Carotenoids are isoprenoid pigments, which are widely distributed in nature. In fruits and flowers, carotenoids are responsible for bright yellow, orange, and red colors and provide a substrate to form flavor compounds, which attract pollinators and seed dispersers. In leaves, carotenoids play an essential role in photosynthesis. When carotenoids are ingested in the diet, they play a vital role in human nutrition and health as a precursor of vitamin A, antioxidants, and anti-inflammatory agents. It is therefore important to control carotenoid accumulation to improve the commercial value of horticultural crops. Carotenoid accumulation is regulated by flux through the carotenoid biosynthetic pathway, and also by degradation and sequestration into plastids, which function as sink organelles. These processes are mostly controlled at the transcriptional levels of relevant genes. In this review, we summarize recent advances in studies on the molecular mechanisms that regulate carotenoid accumulation in vegetables, fruits, and ornamental flowers.
We investigated the vertical 137Cs distribution in soil among five sod culture orchards with different soil textures over six years after 2011, when 137Cs fallout was released by the Fukushima Daiichi Nuclear Power Plant accident, to confirm the long-term 137Cs downward-migration into soil. At each orchard, soil cores were collected to a depth of 30 cm and subdivided into intervals of 3 to 9 cm. The 137Cs within the 3 cm of topsoil decreased from 84–94% during the first 7 months after deposition in 2011 to 41–75% in 2017. From 2012 onward, the vertical 137Cs profiles in the soils were explained by a two-component negative exponential model composed of a rapid and a slow component with a change of slope at a depth of 6 to 9 cm. It took 4 years after deposition to show a significant difference in the value of the average 137Cs migration distance (Md) among the orchards. The speed of 137Cs migration in the orchards during the 6 years after the accident year was 0.44 to 0.97 cm year−1 based on the Md. There was a significant positive correlation between Md and fine sand content in the 3 cm of topsoil between Md and the ratio of the total carbon content (TC) at a depth of 3 to 6 cm to that in the top 3 cm of soil. Furthermore, the percentage of exchangeable 137Cs (ex-137Cs) to 137Cs at 3 to 6 cm depth increased significantly in proportion to the ratio of TC at 3 to 6 cm depth to TC at 0 to 3 cm depth in soil collected in 2013. These findings indicate that one of the mobile forms of 137Cs was ex-137Cs combined with TC and that the fine sand content and TC influenced the 137Cs downward-migration in the 3 cm of topsoil in the orchard in which organic matter accumulated by sod culture.
Sheet-mulching cultivation during the fruit developmental stage is often carried out to produce high-quality Satsuma mandarin (Citrus unshiu Marc.) and ‘Harehime’ ((‘Kiyomi’ × ‘Osceola’) × ‘Miyagawa-wase’) fruits because they show high Brix% by exposure to drought stress conditions. In this study, we investigated the effect of drought stress on the number of floral buds in ‘Haraguchi-wase’ Satsuma mandarins and ‘Harehime’. To clarify the relationship between drought stress and the number of floral buds, we applied four different drying treatments to the fruit trees, (i) first-half drying (drying treatment during the first-half of the fruit development stage), (ii) second-half drying (drying treatment during the second-half of the fruit development stage), (iii) all-drying (drying during the full fruit development stage), and (iv) well-watered (non-drought stress during the fruit development stage). The drying treatment was applied to the fruits at ψ max −0.7 to −1.2 MPa at an intensity comparable to proper drought stress for high-quality fruit production according to our previous studies. In ‘Haraguchi-wase’, the all-drying treatment produced a higher number of floral buds in the following spring season compared with the well-watered treatment, in which the increase in the number of floral buds took place concomitant with the enhancement of CiFT expression in December. As expected, the fruits after all-drying were smaller with a significantly higher Brix% and a similar level of citric acid content, suggesting that drought stress of suitable intensity resulted not only in high-quality fruit production, but also in an increased number of floral buds in the following spring season. The results also demonstrated that the first-half drying caused higher CiFT expression and more inflorescences than in the well-watered plants, while there were no differences in CiFT expression or number of floral buds between the second-half drying and well-watered treatments. These tendencies observed in ‘Haraguchi-wase’ were the same as in ‘Harehime’. Therefore, the drying treatment during the first-half of fruit development could be an effective method to increase the number of floral buds.
