Ethylene Biosynthesis Inhibitor Research Articles

Ethylene, a key factor in the regulation of seed dormancy.

Ethylene is an important component of the gaseous environment, and regulates numerous plant developmental processes including seed germination and seedling establishment. Dormancy, the inability to germinate in apparently favorable conditions, has been demonstrated to be regulated by the hormonal balance between abscisic acid (ABA) and gibberellins (GAs). Ethylene plays a key role in dormancy release in numerous species, the effective concentrations allowing the germination of dormant seeds ranging between 0.1 and 200 μL L-1. Studies using inhibitors of ethylene biosynthesis or of ethylene action and analysis of mutant lines altered in genes involved in the ethylene signaling pathway (etr1, ein2, ain1, etr1, and erf1) demonstrate the involvement of ethylene in the regulation of germination and dormancy. Ethylene counteracts ABA effects through a regulation of ABA metabolism and signaling pathways. Moreover, ethylene insensitive mutants in Arabidopsis are more sensitive to ABA and the seeds are more dormant. Numerous data also show an interaction between ABA, GAs and ethylene metabolism and signaling pathways. It has been increasingly demonstrated that reactive oxygen species (ROS) may play a significant role in the regulation of seed germination interacting with hormonal signaling pathways. In the present review the responsiveness of seeds to ethylene will be described, and the key role of ethylene in the regulation of seed dormancy via a crosstalk between hormones and other signals will be discussed.

Influence of the use of biosynthesis inhibitor ethylene on the efficiency of combine harvesting.

The mechanized harvesting is evolving daily and has become an increasing and irreversible process. However, one of the limitations of the harvest, either manual or mechanized, is the uneven ripening, which affects the operating performance and the product quality, resulting economic losses to producers. Thus, this study was carried out with the objective of evaluating the operation of the mechanized coffee harvesting using the inhibitor of ethylene biosynthesis, seeking to understand their influence on the natural fall. The study was conducted in Ouro Verde farm, located in Lavras-MG. The tests were conducted in the experimental area of 1.0 ha for Catuai Vermelho IAC 15 in the years 2012 and 2013 and Acaia Cerrado MG 1474 only in 2013, loading parameters were determined the plant load, maturation index, natural fruit fall and efficiency of mechanical harvesting . Based on the result obtained, the application of the inhibitor of ethylene biosynthesis at dosage of five liters per hectare showed greater efficiency in crop cultivar Catuai Vermelho IAC 15. The natural fruit fall decreased with the application of two dosage of ethylene inhibitor (5 + 5 liters per hectare) for the Acaia Cerrado MG 1474 in the year 2013.

Selenium and sulfur influence ethylene formation and alleviate cadmium-induced oxidative stress by improving proline and glutathione production in wheat

We have studied the influence of selenium (Se) and sulfur (S) in the protection of photosynthetic capacity of wheat (Triticum aestivum) against cadmium (Cd) stress. The involvement of ethylene and its interaction with proline and antioxidant metabolism in the tolerance of plants to Cd stress was evaluated. Application of Se or S alleviated Cd-induced oxidative stress by increasing proline accumulation as a result of increased activity of glutamyl kinase (GK) and decreased activity of proline oxidase (PROX). These nutrients also induced the activity of ATP-sulfurylase and serine acetyl transferase and the content of cysteine (Cys), a precursor for the synthesis of both reduced glutathione (GSH) and ethylene. Further, application of Se and S to plants under Cd stress reduced ethylene level and increased the activity of glutathione reductase (GR) and glutathione peroxidase (GPX), reduced oxidative stress and improved photosynthesis and growth. The involvement of ethylene in Se and S-mediated alleviation of Cd stress was substantiated with the use of ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). The use of AVG reversed the effects of Se and S on ethylene, content of proline and GSH and photosynthesis. The results suggested that Se and S both reversed Cd-induced oxidative stress by regulating ethylene formation, proline and GSH metabolism. Thus, Se or S-induced regulatory interaction between ethylene and proline and GSH metabolism may be used for the reversal of Cd-induced oxidative stress.

Transcriptomic analysis reveals ethylene as stimulator and auxin as regulator of adventitious root formation in petunia cuttings.

