Ethylene Synthesis Inhibitor Research Articles

Contrasting effects of ethylene perception and synthesis inhibitors on GA 3-induced antheridiogenesis and the level of 1-aminocyclopropane-1-carboxylic acid in Anemia phyllitidis gametophytes

In Anemia phyllitidis gametophytes two of the ethylene perception inhibitors (silver ions, Ag +; 2,5-norbornadiene, NBD) caused opposite effects on GA 3-induced antheridia formation and on the increment of ACC (1-aminocyclopropane-1-carboxylic acid) content accompanying this process. Ag + enhanced while NBD inhibited GA 3-induced antheridiogenesis and each inhibitor modulated the level of ACC in a different manner. Cobalt ions (Co 2+) and aminooxyacetic acid (AOA; the ethylene synthesis inhibitors), also modulated the level of GA 3-induced ACC content differently. These results strongly confirm the earlier suggestion that ethylene plays a role of the second messenger in GA 3-induced antheridiogenesis during “induction” and “expression” phases, and the 3rd h of the former phase is the time when elevation of ACC content induced while in the 6th h inhibited antheridiogenesis. Timing of changes in ACC content and morphogenetic effects of GA 3-induced antheridiogenesis in A. phyllitidis gametophytes allowed to indicate that AOA together with NBD could participate in one while Co 2+ and Ag + in another ethylene synthesis and signaling pathway.

Ethylene Is Not Involved in Hormone- and Bromoethane-Induced Dormancy Break in Russet Burbank Minitubers

The involvement of ethylene in the dormancy breaking actions of cytokinins, GA, and BE was investigated using Russet Burbank minitubers. Injection of 10 µg tuber−1 BA, CP, GA, NG, or ZEA or 24 hour exposure to BE effectively broke dormancy and stimulated sprout growth over a two-week period. Although ethylene production was slightly enhanced by all treatments, a significant increase in ethylene production was observed in minitubers treated with BE, CP, or NG. Pretreatment with the ethylene antagonists STS or MCP did not affect the dormancy breaking actions of any of the agents tested. Application of the ethylene synthesis inhibitor AVG to NG-treated minitubers, completely suppressed ethylene production but had no effect on dormancy break. Application of exogenous ethylene or stimulation of endogenous ethylene production by ACC treatment did not break minituber dormancy or stimulate sprout growth. Collectively, these results indicate that endogenous ethylene does not play a role in the dormancy breaking actions of cytokinins, GA, or BE.

The relationship of grain filling with abscisic acid and ethylene under non-flooded mulching cultivation

SUMMARYGrain filling is an intensive transportation process regulated by plant hormones. The present study investigated whether and how the interaction between abscisic acid (ABA) and ethylene is involved in mediating the grain filling of rice (Oryza sativaL.) under non-flooded mulching cultivation. A field experiment repeated over 2 years was conducted with two high-yielding rice cultivars, Zhendao 88 (ajaponicacultivar) and Shanyou 63 (anindicahybrid cultivar), and four cultivation treatments were imposed from transplanting to maturity: traditional flooding as control (TF), non-flooded plastic film mulching (PM), non-flooded wheat straw mulching (SM) or non-flooded no mulching (NM). Compared with that under TF, grain yield was reduced by 21·0–23·1% under PM (P<0·05), 1·4–1·8% under SM (P>0·05) and 50·9–55·4% under NM (P<0·05). Both PM and NM significantly (P<0·05) reduced the proportion of filled grains and grain weight and were associated with decreased grain filling rates. In SM there was a significant increase in the grain filling rate. The concentration of ABA in the grains was very low at the early grain filling stage, reaching a maximum when the grain filling rate was the highest, and showed no significant differences (P>0·05) between TF, PM and SM. However, it was significantly higher in NM. In contrast to ABA, the ethylene evolution rate and 1-aminocyclopropane-1-carboxylic acid (ACC) concentration in the grains were very high at the start of grain filling and sharply decreased during the active grain filling period. Both PM and NM increased the ethylene evolution rate and ACC concentration, whereas these were reduced in SM. The ratio of ABA to ACC was increased under SM but decreased under PM and NM, indicating that ethylene was more enhanced than ABA when plants were grown under NM and PM. The concentration of ABA correlated with the grain filling rate as a hyperbolic curve, whereas the ethylene evolution rate correlated with the grain filling rate as an exponential decay equation. The ratio of ABA to ACC significantly correlated with the grain filling rate with a linear relationship. Application of amino-ethoxyvinylglycine (inhibitor of ethylene synthesis by inhibiting ACC synthase) or ABA to panicles under TF and PM at the early grain filling stage significantly increased activities of the key enzymes involved in sucrose to starch conversion in the grains, sucrose synthase, ADP glucose pyrophosphorylase and soluble starch synthase, grain filling rate and grain weight. Application of ethephon (ethylene-releasing agent) or fluridone (inhibitor of ABA synthesis) had the opposite effect. The results suggest that antagonistic interactions between ABA and ethylene may be involved in mediating the effect of non-flooded mulching cultivation on grain filling, and a high ratio of ABA to ethylene enhances grain filling rate.