We monitored sugar accumulation profiles and developmental changes in fruit traits during the ripening process in pollination-constant non-astringent (PCNA)-type persimmon cultivars of ‘Akiou’, ‘Fuyu’ and ‘Taishuu’. As the fruit ripened, transverse and longitudinal diameter, fruit weight, soluble solids content (SSC), and flesh juiciness increased significantly, with a constant varietal ranking throughout the ripening process. Color development of ‘Akiou’ and ‘Taishuu’ seemed to be faster than that of ‘Fuyu’ during the initial stages of fruit ripening, but there was little difference in color chart values toward the latter stage of fruit ripening. Flesh firmness decreased steadily over time, whilst varietal ranking remained constant. The varietal ranking of SSC in the latter stage of ripening was ‘Akiou’ ≥ ‘Taishuu’ > ‘Fuyu’. Significant varietal differences were observed in sucrose, glucose, and fructose contents. Based on sugar accumulation profiles, the cultivars could be classified into two types: hexose accumulators (‘Taishuu’) and sucrose accumulators (‘Akiou’ and ‘Fuyu’). The transcriptional profiles of key sugar accumulation-related genes: sucrose synthase (SuSy), vacuolar acid invertase (VAI), and sucrose phosphate synthase (SPS), were also examined. Transcriptional levels of SuSy and VAI in sucrose accumulators were lower than those in the hexose accumulator. Conversely, transcriptional levels of SPS were higher in the sucrose accumulators than in the hexose accumulator. In particular, the concomitant and rapid increase of both SPS expression and sucrose accumulation in mid-October, suggests that this period is crucial for ‘Akiou’ in terms of the SSC elevation.
Blueberries are handpicked because of irregular maturation of fruits within clusters. Therefore, harvesting is labor intensive and results in a short shelf life of the product. Cluster harvesting, as performed for grapes, could solve these problems. Previously, we produced many interspecific hybrids between the highbush blueberry (HB; Vaccinium corymbosum L.) and rabbiteye blueberry (RB; Vaccinium virgatum Aiton) and found that some individuals were parthenocarpic and maturation of berries within fruit clusters was relatively uniform. In the present study, we investigated the degree of parthenocarpy and suitability of the hybrids for cluster harvesting and considered the use of parthenocarpic hybrids to breed cultivars for cluster harvesting. The degree of parthenocarpy was evaluated in 21 blueberry plants (hybrids and cultivars) based on the average fruit set without pollination. It was found that 2 hybrid individuals had the highest frequencies of parthenocarpy and their fruit set and weight were close to those of pollinated fruits; moreover, pollinated fruits of these hybrids were seedless. Thereafter, the uniformity of flowering and fruit maturation was evaluated, and the 2 hybrids showed a relatively uniform maturity of fruits in a cluster; furthermore, fruit dropping occurred later. In addition, correlation analysis was performed for 5 parameters related to parthenocarpy and suitability for cluster harvesting. For seeded fruits, it was found that the flowers that bloomed earlier in a cluster formed a fruit containing more seeds and matured earlier. Comparison of cluster and individual harvesting showed that the percentages of mature fruits within clusters in the 2 hybrids were markedly higher than those in the HB cultivars. Moreover, cluster harvesting of the hybrids greatly shortened the working time needed for harvest and subsequent fruit sorting to 59% of that of individual harvesting. Thus, the 2 hybrids that had a higher degree of parthenocarpy than that in the existing blueberry cultivars were assessed to be highly suitable for cluster harvesting. Factors underlying this suitability may be related to the seedlessness of interspecific hybrids. These results suggest that interspecific hybridization between HB and RB is useful as a breeding method to produce cultivars suitable for cluster harvesting.