Adventitious root (AR) formation in the stem base (SB) of cuttings is the basis for propagation of many plant species and petunia is used as model to study this developmental process. Following AR formation from 2 to 192 hours post-excision (hpe) of cuttings, transcriptome analysis by microarray revealed a change of the character of the rooting zone from SB to root identity. The greatest shift in the number of differentially expressed genes was observed between 24 and 72 hpe, when the categories storage, mineral nutrient acquisition, anti-oxidative and secondary metabolism, and biotic stimuli showed a notable high number of induced genes. Analyses of phytohormone-related genes disclosed multifaceted changes of the auxin transport system, auxin conjugation and the auxin signal perception machinery indicating a reduction in auxin sensitivity and phase-specific responses of particular auxin-regulated genes. Genes involved in ethylene biosynthesis and action showed a more uniform pattern as a high number of respective genes were generally induced during the whole process of AR formation. The important role of ethylene for stimulating AR formation was demonstrated by the application of inhibitors of ethylene biosynthesis and perception as well as of the precursor aminocyclopropane-1-carboxylic acid, all changing the number and length of AR. A model is proposed showing the putative role of polar auxin transport and resulting auxin accumulation in initiation of subsequent changes in auxin homeostasis and signal perception with a particular role of Aux/IAA expression. These changes might in turn guide the entrance into the different phases of AR formation. Ethylene biosynthesis, which is stimulated by wounding and does probably also respond to other stresses and auxin, acts as important stimulator of AR formation probably via the expression of ethylene responsive transcription factor genes, whereas the timing of different phases seems to be controlled by auxin.

2-Aminooxyisobutyric acid inhibits the in vitro activities of both 1-Aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase in ethylene biosynthetic pathway and prolongs vase life of cut carnation flowers

2-Aminooxyisobutyric acid (AOIB) has a partial structure of aminooxyacetic acid (AOA) in its whole structure, and resembles 2-aminoisobutyric acid (AIB) in their tetrahedral structures. Both AOA and AIB are inhibitors of ethylene biosynthesis; AOA inhibits the action of 1-aminocyclopropane-1-carboxylate (ACC) synthase and AIB inhibits that of ACC oxidase. The present study showed that AOIB inhibited the in vitro activities of both ACC synthase and ACC oxidase, which were synthesized heterologously in E. coli cells from corresponding carnation cDNAs, and the magnitudes of inhibition were similar to those caused by AOA and AIB; AOIB and AOA at 0.1 mM inhibited ACC synthase action by 75%, and AOIB and AIB at 10 mM inhibited ACC oxidase action by 16.3 and 22.5%, respectively. AOIB at 1 mM caused 91.5% reduction of maximum ethylene production rate as compared to the control in cut ‘Excerea’ carnation flowers undergoing senescence, thereby lengthening their vase life to 7 d from 3 d of the control flowers. The inhibition by AOIB was probably caused by its action resembling AOA, but not AIB. AOIB also extended significantly the vase life of cut flowers of ‘Pax’ carnation, and tended to do so in ‘Primero Mango’ carnation. The present findings suggest the potential of AOIB as a new preservative for carnations and other ornamentals in which ethylene plays a key role in the induction of senescence.

