Effect of 1-aminocyclopropane-1-carboxylic acid on maize kernel development in vitro

Pollination stimulates ethylene production in maize ears, and the application of ethephon during the pollination period can cause kernel abortion. The objective of this study was to determine if kernel abortion could be induced in vitro by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). Adding ACC to the culture medium resulted in the evolution of ethylene which caused abortion and reduced mature kernel mass. The effect of ethylene on kernel abortion and dry matter accumulation was partially negated by the addition of the ethylene-binding site inhibitor, 2,5-norbornadiene (NBD). The effect of ethylene on kernel abortion was greatest during the early stage of kernel development and was intensified by an increase in media sucrose concentration. These data suggest that ethylene could regulate kernel abortion in maize.Contribution of the Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108. Paper No. 17,088, Scientific Journal Series, Minnesota Agriculture Experimental Station.     

Transport of 1-aminocyclopropane-1-carboxylic acid into isolated maize mesophyll vacuoles

Intracellular transport of the ethylene precursor, I-aminocyclopropane-1-carboxylic acid (ACC) can change the ACC concentration in cell compartments and impact ethylene biosynthesis. Transport of ACC into isolated maize ( Zea mays L.) mesophyll vacuoles was studied by silicon layer flotation filtering. The transport of ACC across the tonoplast was stimulated 2. 4- to 8. 1-fold by 5 m M MgATP, showed saturation kinetics with an apparent K_m for ACC of 20 μ M , and was optimal at 25°C. Transport of ACC was sensitive to the pH of the medium, falling as external pH rose. Effectors known to inhibit proton-translocating ATPases (N, N-dicyclohexylcarbodiimide) and to collapse the electrical (thiocyanate, valinomycin) and chemical (carbonylcyanide m -chlorophenylhydrazone, gramicidin) potential gradients for protons across the tonoplast all reduced ACC transport. The nonhydrolyzable MgATP analog. Mg adenylyl-imidodiphosphate, stimulated ACC transport as effectively as MgATP. Other nucleotides (MgADP, MgCTP, MgUTP, MgGTP) and MgPP_i had little or no effect. These results suggest that ACC uptake into isolated maize mesophyll vacuoles is carrier mediated, is dependent upon an electrochemical potential gradient for protons and is specifically regulated, but not necessarily energized, by MgATP     

Intervening in sibling competition for assimilates by controlled pollination prevents seed abortion under postpollination drought in maize

During maize production, drought throughout the flowering stage usually induces seed abortion and yield losses. The influence of postpollination drought stress on seed abortion and its underlying mechanisms are not well characterized. By intervening in the competition for assimilates between kernel siblings under different degrees of postpollination drought stresses accompanied by synchronous pollination (SP) and incomplete pollination (ICP) approaches, the mechanisms of postpollination abortion were investigated at physiological and molecular levels. Upon SP treatment, up to 15% of the fertilized apical kernels were aborted in the drought-exacerbated competition for assimilates. The aborted kernels exhibited weak sucrose hydrolysis and starch synthesis but promoted the synthesis of trehalose-6-phosphate and ethylene. In ICP where basal pollination was prevented, apical kernel growth was restored with reinstated sucrose metabolism and starch synthesis and promoted sucrose and hexose levels under drought stress. In addition, the equilibrium between ethylene and polyamine in response to the drought and pollination treatments was associated with the abortion process. We conclude that competition for assimilates drives postpollination kernel abortion, whereas differences in sugar metabolism and the equilibrium between ethylene and polyamines may be relevant to the “live or die” choice of kernel siblings during this competition.     