Abscisic acid (ABA) and ethylene are well-known phytohormones that are involved in the maturation of grape berries and other fruits. However, the process of yellow-green skinned grape berry maturation is not well understood due to difficulties in determining grape maturity from changes in skin color. Skin browning during maturation is a major commercial problem in some yellow-green skinned grape cultivars including ‘Shine Muscat’. To resolve this issue, a better understanding of the mechanisms involved in grape maturation and skin-browning is needed. We treated ‘Shine Muscat’ grape clusters at the veraison stage (45–50 DAFB) with spray applications of ABA or ethephon. These treatments produced darker colors and increased the trans-resveratrol and flavonol contents of berry skins. The ABA and ethephon treatments significantly increased the severity of skin browning. Changes in the expression of genes involved in polyphenol biosynthesis and oxidation were consistent with increases in polyphenols and the severity of browning in berry skins. The expression of VvACO2 and VvYUC1 genes, which are involved in ethylene and auxin biosynthesis, respectively, were upregulated in berries with brown skins. Although ABA treatment also increased the size of the berries, the effect of ethephon treatment on berry maturation was similar to, or greater than, that of ABA treatment. In berry skins, the expression of VvACO3, which is involved in phytohormone biosynthesis, increased significantly in response to ABA treatment. Overall, the changes in gene expression produced by ABA and ethephon treatments differed. Therefore, different mechanisms may regulate the physiological responses to ABA and ethephon, although both treatments accelerate berry maturation.
Phytohormones play major roles in the berry maturation process. Gibberellic acid (GA) and cytokinin (CK) are phytohormones used in seedless table grape production. Several studies have been conducted on the effects of GA and CK application on berry development. However, the detailed mechanisms underlying their physiological effects on berry maturation after the veraison stage have not been clarified. Skin browning during maturation is a major commercial problem in yellow-green skinned grape cultivars including ‘Shine Muscat’, and expanding our knowledge of these mechanisms is a necessary step towards addressing this problem. In this study, we investigated the effects of GA and CK treatments from the veraison stage to the subsequent developmental stages of this grape berry. Both treatments resulted in enlarged berries and the suppression of increases in sugar content. Chlorophyll in the berry skin was less decomposed after GA/CK treatment, and the occurrence of skin browning in the maturation stage was reduced, as expression of the VvPP2Cs gene decreased. GA/CK treatment at the veraison stage (45–50 DAFB) reduced the expression levels of phytohormone-related genes, particularly those of VvGID1 and VvCHKs, which are involved in GA and CK signaling, respectively. These similar changes in gene expression patterns suggest phytohormonal crosstalk and a common expressional regulatory mechanism. VvACO2 and VvYUC1 expressions were significantly increased in skin browning samples, regardless of treatment, indicating involvement of the ethylene and auxin biosynthesis pathways in skin browning. Therefore, GA/CK treatment at the veraison stage may broadly affect phytohormone biosynthesis and signaling pathways in subsequent developmental stages, although the effect size greatly differs depending on the experimental conditions, including year and plant.
In satsuma mandarin fruit (Citrus unshiu Marc.), β-cryptoxanthin is a major carotenoid and an important quality component in the juice sacs. The stage of maturity and storage conditions of satsuma mandarin fruit shipped to markets varies. However, the effects of maturation stage, storage temperature and duration on changes in β-cryptoxanthin content have not been fully studied. In the present study, fruits were harvested at different maturation stages, and changes in β-cryptoxanthin content in the juice sacs were investigated during storage at temperatures from 5 to 20°C. At 20°C, in fruit harvested while β-cryptoxanthin is still being accumulated on the tree, the content continued to increase following 15 days of storage. However, in the fruit without β-cryptoxanthin accumulation on the tree, the content did not increase. At 10°C, in the fruit accumulating β-cryptoxanthin on the tree, the content continued to increase after 14 days’ storage, whereas in the fruit without β-cryptoxanthin accumulation, the content did not increase after 14 days’ storage but increased after 30 days’ storage. At 8°C, the increase in content was also observed in the fruit when stored for 80 days. In contrast, at 5°C, the content did not change notably at any maturation stage regardless of the experimental period. The changes in the carotenoid content and gene expression suggest that carotenoid accumulation during on-tree maturation continues after harvest at 20°C, but not at 5°C. The present results suggest that β-cryptoxanthin content will not decrease at a range from 5 to 20°C irrespective of the maturation stage. Moreover, at 8°C and above, the β-cryptoxanthin content will gradually increase, and the rate will be more rapid in fruit harvested when carotenoid accumulation is in progress on the tree.
