Resveratrol: a molecule whose time has come? And gone?

OBJECTIVES

Resveratrol (3,5,4'-trihydroxystilbene) is the parent compound of a family of molecules, including glucosides and polymers, existing in cis and trans configurations in a narrow range of spermatophytes of which vines, peanuts and pines are the prime representatives. Its synthesis from p-coumaroyl CoA and malonyl CoA is induced by stress, injury, infection or UV-irradiation, and it is classified as a phytoalexin anti-fungicide conferring disease resistance in the plant kingdom.

RESULTS

In vitro, ex vivo and animal experiments have shown that it possesses many biological attributes that favour protection against atherosclerosis, including antioxidant activity, modulation of hepatic apolipoprotein and lipid synthesis, inhibition of platelet aggregation as well as the production of pro-atherogenic eicosanoids by human platelets and neutrophils. Red wine represents its main source in the human diet, and it has been proposed as a major constituent of the polyphenol fraction to which the health benefits of red wine consumption have been attributed.

CONCLUSIONS

The past several years have witnessed intense research devoted to its measurement in wine and the factors likely to promote its enrichment in this beverage. Up to the present, conclusive evidence for its absorption by human subjectsin biologically significant amounts is lacking, and it is questionable (but not yetexcluded) that its powerful and beneficial in vitro activities are reproduced as a consequence of sustained moderate red wine consumption.

Ethylene biosynthesis and action in tomato: a model for climacteric fruit ripening

Elucidating the mechanisms involved in ripening of climacteric fruit and the role that ethylene plays in the process are key to understanding fruit production and quality. In this review, which is based largely on research in tomato, particular attention is paid to the role of specific isoforms of ACC synthase and ACC oxidase in controlling ethylene synthesis during the initiation and subsequent autocatalytic phase of ethylene production during ripening. Recent information on the structure and role of six different putative ethylene receptors in tomato is discussed, including evidence supporting the receptor inhibition model for ripening, possible differences in histidine kinase activity between receptors, and the importance of receptor LeETR4 in ripening. A number of ethylene-regulated ripening-related genes are discussed, including those involved in ethylene synthesis, fruit texture, and aroma volatile production, as well as experiments designed to elucidate the ethylene signalling pathway from receptor through intermediate components similar to those found in Arabidopsis, leading to transcription factors predicted to control the expression of ethylene-regulated genes.

Antibiotic use in plant agriculture

Antibiotics have been used since the 1950s to control certain bacterial diseases of high-value fruit, vegetable, and ornamental plants. Today, the antibiotics most commonly used on plants are oxytetracycline and streptomycin. In the USA, antibiotics applied to plants account for less than 0.5% of total antibiotic use. Resistance of plant pathogens to oxytetracycline is rare, but the emergence of streptomycin-resistant strains of Erwinia amylovora, Pseudomonas spp., and Xanthomonas campestris has impeded the control of several important diseases. A fraction of streptomycin-resistance genes in plant-associated bacteria are similar to those found in bacteria isolated from humans, animals, and soil, and are associated with transfer-proficient elements. However, the most common vehicles of streptomycin-resistance genes in human and plant pathogens are genetically distinct. Nonetheless, the role of antibiotic use on plants in the antibiotic-resistance crisis in human medicine is the subject of debate.

Biological control of postharvest diseases of fruits

Losses from postharvest fruit diseases range from 1 to 20 percent in the United States, depending on the commodity. The application of fungicides to fruits after harvest to reduce decay has been increasingly curtailed by the development of pathogen resistance to many key fungicides, the lack of replacement fungicides, negative public perception regarding the safety of pesticides and consequent restrictions on fungicide use. Biological control of postharvest diseases (BCPD) has emerged as an effective alternative. Because wound-invading necrotrophic pathogens are vulnerable to biocontrol, antagonists can be applied directly to the targeted area (fruit wounds), and a single application using existing delivery systems (drenches, line sprayers, on-line dips) can significantly reduce fruit decays. The pioneering biocontrol products BioSave and Aspire were registered by EPA in 1995 for control of postharvest rots of pome and citrus fruit, respectively, and are commercially available. The limitations of these biocontrol products can be addressed by enhancing biocontrol through manipulation of the environment, using mixtures of beneficial organisms, physiological and genetic enhancement of the biocontrol mechanisms, manipulation of formulations, and integration of biocontrol with other alternative methods that alone do not provide adequate protection but in combination with biocontrol provide additive or synergistic effects.