Induction of Enzymes Associated with Lysigenous Aerenchyma Formation in Roots of Zea mays during Hypoxia or Nitrogen Starvation

Either hypoxia, which stimulates ethylene biosynthesis, or temporary N starvation, which depresses ethylene production, leads to formation of aerenchyma in maize (Zea mays L.) adventitious roots by extensive lysis of cortical cells. We studied the activity of enzymes closely involved in either ethylene formation (1-amino-cyclopropane-1-carboxylic acid synthase [ACC synthase]) or cell-wall dissolution (cellulase). Activity of ACC synthase was stimulated in the apical zone of intact roots by hypoxia, but not by anoxia or N starvation. However, N starvation, as well as hypoxia, did enhance cellulase activity in the apical zone, but not in the older zones of the same roots. Cellulase activity did not increase during hypoxia or N starvation in the presence of aminoethoxyvinylglycine, an inhibitor of ACC synthase, but this inhibition of cellulase induction was reversed during simultaneous exposure to exogenous ethylene. Together these results indicate both the role of ethylene in signaling cell lysis in response to two distinct environmental factors and the significance of hypoxia rather than anoxia in stimulation of ethylene biosynthesis in maize roots.     

Calcium effects on ethylene and ethane production and 1-aminocyclopropane-1-carboxylic acid content in potato disks

Potato ( Solanum tuberosum L. cv. Katahdin) disks produce ethyline in increasing amounts from 6 to 24 h incubation in buffer at pH 4.0. Ethylene production is increased 2–3 times in the presence of 50 m M CaCl₂. Levels of endogenous 1-amino-cyclopropane-1-carboxylic acid (ACC) increase in parallel with ethylene production, and ACC levels are 3–5 times higher in calcium-treated disks than in controls. Most of the calcium-induced stimulation of ethylene production can be accounted for by its effect on ACC production, indicating that the primary effect of calcium is on a step of ethylene biosynthesis preceeding ACC production. However, calcium may also have an effect on conversion of ACC to ethylene, since a consistent increase in ACC-de-pendent ethylene production was observed in the presence of calcium. Production of ethane, a marker of lipid peroxidation, was reduced by calcium, so it is possible that membrane stabilization by calcium could be involved in its effects on ethylene production.     

The ethylene biosynthetic and perception machinery is differentially expressed during endosperm and embryo development in maize

The maize endosperm undergoes programmed cell death late in its development so that, with the exception of the aleurone layer, the tissue is dead by the time the kernel matures. Although ethylene is known to regulate the onset of endosperm cell death, the temporal and spatial control of the ethylene biosynthetic and perception machinery during maize endosperm development has not been examined. In this study, we report the isolation of the maize gene families for ACC synthase, ACC oxidase, the ethylene receptor, and EIN2 and EIL, which act downstream of the receptor. We show that ACC oxidase is expressed primarily in the endosperm, and only at low levels in the developing embryo late in its development. ACC synthase is expressed throughout endosperm development but, in contrast to ACC oxidase, it is transiently expressed to a significantly higher level in the developing embryo at a time that corresponds with the onset of endosperm cell death. Only two ethylene receptor gene families were identified in maize, in contrast to the five types previously identified in Arabidopsis. Members of both ethylene receptor families were expressed to substantially higher levels in the developing embryo than in the endosperm, as were members of the EIN2 and EIL gene families. These results suggest that the endosperm and embryo both contribute to the synthesis of ethylene, and they provide a basis for understanding why the developing endosperm is especially sensitive to ethylene-induced cell death while the embryo is protected.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by G. Jürgens     

Promotion by Ethylene of the Capability to Convert 1-Aminocyclopropane-1-carboxylic Acid to Ethylene in Preclimacteric Tomato and Cantaloupe Fruits

The intact fruits of preclimacteric tomato (Lycopersicon esculentum Mill) or cantaloupe (Cucumis melo L.) produced very little ethylene and had low capability of converting 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. When these unripe tomato or cantaloupe fruits were treated with ethylene for 16 hours there was no increase in ACC content or in ethylene production rate, but the tissue's capability to convert ACC to ethylene increased markedly. Such an effect was also observed in fruits of tomato mutants rin and nor, which do not undergo ripening and the climacteric increase in ethylene production during the senescence. The development of this ethylene-forming capability induced by ethylene increased with increasing ethylene concentration (from 0.1 to 100 microliters per liter) and duration (1 to 24 hours); when ethylene was removed this capability remained high for sometime (more than 24 hours). Norbornadiene, a competitive inhibitor of ethylene action, effectively eliminated the promotive effect of ethylene in tomato fruit. These data indicate that the development of the capability to convert ACC to ethylene in preclimacteric tomato and cantaloupe fruits are sensitive to ethylene treatment and that when these fruits are exposed to exogenous ethylene, the increase in ethylene-forming enzyme precedes the increase in ACC synthase.     

