Increase In Ethylene Biosynthesis Research Articles

Transcriptional regulation of MbACO2-mediated ethylene synthesis during postharvest banana ripening

Ethylene plays a central role in climacteric fruit ripening. 1-Aminocyclopropane-1-carboxylic acid oxidase (ACO) is a crucial enzyme for ethylene biosynthesis. Edible cultivated banana varieties are mainly composed of the A- or A/B-genome. Nevertheless, the function and regulatory mechanism of ACO genes in the B-genome of banana fruit are unknown. The present study revealed the function and regulatory mechanism of the B-genome-specific gene MbACO2 in ethylene biosynthesis during postharvest banana ripening. MbACO2 expression significantly increased at 6 d postharvest. MbACO2 overexpression in tomato resulted in an increase in ethylene biosynthesis and the acceleration of fruit ripening. MaNAC29 and MbERF71/MbERF113 showed induction during the postharvest periods and directly activated the transcription of MbACO2 through the CGTC-element and GCC-box in its promoter, respectively. In addition, MaMAPK1 interacted with MaNAC29 to further enhance the transcription of MbACO2. Collectively, our findings demonstrate a novel regulatory cascade involving MaMAPK1, MaNAC29, and MbERF71/MbERF113 that promotes MbACO2 transcription during postharvest banana ripening, which helps design breeding strategies to extend the shelf life of fruit.

Extracellular self-DNA induced a PTI-related local defence against Rhizopus rot in postharvest peach fruit

The plant immune response against various pathogens relies on a convoluted recognition system based on perceiving exogenous or endogenous stimuli, such as pathogen- or damage-associated molecular patterns (PAMPs or DAMPs). Extracellular self-DNA (sDNA) is an established DAMP source, but the plant intracellular signaling mechanism after sDNA perception remains largely unclear. Here, we observed that peach fruit was more resistant to the fungus Rhizopus stolonifer after sDNA perception. We identified a complete MAPK cascade (MAPKKK1, MAPKK2 and MAPK1) that functions downstream of the FLS2-BAK1 receptor complex following the perception of sDNA-derived DAMPs by means of transcriptome sequencing. The results of yeast two-hybrid (Y2H) and glutathione S-transferase (GST) pull-down assays confirmed the protein interaction of FLS2 and BAK1; meanwhile, the interaction of MAPKKK1 and MAPKK2 and its downstream interaction of MAPKK2 and MAPK1 were both exhibited following the another Y2H results. Accordingly, MAPK1 interacted with 1-aminocyclopropane-1-carboxylate oxidase (ACO1), which was directly associated with increased ethylene production and upregulation of the transcription profile of ethylene synthesis-related genes (PpSAMDC, PpACS1 and PpACO1), ethylene receptors (ETRs and ERS1), ethylene-responsive transcription factors (ERFs) and three ethylene-inducible marker genes, PLANT DEFENSIN1.2 (PDF1.2), CHITINASE (CHI) and HOOKLESS1 (HLS1). Accordingly, the overexpression of MAPK1 enhanced the disease resistance of transgenic tomato against the fungus R. stolonifer and increased ethylene biosynthesis and ethylene signaling-related gene transcription. Taken together, our data provide insight into the putative mechanism underlying the recognition of sDNA components by the FLS2-BAK1 complex and its downstream events in the transduction of ethylene signaling by the MAPK cascade to mediate local resistance in postharvest peach fruit.

SnRK2 subfamily I protein kinases regulate ethylene biosynthesis by phosphorylating HB transcription factors to induce ACO1 expression in apple.

Summary Ethylene (ETH) controls climacteric fruit ripening and can be triggered by osmotic stress. However, the mechanism regulating ETH biosynthesis during fruit ripening and under osmotic stress is largely unknown in apple (Malus domestica).Here, we explored the roles of SnRK2 protein kinases in ETH biosynthesis related to fruit ripening and osmoregulation. We identified the substrates of MdSnRK2‐I using phosphorylation analysis techniques. Finally, we identified the MdSnRK2‐I‐mediated signaling pathway for ETH biosynthesis related to fruit ripening and osmoregulation.The activity of two MdSnRK2‐I members, MdSnRK2.4 and MdSnRK2.9, was significantly upregulated during ripening or following mannitol treatment. Overexpression of MdSnRK2‐I increased ETH biosynthesis under normal and osmotic conditions in apple fruit. MdSnRK2‐I phosphorylated the transcription factors MdHB1 and MdHB2 to enhance their protein stability and transcriptional activity on MdACO1. MdSnRK2‐I also interacted with MdACS1 and increased its protein stability through two phosphorylation sites. The increased MdACO1 expression and MdACS1 protein stability resulted in higher ETH production in apple fruit. In addition, heterologous expression of MdSnRK2‐I or manipulation of SlSnRK2‐I expression in tomato (Solanum lycopersicum) fruit altered fruit ripening and ETH biosynthesis.We established that MdSnRK2‐I functions in fruit ripening and osmoregulation, and identified the MdSnRK2‐I‐mediated signaling pathway controlling ETH biosynthesis.