Enzymatic browning reactions in apple and apple products

This review examines the parameters of enzymatic browning in apple and apple products that is, phenolic compounds, polyphenoloxidases, and other factors (ascorbic acid and peroxidases), both qualitatively and quantitatively. Then the relationships between intensity of browning and the browning parameters are discussed, including a paragraph on the methods used for browning evaluation. Finally, the different methods for the control of browning are presented.

Fleshy fruit expansion and ripening are regulated by the Tomato SHATTERPROOF gene TAGL1

The maturation and ripening of fleshy fruits is a developmental program that synchronizes seed maturation with metabolism, rendering fruit tissues desirable to seed dispersing organisms. Through RNA interference repression, we show that Tomato AGAMOUS-LIKE1 (TAGL1), the tomato (Solanum lycopersicum) ortholog of the duplicated SHATTERPROOF (SHP) MADS box genes of Arabidopsis thaliana, is necessary for fruit ripening. Tomato plants with reduced TAGL1 mRNA produced yellow-orange fruit with reduced carotenoids and thin pericarps. These fruit are also decreased in ethylene, indicating a comprehensive inhibition of maturation mediated through reduced ACC Synthase 2 expression. Furthermore, ectopic expression of TAGL1 in tomato resulted in expansion of sepals and accumulation of lycopene, supporting the role of TAGL1 in ripening. In Arabidopsis, the duplicate SHP1 and SHP2 MADS box genes regulate the development of separation layers essential for pod shatter. Expression of TAGL1 in Arabidopsis failed to completely rescue the shp1 shp2 mutant phenotypes, indicating that TAGL1 has evolved distinct molecular functions compared with its Arabidopsis counterparts. These analyses demonstrate that TAGL1 plays an important role in regulating both fleshy fruit expansion and the ripening process that together are necessary to promote seed dispersal of fleshy fruit. From this broad perspective, SHP1/2 and TAGL1, while distinct in molecular function, regulate similar activities via their necessity for seed dispersal in Arabidopsis and tomato, respectively.

The use of 1-methylcyclopropene (1-MCP) on fruits and vegetables

The recent availability of the inhibitor of ethylene perception, 1-methylcyclopropene (1-MCP), has resulted in an explosion of research on its effects on fruits and vegetables, both as a tool to further investigate the role of ethylene in ripening and senescence, and as a commercial technology to improve maintenance of product quality. The commercialization of 1-MCP was followed by rapid adoption by many apple industries around the world, and strengths and weaknesses of the new technology have been identified. However, use of 1-MCP remains limited for other products, and therefore it is still necessary to speculate on its commercial potential for most fruits and vegetables. In this review, the effects of 1-MCP on fruits and vegetables are considered from two aspects. First, a selected number of fruit (apple, avocado, banana, pear, peaches and nectarines, plums and tomato) are used to illustrate the range of responses to 1-MCP, and indicate possible benefits and limitations for commercialization of 1-MCP-based technology. Second, an outline of general physiological and biochemical responses of fruits and vegetables to the chemical is provided to illustrate the potential for use of 1-MCP to better understand the role of ethylene in ripening and senescence processes.