Pistil-Specific and Ethylene-Regulated Expression of 1-Aminocyclopropane-1-Carboxylate Oxidase Genes in Petunia Flowers

The differential expression of the petunia 1-aminocyclopropane-1-carboxylate (ACC) oxidase gene family during flower development and senescence was investigated. ACC oxidase catalyzes the conversion of ACC to ethylene. The increase in ethylene production by petunia corollas during senescence was preceded by increased ACC oxidase mRNA and enzyme activity. Treatment of flowers with ethylene led to an increase in ethylene production, ACC oxidase mRNA, and ACC oxidase activity in corollas. In contrast, leaves did not exhibit increased ethylene production or ACC oxidase expression in response to ethylene. Gene-specific probes revealed that the ACO1 gene was expressed specifically in senescing corollas and in other floral organs following exposure to ethylene. The ACO3 and ACO4 genes were specifically expressed in developing pistil tissue. In situ hybridization experiments revealed that ACC oxidase mRNAs were specifically localized to the secretory cells of the stigma and the connective tissue of the receptacle, including the nectaries. Treatment of flower buds with ethylene led to patterns of ACC oxidase gene expression spatially distinct from the patterns observed during development. The timing and tissue specificity of ACC oxidase expression during pistil development were paralleled by physiological processes associated with reproduction, including nectar secretion, accumulation of stigmatic exudate, and development of the self-incompatible response.     

Metabolism of 1-Aminocyclopropane-1-Carboxylic Acid in Etiolated Maize Seedlings Grown under Mechanical Impedance

We investigated the metabolism of 1-aminocyclopropane-1-carboxylic acid (ACC) in etiolated maize (Zea mays L.) seedlings subjected to mechanical impedance by applying pressure to the growing medium. Total concentrations of ACC varied little in unimpeded seedlings, but impeded organs accumulated ACC. Roots had consistently higher concentrations of ACC than shoots or seeds, regardless of treatment. The concentration of ACC in the roots increased more than 100% during the first hour of treatment irrespective of the pressure applied; in shoots, total ACC concentration increased 46% at either low or high pressure during the first hour of treatment. The bulk of ACC synthesized under impeded and unimpeded conditions was present in a conjugated form, presumably, 1-(malonylamino)-cyclopropane-1-carboxylic acid. However, 1-(malonylamino)-cyclopropane-1-carboxylic acid increased 73% over controls after 10 hours at 25 kilopascals of pressure. Unimpeded tissue had about 77% ACC as the conjugate and 17% as free ACC, and less than 6% was used in ethylene production. Increased amounts of ACC were converted into ethylene under stress. In vivo ACC synthase activity in roots became six and seven times higher only 1 hour after initiation of treatment at 25 and 100 kilopascals of pressure, respectively, and remained high for at least 6 hours. However, the immediate and massive conjugation of mechanically induced ACC suggests that ACC N-malonyltransferase may play an important role in the regulation of mechanically induced ethylene production. After 8 hours, in vivo activity of the ethylene-forming enzyme complex increased 100 and 50% above normal level at 100 and 25 kilopascals, respectively. Furthermore, ethylene-forming enzyme complex activity was significantly greater at 100 kilopascals than in controls as early as 1 hour after treatment initiation. These data suggest that regulation of ethylene production under mechanical impedance involves the concerted action of ACC synthase, the ethylene-forming enzyme complex, and ACC N-malonyltransferase.     

