2022 Volume 91 Issue 3 Pages 312-321
Changes in anthocyanin and endogenous abscisic acid (ABA) contents in the berry skins of Vitis labruscana × V. vinifera cultivars, ‘Aki Queen’, and ‘Ruby Roman’ were investigated during the fruit development period. Color development of ‘Aki Queen’ berries mainly occurred within 20 days post véraison, while that of the ‘Ruby Roman’ was prolonged for about 40 days. In both cultivars, the ABA level in the berry skin started to increase a few days before véraison; however, ABA accumulation ceased approximately 10 days after véraison in ‘Aki Queen’, while it continued until the late stage of maturation in ‘Ruby Roman’. In addition, higher indole-3-acetate aspartate (IAA-Asp) and lower isopentenyladenine (iP) contents were observed in ‘Ruby Roman’ than in ‘Aki Queen’ at the late development stage. The expression analysis of genes involved in ABA metabolism revealed that V. vinifera 9-cis-epoxycarotenoid dioxygenase 3 (VviNCED3), which is assumed to play a major role in ABA biosynthesis, remained relatively higher in ‘Ruby Roman’ than in ‘Aki Queen’ after véraison. Considering that ABA plays a regulatory role in grape maturation, these results may indicate that the coloration of ‘Ruby Roman’ at the later stage of maturation is partly attributable to an increased ABA pool in berry skins.
The quantities and composition of anthocyanins are determined by the skin color of the grape berry. In grapes, anthocyanins are accumulated after the onset of ripening, which is known as véraison. For nonclimacteric fruits, such as grape, abscisic acid (ABA), brassinosteroids, and ethylene have been proposed to promote berry ripening, while auxins, cytokinins, gibberellins, and jasmonates delay some associated ripening processes, and these hormones may be involved in ripening regulation through complex interactions (Böttcher et al., 2015; Corso et al., 2016; Fortes et al., 2015; Gouthu and Deluc, 2015; Jia et al., 2016; Kuhn et al., 2014; Pilati et al., 2017; Ziliotto et al., 2012). The degree of anthocyanin accumulation is primarily determined by genetic variation and is also affected by environmental factors, such as light, temperature, and available assimilates, which limit the carbon flow of secondary metabolism.
Based on genetics, Ban et al. (2014) reported quantitative trait loci (QTLs) for anthocyanin content in linkage groups (LGs) 2 (MYB haplotype), 8, and 14 in interspecific hybrid grapes. Costantini et al. (2015) also detected 19 QTLs for the total anthocyanin content in a V. vinifera cross (‘Syrah’ × ‘Pinot Noir’). The number and type of functional MYB haplotypes at the color locus (LG2) are the major genetic factors that determine the variation of anthocyanin content in grape berry skin (Azuma, 2018). The locus appears to be a tandemly arrayed MYB gene that spans a region of 200-kb. In this cluster, the VviMYBA1 locus and the VviMYBA2 locus are functionally crucial for berry pigmentation in V. vinifera. Since the two adjacent MYB alleles in the color locus are inherited together, they are described as MYB haplotypes (Azuma, 2018; Azuma et al., 2011). Among these haplotypes, Hap A is nonfunctional (Kobayashi et al., 2004, 2005; Walker et al., 2007). In the interspecific hybrid grapes of V. vinifera and V. labrusca, three functional MYB alleles derived from V. labrusca, named VlMYBA1-2, VlMYBA1-3, and VlMYBA2, have been identified (Azuma et al., 2011). The allele combination of VlMYBA1-2 and VlMYBA1-3 has been named Hap E1, while the VlMYBA2 and VlMYBA1-3 combination was named Hap E2. These two haplotypes are identified only in hybrid grapes (Azuma, 2018).
‘Ruby Roman’ is a red table grape cultivar selectively bred from seedlings of ‘Fujiminori’, a tetraploid black table grape obtained from progeny of Ikawa Selection 682 × ‘Pione’ (Yamada and Sato, 2016), while ‘Aki Queen’ is a self-bred seedling of ‘Kyoho’. ‘Ruby Roman’ and ‘Aki Queen’ bear red berries and their LG2 loci have similar components, which consist of three nonfunctional Hap As and one Hap E1 (Azuma et al., 2011). The pattern of berry coloration, however, is slightly different between them. The accumulation of anthocyanin in ‘Ruby Roman’ berries was slow until 15 days after véraison and accelerated from 15 to 35 days (Matsuda et al., 2020), while it accumulated within 20 days after véraison in ‘Aki Queen’ (Katayama-Ikegami et al., 2017; Yamane and Shibayama, 2006).