Combined transcriptome, genetic diversity and metabolite profiling in tomato fruit reveals that the ethylene response factor SlERF6 plays an important role in ripening and carotenoid accumulation

Solanum lycopersicum (tomato) and its wild relatives harbor genetic diversity that yields heritable variation in fruit chemistry that could be exploited to identify genes regulating their synthesis and accumulation. Carotenoids, for example, are essential in plant and animal nutrition, and are the visual indicators of ripening for many fruits, including tomato. Whereas carotenoid synthesis is well characterized, factors regulating flux through the pathway are poorly understood at the molecular level. To exploit the impact of tomato genetic diversity on carotenoids, Solanum pennellii introgression lines were used as a source of defined natural variation and as a resource for the identification of candidate regulatory genes. Ripe fruits were analyzed for numerous fruit metabolites and transcriptome profiles generated using a 12,000 unigene oligoarray. Correlation analysis between carotenoid content and gene expression profiles revealed 953 carotenoid-correlated genes. To narrow the pool, subnetwork analysis of carotenoid-correlated transcription revealed 38 candidates. One candidate for impact on trans-lycopene and β-carotene accumulation was functionally charaterized, SlERF6, revealing that it indeed influences carotenoid biosynthesis and additional ripening phenotypes. Reduced expression of SlERF6 by RNAi enhanced both carotenoid and ethylene levels during fruit ripening, demonstrating an important role for SlERF6 in ripening, integrating the ethylene and carotenoid synthesis pathways.

Transcriptional control of fleshy fruit development and ripening

Fleshy fruits have evolved to be attractive to frugivores in order to enhance seed dispersal, and have become an indispensable part of the human diet. Here we review the recent advances in the understanding of transcriptional regulation of fleshy fruit development and ripening with a focus on tomato. While aspects of fruit development are probably conserved throughout the angiosperms, including the model plant Arabidopsis thaliana, it is shown that the likely orthologues of Arabidopsis genes have distinct functions in fleshy fruits. The model for the study of fleshy fruit development is tomato, because of the availability of single gene mutants and transgenic knock-down lines. In other species, our knowledge is often incomplete or absent. Tomato fruit size and shape are co-determined by transcription factors acting during formation of the ovary. Other transcription factors play a role in fruit chloroplast formation, and upon ripening impact quality aspects such as secondary metabolite content. In tomato, the transcription factors NON-RIPENING (NOR), COLORLESS NON-RIPENING (CNR), and RIPENING INHIBITOR (MADS-RIN) in concert with ethylene signalling regulate ripening, possibly in response to a developmental switch. Additional components include TOMATO AGAMOUS-LIKE1 (TAGL1), APETALA2a (AP2a), and FRUITFULL (FUL1 and FUL2). The links between this highly connected regulatory network and downstream effectors modulating colour, texture, and flavour are still relatively poorly understood. Intertwined with this network is post-transcriptional regulation by fruit-expressed microRNAs targeting several of these transcription factors. This important developmental process is also governed by changes in DNA methylation levels and possibly chromatin remodelling.

The Jasmonate-Activated Transcription Factor MdMYC2 Regulates ETHYLENE RESPONSE FACTOR and Ethylene Biosynthetic Genes to Promote Ethylene Biosynthesis during Apple Fruit Ripening

The plant hormone ethylene is critical for ripening in climacteric fruits, including apple (Malus domestica). Jasmonate (JA) promotes ethylene biosynthesis in apple fruit, but the underlying molecular mechanism is unclear. Here, we found that JA-induced ethylene production in apple fruit is dependent on the expression of MdACS1, an ACC synthase gene involved in ethylene biosynthesis. The expression of MdMYC2, encoding a transcription factor involved in the JA signaling pathway, was enhanced by MeJA treatment in apple fruits, and MdMYC2 directly bound to the promoters of both MdACS1 and the ACC oxidase gene MdACO1 and enhanced their transcription. Furthermore, MdMYC2 bound to the promoter of MdERF3, encoding a transcription factor involved in the ethylene-signaling pathway, thereby activating MdACS1 transcription. We also found that MdMYC2 interacted with MdERF2, a suppressor of MdERF3 and MdACS1 This protein interaction prevented MdERF2 from interacting with MdERF3 and from binding to the MdACS1 promoter, leading to increased transcription of MdACS1 Collectively, these results indicate that JA promotes ethylene biosynthesis through the regulation of MdERFs and ethylene biosynthetic genes by MdMYC2.