Nitric oxide supply reduces ethylene production, softening and weight loss in papaya fruit

Nitric oxide application has been seen as a promising technique to extend the postharvest life of various fresh fruits and vegetables. This is the first work involving the spray application of nitric oxide donor S-nitrosoglutathione (GSNO) on Golden papaya. Considering that results are very distinct depending on the type of the nitric oxide donor, the form of application, the concentration used and the species studied, the application must be adapted to each necessity. The aim of this study was to relate the application of GSNO, spray applied at 10, 100, 1,000 ?M, with the physiological, physical-chemical, and biochemical changes of Golden papaya, in the first 72 h of ripening. Control fruit was sprayed with distilled water. GSNO application did not interfere on color and chlorophyll fluorescence of the peel, on soluble solids, titratable acidity, lipid peroxidation, and in the level of S-nitrosothiols. Control fruit and 10-?M GSNO sprayed showed lower respiration. After 72 h of ripening at 25°C, all fruits showed an increase in ethylene biosynthesis, except for those treated with 10 ?M GSNO. Papaya sprayed with 10-?M GSNO showed the highest pulp firmness and 52% less weight loss when compared to control fruit. GSNO was also responsible for increasing the ascorbic acid in papayas, besides showing an increase in total antioxidant activity production. The results indicated that the application of 10 ?M of GSNO by spray can potentially preserve the quality characteristics of Golden papaya, mainly due to the lower ethylene production, the delay in the firmness loss, and the less weight loss.

Interaction between reactive oxygen species and hormones during the breaking of embryo dormancy in Sorbus pohuashanensis by exogenous nitric oxide

The breaking of dormancy mediated by reactive nitrogen species (RNS) is related to the accumulation of reactive oxygen species (ROS) in germinating embryos but the underlying mechanism is unclear. The objectives of this study were: (1) to explore the relationship between RNS-mediated dormancy release and ROS accumulation in germinating embryos of Sorbus pohuashanensis; and, (2) to investigate the relationships among germination time, ROS metabolism, and endogenous hormone synthesis. We studied the effects of exogenous nitric oxide (NO) donor sodium nitroprusside (SNP), the NO scavenger (4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), abscisic acid (ABA), the exogenous ethylene donor ethrel, and the ethylene receptor inhibitor 2,5-norbornadien (NBD) on embryo germination and seedling growth. Embryos were released from dormancy by pretreatment with NO or ethylene, which was related to increased ethylene biosynthesis and decreased ABA levels. Breaking of dormancy by SNP was related to increased levels of ethylene, hydrogen peroxide, and glutathione, increased activities of superoxide dismutase and glutathione peroxidase, and decreased levels of ABA, superoxide anions, and malondialdehyde. These effects of nitric oxide were especially significant in seedling hypocotyls and radicles. These results demonstrate that NO can break S. pohuashanensis embryo dormancy by inducing ethylene biosynthesis, and that this signalling pathway is closely related to ROS accumulation and the antioxidant defence response.

Ethylene involvement in the regulation of heat stress tolerance in plants.

Because of the rise in global temperature, heat stress has become a major concern for crop production. Heat stress deteriorates plant productivity and alters phenological and physiological responses that aid in precise monitoring and sensing of mild-to-severe transient heat stress. Plants have evolved several sophisticated mechanisms including hormone-signaling pathways to sense heat stimuli and acquire heat stress tolerance. In response to heat stress, ethylene, a gaseous hormone, is produced which is indispensable for plant growth and development and tolerance to various abiotic stresses including heat stress. The manipulation of ethylene in developing heat stress tolerance targeting ethylene biosynthesis and signaling pathways has brought promising out comes. Conversely increased ethylene biosynthesis and signaling seem to exhibit inhibitory effects in plant growth responses from primitive to maturity stages. This review mainly focuses on the recent studies of ethylene involvement in plant responses to heat stress and its functional regulation, and molecular mechanism underlying the plant responses in the mitigation of heat-induced damages. Furthermore, this review also describes the crosstalk between ethylene and other signaling molecules under heat stress and approaches to improve heat stress tolerance in plants.