HISTORY AND PERSPECTIVES ON THE ROLE OF ETHYLENE IN PINEAPPLE FLOWERING

Pineapple is an ancient Amerindian crop that was spread throughout the tropics by early Spanish and Portuguese explorers. They were grown in heated greenhouses in Europe and Britain by 1720 and a greenhouse-based commercial pineapple industry began in the Azores in about 1872. It was discovered by accident there in 1874 that plants could be forced into flower (forced) with smoke and growers adopted the practice as a way to schedule fruiting when prices were high. By the 1920s, growers in Puerto Rico had adapted the practice for in-field use by building smudge fires beneath blocks of pineapple covered with muslin cloth. It was known that distillation of wood produced ethylene and it was shown in 1932 that smoke and ethylene gas were both effective in forcing pineapple. That discovery led the Hawaiian pineapple industry, then the largest and most technologically advanced in the world, to improve on the new forcing technology. Hawaiian Pineapple Company patented a method of forcing pineapple with calcium carbide in 1936 and the industry-supported Pineapple Research Institute (PRI) patented a method of forcing pineapple with acetylene or ethylene as a gas or as a water solution. In 1941, California Packing Corporation patented an apparatus that could mix and apply a water-oil-colloidal earth emulsion containing acetylene or ethylene to field-grown pineapple plants to force them. In 1942, the PRI reported that pineapple plants could be forced with a low concentration of 1-naphthaleneacetic acid (NAA) while higher concentrations inhibited natural induction (NI) of flowering. It was shown in 1966 that auxins forced pineapple by stimulating the plant to produce ethylene. Over a ten year period, the PRI screened thousands of compounds as potential forcing agents and in 1956 reported that 2-hydroxyethylhydrazine (BOH) would force pineapple; in 1967 it was shown that BOH was an ethylene delivery agent. In 1968, pineapple plants were forced with 2-chloroethylphosphonic acid (ethephon), another ethylene delivery agent. Currently, pineapples on large plantations typically are forced approximately weekly with ethephon or ethylene. On smaller farms, forcing pineapples with calcium carbide or acetylene is more common. Natural induction, which is believed to be an ethylene-driven event, disrupts this orderly process of fruit production and is a serious management problem for growers of 'MD2-(Gold') pineapple. 'MD-2' is considered sensitive to NI in most environments where the winter photoperiod is less than about 11.5 h. High concentrations of auxins inhibit flowering, but with inconsistent results. A 1983 study showed that aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, prevented NI of ornamental bromeliads, which like pineapple can be forced with ethephon. When AVG was commercialized in 1997, field trials were established to explore its potential to control NI of pineapple. Research over about a 10-year period showed that AVG could consistently control NI with an acceptable cost/benefit in commercial pineapple fields. AVG is registered for that use in Hawaii and a number of other countries where large commercial pineapple industries are located. From a historical perspective, when it comes to natural or forced induction of flowering, or its inhibition, all paths eventually lead to ethylene.

Abscisic acid inhibits root growth in Arabidopsis through ethylene biosynthesis.

When first discovered in 1963, abscisic acid (ABA) was called abscisin II because it promotes abscission. Later, researchers found that ABA accelerates abscission via ethylene. In Arabidopsis, previous studies have shown that high concentrations of ABA inhibit root growth through ethylene signaling but not ethylene production. In the present study in Arabidopsis, we found that ABA inhibits root growth by promoting ethylene biosynthesis. The ethylene biosynthesis inhibitor L-α-(2-aminoethoxyvinyl)-glycine reduces ABA inhibition of root growth, and multiple mutants of ACS (1-aminocyclopropane-1-carboxylate synthase) are more resistant to ABA in terms of root growth than the wild-type is. Two ABA-activated calcium-dependent protein kinases, CPK4 and CPK11, phosphorylate the C-terminus of ACS6 and increase the stability of ACS6 in ethylene biosynthesis. Plants expressing an ACS6 mutant that mimics the phosphorylated form of ACS6 produce more ethylene than the wild-type. Our results reveal an important mechanism by which ABA promotes ethylene production. This mechanism may be highly conserved among higher plants.

English

Different genera of bacteria are present as endophytic in roots and nodules of legumes and roots of non legumes grown in different parts of the world. A number of these endophytic inhabitants vary from few to large numbers. Predominantly, endophytes belongs to three major phyla, Actinobacteria, Proteobacteria and Firmicutes and includes members of Streptobyces, Azocareus, Gluconobacter, Pseudomonas, Serratia, Stenophomonas, Bacillus, Paenibacillus and Enterobacter. Majority of the endophytes show plant growth promotion and have other beneficial traits like enhancement of biological nitrogen fixation, phytohormone production, phosphate solubilization, inhibition of ethylene biosynthesis in response to biotic or  abiotic stress and above all have biocontrol activity. These endophytes colonize inside the root or nodules. It seems no host specificity exist between different endophytic bacteria and plant host. These opportunist bacteria can enter the plant tissue whenever they have the opportunity either after dissolving the cell wall or through crack entry. Beneficial effects of bacterization of these endophytes have been shown in different plant host under green house and even under field conditions. Therefore endophytic bacteria are better alternate to sustain crop productivity.   Key words: Nodules, endophytic bacteria, legumes, roots, genera.

