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, GA(1), and castasterone from anthesis to fully ripened fruit are reported. The levels of IAA and GA(1) 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 GA(3), 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 GA(4) 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.     

Cloning and Characterization of the H Subunit of a Magnesium Chelatase Gene (PpCHLH) in Peach

It has been suggested that the phytohormone abscisic acid (ABA) plays an important role in the ripening of climatic fruit, although relevant genetic/molecular evidence is lacking. In the present study, a peach gene homologous to the putative Arabidopsis ABA receptor gene ABAR/CHLH, named PpCHLH, was isolated and characterized. PpCHLH is expressed ubiquitously as a single-copy gene in peach. Using tobacco rattle virus-induced gene silencing (VIGS), the PpCHLH gene was silenced in both peach leaves and fruit. The silenced PpCHLH gene affected leaf stomatal movement and delayed fruit ripening significantly. Although exogenously applied ABA promoted the ripening of the wild-type fruits, it could not rescue the RNAi chimeric fruit ripening. Collectively, these results demonstrate that PpCHLH plays a critical role in peach fruit ripening, and suggest that ABA might function as an important signal in the regulation of climacteric fruit development.     

Indole-3-acetic acid, ethylene, and abscisic acid metabolism in developing muskmelon (Cucumis melo L.) fruit

Hormonal metabolism associated with fruit development in muskmelon was investigated by measuring IAA, ABA, and ACC levels in several tissues at various stages of development. In addition, levels of conjugated IAA and ABA were determined in the same tissues. Ethylene production, which is believed to signal the ripening and senescence of mature fruit, was also measured. Ethylene production was highest in the outer tissue near the rind and gradually declined during maturation, except for a dramatic increase in all fruit tissues at the climacteric. In contrast to ethylene production, ACC levels increased during maturation and remained equal throughout the fruit until the climacteric, when levels in the outer tissues increased nearly 5-fold over levels in the inner tissues. The consistent presence of ACC indicates that ACC oxidase rather than the availability of ACC regulates ethylene production in developing fruits. ABA and ABA esters generally declined during maturation, however an increase in ABA esters associated with the outer mesocarp tissue was observed in fully mature, climacteric fruit. IAA and IAA conjugates were only found in the outer tissue near the rind, and their levels remained low until the fruit was fully mature and entering the climacteric. At that time, increased levels of conjugates were detected. The late burst of hormonal metabolism in the outer mesocarp tissue appeared to signal its degeneration and the deterioration that typically occurs in ripening fruit. The tissue-specific conjugation of IAA and ABA, in addition to the production of climacteric ethylene, may represent part of the signaling mechanism initiating ripening and eventual deterioration of tissues in muskmelon fruits.Abbreviations ABA abscisic acid - ACC 1-aminocylopropane-1-carboxylic acid - DAP days after pollination - IAA indole-3-acetic acid     

植物内源ABA水平的动态调控机制

ABA具有调节植物生长发育和对环境胁迫做出快速反应的重要功能, 植物内源ABA水平受到ABA合成、代谢及转运等途径的复杂调控。该文综述了近年来植物ABA从头合成、羟基化代谢、可逆糖基化代谢及ABA转运等领域的最新研究进展, 重点讨论ABA合成与代谢基因的表达调控机制, 并展望了今后的研究方向。     

Cloning of 9-cis-epoxycarotenoid dioxygenase (NCED) gene and the role of ABA on fruit ripening

In order to understand more details about the role of abscisic acid (ABA) in fruit ripening and senescence, six 740 bp cDNAs (LeNCED1, LeNCED2, PpNCED1, VVNCED1, DKNCED1 and CMNCED1) which encode 9-cis-epoxycarotenoid dioxygenase (NCED) as a key enzyme in ABA biosynthesis, were cloned from fruits of tomato, peach, grape, persimmon and melon using an RT-PCR approach. A Blast homology search revealed a similarity of amino acid 85.76% between the NCEDs. A relationship between ABA and ethylene during ripening was also investigated. At the mature green stage, exogenous ABA treatment increased ABA content in flesh, and promoting ethylene synthesis and fruit ripening, while treatment with nordihydroguaiaretic acid (NDGA), inhibited them, delayed fruit ripening and softening. However, ABA inhibited the ethylene synthesis obviously while NDGA promoted them when treated the immature fruit with these chemicals. At the breaker, NDGA treatment cannot block ABA accumulation and ethylene synthesis. Based on the results obtained in this study, it was concluded that ABA plays different role in ethylene synthesis system in different stages of tomato fruit ripening.Key words: tomato, NCED gene, ABA, ethylene, fruit ripening, peach, grape, persimmon, melon     

植物激素在苔藓生长发育与逆境响应过程中的作用机制研究进展

植物激素是由植物自身代谢产生的一类从产生部位移动到作用部位发挥调控功能的微量小分子有机物质,在植物生长发育、响应环境胁迫过程中起到关键作用.苔藓植物作为早期登陆的非维管植物,处于陆生植物进化早期的阶段,具有许多不同于维管植物的形态和生理特征.大部分苔藓中普遍存在8种主要的植物激素及其衍生物(包括ABA、JA、ET、SA...     