Ethylene signaling induces gelatinous layers with typical features of tension wood in hybrid aspen.

The phytohormone ethylene impacts secondary stem growth in plants by stimulating cambial activity, xylem development and fiber over vessel formation. We report the effect of ethylene on secondary cell wall formation and the molecular connection between ethylene signaling and wood formation. We applied exogenous ethylene or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) to wild-type and ethylene-insensitive hybrid aspen trees (Populus tremula×tremuloides) and studied secondary cell wall anatomy, chemistry and ultrastructure. We furthermore analyzed the transcriptome (RNA Seq) after ACC application to wild-type and ethylene-insensitive trees. We demonstrate that ACC and ethylene induce gelatinous layers (G-layers) and alter the fiber cell wall cellulose microfibril angle. G-layers are tertiary wall layers rich in cellulose, typically found in tension wood of aspen trees. A vast majority of transcripts affected by ACC are downstream of ethylene perception and include a large number of transcription factors (TFs). Motif-analyses reveal potential connections between ethylene TFs (Ethylene Response Factors (ERFs), ETHYLENE INSENSITIVE 3/ETHYLENE INSENSITIVE3-LIKE1 (EIN3/EIL1)) and wood formation. G-layer formation upon ethylene application suggests that the increase in ethylene biosynthesis observed during tension wood formation is important for its formation. Ethylene-regulated TFs of the ERF and EIN3/EIL1 type could transmit the ethylene signal.

Methyl jasmonate treatments influence bioactive compounds and red peel color development of Braeburn apple

The present study was carried out to determine the effects of methyl jasmonate (MeJA) treatments on the fruit peel color parameters, anthocyanin content, ethylene biosynthesis, phenolic content, and antioxidant capacity of Braeburn apples. Experimental trees were treated with 1120, 2240, or 4480 mg L-1 MeJA at 1- and 2-week intervals between the 105th and 175th days of growth after full bloom. L* and hue decreased linearly with increasing MeJA concentrations in both experimental years. While MeJA treatments did not cause significant changes in chroma, except for in the final harvest in 2010, it decreased chroma values significantly on all sampling dates of 2011. Anthocyanin content, internal ethylene concentration, phenolic content, and antioxidant capacity increased linearly with increasing MeJA concentrations, regardless of the application interval: MeJA treatments with 1-week intervals were found to be as effective as those with 2-week intervals. Although MeJA treatments increased ethylene biosynthesis, they did not cause any softening; on the other hand, fruit firmness increased linearly with increasing MeJA concentrations. Preharvest MeJA treatments can be a good management strategy for red peel color development and fruit firmness preservation in Braeburn apples. Although both application regimes of MeJA significantly increased red color development, the treatments with 1-week intervals were found to be more effective than 2-week intervals with regard to phenolic content and antioxidant capacity.

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.

The ethylene pathway contributes to root hair elongation induced by the beneficial bacteria Phyllobacterium brassicacearum STM196

In Arabidopsis roots, some epidermal cells differentiate into root hair cells. Auxin regulates root hair positioning, while ethylene controls cell elongation. Phyllobacterium brassicacearum STM196, a beneficial strain of plant growth promoting rhizobacteria (PGPR) isolated from the roots of field-grown oilseed rape, stimulates root hair elongation in Arabidopsis thaliana seedlings. We investigated the role of ethylene in the response of root hair cells to STM196 inoculation. While we could not detect a significant increase in ethylene biosynthesis, we could detect a slight activation of the ethylene signalling pathway. Consistent with this, an exhaustive survey of the root hair elongation response of mutants and transgenic lines affected in the ethylene pathway showed contrasting root hair sensitivities to STM196. We propose that local ethylene emission contributes to STM196-induceed root hair elongation.