Involvement of ethylene in reversal of salt‐inhibited photosynthesis by sulfur in mustard

Sulfur (S) assimilation results in the synthesis of cysteine (Cys), a common metabolite for the formation of both reduced glutathione (GSH) and ethylene. Thus, ethylene may have regulatory interaction with GSH in the alleviation of salt stress. The involvement of ethylene in the alleviation of salt stress by S application was studied in mustard (Brassica juncea cv. Pusa Jai Kisan). First, the effects of 0, 0.5, 1.0 and 2.0 mM SO4 (2) (-) were studied on photosynthetic and growth parameters to ascertain the S requirement as sufficient-S and excess-S for the plant. In further experiments, the effects of sufficient-S (1 mM SO4 (2) (-) ) and excess-S (2 mM SO4 (2) (-) ) were studied on the alleviation of salt stress-induced by 100 mM NaCl, and ethylene involvement in the alleviation of salt stress by S. Under non-saline condition, excess-S increased ethylene with less content of Cys and GSH and adversely affected photosynthesis and growth. In contrast, excess-S maximally alleviated salt stress due to high demand for S and optimal ethylene formation, which maximally increased GSH and promoted photosynthesis and growth. The involvement of ethylene in S-mediated alleviation of salt stress was further substantiated by the reversal of the effects of excess-S on photosynthesis by aminoethoxyvinylglycine (AVG), ethylene biosynthesis inhibitor. The studies suggest that plants respond differentially to the S availability under non-saline and salt stress and excess-S was more potential in the alleviation of salt stress. Further, ethylene regulates plants' response and excess S-induced alleviation of salt stress and promotion of photosynthesis.

Alleviation of salt-induced photosynthesis and growth inhibition by salicylic acid involves glycinebetaine and ethylene in mungbean (Vigna radiata L.)

The influence of salicylic acid (SA) in alleviation of salt stress in mungbean (Vigna radiata L.) through modulation of glycinebetaine (GB) and ethylene was studied. SA application at 0.5 mM increased methionine (Met) and GB accumulation in plants concomitant with the suppression of ethylene formation by inhibiting 1-aminocyclopropane carboxylic acid synthase (ACS) activity more conspicuously under salt stress than no stress. The increased GB accumulation together with reduced ethylene under salt stress by SA application was associated with increased glutathione (GSH) content and lower oxidative stress. These positive effects on plant metabolism induced by SA application led to improved photosynthesis and growth under salt stress. These results suggest that SA induces GB accumulation through increased Met and suppresses ethylene formation under salt stress and enhances antioxidant system resulting in alleviation of adverse effects of salt stress on photosynthesis and growth. These effects of SA were substantiated by the findings that application of SA-analogue, 2, 6, dichloro-isonicotinic acid (INA) and ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG) resulted in similar effects on Met, GB, ethylene production, photosynthesis and growth under salt stress. Future studies on the interaction between SA, GB and ethylene could be exploited for adaptive responses of plants under salt stress.

Involvement of glucose in the regulation of ethylene biosynthesis and sensitivity in cut Paeonia suffruticosa flowers

Exogenous application of sugars has been known for decades to extend flower longevity effectively. The prevailing view is that sugars provide respirable substrates, structural constituents and osmolytes; however, interaction with plant hormone ethylene seems to be more important for several ethylene-sensitive flowers. To determine whether and how sugars interact with ethylene to regulate postharvest flower senescence in Paeonia suffruticosa, a traditional ornamental plant in China with most ethylene-sensitive cultivars, we investigated the effects of glucose on ethylene biosynthesis and sensitivity in relation to postharvest flower development. Cut P. suffruticosa flowers continuously treated with glucose, but not the osmolyte mannitol, showed delayed visible senescence and extended vase life. Glucose treatment delayed and inhibited the climacteric increase in ethylene production of cut flowers associated with the delay and inhibition of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) activity, as well as the suppression of ACC oxidase (ACO) activity in petals, which is at least partially explained by the repression of PsACS1 mRNA accumulation. Exposure of cut flowers to ethylene shortened vase life and stimulated autocatalytic ethylene production. However, these effects of ethylene were markedly reduced in the flowers with prior glucose treatment rather than mannitol, suggesting that glucose directly decreases the sensitivity to ethylene. Additionally, glucose prevented the effect of ethylene in inducing PsACS1 mRNA accumulation but did not affect PsACO1 mRNA level. These results indicate that glucose extends the vase life of cut P. suffruticosa flowers, possibly through both a delay and inhibition of ethylene biosynthesis, and a decrease in sensitivity to ethylene.