Japanese apricot (Prunus mume Sieb. et Zucc.) is one of the major fruit tree crops in Japan. However, a paucity of molecular tools has limited studies on the species’ genetic diversity and clone identification. Therefore, we newly designed 201 microsatellite markers using the P. mume reference genome and selected 20 highly polymorphic markers. The markers showed higher polymorphism detectability than those previously developed using peach and apricot genomes. They were used successfully for fingerprinting most of the Prunus cultivars examined (124 P. mume accessions and one accession each of P. armeniaca, P. salicina, P. persica, and P. dulcis), and the resulting genotype data were used to examine the genetic differentiation of six Japanese apricot cultivar groups, including those producing normal fruit, small-fruit, and ornamental flowers, as well as Taiwanese cultivars, putative hybrids of P. armeniaca and P. mume, and putative hybrids of P. salicina and P. mume. Phylogenetic cluster analysis showed three clades with high support values; one clade comprised the putative P. armeniaca × P. mume hybrids, and the two others included Taiwanese and ornamental cultivars. The rest of the accessions were grouped into two wide clusters, but not clearly divided into the respective cultivar groups. These complex relationships were supported by the principal coordinate and STRUCTURE analyses. Since Japanese apricot is thought to have originated in China, many factors such as human preference, geographical separation, introgression, and local breeding, may have been involved to form the present complex genetic structure in Japanese apricot.
An excess or lack of soil moisture are significant abiotic stresses that reduce the average yield for vegetable crops worldwide. The responses of ‘Natsunoshun’, a processing tomato cultivar, to water stress at three growth stages, first flower differentiation, first flowering, and fruit development, were investigated over a two-year period. The year effect on yield was not significant; however, the growth stage and the type of water stress at a particular growth stage affected yield significantly. Either an excess or lack of soil moisture after the first flowering stage were significant in reducing yield. The decrease was related to the average weight of the fruit rather than the number per plant. Under dry conditions, fruit number was the same as control plants, but there was a decrease in the reddish mature fruit ratio. On the other hand, under wet conditions plant biomass decreased, especially in the roots, even if there was a transition from wet to dry conditions. We conclude that excessive soil moisture during the first flowering stage produces slower CGR and decreased biomass in the roots, which we believe is the reason for the yield decline.
This study was conducted to evaluate the influence of fruit maturity and postharvest storage on the physiological qualities of chili seeds during development. Two types of chili were used (ancho and guajillo). Fruits were harvested at 40, 60, 80, 100, 120 and 140 days after anthesis (daa) and stored for 0, 7 and 14 days after harvest (dah). The moisture content of guajillo seeds throughout development decreased from 86 to 17%, while ancho maintained moisture at 47% at 80 dda. It was confirmed that precocious harvest (40 daa) was not beneficial to the physiological quality of chili seeds, even when it was associated with 14 dah. Germinability was correlated with electrical conductivity (R = −0.76): Ancho seeds germinated starting from 472.5 μS·cm−1·g−1 and guajillo seeds from 679.3 μS·cm−1·g−1. In fruits harvested 80 daa, 14 dah was essential to ensure the physiological quality of seeds in both types of chilies: mean germination was above 93%, and seed vigor was higher (germination after accelerated aging and mean germination speed were more than 90% and 5.6 radicle d−1, respectively). Seeds harvested 120 daa were of high quality, and post-harvest storage of fruits was not necessary. Expression of two late embryogenesis abundant (LEA) proteins was detected in both types of chilies: the first synthesis (65 kDa) occurred 80 daa, and the second (50 kDa) occurred 120 daa and this was directly related to the maximal physiological quality of chili seeds.