Ethylene-regulated hastening of perianth senescence after pollination in Dendrobium flowers is not due to an increase in perianth ethylene production

Flowers of Dendrobium cv. Kenny were hand-pollinated using pollinia from cv. Sakura. This resulted in a large increase in flower ethylene emission and rapid perianth (tepal) senescence. The increase in flower ethylene emission was correlated in time with an increase in ethylene emitted by the column (the fused stigma, style and stamens) plus the ovary. No ethylene emission was observed from perianth parts that were isolated at various periods after pollination. The increased ethylene emission by the column plus ovary was correlated with an increase in ACC synthase and ACC oxidase activity in these flower parts. The perianth parts, in contrast, only showed an increase in ACC oxidase activity, following pollination. The data show that pollination-induced early perianth senescence in Dendrobium is mediated by increased ethylene biosynthesis by the column + ovary, and not due to increased ethylene biosynthesis in the perianth parts. Apparently, ethylene synthesized in the gynoecium diffuses to the perianth parts where it induces senescence. The data are very similar to those found previously in pollinated Phaleanopsis orchids and in emasculated Cymbidium orchids, with the exception that ethylene was emitted from the tepals of these two orchids and not from Dendrobium.

Increased ethylene biosynthesis elevates incidence of chilling injury in cold‐stored ‘Amber Jewel’ Japanese plum (Prunus salicina Lindl.) during fruit ripening

SummaryMature ‘Amber Jewel’ Japanese plum fruit were stored at 0 or 5 °C for 3 and 6 weeks to investigate their effects on ethylene (C2H4) biosynthesis during ripening at ambient temperature in the development of chilling injury (CI) and fruit quality. CI (internal breakdown and browning) and fruit softening were higher during ripening, in the fruit stored at 5 °C than 0 °C, irrespective of storage period (SP). C2H4 production and activities of 1‐aminocyclopropane‐1‐carboxylic acid synthase (ACS) and 1‐aminocyclopropane‐1‐carboxylic acid oxidase (ACO) enzymes, and 1‐aminocyclopropane‐1‐carboxylic acid (ACC) content were higher during ripening in fruit stored at 5 °C than 0 °C. The fruit stored at 5 °C also exhibited higher respiration rate and higher soluble solids concentration/titratable acidity ratio. In conclusion, increase in storage temperature and SP elevates the activities of ACS and ACO enzymes and consequently C2H4 production which leads to the development of CI in plum fruit with advancement of ripening.

Induction of ethylene in avocado fruit in response to chilling stress on tree

Chilling of avocado fruit (Persea americana cv. Arad) in the orchard caused a dramatic induction of fruit ripening and a parallel increase in ethylene biosynthesis and receptor genes' expression during shelf life. In-orchard chilling stress stimulated ethylene and CO(2) production already in fruit attached to the tree, and these reduced thereafter during 20 degrees C storage. In non-chilled control fruit, ethylene and CO(2) production started after 3d at 20 degrees C and exhibited a climacteric peak. In-orchard chilling stress also led to membrane destruction expressed as higher electrical conductivity (EC) in chilling stressed (CS) fruit and accelerated softening compared with control fruit. The increase in ethylene production on the day of harvest in CS fruit was accompanied by high expression of two 1-aminocyclopropane-1-carboxylic aCSd (ACC) synthase genes: PaACS1 and PaACS2, and ACC oxidase PaACO. The initial gene expressions of PaACS1, PaACS2, and PaACO in the CS fruit at the day of harvest was similar to the levels reached by the control fruit after 4d at 20 degrees C. The expression levels of both PaETR and PaERS1 in CS fruit on tree were 25 times higher than the control. In control fruit, expression of ethylene receptor genes was very low at harvest and increased in parallel to the onset of the climacteric ethylene peak. PaCTR1 transcript levels were less affected by chilling stress, and small changes (less than 3-fold) were observed in CS fruit on the day of harvest. Together, our results suggest that ethylene biosynthesis and ethylene response-pathway genes are involved in regulation of ethylene responsiveness in response to in-orchard chilling stress and during ripening.