Cold acclimation-induced freezing tolerance ofMedicago truncatulaseedlings is negatively regulated by ethylene

To evaluate the role of ethylene in cold acclimation and cold stress, freezing tolerance and characteristics associated with cold acclimation were investigated using legume model plant Medicago truncatula Gaertn Jemalong A17. There was a rapid suppression of ethylene production during cold acclimation in A17 plants. Ethylene level was negatively correlated with freezing tolerance as inhibition of ethylene biosynthesis by inhibitors of ethylene biosynthesis enhanced freezing tolerance, while exogenous application of ethylene reduced cold acclimation-induced freezing tolerance. The involvement of ethylene signaling in modulation of freezing tolerance and cold acclimation was further studied using ethylene-insensitive mutant sickle skl. Although skl mutant was more tolerant to freezing than its wild-type counterpart A17 plants, cold acclimation enhanced freezing tolerance in 17 plants, but not in skl mutant. Expression of several ethylene response genes including EIN3, EIN3/EIL and ERFs was suppressed in skl mutant compared to A17 plants under non-cold-acclimated conditions. Cold acclimation downregulated expression of EIN3, EIN3/EIL and ERFs in A17 plants, while expression patterns of these genes were relatively constant in skl mutant during cold acclimation. Cold acclimation-induced increases in transcription of MtCBFs and MtCAS15 were suppressed in skl mutant compared with A17 plants. These results suggest that MtSKL1 is required for perception of the change of ethylene level in M. truncatula plants for the full development of the cold acclimation response by suppressing expression of MtEIN3 and MtEIN3/EIL1, which in turn downregulates expression of MtERFs, leading to the enhanced tolerance of M. truncatula to freezing by upregulating MtCBFs and MtCAS15.

Ethylene, auxin, and abscisic acid interactions in the control of photoperiodic flower induction in Pharbitis nil

Interactions between indole-3-acetic acid (IAA), abscisic acid (ABA), and ethylene (ET) in the photoperiodic flower induction of a short-day (SD) plant Pharbitis nil were investigated. It was shown that both IAA and ABA applied just before and during the first half of the 16-h-long inductive night inhibited flower induction in P. nil. Ethylene is also thought to be a strong flowering inhibitor of SD plants but only when it is applied in the second half of the inductive night. The application of IAA just before the inductive night decreased the content of endogenous ABA in cotyledons only during the first half of the inductive night. Additionally, the application of 2-aminoethoxyvinylglycine (AVG) — an ethylene biosynthesis inhibitor — partially reversed the inhibitory effect of IAA and ABA on flowering. The results suggest that the mechanisms of P. nil flower inhibition by IAA and ABA might be independent. However, both the hormones influenced ethylene production which directly inhibited flowering. We also show that ABA applied on the cotyledons of P. nil seedlings just before the inductive night caused a clear increase in the expression of PnACS1 and PnACS2 genes (encoding enzymes involved in ethylene biosynthesis) from the first hours after its application. The transcripts of PnACO1 and PnACO3 genes were also increased but their maximal values were shifted in relation to the PnACS1 and PnACS2. The data presented here strongly support the idea that both IAA and ABA inhibit P. nil flowering through the modulation of ethylene biosynthesis.

Ethylene in the control of photoperiodic flower induction in Pharbitis nil Chois.

The content of endogenous ethylene in the seedlings of <em>Pharbitis nil</em> subjected to 16-hour long inductive night is low during the first half of a dark period, then it increases considerably in the second half of the night. Ethrel, the compound releasing ethylene, applied to the cotyledons of the seedlings, increases the amount of endogenous ethylene in them and at the same time inhibits the flowering, especially when ethrel was applied during the first half of an inductive night, when the content of endogenous ethylene in the seedlings is low. The auxin, inhibiting the flowering of <em>Pharbitis</em>, causes at the same time the increase in the production of endogenous ethylene. PCIB, an inhibitor of auxin action reverses the inhibiting influence of ethrel on flowering. On the other hand the combined application of ethrel and TIBA, the inhibitor of auxin polar transport, causes the increase of the flowering inhibition. CoCl<sub>2</sub>, the inhibitor of ethylene biosynthesis, and AgNO<sub>3</sub>, the inhibitor of ethylene action, reverse partly the inhibiting influence of auxin. It suggests that ethylene could take part in auxininhibition of flowering. The all obtained results seem to suggest the participation of ethylene in the control of the flower photoperiodic induction.