弱光胁迫对不同耐荫型玉米果穗发育及内源激素含量的影响

2010—2011年以耐荫性较弱的玉米杂交种豫玉22和耐荫性较强的玉米杂交种郑单958为材料,在抽雄前3 d开始进行弱光胁迫处理,吐丝后10 d恢复自然光照,研究弱光胁迫及光恢复对不同耐荫型玉米果穗生长发育及其内源激素含量的影响。结果表明:弱光胁迫下,玉米果穗生长发育明显减缓,穗长、穗粗和果穗干物质积累显著减小,秃尖度变大;穗行数、穗粒数和籽粒库容显著降低;吐丝期果穗顶部小穗子房发育停滞,已有败育迹象的籽粒在恢复自然光照后无明显改善;豫玉22果穗和籽粒性状在处理间的差异程度均大于郑单958。弱光胁迫下,两玉米杂交种果穗的ABA和ZR含量均升高,而GA含量和GA/ABA比值均降低;IAA含量和IAA/ABA比值在郑单958果穗中表现为升高,而豫玉22则表现为下降。     

Endogenous Levels and Transport of 1-Aminocyclopropane-1-Carboxylic Acid in Stamens of Ipomoea nil (Convolvulaceae)

Filament and corolla growth in flowers of Ipomoea nil are inhibited by ethylene production. Anthers inhibited filament growth in vitro during younger stages of development even in the presence of the growth promoter gibberellic acid (GA₃). To test whether the anthers could be sources of 1-aminocyclopropane-1-carboxylic acid (ACC) endogenous levels of ACC and ethylene production were monitored using gas chromatography. To also test whether the filaments could be transport vectors for ACC the movement of [¹⁴C]ACC was assessed by scintillation counting from donor agarose blocks, through filament sections, and into receiver agarose blocks. While ACC levels fluctuated in anthers 87 to 21 h before anthesis, anthers contained increased levels of ACC from 15 to 6 hours before anthesis. Ethylene production also fluctuated but peak levels were shifted about 6 hours closer to anthesis than ACC levels within the anthers. Both ACC and ethylene levels in filaments showed fluctuations similar to those in the anthers. [¹⁴C]ACC movement became increasingly basipetal during development. Older stages showed greater polar [¹⁴C]ACC efflux rates, while all stages showed constant polar influx rates. Low levels of endogenous ACC were transported basipetally from the anther through the filament into agarose blocks at all stages of development. Corresponding levels of endogenous ethylene production remained constant between the various stages during ACC transport. We have evidence that stamens of I. nil have a role as source tissues and transport vectors for ACC, to stimulate corolla growth, such as corolla unfolding and senescence.     

Synergistic enhancement of ethylene production and germination with kinetin and 1-aminocyclopropane-1-carboxylic Acid in lettuce seeds exposed to salinity stress

Relief of salt (0.1 molar NaCl) stress on germination of lettuce (Lactuca sativa L., cv Mesa 659) seeds occurred with applications of 0.05 millimolar kinetin (KIN) and 1 to 10 millimolar 1-aminocyclopropane 1-carboxylic acid (ACC). Treatment with KIN enhanced the pregermination ethylene production under saline condition. A synergistic or an additive enhancement of pregermination ethylene production and germination occurred under saline condition in the presence of KIN and a saturating dose (10 millimolar) of ACC. No KIN-ACC synergism was noted in ethylene production or germination under nonsaline condition. Addition of 1 millimolar aminoethoxyvinylglycine (AVG) inhibited the KIN-enhanced pregermination ethylene production (85 to 89%) and germination (58%) under saline condition but not the synergistic effect of KIN + ACC on ethylene production. Under nonsaline condition, AVG had no effect on germination even though ethylene production was strongly inhibited. Alleviation of salt stress by KIN was inhibited in a competitive manner by 2,5-norbornadiene (NBD) (0.02-0.2 milliliter per liter), and the addition of ACC and/or ethylene reduced this inhibition. An increase in the pregermination ethylene production and germination occurred also by cotylenin E (CN) under saline condition. However, neither AVG (1 millimolar) nor NBD (0.02 to 0.2 milliliter per liter) prevented the relief of salt stress by CN. Thus, KIN may alleviate salt stress on germination by promoting both ACC production and its conversion to ethylene. Rapid utilization of ACC may be the basis for the synergistic or the additive effect of KIN plus ACC. The need for ethylene production and action for the relief of salt stress is circumvented by a treatment with CN.     