Ripening related processes in strawberry, a nonclimacteric fruit: a short overview

Fruits are essential part of the human diet: they provide vitamins, minerals, antioxidants to the mankind. Physiologically they can be divided into two groups-climacteric and nonclimacteric - depending if they display any respiratory peak and dramatic increase in ethylene biosynthesis or do not. Ethylene is a gaseous hormone playing a very important role in several physiological processes in plants. While climacteric fruits, like apples, bananas, tomatoes, peaches, apricots show increased ethylene biosynthesis and dramatic respiratory peak during their ripening, nonclimacteric fruits, like strawberries, grapes, citrus do not.
 The most widely used fruits for studying nonclimacteric ripening are strawberries: several papers are focusing on the identification and characterization of ripening related genes from this plant. Therefore here we attempt to summarize the most important advances in strawberry fruit development, and ripening.

Unique ethylene-regulated touch responses of Arabidopsis thaliana roots to physical hardness

Although touch responses of plant roots are an important adaptive behavior, the molecular mechanism remains unclear. We have developed a bioassay for measuring root-bending responses to physical hardness in Arabidopsis thaliana seedlings. Our test requires a two-layer solid medium. Primary roots growing downward through an upper layer of 0.3% phytagel either penetrate the lower layer or bend along an interface between the upper and lower layers with different concentrations (0.2-0.5%, corresponding to 1.57-6.79 gw mm(-2) in hardness). In proportion to increasing hardness of the lower layer, we found that the percentage of bending roots increased and ethylene production decreased, suggesting an inverse relationship between the root-bending response and ethylene production. Studies with ethylene biosynthesis modulators and mutants also suggested that bending and non-bending responses of roots to medium hardness depend, respectively, on decreased and increased ethylene biosynthesis. In addition, the degrees of root-tip softening and differential root-cell growth, both possible factors determining root-bending response, were enhanced and attenuated by decreased and increased amounts of ethylene, respectively--also in bending roots and non-bending roots. Our findings indicate that ethylene regulates root touch responses, probably through a combination of root-tip softening (or hardening) and differential root-cell growth.

Reduced gibberellin response affects ethylene biosynthesis and responsiveness in the Arabidopsis gai eto2‐1 double mutant

Ethylene and gibberellins (GAs) control similar developmental processes in plants. The role of ethylene is at least in part to regulate the accumulation of DELLA proteins, key regulators of plant growth, which suppress the GA response. To expand our knowledge of ethylene-GA crosstalk and to reveal how the modulation of the ethylene and GA pathways affects global plant growth, the gibberellin-insensitive (gai), ethylene-overproducing 2-1 (eto2-1) double mutant, which has decreased GA signalling (resulting from gai) and increased ethylene biosynthesis (resulting from eto2-1), was characterized. Both single mutations resulted in reduced elongation growth. The double mutant showed synergistic responses in root and shoot growth, in induction of floral transition, and in inflorescence length, showing that crosstalk between the two pathways occurs in different plant organs throughout development. Furthermore, the altered ethylene-GA interactions affected root-shoot communication, as evidenced by an enhanced shoot:root ratio in the double mutant. When compared with both single mutants and the wild type, double mutants had enhanced content of active GA(4) at both the seedling and the rosette stages, and, unlike the gai mutant, they were sensitive to GA treatment. Finally, it was shown that synergistic responses in the double mutant were not caused by elevated ethylene biosynthesis but that, in the light, enhanced sensitivity to ethylene may, at least in part, be responsible for the observed phenotype.

Effect of the ethylene action inhibitor 1-methylcyclopropene on parsley leaf senescence and ethylene biosynthesis

Abstract Harvested parsley bunches were treated with the ethylene action inhibitor 1-methylcyclopropene (1-MCP) to evaluate its ability to retard senescence. Our results demonstrate that a single application of the inhibitor at a concentration of 10 μl l −1 can be used efficiently to retard postharvest senescence of stored parsley leaves. The use of too low concentrations of 1-MCP may lead to some degree of senescence acceleration, possibly because of relief from ethylene auto-inhibition. The effect of 1-MCP in inducing massive ethylene biosynthesis was found to be rapid and to reach a maximum within a few hours. The ability of the inhibitor to induce ethylene production was maximal when it was applied at 10 μl l −1 early in the storage life. When expression of genes related to ethylene biosynthesis was examined, it was found that the level of ACC oxidase (ACO) mRNA decreased during storage, irrespective of the 1-MCP treatment, whereas ACC synthase (ACS) mRNA could not be detected. The finding that 1-MCP could increase ethylene biosynthesis in parsley and, probably, in other leafy vegetables, warrants special care in its application. The high level of ethylene emitted may lead to postharvest damage to other mixed-load fresh products which are sensitive to the hormone but are not protected against it.