Bitterness, caused by cucurbitacins, is present in some melon fruit. Although bitter compound biosynthesis and regulation in Cucurbitaceae plants have been reported, the dynamic changes in bitterness during fruit development are unknown. Bitterness severity was measured for 19 inbred melon lines, including 14 lines of Cucumis melo var. chinensis, two var. inodorus and three var. conomon, using a panel tasting method. The data showed that bitterness severity was different in several lines of var. chinensis during fruit growth and maturation. Nb46 and Nb320, two elite parental lines of var. chinensis used in melon breeding, were used as experimental materials. Bitterness was severe at stage I, but moderate and disappeared at stage II and III in the fruit of Nb46. There was non-bitterness in the fruit of Nb320 throughout the development period. Furthermore, the cucurbitacin B (CuB) content gradually decreased in Nb46, while in Nb320, the CuB content changed little and remained at a quite low level during fruit development. Different expression patterns of the genes involved in CuB biosynthesis and regulation were found between Nb46 and Nb320. The expression levels of these genes were significantly higher in Nb46 than Nb320 in the early developmental stages, and this correlated with a higher concentration of CuB in Nb46 than Nb320. These results demonstrate that bitterness severity is different in var. chinensis during fruit developmental stages, and that the CuB biosynthesis-related genes are a critical factor in this process. We hope these findings will contribute to the breeding of non-bitter melon cultivars.
Internally brown (IB) tomato fruit is a physiological disorder in which the inside of the fruit turns brown or black. The mechanisms underlying the development of IB are not well understood. In this study, we examined the incidence of IB using hydroponics, and investigated the anatomical features and the ratio of dimeric rhamnogalacturonan II-borate (dRG-II-B) to total rhamnogalacturonan II (RG-II) (boron cross-linking ratio) in cell walls that decreased with boron deficiency. IB fruit developed when the growth of the stem and leaves were normal and the micro-element concentrations were low. The IB region was observed to be brown inside the fruit at an early stage, and this changed to black in the mature fruit. It was detected around the pericarp, locular gel, placenta and columella in the tomato fruit. An abnormality was observed around the vascular bundle in IB fruit. The interior of the cells near the vascular bundle was changed to a substance with a high electron density, and a disintegrated image was observed. Few Ca precipitates were observed on plasma membranes or cell walls in the collapsed cells by an antimonite precipitation method. It is suggested that Ca deficiency appears to be related to the cell collapse in IB. There was no significant difference in the boron cross-linking ratio between the IB and normal fruit. This suggested that IB was not related to B deficiency directly. We concluded that IB was caused by necrosis of cells around the inner vascular bundle due to Ca deficiency.
Despite increasing demand for sweet potato foliage, which is rich in functional components, efficient methods to maximize yield are still needed. In this study, cultivation tests for sweet potato (line Kyukei05303-3) were conducted over three consecutive years at a greenhouse to characterize seasonal changes in the foliage yield (leaves and stem-petioles), as well as the polyphenol content. The sweet potato foliage was harvested from May to November every week, and the average leaf yield was 855.3 g·m−2·year−1 on a dry weight (DW) basis. The yield and polyphenol content of the leaves were negatively correlated. The yield increased from spring to summer but decreased after mid-August. In contrast, the polyphenol content was highest in May, lower during the summer (June to August), and increased again after September. The average polyphenol content in the leaves was 6.9 g·100 g−1 DW and the total annual polyphenol yield was 59.0 g·m−2. The major component of polyphenols was caffeoylquinic acids. The seasonal changes in caffeoylquinic acids were highly correlated with the changes in total polyphenols. The polyphenol content was significantly correlated with air temperature, but not with sunshine duration, suggesting that air temperature is an important determinant of the polyphenol content during cultivation. These results provide a basis for the rapid cultivation of sweet potato for foliage production.