MYB10 plays a major role in the regulation of flavonoid/phenylpropanoid metabolism during ripening of Fragaria x ananassa fruits

This work characterized the role of the R2R3-MYB10 transcription factor (TF) in strawberry fruit ripening. The expression of this TF takes place mainly in the fruit receptacle and is repressed by auxins and activated by abscisic acid (ABA), in parallel to the ripening process. Anthocyanin was not produced when FaMYB10 expression was transiently silenced in fruit receptacles. An increase in FaMYB10 expression was observed in water-stressed fruits, which was accompanied by an increase in both ABA and anthocyanin content. High-throughput transcriptomic analyses performed in fruits with downregulated FaMYB10 expression indicated that this TF regulates the expression of most of the Early-regulated Biosynthesis Genes (EBGs) and the Late-regulated Biosynthesis Genes (LBGs) genes involved in anthocyanin production in ripened fruit receptacles. Besides, the expression of FaMYB10 was not regulated by FaMYB1 and vice versa. Taken together, all these data clearly indicate that the Fragaria × ananassa MYB10 TF plays a general regulatory role in the flavonoid/phenylpropanoid pathway during the ripening of strawberry.

Aluminum tolerance in transgenic plants by alteration of citrate synthesis

Aluminum when in soluble form, as found in acidic soils that comprise about 40 percent of the world's arable land, is toxic to many crops. Organic acid excretion has been correlated with aluminum tolerance in higher plants. Overproduction of citrate was shown to result in aluminum tolerance in transgenic tobacco (Nicotiana tabacum) and papaya (Carica papaya) plants.

Berry ripening: recently heard through the grapevine

Grapevine (Vitis vinifera L.) is a non-climacteric fruit species used as table fruit, dried raisins, and for vinification (wines) and distillation (liquors). In recent years, our knowledge of the molecular basis of ripening regulation has improved. Water status, light conditions, and temperature may hasten, delay, or enhance ripening. Hormones seem to play a central role, as their concentrations change prior to and during ripening and in response to several environmental cues. The review summarizes recent data related to the molecular and hormonal control of grape berry development and ripening, with special emphasis on secondary metabolism and its response to the environment, and pinpoints some experimental limitations.

Molecular and genetic regulation of fruit ripening

Fleshy fruit undergo a novel developmental program that ends in the irreversible process of ripening and eventual tissue senescence. During this maturation process, fruit undergo numerous physiological, biochemical and structural alterations, making them more attractive to seed dispersal organisms. In addition, advanced or over-ripening and senescence, especially through tissue softening and eventual decay, render fruit susceptible to invasion by opportunistic pathogens. While ripening and senescence are often used interchangeably, the specific metabolic activities of each would suggest that ripening is a distinct process of fleshy fruits that precedes and may predispose the fruit to subsequent senescence.

Hormonal changes during non-climacteric ripening in strawberry

In contrast to climacteric fruits, where ethylene is known to be pivotal, the regulation of ripening in non-climacteric fruits is not well understood. In the non-climacteric strawberry (Fragaria anannassa), auxin and abscisic acid (ABA) are thought to be important, but the roles of other hormones suggested to be involved in fruit development and ripening are not clear. Here changes in the levels of indole-3-acetic acid (IAA), ABA, GA1, and castasterone from anthesis to fully ripened fruit are reported. The levels of IAA and GA1 rise early in fruit development before dropping to low levels prior to colour accumulation. Castasterone levels are highest at anthesis and drop to very low levels well before ripening commences, suggesting that brassinosteroids do not play an important role in ripening in strawberry. ABA levels are low at anthesis and gradually rise through development and ripening. The synthetic auxin, 1-naphthaleneacetic acid (NAA), can delay ripening, but the application of GA3, the gibberellin biosythesis inhibitor paclobutrazol, and ABA had no significant effect. IAA and ABA levels are higher in the developing achenes than in the receptacle tissue and may be important for receptacle enlargement and ripening, and seed maturation, respectively. Contrary to a recent report, the biologically active GA4 was not detected. The pattern of changes in the levels of the hormones are different from those reported in another well studied non-climateric fruit, grape, suggesting that a single consistent pattern of hormone changes does not occur in this group of fruit during ripening.