Longevidade de inflorescências de Epidendrum ibaguense tratadas com aminoetoxivinilglicina

O objetivo deste trabalho foi avaliar a influência do inibidor da síntese de etileno aminoetoxivinilglicina (AVG) aplicado na forma de solução de condicionamento e pulverização sobre a abscisão e longevidade de inflorescências de Epidendrum ibaguense Kunth. As hastes foram colhidas e imediatamente condicionadas em solução com 0, 0,5, 1, 1,5 e 2 mM de AVG por 6, 12, 18 e 24 horas. Os mesmos tratamentos foram aplicados na forma de pulverização até o molhamento completo da inflorescência. O experimento foi conduzido em um esquema fatorial entre tempo de aplicação e doses de AVG, mais doses de AVG aplicadas em pulverização nas flores, e o delineamento foi em blocos ao acaso, com cinco repetições, com três hastes por unidade experimental. Independentemente do modo de aplicação do AVG, as concentrações utilizadas promoveram aumento da longevidade das flores em aproximadamente 70% em comparação ao controle, com resposta máxima nas concentrações de 1,5 e 2 mM. Apercentagem de abscisão de flores foi reduzida em todos os tratamentos com AVG, principalmente quando se utilizou pulverização, com decréscimo na abscisão acumulada superior a 80% nas concentrações entre 1 e 2 mM de AVG.A aplicação de AVG prolongaa longevidadee reduz a abscisãode flores de Epidendrum ibaguense.

After-ripening alters the gene expression pattern of oxidases involved in the ethylene and gibberellin pathways during early imbibition of Sisymbrium officinale L. seeds

After-ripening (AR) in Sisymbrium officinale seeds altered SoACS7, SoACO2, SoGA20ox2, SoGA3ox2, and SoGA2ox6 gene expression. Except for SoGA20ox2 expression, which sharply diminished, the expression of the other genes rose during development, particularly that of SoACS7. In contrast, only the SoACO2 and SoGA2ox6 transcripts increased with seed desiccation; the others decreased. AR increased the SoGA3ox2 transcript in dry seed, but dramatically decreased the SoACS7 transcript. At the onset of imbibition, AR inhibited SoACS7 and SoACO2 expression and stimulated that of SoGA20ox2, SoGA3ox2, and SoGA2ox6, demonstrating that the participation of ethylene (ET) and gibberellins (GAs) differs in after-ripened and non-after-ripened seeds. The inhibition of SoACO2 expression in the presence of GA4+7, paclobutrazol (PB), inhibitors of ET synthesis and signalling (IESS), and notably ET+GA4+7 indicated ET–GA cross-talk in non-after-ripened seeds. A positive effect of AR in reversing this inhibition was found. The idea of ET–GA cross-talk is also supported by the effect of ET on SoGA3ox2 expression, notably induced by the AR process. In contrast, SoGA20ox2 expression did not appear to be susceptible to AR. SoGA2ox6 expression, poorly known in seeds, suggests that AR prompted an up-regulation under all treatments studied, whereas in non-after-ripened seeds expression was down-regulated. On the other hand, the β-mannanase (MAN) activity dramatically increased in dry after-ripened seed, being significantly boosted by ET. The absence of MAN inhibition by IESS suggests that although ET seems to be one of the factors controlling MAN, its presence did not appear to be essential. GA4+7 only increased MAN in seeds wich were after-ripened. Here, it is proposed that ET and GAs participate actively in establishing the AR process.