CGMP and ethylene are involved in maintaining ion homeostasis under salt stress in Arabidopsis roots

cGMP promotes ethylene production and enhances the perception of ethylene. Endogenous ethylene or cGMP accumulation maintains ion homeostasis to enhancing salt resistance. etr1 - 3 is insensitive to cGMP under salt stress. In the present study, we presented a signaling network involving ethylene and cGMP in salt resistance pathway of Arabidopsis roots. Results showed that the ethylene-insensitive mutant etr1-3 was more sensitive to salt stress than the wild type (WT). etr1-3 displayed a greater electrolyte leakage, thiobarbituric acid reactive substances and Na(+)/K(+) ratio, but a lower plasma membrane (PM) H(+)-ATPase activity compared to WT under the different NaCl contents. Application of 1-aminocyclopropane-1-carboxylic acid (ACC, an ethylene precursor) or 8-Br-cGMP (the cGMP analog) alleviated NaCl-induced injury by maintaining a lower Na(+)/K(+) ratio and increasing PM H(+)-ATPase activity in WT, but not in etr1-3. Roots treated with 8-Br-cGMP could promote ethylene production and enhance the expression of ACC synthase gene in WT. In addition, the 8-Br-cGMP action in NaCl stress was inhibited by aminooxyacetic acid (an inhibitor of ethylene biosynthesis), but 6-Anilino-5,8-quinolinedione (Ly83583, a guanylate cyclase inhibitor) could not affect ACC action in WT. These results suggest that ethylene functions as a downstream signal of cGMP that stimulates the PM H(+)-ATPase activity, which finally results in regulating ion homeostasis in Arabidopsis tolerance to salt. Moreover, cGMP enhanced the perception of ethylene in Arabidopsis under salt stress, which reversed the salt-induced increase of ETR1 and increased ERF1 at the transcript levels in WT. In a word, cGMP modulates salt resistance pathway of ethylene through regulating biosynthesis and perception of ethylene in Arabidopsis roots.

Interactions between ethylene and auxin are crucial to the control of grape (Vitis vinifera L.) berry ripening.

BackgroundFruit development is controlled by plant hormones, but the role of hormone interactions during fruit ripening is poorly understood. Interactions between ethylene and the auxin indole-3-acetic acid (IAA) are likely to be crucial during the ripening process, since both hormones have been shown to be implicated in the control of ripening in a range of different fruit species.ResultsGrapevine (Vitis vinifera L.) homologues of the TRYPTOPHAN AMINOTRANSFERASE RELATED (TAR) and YUCCA families, functioning in the only characterized pathway of auxin biosynthesis, were identified and the expression of several TAR genes was shown to be induced by the pre-ripening application of the ethylene-releasing compound Ethrel. The induction of TAR expression was accompanied by increased IAA and IAA-Asp concentrations, indicative of an upregulation of auxin biosynthesis and conjugation. Exposure of ex planta, pre-ripening berries to the ethylene biosynthesis inhibitor aminoethoxyvinylglycine resulted in decreased IAA and IAA-Asp concentrations. The delayed initiation of ripening observed in Ethrel-treated berries might therefore represent an indirect ethylene effect mediated by increased auxin concentrations. During berry development, the expression of three TAR genes and one YUCCA gene was upregulated at the time of ripening initiation and/or during ripening. This increase in auxin biosynthesis gene expression was preceded by high expression levels of the ethylene biosynthesis genes 1-aminocyclopropane-1-carboxylate synthase and 1-aminocyclopropane-1-carboxylate oxidase.ConclusionsIn grape berries, members of both gene families involved in the two-step pathway of auxin biosynthesis are expressed, suggesting that IAA is produced through the combined action of TAR and YUCCA proteins in developing berries. The induction of TAR expression by Ethrel applications and the developmental expression patterns of auxin and ethylene biosynthesis genes indicate that elevated concentrations of ethylene prior to the initiation of ripening might lead to an increased production of IAA, suggesting a complex involvement of this auxin and its conjugates in grape berry ripening.

A Novel Effect for Glycine on Root System Growth of Habanero Pepper

Amino acids, a major fraction of the low-molecular-weight organic nitrogen in soil, act as signaling molecules that indicate the presence of nutrient-rich patches to the roots. To characterize the effects of amino acids on root growth, we used seedlings of habanero pepper (Capsicum chinense), one of the most widely cultivated annual spice crops in the world. We tested the effect of L-glutamate, L-aspartate, and glycine on the primary root of seedlings grown aseptically under different conditions of pH and light. L-glutamate and L-aspartate did not inhibit the root growth of habanero pepper. In contrast, glycine inhibited the growth of roots, stimulated root hair growth, and induced a significant accumulation of starch grains in the root apex. The use of aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, and the evaluation of 1-aminocyclopropane-1-carboxylic acid oxidase expression provided evidence of a role for ethylene in the root responses to glycine. We suggest that these changes in the root apex in response to exogenous glycine could be an important adaptive response that allows plants to efficiently access the fluctuating availability of nutrients in the soil.