Composition and content of glucosinolates in developing Arabidopsis thaliana

The glucosinolate composition and content in various tissues of Arabidopsis thaliana (L.) Heynh. ecotype Columbia during development from seeds to bolting plants were determined in detail by high-performance liquid chromatography. Comparison of the glucosinolate profiles of leaves, roots and stems from mature plants with those of green siliques and mature seeds indicated that a majority of the seed glucosinolates were synthesized de novo in the silique. A comparison of the glucosinolate profile of mature seeds with that of cotyledons indicated that a major part of seed glucosinolates was retained in the cotyledons. Turnover of glucosinolates was studied by germination of seeds containing radiolabelled p-hydroxybenzylglucosinolate (p-OHBG). Approximately 70% of the content of [14C]p-OHBG in the seeds was detected in seedlings at the cotyledon stage and [14C]p-OHBG was barely detectable in young plants with rosettes of six to eight leaves. The turn-over of p-OHBG was found to coincide with the expression of the glucosinolate-degrading enzyme myrosinase, which was detectable at very low levels in seedlings at the cotyledon stage, but which dramatically increased in leaves from plants at later developmental stages. This indicates that there is a continuous turnover of glucosinolates during development and not only upon tissue disruption.

Sucrose functions as a signal involved in the regulation of strawberry fruit development and ripening

Fleshy fruits are classically divided into climacteric and nonclimacteric types. It has long been thought that the ripening of climacteric and nonclimacteric fruits is regulated by ethylene and abscisic acid (ABA), respectively. Here, we report that sucrose functions as a signal in the ripening of strawberry (Fragaria × ananassa), a nonclimacteric fruit. Pharmacological experiments, as well as gain- and loss-of-function studies, were performed to demonstrate the critical role of sucrose in the regulation of fruit ripening. Fruit growth and development were closely correlated with a change in sucrose content. Exogenous sucrose and its nonmetabolizable analog, turanose, induced ABA accumulation in fruit and accelerated dramatically fruit ripening. A set of sucrose transporters, FaSUT1-7, was identified and characterized, among which FaSUT1 was found to be a major component responsible for sucrose accumulation during fruit development. RNA interference-induced silencing of FaSUT1 led to a decrease in both sucrose and ABA content, and arrested fruit ripening. By contrast, overexpression of FaSUT1 led to an increase in both sucrose and ABA content, and accelerated fruit ripening. In conclusion, this study demonstrates that sucrose is an important signal in the regulation of strawberry fruit ripening.