Hormonal control of floral abscission in zucchini squash (Cucurbita pepo)

In the zucchini squash, Cucurbita pepo, a well coordinated abscission of the female flower during fruit set is essential to obtain a fruit of commercial value. In Spain zucchini is mainly produced in greenhouses in Almeria, where high temperatures during the spring-summer period provoke a cultivar-dependent defect in fruits known as the “sticky flower” syndrome. This disorder is characterised by an arrest in growth and maturation of floral organs, and a lack of female floral abscission, thus diminishing fruit shelf-life, commercial quality and value. The aim of the present work was to improve knowledge of the abscission process in C. pepo to better understand the fundamental causes of this disorder. The anatomical analysis of abscission shows a well defined male floral abscission zone (AZ), few hours after anthesis, which differs from the female zone which is not differentiated from the adjacent tissue until the abscission process has begun, and which occurs as a consequence of AZ cell enlargement and the dissolution of their cell walls. To evaluate the role of ethylene and auxins in the regulation of floral abscission in zucchini we performed several treatments, with: ethylene, added as 0.25% ethrel solution; AVG, the inhibitor of ethylene synthesis, at 100 μM; indol-3-acetic acid, 100 μM; and TIBA, the inhibitor of auxin polar transport, at 10 mM. These treatments show that ethylene is an accelerator of zucchini floral abscission, and also promotes abscission in isolated AZs of sticky flowers. On the other hand, IAA delays abscission of the female flowers, whilst the inhibitor of auxin polar transport promotes it. The activity of the cell wall hydrolytic enzymes, polygalacturonase and cellulase, sharply increased just before the shedding of zucchini floral organs (72 h after anthesis). Moreover, both enzyme activities were induced by ethylene, which partly explains the ethylene promoting effect.

2,4-Dichlorophenoxyacetic Acid Increases Peonidin Derivatives in Red Norland Periderm

Studies were conducted to determine the effects of selected plant growth regulators on red color development of Red Norland potato periderm, and the mechanism by which color changes occurred. Two derivatives of the auxin 2,4-dichlorophenoxyacetic acid (2,4-D ester and 2,4-D amine), S-abscisic acid, n-propyl dihydrojasmonate, and the ethylene synthesis inhibitor aminoethoxyvinylglycine were foliar applied at 4, 6, and 8 weeks after emergence. Only the 2,4-D ester and 2,4-D amine significantly improved tuber periderm red color in two seasons of evaluation. Red color faded during storage regardless of treatment. Anthocyanin content at vine kill was significantly increased by 2,4-D treatment in 2004 but not 2005. The 2,4-D treatments increased the ratio of peonidin derivatives to pelargonidin derivatives compared with controls. This change in ratio may explain the observed change in hue angle with 2,4-D treatment compared to controls.

Ethylene and rooting of mung bean cuttings. The role of auxin induced ethylene synthesis and phase-dependent effects

We have re-examined the role of ethylene during rooting of mung bean cuttings. Cuttings were treated for 5 days with a low or a high concentration of NAA (naphthaleneacetic acid). During this 5 days period, we also applied STS (silverthiosulfate, an inhibitor of ethylene action) or ACC (1-aminocyclo-propane-l-carboxylic acid, a direct precursor of ethylene). At high NAA concentration, STS promoted and ACC inhibited rooting, respectively. At low NAA concentration, the effects were opposite, STS being inhibitory and ACC promotive. AVG (aminoethoxyvinylglycine, an inhibitor of ethylene synthesis) gave similar results as STS. Together, these data suggest supraoptimal and suboptimal ethylene levels in the tissue at high and low NAA concentration, respectively. We also examined whether the effect of ethylene varied during the successive phases of the rooting process. Thus, we gave 24 h pulses with either STS or ACC during the rooting treatment. During the first two days (0–48 h), ACC-pulses were promotive and STS-pulses inhibitory. Later on (48–168 h), the ACC-pulses were inhibitory and the STS-pulses promotive. Whether this effect was observed or not was dependent on the NAA concentration. These data indicate that ethylene promotes or inhibits rooting depending on the stage in the rooting process. When ACC was added only during the initial period, rooting was increased at all NAA concentrations in a NAA dose-response curve and the optimal NAA concentration remained the same. This suggests that ethylene renders more cells responsive to NAA.