The influence of oxygen deficiency on ethylene synthesis, 1-aminocyclopropane-1-carboxylic acid levels and aerenchyma formation in roots of Zea mays

The relationship between ethylene production, 1-aminocyclopropane-l-carboxylic acid (ACC) concentration and aerenchyma formation (ethylene-promoted cavitation of the cortex) was studied using nodal roots of maize (Zea mays L. cv. LG11) subjected to various O₂ treatments. Ethylene evolution was 7–8 fold faster in roots grown at 3 kPa O₂ than in those from aerated solution (21 kPa O₂), and transferring roots from aerated solution to 3 kPa O₂ enhanced ethylene synthesis within less than 2 h. Ethylene production and ACC accumulation were closely correlated in different zones of hypoxic roots, regardless of whether O₂ was furnished to the roots through aerenchyma or external solution. Both ethylene production and ACC concentrations (fresh weight basis) were more than 10-fold greater in the distal 0–10 mm than in the fully expanded zone of roots at 3 kPa O₂. Aerenchyma formation occurred in the apical 20 mm of these roots. Roots transferred from air to anoxia accumulated less than 0. 1 nmol ACC (mg protein)^-1 for the first 1.75 h; no ethylene was produced in this time. The subsequent rise in ACC levels shows that ACC can reach high concentrations even in the absence of O₂, presumably due to a de-repression of ACC synthase. The hypothesis was therefore tested that anoxia in the apical region of the root caused enhanced synthesis of ACC, which was transported to more mature regions (10–20 mm behind the apex), where ethylene could be produced and aerenchyma formation stimulated. Surprisingly, exposure of intact root tips to anoxia inhibited aerenchyma formation in the mature root axis. High osmotic pressures around the growing region or excision of apices had the same effect, demonstrating that a growing apex is required for high rates of aerenchyma formation in the adjacent tissue.     

The site of 1-aminocyclopropane-1-carboxylic acid synthesis in senescing carnation petals

To study the cause of the uneven production of ethylene by upper and basal portions of detached petals of carnation ( Dianthus caryophyllus L. cv. White Sim), the petals were divided and exposed to ethylene (30 μl 1^-1 for 16 h). The treatment induced rapid wilting and autocatalytic ethylene production in the basal portion similar to that induced in entire petals. In contrast to the response in entire petals and the basal portions, the upper portions responded to ethylene by delayed wilting and much lower ethylene production. Aminocyclopropane carboxylic acid (ACC)-synthase activity in the basal portion of the petals was 38 to 400 times that in the upper portion. In untreated detached petal pieces from senescing carnation flowers, ethylene production by the upper portion declined after 6 h while the basal portion was still producing ethylene at a steady rate 18 h later. Application of ACC to the upper portion of senescing petals increased their ethylene production. α-Aminooxyacetic acid (0.5 m M ), reduced the ethylene production of the senescing basal portion more than that of the upper portion. Endogenous ACC content in basal portions of senescing carnation petals was 3 to 4 times higher than in the upper parts. When detached senescing petals were divided immediately after detaching, the endogenous ACC levels in upper portions remained steady or declined during 24 h after division, while in the basal portions the ACC level rose steadily as in the intact petals. There was no change in the conjugated ACC in either portion after 24 h. Benzyladenine (BA) applied as a pretreatment to entire preclimacteric petals greatly reduced the development of ACC-synthase activity of the basal portion, but had little effect on the activity in the upper portion of the petal. In both portions, however, BA effectively reduced the conversion of ACC to ethylene.     