Cold-induced ethylene biosynthesis is differentially regulated in peel and pulp tissues of ‘Granny Smith’ apple fruit

Abstract Ethylene biosynthesis and endogenous abscisic acid (ABA) concentrations were examined in commercially mature ‘Granny Smith’ apples during and following chilling exposure, in order to study the mechanism(s) leading to induction of ethylene biosynthesis in chilled fruit upon rewarming. The effects of exogenous ABA and ethylene during exposure to low temperature were also tested to assess the role of both growth regulators in the onset of increased ethylene biosynthesis upon removal from cold storage. Ethylene production rates, ACC oxidase (ACO) activity, ACC levels, presence of both ACO and ripening-related ACC synthase (ACS) proteins and endogenous ABA concentrations were monitored in both peel and pulp of fruit, based on previous results showing noticeable differences in maturation and ripening of both tissues in ‘Granny Smith’ apples. Remarkable differences were observed in the regulation of ethylene biosynthesis in peel and pulp of ‘Granny Smith’ apple fruit. ACO and ripening-related ACS were found to respond differentially to chilling and exogenous ethylene or ABA. It is suggested that increased endogenous ABA levels in the peel tissue might play a major role in cold-induced ethylene biosynthesis upon rewarming. This hypothesis would also imply a significant role for the peel tissue in climacteric ethylene biosynthesis.

Polyamine oxidase, a hydrogen peroxide-producing enzyme, is up-regulated by light and down-regulated by auxin in the outer tissues of the maize mesocotyl.

Exogenously supplied auxin (1-naphthaleneacetic acid) inhibited light-induced activity increase of polyamine oxidase (PAO), a hydrogen peroxide-producing enzyme, in the outer tissues of maize (Zea mays) mesocotyl. The same phenomenon operates at PAO protein and mRNA accumulation levels. The wall-bound to extractable PAO activity ratio was unaffected by auxin treatment, either in the dark or after light exposure. Ethylene treatment did not affect PAO activity, thus excluding an effect of auxin via increased ethylene biosynthesis. The auxin polar transport inhibitors N(1)-naphthylphthalamic acid or 2,3,5-triiodobenzoic acid caused a further increase of PAO expression in outer tissues after light treatment. The small increase of PAO expression, normally occurring in the mesocotyl epidermis during plant development in the dark, was also inhibited by auxin, although to a lesser extent with respect to light-exposed tissue, and was stimulated by N(1)-naphthylphthalamic acid or 2,3,5-triiodobenzoic acid, thus suggesting a complex regulation of PAO expression. Immunogold ultrastructural analysis in epidermal cells revealed the association of PAO with the secretory pathway and the cell walls. The presence of the enzyme in the cell walls of this tissue greatly increased in response to light treatment. Consistent with auxin effects on light-induced PAO expression, the hormone treatment inhibited the increase in immunogold staining both intraprotoplasmically and in the cell wall. These results suggest that both light and auxin finely tune PAO expression during the light-induced differentiation of the cell wall in the maize mesocotyl epidermal tissues.

The eto1, eto2, and eto3 mutations and cytokinin treatment increase ethylene biosynthesis in Arabidopsis by increasing the stability of ACS protein.

The Arabidopsis ethylene-overproducing mutants eto1, eto2, and eto3 have been suggested to affect the post-transcriptional regulation of 1-aminocyclopropane-1-carboxylic acid synthase (ACS). Here, we present the positional cloning of the gene corresponding to the dominant eto3 mutation and show that the eto3 phenotype is the result of a missense mutation within the C-terminal domain of ACS9, which encodes one isoform of the Arabidopsis ACS gene family. This mutation is analogous to the dominant eto2 mutation that affects the C-terminal domain of the highly similar ACS5. Analysis of purified recombinant ACS5 and epitope-tagged ACS5 in transgenic Arabidopsis revealed that eto2 does not increase the specific activity of the enzyme either in vitro or in vivo; rather, it increases the half-life of the protein. In a similar manner, cytokinin treatment increased the stability of ACS5 by a mechanism that is at least partially independent of the eto2 mutation. The eto1 mutation was found to act by increasing the function of ACS5 by stabilizing this protein. These results suggest that an important mechanism by which ethylene biosynthesis is controlled is the regulation of the stability of ACS, mediated at least in part through the C-terminal domain.