Hormonal control of root development on epiphyllous plantlets of Bryophyllum (Kalanchoe) marnierianum: role of auxin and ethylene

Epiphyllous plantlets develop on leaves of Bryophyllum marnierianum when they are excised from the plant. Shortly after leaf excision, plantlet shoots develop from primordia located near the leaf margin. After the shoots have enlarged for several days, roots appear at their base. In this investigation, factors regulating plantlet root development were studied. The auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) abolished root formation without markedly affecting shoot growth. This suggested that auxin transport from the plantlet shoot induces root development. Excision of plantlet apical buds inhibits root development. Application of indole-3-acetic acid (IAA) in lanolin at the site of the apical buds restores root outgrowth. Naphthalene acetic acid (NAA), a synthetic auxin, reverses TIBA inhibition of plantlet root emergence on leaf explants. Both of these observations support the hypothesis that auxin, produced by the plantlet, induces root development. Exogenous ethylene causes precocious root development several days before that of a control without hormone. Ethylene treatment cannot bypass the TIBA block of root formation. Therefore, ethylene does not act downstream of auxin in root induction. However, ethylene amplifies the effects of low concentrations of NAA, which in the absence of ethylene do not induce roots. Ag2S2O3, an ethylene blocker, and CoCl2, an ethylene synthesis inhibitor, do not abolish plantlet root development. It is therefore unlikely that ethylene is essential for root formation. Taken together, the experiments suggest that roots develop when auxin transport from the shoot reaches a certain threshold. Ethylene may augment this effect by lowering the threshold and may come into play when the parent leaf senesces.

Responses of ethylene and ACC in rice grains to soil moisture and their relations to grain filling

The objectives of this study were to investigate ethylene and 1-aminocylopropane-1-carboxylic acid (ACC) in rice grains and root bleeding sap during the grain filling period and their relationship to the grain filling rate. Two high lodging-resistant rice (Oryza sativa L.) cultivars were grown in pots or tanks. Three treatments, including well watered (WW), moderate soil-drying (MD) and severe soil-drying (SD), were conducted from 9 days of post-anthesis until maturity. The effects of chemical regulators on the concentrations of ethylene and ACC in the grains were also studied. The results show that MD significantly increased the grainfilling rate and grain weight, whereas SD significantly reduced the grain-filling rate and grain weight. Concentrations of ethylene and ACC in the grains were very high at the early grain filling stage and then sharply decreased during the linear period of grain growth. MD reduced the ACC concentrations and ethylene evolution rate, whereas SD remarkably increased the ACC concentrations and ethylene evolution rate. Both the ethylene evolution rate in rice grains and the ACC concentrations in the root-bleeding sap were significantly and positively correlated with the ACC concentrations in rice grains. The ethylene evolution rate was significantly and negatively correlated with the grain-filling rate. The application of amino-ethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, at 9–13 days of postanthesis significantly reduced the ACC concentrations and ethylene evolution rate of grains, but significantly enhanced the activities of sucrose synthase, ADP glucose pyrophosphorylase and soluble starch synthase. The results were reversed when ethephon, an ethylenereleasing agent, was applied. The results suggest that moderate soil drying during the grain-filling period in rice could inhibit the production of ethylene and ACC and therefore accelerate grain filling and increase grain weight.

Hormones in Rice Spikelets in Responses to Water Stress During Meiosis

Meiosis stage is the most stress-sensitive period of reproduction in rice ( Oryza sativa L.). However, the underlying biochemical mechanism is poorly understood. This study was carried out to investigate whether and how plant hormones are involved in the regulation of spikelet sterility when exposed to water stress during meiosis. Two rice cultivars, Han A-3 (HA-3, drought-resistant) and Wuyujing 7 (WY-7, drought-susceptible), were used and subjected to well-watered (WW) and water-stressed (WS) treatments during meiosis (15 to 2 d before heading). Leaf water potentials of both cultivars markedly decreased during the period as a result of WS treatment, but panicle water potentials remained constant. The percentage of sterile spikelets in WS plants was increased by 48.5% to 50.9% for WY-7, whereas only by 12.6% to 12.8% for HA-3. The concentrations of zeatin + zeatin riboside (Z+ZR), indole-3-acetic acid and gibberellins (GA 1+GA 4) in spikelets showed no significant differences either between the WW and WS treatments or between the 2 cultivars. Abscisic acid (ABA), ethylene, and 1-aminocylopropane-1-carboxylic acid were all enhanced in spikelets following water stress, with further enhancement for ethylene than for ABA in WY-7, whereas elevated ABA balanced ethylene production in HA-3. The spikelet sterility was significantly reduced when amino-ethoxyvinylglycine (an inhibitor of ethylene synthesis) or ABA was applied to the panicles of WS plants at the early meiosis stage. Application of ethephon (an ethylene-releasing agent) or fluridone (an inhibitor of ABA synthesis) had the opposite effect. These results indicate that antagonistic interactions between ABA and ethylene may be involved in mediating the effect of water stress on spikelet fertility. A higher ratio of ABA to ethylene would be a physiological trait of rice adaptation to water stress.