Linking ethylene to nitrogen-dependent leaf longevity of grass species in a temperate steppe

Leaf longevity is an important plant functional trait that often varies with soil nitrogen supply. Ethylene is a classical plant hormone involved in the control of senescence and abscission, but its role in nitrogen-dependent leaf longevity is largely unknown. Pot and field experiments were performed to examine the effects of nitrogen addition on leaf longevity and ethylene production in two dominant plant species, Agropyron cristatum and Stipa krylovii, in a temperate steppe in northern China. Nitrogen addition increased leaf ethylene production and nitrogen concentration but shortened leaf longevity; the addition of cobalt chloride, an ethylene biosynthesis inhibitor, reduced leaf nitrogen concentration and increased leaf longevity. Path analysis indicated that nitrogen addition reduced leaf longevity mainly through altering leaf ethylene production. These findings provide the first experimental evidence in support of the involvement of ethylene in nitrogen-induced decrease in leaf longevity.

Germination of salt-stressed seeds as related to the ethylene biosynthesis ability in three Stylosanthes species

Stylosanthes, a genus of tropical forage legume, is known to exhibit good persistence in saline soils, yet mechanisms for regulation of seed germination under salt stress are poorly understood. This study was carried out to evaluate the mode of action of salt stress on seed germination of Stylosanthes. 1-Aminocyclopropane-1-carboxylic acid (ACC) increased ethylene biosynthesis and germination of NaCl-inhibited seeds in a dose-dependent manner. Contents of ACC and germination of Stylosanthes humilis seeds increased following transfer from NaCl solution to deionised water, but not after transfer to l-α-(2-aminoethoxyvinyl)-glycine (AVG) solution, an inhibitor of ethylene biosynthesis. Ethylene biosynthesis was much larger in NaCl-treated seeds of Stylosanthes guianensis than in seeds of S. humilis and Stylosanthes capitata, a fact which was reflected in higher germination rates. S. guianensis seedlings also displayed higher growth and survival rates than S. humilis and S. capitata under salt stress. Moreover, smaller ACC levels, as well as reduced ethylene biosynthesis of S. capitata seeds were accompanied by lower germination under salt stress. In addition, S. capitata seedlings treated with NaCl solutions exhibited relatively lower growth and survival rates in comparison with S. humilis and S. guianensis. Thus, different abilities to synthesize ethylene by S. guianensis, S. humilis and S. capitata seeds explain the differences in tolerance to salt stress of the three species.

Ethylene promotes germination of Arabidopsis seed under salinity by decreasing reactive oxygen species: Evidence for the involvement of nitric oxide simulated by sodium nitroprusside

Both ethylene and nitric oxide (NO) are involved in modulating seed germination in adverse environments. However, the mechanisms by which they interact and affect germination have not been explained. In this study, the relationship between ethylene and NO during germination of Arabidopsis seed under salinity was analysed. Application of exogenous 1-aminocyclopropane-1-carboxylate (ACC, a precursor of ethylene biosynthesis) or sodium nitroprusside (SNP, an NO donor) largely overcame the inhibition of germination induced by salinity. The effects of ACC and SNP were decreased by 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger, or by aminoisobutyric acid (AIB), an inhibitor of ethylene biosynthesis, indicating that ethylene and NO interact during germination under salinity. Further, we demonstrated that ACC increased NO production and that SNP greatly induced the expression of the ACS2 gene involved in ethylene synthesis in Arabidopsis seeds germinating under salinity stress, suggesting that each substance influences the production of the other. Application of exogenous ACC increased germination under oxidative stress induced by hydrogen peroxide (H2O2) while SNP had a much smaller effect on wild-type Arabidopsis (Col-0) and no effect on the ethylene insensitive mutant (ein3-1) seeds, respectively. This shows that NO increased germination under salinity indirectly through H2O2 acting via the ethylene pathway. The endogenous concentration of H2O2 was increased by salinity in germinating seeds but was decreased by exogenous ACC, which stimulated germination ultimately. To explain all these results and the regulation of germination of Arabidopsis seed under salinity we propose a model involving ethylene, NO and H2O2 interaction.