-carboxylic Acid in Sunflower (Helianthus annuus L.) Seedlings

Transport and metabolism of [2,3-¹⁴C] 1-aminocyclopropane-1-carboxylic acid (ACC) from roots to shoots in 4-day-old sunflower (Helianthus annuus L.) seedlings were studied. [¹⁴C]ACC was detected in, and ¹⁴C₂H₄ was evolved from, shoots 0.5 hours after [¹⁴C]ACC was supplied to roots. Ethylene emanation from the shoots returned to normal levels after 6 hours. The roots showed a similar pattern, although at 24 hours ethylene emanation was still slightly higher than in those plants that did not receive ACC. [¹⁴C]N-malonyl-ACC (MACC) was detected in both tissues at all times sampled. [¹⁴C]MACC levels surpassed [¹⁴C]ACC levels in the shoot at 2 hours, whereas [¹⁴C]MACC levels in the root remained below [¹⁴C]ACC levels until 6 hours, after which they were higher. Thin-layer chromatography analysis identified [¹⁴C] ACC in 1-hour shoot extracts, and [¹⁴C]MACC was identified in root tissues at 1 and 12 hours after treatment. [¹⁴C]ACC and [¹⁴C] MACC in the xylem sap of treated seedlings were identified by thin-layer chromatography. Xylem transport of [¹⁴C]ACC in treated seedlings, and transport of ACC in untreated seedlings, was confirmed by gas chromatography-mass spectrometry. Some evidence for the presence of [¹⁴C]MACC in xylem sap in [¹⁴C]ACC-treated seedlings is presented. A substantial amount of radioactivity in both ACC and MACC fractions was detected leaking from the roots over 24 hours. A second radiolabeled volatile compound was trapped in a CO₂-trapping solution but not in mercuric perchlorate. Levels of this compound were highest after the peak of ACC levels and before peak MACC levels in both tissues, suggesting that an alternate pathway of ACC metabolism was operating in this system.     

The quantification of 1-(malonylamino)cyclopropane-1-carboxylic acid in plant tissues by quantitative mass spectrometry

A method for the quantitation of 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), a conjugated form of 1-aminocyclopropane-1-carboxylic acid (ACC), in plants is described. [2,2,3,3-²H₄]MACC has been used as an internal standard for selected ion monitoring/isotope dilution quantitation of MACC in wheat seedlings and in tomato leaves. This method is compared with a widely-used two step indirect assay for MACC, which is based upon hydrolysis of MACC to ACC and conversion of ACC by hypochlorite reagent to ethylene which is subsequently quantified by gas chromatography.     

Intracellular Sites of Synthesis and Storage of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid in Acer pseudoplatanus Cells

Vacuoles were isolated from Acer pseudoplatanus cells that were incubated with [¹⁴C]1-aminocyclopropane-1-carboxylic acid (ACC). The kinetics of [¹⁴C]1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) formation are consistent with the interpretation that MACC is synthesized in the cytosol, transported through the tonoplast, and accumulated in the vacuole. Twenty hours after chasing the labeled ACC with unlabeled ACC and adding 1 millimolar unlabeled MACC, all the [¹⁴C]MACC synthesized is located in the vacuole. Whole cells preloaded with [¹⁴C]MACC and then submitted to a continuous washing out, readily release their cytosolic MACC until complete exhaustion. The half-time of MACC efflux from the cytosol, calculated by the technique of compartmental analysis, is about 22 minutes. In contrast, vacuolar MACC remains sequestered within the vacuole. The transport of labeled MACC into the vacuole is stimulated by the presence of unlabeled MACC in the suspension medium, probably as a result of a reduced efflux of the labeled MACC from the cytosol into the suspending medium.     

Evidence for 1-(Malonylamino)cyclopropane-1-Carboxylic Acid Being the Major Conjugate of Aminocyclopropane-1-Carboxylic Acid in Tomato Fruit

Tomato (Lycopersicon esculentum Miller) fruit discs fed with [2,3-¹⁴C]1-aminocyclopropane-1-carboxylic acid (ACC) formed 1-malonyl-ACC (MACC) as the major conjugate of ACC in fruit throughout all ripening stages, from immature-green through the red-ripe stage. Another conjugate of ACC, γ-glutamyl-ACC (GACC), was formed only in mature-green fruit in an amount about 10% of that of MACC; conjugation of ACC into GACC was not detected in fruits at other ripening stages. No GACC formation was observed from etiolated mung bean (Vigna radiata [L.] Wilczek) hypocotyls, etiolated common vetch (Vicia sativum L.) epicotyls, or pea (Pisum sativum L.) root tips, etiolated epicotyls, and green stem tissue, where active conversion of ACC into MACC was observed. GACC was, however, formed in vitro in extracts from fruit of all ripening stages. GACC formation in an extract from red fruit at pH 7.15 was only about 3% of that at pH 8.0, the pH at which most assays were run. Our present in vivo data support the previous contention that MACC is the major conjugate of ACC in plant tissues, whereas GACC is a minor, if any, conjugate of ACC. Thus, our data do not support the proposal that GACC formation could be more important than MACC formation in tomato fruit.     

Activity of Ageing Carnation Flower Parts and the Effects of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid-Induced Ethylene

Peak levels of 1-aminocyclopropane-l-carboxylic acid (ACC) in flower parts of ageing carnations (Dianthus caryophyllus L. cv Scanea 3C) were detected 6 to 9 days after flower opening. The ethylene climacteric and the first visible sign of wilting was observed 7 days after opening. The concentration of conjugated ACC in these same tissues peaked at day three with reduction of 70% by day 4. From day 5 to day 9 all parts followed a diurnal pattern of increasing in conjugate levels 1 day and decreasing the next. Concentrations of conjugated ACC were significantly higher than those of ACC in all ageing parts. Preclimacteric petals treated with ACC or 1-(malonylamino)-cycloprane-1-carboxylic acid (MACC), started to senesce 30 to 36 hours after treatment. When petals were treated with MACC plus by 0.1 millimolar aminoethyoxyvinylglycine, premature senescence was induced, while ethylene production was suppressed relative to MACC-treated petals. Petals treated with MACC and silver complex produced ethylene, but did not senesce. The MACC-induced ethylene was inhibited by the addition of 1.0 millimolar CoC1₂. These results demonstrate MACC-induced senescence in preclimacteric petals. The patterns of ACC and MACC detected in the flower parts support the view that an individual part probably does not export an ethylene precursor to the remainder of the flower inducing senescence.