Abscisic Acid and Ethylene Interact in Rice Spikelets in Response to Water Stress During Meiosis

This study investigated whether and how the interaction between abscisic acid (ABA) and ethylene is involved in the regulation of rice (Oryza sativa L.) spikelet sterility when subjected to water stress during meiosis. Two rice cultivars, HA-3 (drought-resistant) and WY-7 (drought-susceptible), were used and subjected to well-watered and water-stressed (WS) treatments during meiosis (15–2 days before heading). Leaf water potentials of both cultivars markedly decreased during the day as a result of the WS treatment, but panicle water potentials remained constant. The percentage of sterile spikelets in WS plants was increased by 49.7% for WJ-7 but only 12.7% for HA-3. ABA, ethylene, and 1-aminocyclopropane-1-carboxylic acid were all enhanced in spikelets by the water stress, but ethylene was enhanced more than ABA in WY-7 when compared with that in HA-3. Spikelet sterility was significantly reduced when ABA or amino-ethoxyvinylglycine, an inhibitor of ethylene synthesis, was applied to the panicles of WS plants at the early meiosis stage. Application of ethephon, an ethylene-releasing agent, or fluridone, an inhibitor of ABA synthesis, had the opposite effect, and sterility was increased. The results suggest that antagonistic interactions between ABA and ethylene may be involved in mediating the effect of water stress on spikelet fertility. A higher ratio of ABA to ethylene would be a physiologic trait of rice adaptation to water stress.

Causes of Poor Grain Plumpness of Two-Line Hybrids and Their Relationships to the Contents of Hormones in the Rice Grain

Abstract This study was designed to elucidate the grain filling characteristics and the causes of poor grain plumpness of some two-line hybrid rice combinations and their hormonal mechanism. Six varieties, including three two-line hybrid rice combinations, that show differences in seed-setting and grain filling, were used. And the contents of starch, sucrose, zeatin (Z) + zeatin riboside (ZR), indole-3-acetic acid (IAA), and abscisic acid (ABA), the ethylene evolution rate, activities of sucrose synthase (SuSase) and starch synthase (StSase) in grains, the seed-setting and grain filling rate were investigated. The correlations amongst these were analyzed. The results showed that the poor grain filling of two-line hybrids was mainly attributed to the higher unfilled grain rate and the lower filling degree of inferior grains. During the early and mid grain filling periods, the sucrose content in inferior grains was greater than that in superior grains for the combinations with poor grain filling, indicating that the substrate concentration was not the principal factor for their slow grain filling and poor grain plumpness of the inferior grains of two-line hybrids. Z + ZR, IAA, and ABA in superior grains were obviously greater than those in inferior grains at early grain filling stage. The maximum and mean contents of Z + ZR, IAA, and ABA were positively very significantly correlated with the maximum and mean grain-filling rate, filling degree, and grain weight. The evolution rate of ethylene was greater in inferior grains than in superior grains and greater for the combinations with poor grain plumpness than those with good grain plumpness at the early or mid filling stages. The evolution rate of ethylene was negatively and significantly correlated with the grain filling rate, the grain filling degree, and the grain weight. Spraying ethephon (ethylene-releasing agent) at the early grain filling stage increased the evolution rate of ethylene, reduced the ABA content and activities of SuSase and StSase, and decreased the grain filling degree and the grain weight. The results were reversed when cobatous nitrate (an inhibitor of ethylene synthesis) was applied. The results suggested that the hormones and their balance play a role in the regulation of grain filling and enzymatic activities, and the poor grain filling is attributed to the low contents of Z + ZR, IAA, and ABA, and the high evolution rate of ethylene in the inferior grains of some two-line hybrid rice combinations. The results suggested that hormones play important roles in the grain filling of some two-line hybrid rice combinations, and their filling degree can be improved by regulating the hormonal contents.