Auxin-induced fruit-set in tomato is mediated in part by gibberellins

Tomato (Solanum lycopersicum L.) fruit-set and growth depend on gibberellins (GAs). Auxins, another kind of hormone, can also induce parthenocarpic fruit growth in tomato, although their possible interaction with GAs is unknown. We showed that fruit development induced by the auxins indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid (2,4-D) were significantly reduced by the simultaneous application of inhibitors of GA biosynthesis, and that this effect was reversed by the application of GA(3). This suggested that the effect of auxin was mediated by GA. Parthenocarpic fruits induced by 2,4-D had higher levels of the active GA(1), its precursors and metabolites, than unpollinated non-treated ovaries, but similar levels as those found in pollinated ovaries. Application experiments of radioactive-labelled GAs to unpollinated ovaries showed than 2,4-D altered GA metabolism (both biosynthesis and catabolism) in vivo. Transcript levels of genes encoding copalyldiphosphate synthase (SlCPS), SlGA20ox1, SlGA20ox2 and SlGA20ox3, and SlGA3ox1 were higher in unpollinated ovaries treated with 2,4-D. In contrast, transcript levels of SlGA2ox2 (out of the five SlGA2ox genes known to encode this kind of GA-inactivating enzyme) were lower in ovaries treated with 2,4-D. Our results support the idea that auxins induce fruit-set and growth in tomato, at least partially, by enhancing GA biosynthesis (GA 20-oxidase, GA 3-oxidase and CPS), and probably by decreasing GA inactivation (GA2ox2) activity, thereby leading to higher levels of GA(1). The expression of diverse Aux/indole-3-acetic acid (IAA) and auxin response factors, which may be involved in this effect of auxin, was also altered in 2,4-D-induced ovaries.

Expression profiling of ascorbic acid-related genes during tomato fruit development and ripening and in response to stress conditions

L-ascorbate (the reduced form of vitamin C) participates in diverse biological processes including pathogen defence mechanisms, and the modulation of plant growth and morphology, and also acts as an enzyme cofactor and redox status indicator. One of its chief biological functions is as an antioxidant. L-ascorbate intake has been implicated in the prevention/alleviation of varied human ailments and diseases including cancer. To study the regulation of accumulation of this important nutraceutical in fruit, the expression of 24 tomato (Solanum lycopersicon) genes involved in the biosynthesis, oxidation, and recycling of L-ascorbate during the development and ripening of fruit have been characterized. Taken together with L-ascorbate abundance data, the results show distinct changes in the expression profiles for these genes, implicating them in nodal regulatory roles during the process of L-ascorbate accumulation in tomato fruit. The expression of these genes was further studied in the context of abiotic and post-harvest stress, including the effects of heat, cold, wounding, oxygen supply, and ethylene. Important aspects of the hypoxic and post-anoxic response in tomato fruit are discussed. The data suggest that L-galactose-1-phosphate phosphatase could play an important role in regulating ascorbic acid accumulation during tomato fruit development and ripening.

Melatonin treatment attenuates postharvest decay and maintains nutritional quality of strawberry fruits (Fragaria×anannasa cv. Selva) by enhancing GABA shunt activity

Fresh strawberry fruits as perishable commodities have a short postharvest life and are prone to postharvest fungal decay. In this study, the impact of 0, 1, 10, 100 and 1000μmol/L melatonin on attenuating fungal decay and maintaining nutritional quality of strawberry fruits was investigated during storage at 4°C for 12days. Melatonin treatment at 100μmol/L triggered H₂O₂ accumulation, which result from higher superoxide dismutase (SOD) activity, associated with lower catalase (CAT) and ascorbate peroxidase (APX) activities, leading to fruits with lower decay. Higher H₂O₂ accumulation was concurrent with higher phenylalanine ammonia lyase (PAL) enzyme activity leading to higher total phenols and anthocyanins accumulation along with higher DPPH scavenging capacity. Also, strawberry fruits treated with melatonin exhibited higher γ-aminobutyric acid transaminase (GABA-T) enzyme activity which ensured sufficient ATP supplying leading to higher unsaturated/saturated fatty acids (unSFA/SFA) ratio.