The postharvest physiology of cut astilbe inflorescences (Astilbe × arendsii), which consist of many small florets with a short vase life, was studied in response to treatments to extend their vase life. Exogenous ethylene treatment at 0.3 μL·L−1 for 7 h did not affect the senescence of inflorescences or leaves of five cultivars and 0.2 mM silver thiosulfate for 2 h did not improve the quality of inflorescences of three cultivars, which indicated that ethylene is not a critical factor for senescence in astilbe florets. Continuous treatment with 2% sucrose or 2% trehalose solutions prolonged the cut inflorescence vase life of one or two of five astilbe cultivars, respectively. Pulse treatment with 2% trehalose in combination with 6% sucrose increased total soluble sugar contents from 11.4 to 57.6 mg·g−1 FW and raised the respiration rate of inflorescences from 15.3 to 28.4 μmol CO2·h−1·g−1 FW at 2 days after harvest (DAH) in the cultivar ‘Gloria Purpurea’. However, the effects of pulse treatment diminished at 4 DAH and extended the vase life from 4.0 days to a maximum of 5.6 days, which suggested that pulse treatments were inadequate to maintain sugar contents and respiration activity. Continuous treatment with 6% sucrose extended the vase life from 4.3 to 10.0 days and raised the chroma (C*) value of florets from 28.7 to 54.9 at 8 DAH. Continuous treatment with 2% trehalase + 4% sucrose markedly prolonged the vase life to 11.5 days and increased the C* value to 53.9 at 8 DAH. Under stereomicroscopic observation, continuous treatment with 2% trehalase + 4% sucrose maintained more vivid pink color of petals, styles, filaments and receptacles than those in control florets at 9 DAH. Combined treatment with 2% trehalose and 30 μM validamycin A, a potent inhibitor of trehalose metabolizing activity, induced severe wilting of florets and necrotic spots on leaves. Exogenous trehalose may be hydrolyzed by trehalose metabolizing activity in cut astilbe inflorescences. The results suggest that continuous treatment with trehalose and sucrose solutions is effective to maintain development and delay senescence of florets to extend the vase life of cut astilbe inflorescences.
The modified ABC model explains the floral morphology of many monocots, such as the lily and tulip, in which the perianth consists of two layers of almost identical petaloid tepals. According to the modified ABC model, B-class genes are expressed in two perianth whorls, inducing the petaloid structure in both whorls 1 and 2. In this study, we analyzed the expression and function of the B-class genes in the grape hyacinth (Muscari armeniacum). We isolated two DEFICIENS (DEF)-like genes (MaDEF1 and MaDEF2) and three GLOBOSA (GLO)-like genes (MaGLOA1, MaGLOA2, and MaGLOB) from M. armeniacum using rapid amplification of cDNA ends (RACE). Expression analysis showed that MaDEF1 and MaDEF2 were expressed in whorls 1, 2, and 3, whereas MaGLOA1, MaGLOA2, and MaGLOB were expressed in all four whorls. These results support the modified ABC model in M. armeniacum. Overexpression of MaGLOA1 and MaGLOB in Arabidopsis thaliana resulted in a morphological change of sepals to petaloid structures in whorl 1, indicating that the function of these genes is similar that of the B-class orthologs PISTILLATA and GLO in A. thaliana and Antirrhinum majus, respectively. In addition, yeast two-hybrid assays revealed strong protein–protein interactions between MaDEF1 and MaGLOA1, suggesting that MaDEF1–MaGLOA1 is likely to have the main B-function in M. armeniacum. These data support the modified ABC model in M. armeniacum.
Pyridinedicarboxylic acid (PDCA) analogs extend the vase life of spray-type (SP) carnation flowers by accelerating flower opening and retarding senescence. Among the PDCA analogs, 2,3-PDCA and 2,4-PDCA are equally and highly effective. In the present study, we characterized the promotion of flower opening by PDCAs and their analogs, pyridinecarboxylic acids. The present results showed that 3-pyridinecarboxylic acid (3-PCA), and its derivative, 3-PCA amide, are most active in accelerating flower opening of ‘Light Pink Barbara’ carnation cut flowers. 3-PCA treatment promoted flower opening in cut flowers of many SP carnation cultivars, that had been stored dry at 2–4°C for 3 weeks and resulted in extension of their display time.