Differential physiological and morphological responses of inbred lines to the ethylene precursor 1-aminocyclopropane-1-carboxylic acid by cultured Helianthus annuus (sunflower) shoot tips

The four Helianthus annuus (sunflower) inbred lines examined showed different abilities to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene and different morphological responses to exogenous ACC, however, ACC had no effect on precocious flowering. The greatest effect of ACC was seen with inbred SS405B where it suppressed shoot growth and induced hypocotyl enlargement and callus induction. The greatest response did not correlate with the highest ethylene production. Although each inbred responded differently, callus induction and hypocotyl enlargement observed in hypocotyl segments treated with naphthalene acetic acid and benzyladenine could be partially explained as ethylene-mediated effects of the two hormones. It is suggested that inbred differences could be due to different endogenous hormone levels and/or different sensitivities to them.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - BA benzyladenine - NAA naphthalene acetic acid     

Roles of carbohydrate supply and ethylene, polyamines in maize kernel set

Glucose appears to have an antagonistic relationship with ethylene and ethylene and polyamines appear to play antagonistic roles in the abortion of seeds and fruits. Moreover, ethylene, spermidine, and spermine share a common biosynthetic precursor. The synchronous changes of them and the relationships with kernel set are currently unclear. Here, we stimulated maize (Zea mays L.) apical kernel set and studied their changes at 4, 8, 12, and 16 d after pollination (DAP). The status of the apical kernels changed from abortion to set, showing a pattern similar to that of the middle kernels, with slow decrease in glucose and rapid decline in ethylene production, and a sharp increase in spermidine and spermine after four DAP. Synchronous changes in ethylene and spermidine were also observed. However, the ethylene production decreased slowly in the aborted apical kernels, the glucose and polyamines concentrations were lower. Ethephon application did not block the change from abortion to set for the setting apical kernels. These data indicate that the developmental change may be accompanied by an inhibition of adequate glucose to ethylene synthesis and subsequent promotion of spermidine and spermine synthesis, and adequate carbohydrate supply may play a key role in the developmental process.     

Galactose inhibits the conversion of 1-aminocyclopropane-1-carboxylic Acid to ethylene in aged tobacco leaf discs

d-Galactose has been shown to have toxic and growth inhibitory effects in plants. When applied at levels of 50 millimolar to tobacco (Nicotiana tabacum L. cv Xanthi) leaf discs galactose caused a rapid increase in ethylene production during the first 2 days of incubation, followed by a rapid return to the basal level on the third day. This pattern of galactose-stimulated ethylene production was accompanied by increased formation of 1-aminocyclopropane-1-carboxylic acid (ACC), which accumulated without being metabolized to ethylene or to the ACC-conjugate. The inhibitory effect of galactose (50 millimolar) on the conversion of ACC of ethylene was relieved partially by d-glucose or sucrose (50 millimolar), and completely by CO₂ (10%), which were shown to enhance this conversion by themselves. Consequently, application of galactose plus any one of these compounds increased ethylene production and decreased free ACC levels. The data suggest that galactose toxicity may result in both an increased ethylene production as well as in accumulation of free ACC in aged discs. The increased ethylene production rates and ACC levels may, in turn, play a role in the development of symptoms associated with galactose toxicity.     

Identification and Metabolism of 1-(Malonylamino)cyclopropane-1-carboxylic Acid in Germinating Peanut Seeds

Peanut seeds (Arachis hypogea L. Yue-you 551) contain 50 to 100 nanomoles per gram conjugated 1-aminocyclopropanecarboxylic acid (ACC). Based on paper chromatography, paper electrophoresis, and gas chromatography-mass spectrometry, it was verified that the major ACC conjugate was N-malonyl-ACC (MACC). Germinating peanut seeds converted [2-¹⁴C]ACC to ethylene 70 times more efficiently than N-malonyl-[2-¹⁴C]ACC; when ACC was administered, most of it was metabolized to MACC. Germinating peanut seeds produced ethylene and converted l-[3,4-¹⁴C]methionine to ethylene; this ethylene biosynthesis was inhibited by aminoethoxyvinylglycine. These data indicate that MACC occurs in peanut seeds but does not serve as the source of ethylene during germination; ethylene is, however, synthesized from methionine via ACC.