Molecular characterization of banana NAC transcription factors and their interactions with ethylene signalling component EIL during fruit ripening

The plant-specific NAC (NAM, ATAF1/2, and CUC2) transcription factors (TFs) play important roles in plant growth, development, and stress responses. However, the precise role of NAC TFs in relation to fruit ripening is poorly understood. In this study, six NAC genes, designated MaNAC1-MaNAC6, were isolated and characterized from banana fruit. Subcellular localization showed that MaNAC1-MaNAC5 proteins localized preferentially to the nucleus, while MaNAC6 was distributed throughout the entire cell. A transactivation assay in yeast demonstrated that MaNAC4 and MaNAC6, as well as their C-terminal regions, possessed trans-activation activity. Gene expression profiles in fruit with four different ripening characteristics, including natural, ethylene-induced, 1-methylcyclopropene (1-MCP)-delayed, and a combination of 1-MCP with ethylene treatment, revealed that the MaNAC genes were differentially expressed in peel and pulp during post-harvest ripening. MaNAC1 and MaNAC2 were apparently upregulated by ethylene in peel and pulp, consistent with the increase in ethylene production. In contrast, MaNAC3 in peel and pulp and MaNAC5 in peel were constitutively expressed, and transcripts of MaNAC4 in peel and pulp and MaNAC6 in peel decreased, while MaNAC5 or MaNAC6 in pulp increased slightly during fruit ripening. Furthermore, the MaNAC2 promoter was activated after ethylene application, further enhancing the involvement of MaNAC2 in fruit ripening. More importantly, yeast two-hybrid and bimolecular fluorescence complementation analyses confirmed that MaNAC1/2 physically interacted with a downstream component of ethylene signalling, ethylene insensitive 3 (EIN3)-like protein, termed MaEIL5, which was downregulated during ripening. Taken together, these results suggest that MaNACs such as MaNAC1/MaNAC2, may be involved in banana fruit ripening via interaction with ethylene signalling components.

Changes in tomato ovary transcriptome demonstrate complex hormonal regulation of fruit set

Plant hormones are considered to be important mediators of the fruit developmental signal after pollination. The role of phytohormones in tomato (Solanum lycopersicum) fruit set was investigated here. Transcriptome analysis of ovaries was performed using two complementary approaches: cDNA-amplified fragment length polymorphism (AFLP) and microarray analysis. The gene expression profiles obtained suggest that, in addition to auxin and gibberellin, ethylene and abscisic acid (ABA) are involved in regulating fruit set. Before fruit development, many genes involved in biotic and abiotic responses are active in the ovary. In addition, genes involved in ethylene and ABA biosynthesis were strongly expressed, suggesting relatively high ethylene and ABA concentrations before fruit set. Induction of fruit development, either by pollination or by gibberellin application, attenuated expression of all ethylene and ABA biosynthesis and response genes within 24 h. It is proposed that the function of ABA and ethylene in fruit set might be antagonistic to that of auxin and gibberellin in order to keep the ovary in a temporally protected and dormant state; either to protect the ovary tissue or to prevent fruit development before pollination and fertilization occur.

Reciprocity between abscisic acid and ethylene at the onset of berry ripening and after harvest

BACKGROUND

The ripening of grape berry is generally regulated by abscisic acid (ABA), and has no relationship with ethylene function. However, functional interaction and synergism between ABA and ethylene during the beginning of grape berry ripening (véraison) has been found recently.

RESULTS

The expressions of VvNCED1 encoding 9-cis-epoxycarotenoid dioxygenase (NCED) and VvGT encoding ABA glucosyltransferase were all increased rapidly at the stage of véraison and reached the highest level at 9th week after full bloom. However, VvCYP1 encoding ABA 8'-hydroxylase and VvβG1 encoding berry β-glucosidase are different, whose expression peak appeared at the 10th week after full bloom and in especial VvβG1 remained at a high level till harvest. The VvACO1 encoding 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, the VvETR2 (ethylene response 2) and VvCTR1 (constitutive triple response 1) had a transient expression peak at pre-véraison, while the VvEIN4 (ethylene insensitive 4) expression gradually increased from the véraison to one week before harvest stage. The above mentioned changes happened again in the berry after harvest. At one week before véraison, double block treatment with NiCl2 plus 1-methylcyclopropene (1-MCP) not only inhibited the release of ethylene and the expression of related genes but also suppressed the transcription of VvNCED1 and the synthesis of ABA which all might result in inhibiting the fruit ripening onset. Treatment with ABA could relieve the double block and restore fruit ripening course. However, after harvest, double block treatment with NiCl2 plus 1-MCP could not suppress the transcription of VvNCED1 and the accumulation of ABA, and also could not inhibit the start of fruit senescence.