植物内源ABA水平的动态调控机制

ABA具有调节植物生长发育和对环境胁迫做出快速反应的重要功能, 植物内源ABA水平受到ABA合成、代谢及转运等途径的复杂调控。该文综述了近年来植物ABA从头合成、羟基化代谢、可逆糖基化代谢及ABA转运等领域的最新研究进展, 重点讨论ABA合成与代谢基因的表达调控机制, 并展望了今后的研究方向。     

Exogenous sucrose treatment accelerates postharvest tomato fruit ripening through the influence on its metabolism and enhancing ethylene biosynthesis and signaling

The role of sucrose as a signal molecule in plants was in debate for a long time, until recently, it gradually becomes more prominently accepted. Sucrose plays roles in a vast array of developmental processes in plants, however, its function in fruit ripening has not been well elucidated. In this study, the influence of exogenous sucrose treatment (500 mM) on postharvest tomato fruit ripening was investigated. It was found that, in comparison with mannitol treatment (500 mM, set as control), sucrose accelerated the ripening process with higher levels of respiration rate and ethylene production during the storage. Sucrose treatment up-regulated its biosynthetic genes, whilst stimulated expressions of genes encoding degradation related enzymes in the fruits. However, higher sucrose content was observed in sucrose-treated fruits only in the first few days. In addition, sucrose application had minor effect on the contents of its degrading products, glucose and fructose. Moreover, exogenous sucrose treatment up-regulated expressions of ethylene biosynthetic genes, and promoted ethylene signal transduction via influencing critical genes of the signaling pathway in different patterns. These results indicate that sucrose stimulates tomato fruit ripening may through mediating its own metabolism, which facilitates nutrients fluxes and metabolic signaling molecules activation, and also by enhancing ethylene biosynthesis and signal transduction.     

Melatonin: A master regulator of plant development and stress responses

Melatonin is a pleiotropic molecule with multiple functions in plants. Since the discovery of melatonin in plants, numerous studies have provided insight into the biosynthesis, catabolism, and physiological and biochemical functions of this important molecule. Here, we describe the biosynthesis of melatonin from tryptophan, as well as its various degradation pathways in plants. The identification of a putative melatonin receptor in plants has led to the hypothesis that melatonin is a hormone involved in regulating plant growth,aerial organ development, root morphology, and the floral transition. The universal antioxidant activity of melatonin and its role in preserving chlorophyll might explain its anti-senescence capacity in aging leaves. An impressive amount of research has focused on the role of melatonin in modulating postharvest fruit ripening by regulating the expression of ethylene-related genes.Recent evidence also indicated that melatonin functions in the plant's response to biotic stress,cooperating with other phytohormones and wellknown molecules such as reactive oxygen species and nitric oxide. Finally, great progress has been made towards understanding how melatonin alleviates the effects of various abiotic stresses, including salt, drought, extreme temperature, and heavy metal stress. Given its diverse roles, we propose that melatonin is a master regulator in plants.     

Abscisic acid plays an important role in the regulation of strawberry fruit ripening

The plant hormone abscisic acid (ABA) has been suggested to play a role in fruit development, but supporting genetic evidence has been lacking. Here, we report that ABA promotes strawberry (Fragaria ananassa) fruit ripening. Using a newly established Tobacco rattle virus-induced gene silencing technique in strawberry fruit, the expression of a 9-cis-epoxycarotenoid dioxygenase gene (FaNCED1), which is key to ABA biosynthesis, was down-regulated, resulting in a significant decrease in ABA levels and uncolored fruits. Interestingly, a similar uncolored phenotype was observed in the transgenic RNA interference (RNAi) fruits, in which the expression of a putative ABA receptor gene encoding the magnesium chelatase H subunit (FaCHLH/ABAR) was down-regulated by virus-induced gene silencing. More importantly, the uncolored phenotype of the FaNCED1-down-regulated RNAi fruits could be rescued by exogenous ABA, but the ABA treatment could not reverse the uncolored phenotype of the FaCHLH/ABAR-down-regulated RNAi fruits. We observed that down-regulation of the FaCHLH/ABAR gene in the RNAi fruit altered both ABA levels and sugar content as well as a set of ABA- and/or sugar-responsive genes. Additionally, we showed that exogenous sugars, particularly sucrose, can significantly promote ripening while stimulating ABA accumulation. These data provide evidence that ABA is a signal molecule that promotes strawberry ripening and that the putative ABA receptor, FaCHLH/ABAR, is a positive regulator of ripening in response to ABA.     

Relationship Between Abscisic Acid and Apricot Fruit Ripening

Changes in levels of growth regulating substances during fruit development and maturation and the effects of abscisic acid application on ripening of apricot fruits were investigated. The results showed that the levels of growth promoting substances were high, but started to decrease rapidly just before the end of stage Ⅱ and continued throughout stage Ⅲ. The promoting substances almost disappeared in fully ripe fruits. The ABA-like inhibiting substances first appeared during the end of stage Ⅱ, increased significantly in stage Ⅲ, and reached a maximum level in fully ripe fruits. Exogenous ABA application enhanced fruit respiration rate and accelerated the ripening process when applied to preclimacteric fruits but inhibited these processes when applied to post-climacteric fruits. The above results suggested that the ABA may play an important role in apricot fruit ripening. The interrelationship of ABA, ethylene, and fruit ripening was discussed.     

Recent Advances in the Regulation of Citric Acid Metabolism in Citrus Fruit

The regulation of citric acid metabolism during fruit ripening has a major impact on the production of high-quality fruit. The impact of citric acid on organoleptic fruit quality attributes, fruit storage performance and the synthesis of several secondary metabolites has led to an exponential increase in research efforts during the last two decades. Recent research has focused on the relationship among citric acid biosynthesis, transportation, storage, and utilization. Among citrate metabolic processes, activities of a proton pump, especially the plasma membrane H⁺-ATPase on tonoplast and citrate catabolism in cytosol play important roles in the regulation of citrate accumulation in cell vacuoles. Moreover, we highlight recent advances and provide an overview of citrate metabolism, postharvest physiology of citrate metabolism, and the influence of agro-climatic factors on citrus fruits. It is the first review that provides a comprehensive model for citrate metabolism in citrus fruit juice sacs. We anticipate that this model for the regulation of citrate metabolism will facilitate the study of fruit acidity in citrus and other nonclimacteric fruits.