Characterization of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing Methylobacterium oryzae and interactions with auxins and ACC regulation of ethylene in canola (Brassica campestris)

The possible interaction of the plant hormones auxin and ethylene and the role of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing bacteria on ethylene production in canola (Brassica campestris) in the presence of inhibitory concentrations of growth regulators were investigated. The effects of auxin (indole-3-acetic acid and 2,4-dichlorophenoxy acetic acid), auxin transport inhibitor 2-(p-chlorophenoxy)-2-methylpropionic acid, ethylene precursor 1-aminocyclopropane-1-carboxylate and ethylene synthesis inhibitor L-alpha-(2-aminoethoxyvinyl)glycine hydrochloride on root elongation were concentration dependent. Exogenous addition of growth regulators influences the enzyme activities of ethylene production and we have presented here evidences that support the hypothesis that inhibitory effects of auxin on root elongation are independent of ethylene. Additionally, we have proved that inoculation of ACC deaminase containing Methylobacterium oryzae sequester ACC exuded from roots and hydrolyze them lowering the concentration of ACC in root exudates. However, the inhibitory actions of exogenous additions of auxins could not be ameliorated by bacterial inoculation that reduces ethylene concentration in canola seedlings.

Rhizobitoxine-induced Chlorosis Occurs in Coincidence with Methionine Deficiency in Soybeans

Rhizobitoxine, produced by the legume symbiont Bradyrhizobium elkanii, inhibits cystathionine-beta-lyase (EC 4.4.1.8) in methionine biosynthesis and 1-aminocyclopropane-1-carboxylate synthase (ACC) in ethylene biosynthesis. Rhizobitoxine production by B. elkanii enhances nodulation of host legumes via the inhibition of ethylene synthesis, but causes foliar chlorosis in susceptible soybeans, though how it does so remains to be investigated. The aim of this study was to examine the physiological basis of rhizobitoxine-induced chlorosis in soybeans. Wild-type B. elkanii and a rhizobitoxine-deficient mutant were inoculated in Glycine max 'Lee'. Thirty days after inoculation, the upper parts of soybean shoots were analysed for amino acid contents. Chlorotic soybeans inoculated with wild-type B. elkanii were treated with methionine and ACC to assess the effects of the chemicals on the chlorosis. Chlorotic upper shoots of soybeans inoculated with wild-type B. elkanii had a lower methionine content and higher accumulation of the methionine precursors than those with the rhizobitoxine-deficient mutant. In addition, the foliar chlorosis was alleviated by the application of methionine. Rhizobitoxine-induced chlorosis occurs in coincidence with methionine deficiency as a result of cystathione-beta-lyase inhibition during methionine biosynthesis.

Genes associated with opening and senescence of Mirabilis jalapa flowers

A modest ethylene climacteric accompanies flower senescence in Mirabilis jalapa L., and exogenous ethylene accelerates the process. However, inhibitors of ethylene action and synthesis have little effect on the life-span of these ephemeral flowers. Treatment with alpha-amanitin, an inhibitor of DNA-dependent RNA synthesis, substantially delays the onset of senescence. This effect falls linearly between 7 h and 8 h after the start of flower opening. Subtractive hybridization was used to isolate transcripts that were up- and down-regulated during this critical period. Eighty-two up-regulated and 65 down-regulated transcripts were isolated. The genes identified encode homologues of a range of transcription factors, and of proteins involved in protein turnover and degradation. Real-time quantitative RT-PCR was used to examine expression patterns of these genes during flower opening and senescence. Genes that were identified as being down-regulated during senescence showed a common pattern of very high expression during floral opening. These genes included a homologue of CCA1, a 'clock' gene identified in Arabidopsis thaliana and an aspartyl protease. Up-regulated genes commonly showed a pattern of increase during the critical period (4-9 h after opening), and some showed very strong up-regulation. For example, the abundance of transcripts encoding a RING zinc finger protein increased >40 000 fold during the critical period.

Ethylene Production is Associated with Germination but not Seed Dormancy in Red Rice

The relationship between ethylene production and both seed dormancy and germination was investigated using red rice (weedy rice) as a model species. Both fully dormant and after-ripened (non-dormant) naked caryopses were incubated with or without inhibitors of ethylene synthesis [aminoethoxyvinylglycine (AVG)] and perception [silver thiosulfate (STS)], or in the presence of the natural ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). The kinetics of ethylene emissions were measured with a sensitive laser-photoacoustic system. Dormant red rice caryopses did not produce ethylene. In non-dormant caryopses, ethylene evolution never preceded the first visible stage of germination (pericarp splitting), and ethylene inhibitors completely blocked ethylene production, but not pericarp splitting. Accordingly, endogenous ACC appeared to be lacking before pericarp splitting. However, early seedling growth (radicle or coleoptile attaining the length of 1 mm) followed ethylene evolution and was delayed by the inhibitors. Wounding the dormant caryopses induced them to germinate and produce ethylene, but their germination was slow and pericarp splitting could be speeded up by ethylene. The findings suggest that, in red rice, endogenous ethylene stimulates the growth of the nascent seedling, but does not affect seed dormancy or germination inception. Correspondingly, this phytohormone does not play a role in the dormancy breakage induced by wounding, but accelerates germination after such breakage has occurred.

