Interaction of abscisic acid and auxin on gene expression involved in banana ripening

Phytohormones regulate numerous aspects of plant growth and development. Green-mature banana fruit were treated with deionized water (control), abscisic acid (ABA), indole-3-acetic acid (IAA) and ABA + IAA, respectively, to investigate the role of ABA and IAA in fruit ripening. Results showed that ABA accelerated fruit ripening, but IAA delayed the process. However, treatment of ABA + IAA showed little difference in fruit color and firmness. The acceleration of ABA and delay of IAA on banana ripening process seems to be neutralized by ABA + IAA. Digital gene expression revealed that ABA + IAA treated fruit maintained the similar color phenotype with the control by regulating the expression of chlorophyll degradation-related gene PaO (GSMUA_Achr6G25590_001), and carotenoid biosynthesis-related genes DXR (GSMUA_Achr3G20790_001) and PSY (GSMUA_Achr2G12480_001, GSMUA_Achr4G17270_001, GSMUA_Achr4G17290_001). Moreover, ABA + IAA treated fruit maintained the similar softening phenotype with the control by adjusting the expression of pectin degradation-related genes PME (GSMUA_Achr3G05740_001) and PL (GSMUA_Achr6G28160_001, GSMUA_Achr7G04580_001). ABA + IAA treatment nearly abolished the action of individual ABA or IAA through equilibrating the expression of specific genes involved in chlorophyll degradation, carotenoid biosynthesis and pectin degradation pathways in the postharvest ripening of banana. The interaction between ABA and IAA might exercise as an antagonistic mechanism of neutralizing the specific gene expression either induced by ABA or reduced by IAA in the postharvest ripening of banana.     

Hormonal and Nutritional Changes in the Flavedo Regulating Rind Color Development in Sweet Orange [Citrus sinensis (L.) Osb.]

The objective of this research was to determine the changes in the levels of endogenous gibberellins GA₁ and GA₄, abscisic acid (ABA), and ethylene during fruit coloring of on-tree fruits of sweet orange. The time course of carbohydrates and nitrogen content in the flavedo prior to fruit color break and during peel ripening were also studied. To identify nutritional and hormonal changes in the fruit, 45?days before fruit color break the peduncles of 15?C30 fruits per tree of ??Washington?? navel, ??Navelate,?? and ??Valencia Delta Seedless?? sweet orange, located in single-fruited shoots, were girdled to intercept phloem transport. A set of 15?C30 fruits per tree remained intact on the peduncle for control. Girdling significantly delayed fruit coloration for more than 2?months; the delay paralleled higher GA₁ and GA₄ concentrations in the flavedo and retarded the rise of ABA concentration prior to color break. Girdling also reduced carbohydrate concentrations and increased N concentrations in the flavedo compared to control fruits; no ethylene production was detected. Therefore, in sweet orange, fruit changes color by reducing active gibberellin concentrations in the flavedo, which are involved in regulating sugars and ABA accumulation and in reducing N fraction concentration as rind color develops. This was demonstrated in vivo without removing the fruit from the tree. Comparable results were obtained with experiments carried out over four consecutive years in two countries (Spain and Uruguay).     

ClSnRK2.3 negatively regulates watermelon fruit ripening and sugar accumulation

Watermelon(Citrullus lanatus) as non-climacteric fruit is domesticated from the ancestors with inedible fruits. We previously revealed that the abscisic acid(ABA) signaling pathway gene ClSnRK2.3 might infuence watermelon fruit ripening. However,the molecular mechanisms are unclear. Here,we found that the selective variation of ClSnRK2.3 resulted in lower promoter activity and gene expression level in cultivated watermelons than ancestors, which indicated ClSnRK2.3 might be a negative regulator ...     

Effects of Abscisic Acid and Benzyladenine on Fruits of Normal and rin Mutant Tomatoes

Since ethylene application did not induce ripening in detached fruits of the nonripening mutant rin we initiated studies to determine possible involvement of other hormones. We proposed that the lack of ripening in mutant rin tomato fruit may result from a lack of abscisic acid or from excessive endogenous levels of cytokiuin. Application of abscisic acid (3 x 10(-5)m and 10(-3)m) to detached fruits of a normal strain (Lycopersicon esculentum Mill. cv. ;Rutgers') reduced the time to initiate ripening by about 50%. This acceleration of the onset of ripening appeared not to be due to an increased rate of ethylene production. Abscisic acid did not alter respiration or ethylene production or induce ripening in rin fruit. Ripening in Rutgers fruit was not influenced by treatment with 6-benzyladenine (4.44 x 10(-6)m, 4.44 x 10(-5)m or 1.8 x 10(-4)m). Fruits of the mutant rin showed no response to exogenous BA. However, senescence rates of leaf disks of both Rutgers and rin were significantly inhibited by as little as 10(-7)m exogenous benzyladenine. The results are discussed in relation to previous studies of the physiology of rin fruits and it is concluded that endogenous levels of ABA and cytokinins do not account for the lack of ripening in rin fruit.     

Non-targeted metabolomic analysis of orange (Citrus sinensis [L.] Osbeck) wild type and bud mutant fruits by direct analysis in real-time and HPLC-electrospray mass spectrometry

The direct analysis in real-time (DART) ion source and HPLC-electrospray mass spectrometry were applied in non-targeted metabolomic analyses of fruits of an orange bud mutant, ‘Hong Anliu’ along with its parental wild-type, ‘Anliu’. Fruits of the two isogenic cultivars were sampled at three different ripening stages, i.e. 120, 170 and 220 days after flowering. More than 130 metabolites were tentatively identified, including acids, sugars, flavonoids, alkaloids, limonoids, coumarins, amino acids, and plant hormones. Metabolomic analyses revealed that, compared to its wild type, the bud mutant fruit is characterized by higher levels of monosaccharides and disaccharides and lower levels of organic acids such as citric acid, malic acid and quinic acid, which agrees well with the anticipated fruit quality benefits of the mutation. In addition, many secondary metabolites, such as flavonoids, showed significant differences between the two genotypes, indicating that the whole fruit metabolome is significantly changed due to the bud mutation. This study provided a comprehensive assessment of metabolites in orange fruits, and revealed metabolomic differences in fruits between two isogenic orange genotypes. The results are helpful for understanding how the bud mutation in ‘Hong Anliu’ impacts the physiological and biochemical processes of orange fruits.