CONCLUSION

The trace endogenous ethylene induces the transcription of VvNCED1 and then the generation of ABA followed. Both ethylene and ABA are likely to be important and their interplaying may be required to start the process of berry ripening. When the level of ABA reached the peak value, part of it will be stored in the form of ABA-GE. While after harvest, abiotic stresses principally (such as dehydration, harvest shock) could induce the transcription of VvNCED1 and the accumulation of ABA, thus starting the process of fruit senescence.

Hydrogen sulfide prolongs postharvest shelf life of strawberry and plays an antioxidative role in fruits

Accumulating evidence shows that hydrogen sulfide (H(2)S) plays various physiological roles in plants, such as seed germination, root organogenesis, abiotic stress tolerance, and senescence of cut flowers. However, whether H(2)S participates in the regulation of ripening and senescence in postharvest fruits remains unknown. In the present study, the effect of H(2)S on postharvest shelf life and antioxidant metabolism in strawberry fruits was investigated. Fumigation with H(2)S gas released from the H(2)S donor NaHS prolonged postharvest shelf life of strawberry fruits in a dose-dependent manner. Strawberry fruits fumigated with various concentrations of H(2)S sustained significantly lower rot index, higher fruit firmness, and kept lower respiration intensity and polygalacturonase activities than controls. Further investigation showed that H(2)S treatment maintained higher activities of catalase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase and lower activities of lipoxygenase relative to untreated controls. H(2)S also reduced malondialdehyde, hydrogen peroxide, and superoxide anion to levels below control fruits during storage. Moreover, H(2)S treatment maintained higher contents of reducing sugars, soluble proteins, free amino acid, and endogenous H(2)S in fruits. We interpret these data as indicating that H(2)S plays an antioxidative role in prolonging postharvest shelf life of strawberry fruits.

A role for PacMYBA in ABA-regulated anthocyanin biosynthesis in red-colored sweet cherry cv. Hong Deng (Prunus avium L.)

The MYB transcription factors and plant hormone ABA have been suggested to play a role in fruit anthocyanin biosynthesis, but supporting genetic evidence has been lacking in sweet cherry. The present study describes the first functional characterization of an R2R3-MYB transcription factor, PacMYBA, from red-colored sweet cherry cv. Hong Deng (Prunus avium L.). Transient promoter assays demonstrated that PacMYBA physically interacted with several anthocyanin-related basic helix-loop-helix (bHLH) transcription factors to activate the promoters of PacDFR, PacANS and PacUFGT, which are thought to be involved in anthocyanin biosynthesis. Furthermore, the immature seeds of transgenic Arabidopsis plants overexpressing PacMYBA exhibited ectopic pigmentation. Silencing of PacMYBA, using a Tobacco rattle virus (TRV)-induced gene silencing technique, resulted in sweet cherry fruit that lacked red pigment. ABA treatment significantly induced anthocyanin accumulation, while treatment with the ABA biosynthesis inhibitor nordihydroguaiaretic acid (NDGA) blocked anthocyanin production. PacMYBA expression peaked after 2 h of pre-incubation in ABA and was 15.2-fold higher than that of sweet cherries treated with NDGA. The colorless phenotype was also observed in the fruits silenced in PacNCED1, which encodes a key enzyme in the ABA biosynthesis pathway. The endogenous ABA content as well as the transcript levels of six structural genes and PacMYBA in PacNCED1-RNAi (RNA interference) fruit were significantly lower than in the TRV vector control fruit. These results suggest that PacMYBA plays an important role in ABA-regulated anthocyanin biosynthesis and ABA is a signal molecule that promotes red-colored sweet cherry fruit accumulating anthocyanin.