Breaking the apple embryo dormancy by nitric oxide involves the stimulation of ethylene production

Mature seeds of apple (Mallus domestica Borb. cv. Antonówka) are dormant and do not germinate unless their dormancy is removed by several weeks of moist-cold treatment. We investigated the effect of short-term (3 h) nitric oxide (NO) pretreatment on breaking of apple embryonic dormancy expressed as inhibition of germination and morphological abnormalities of young seedlings. Imbibition of embryos isolated from dormant apple seeds with sodium nitroprusside (SNP) or S-nitroso,N-acetyl penicillamine (SNAP) as NO donors resulted in enhanced germination. Moreover, NO treatment removed morphological abnormalities of seedlings developing from dormant embryo. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-teramethylimidazoline-1-oxyl-3 oxide (cPTIO) removed the above effects. NO-mediated breaking of embryonic dormancy correlated well with enhanced ethylene production. Inhibitor of ethylene synthesis (AOA) reversed the stimulatory effect of NO donors on embryo germination. Additionally SNP reduced embryo sensitivity to exogenously applied ABA ensuing dormancy breakage. We can conclude that NO acts as a regulatory factor included in the control of apple embryonic dormancy breakage by stimulation of ethylene biosynthesis.

MOLECULAR CONTROL OF FRUIT RIPENING AND SENSORY QUALITY OF CHARENTAIS MELON

Traditional Charentais melons have a typical climacteric behavior with ethylene playing a major role in the regulation of the ripening process. Genetic studies using climacteric and non-climacteric types of Cucumis melo demonstrated that the climacteric character is dominant and conferred by 2 duplicated loci only which are of great importance for the regulation of storability and sensory quality. Commercial varieties of Charentais melon with long shelf-life have been generated, some of them by crossing with a non-ripening Charentais genotype (Vauclusien). The introduction of the long shelf-life character resulted in undesirable loss of aroma volatiles production. The inhibition of ethylene synthesis by knocking-down ACC oxidase gene expression has been achieved in Charentais melon. It results is a strong inhibition of the synthesis of aroma volatiles while the accumulation of sugars is not affected or is even improved and the softening of the flesh is strongly affected but not abolished. It was also demonstrated that ethylene-inhibited fruit exhibited better resistance to chilling injury. Due to the importance of aroma volatiles in sensory quality and to the strong negative correlation between aroma production and ethylene synthesis, we have developed a research program aimed at isolating genes involved in the synthesis of volatile esters, compounds that are essential for the flavor of Cantaloupe melons. We report here on the recent advances in the field with special emphasis on the characterization of two families of genes encoding aldehyde reductases and alcohol acyl transferases.

Abscisic acid rescues the root meristem defects of the Medicago truncatula latd mutant

The LATD gene of the model legume, Medicago truncatula, is required for the normal function of three meristems, i.e. the primary root, lateral roots and nitrogen-fixing nodules. In latd mutants, primary root growth eventually arrests, resulting in a disorganized root tip lacking a presumptive meristem and root cap columella cells. Lateral root organs are more severely affected; latd lateral roots and nodules arrest immediately after emerging from the primary root, and reveal a lack of organization. Here we show that the plant hormone, abscisic acid (ABA), can rescue the latd root, but not nodule, meristem defects. Growth on ABA is sufficient to restore formation of small, cytoplasm-rich cells in the presumptive meristem region, rescue meristem organization and root growth and formation of root cap columella cells. In contrast, inhibition of ethylene synthesis or signaling fails to restore latd primary root growth. We find that latd mutants have normal levels of ABA, but exhibit reduced sensitivity to the hormone in two other ABA-dependent processes: seed germination and stomatal closure. Together, these observations demonstrate that the latd mutant is defective in the ABA response and indicate a role for LATD-dependent ABA signaling in M. truncatula root meristem function.