ABA promotes the biosynthesis of anthocyanins through upregulation of MYBAs and resultant genes encoding enzymes together with the transporters involved (Jeong et al., 2004; Katayama-Ikegami et al., 2016b; Koyama et al., 2010; Pilati et al., 2017). During the late stage of maturation, exogenous ABA treatment promoted the expression of VlMYbA1-2, VlMybA1-3, and UFGT in ‘Aki Queen’, but did not significantly promoted UFGT expression for ‘Ruby Roman’ (Katayama-Ikegami et al., 2017). Comparison of the expressions of these three genes demonstrated that they tended to be higher in ‘Ruby Roman’ than in ‘Aki Queen’ at the late stage of maturation, implying the presence of a trait(s) other than the LG2 locus that controls the coloration of grape berries.
Therefore, it was assumed that the endogenous ABA content in ‘Ruby Roman’ may be higher than that in ‘Aki Queen’, resulting in the coloration of ‘Ruby Roman’ at the later stage. In this study, to clarify the coloration during the later stage of maturation in ‘Ruby Roman’, we investigated the differences between these two cultivars in terms of endogenous ABA metabolites and associated gene expressions. As mentioned above, the complex and coordinated regulation of endogenous plant hormones affects berry development, especially from the onset of maturation to ripening. The detailed function and/or combinations of these plant hormones are not fully understood. Therefore, in order to better understand the ripening process from the differences between the two cultivars, in addition to ABA, we also analyzed the contents of auxin and cytokinins and their metabolites.
A 30-year-old ‘Aki Queen’ (Vitis labruscana Bailey × V. vinifera L.) and two 8-year-old ‘Ruby Roman’ (Vitis labruscana Bailey × V. vinifera L.) grapevines grown in the same vinyl house at Ishikawa Prefectural University were used for two years, 2014 and 2015, in this study. The ‘Aki Queen’ vine was trained with long cane pruning, and the ‘Ruby Roman’ vines were trained with short cane pruning. The flower clusters were traditionally shaped (left 3.5 cm floret from the bottom) and dipped in a solution of 25 mg·L−1 gibberellic acid (GA3) and 5 mg·L−1 forchlorfenuron (Kyowa Hakko Bio Co., Ltd., Japan) to induce seedlessness at full bloom. Then the clusters were dipped in GA3 (25 mg·L−1) at 10 days after full bloom (DAFB) to stimulate berry enlargement. The day of full bloom of the ‘Aki Queen’ vine was May 19, and véraison (beginning of softening) was June 28 (40 DAFB) in 2014, and May 16 and June 25 (40 DAFB) in 2015. Fruit clusters were thinned for the ‘Aki Queen’ to leave one on each shoot, and were thinned to leave 30–35 berries on each cluster before véraison. The day of full bloom of ‘Ruby Roman’ vines was May 24, véraison was July 5 (42 DAFB) in 2014, and May 19 and July 3 (45 DAFB) in 2015. The fruit clusters were thinned for the ‘Ruby Roman’ to keep one per three shoots, and were thinned to leave 25–30 berries on each cluster before véraison. To investigate their development at different growth stages, berries were collected randomly at an interval of seven days (three days around véraison) from June 4 (16 DAFB) to August 11 (84 DAFB) for ‘Aki Queen’, and from June 9 (16 DAFB) to August 18 (86 DAFB) for ‘Ruby Roman’ in 2014, and seven to 10 days (four days around véraison) from June 1 (16 DAFB) to August 19 (95 DAFB) for ‘Aki Queen’, and from June 5 (17 DAFB) to August 20 (93 DAFB) for ‘Ruby Roman’ in 2015 (see Figures for actual date). Fifteen (2014) and 30 (2015) berries for each sampling were divided into three or five replicates (n = 3 in 2014, n = 5 in 2015). Note that the berry samples used in this 2014 study were the same as previously published for analysis of anthocyanin accumulation and expression of anthocyanin biosynthetic genes, VlMybA1-2, VlMybA1-3, and VviUFGT (Katayama-Ikegami et al., 2017).
Investigation of berry quality and skin colorationAfter measuring the berry diameter and weight, the pulp of peeled berries was squeezed, and the content of total soluble solids (TSS) and titratable acidity (TA) of the juice was determined. TSS (°Brix) was measured using a digital refractometer (PAL-1; Atago Co., Ltd., Japan). TA was measured by titration with 0.1 mol·L−1 NaOH to a phenolphthalein endpoint. TA content was expressed as the mass (in grams) of tartaric acid equivalent per 100 mL juice.
Sugars were extracted in 1 mL 80% (v/v) ethanol from 20 mg lyophilized and ground fine powder of berry skin for 30 min at 30°C on an orbital shaker. After centrifuging at 14,000 rpm, the supernatants were filtered using a 0.22 μm polyvinylidene difluoride filter (EMD Millipore Co., Germany). Sucrose (Suc), glucose (Glu), and fructose (Fru) were quantified using a high-performance liquid chromatograph equipped with an Asahipak NH2P-50 4E (4.6 mm × 250 mm column; Showa Denko K.K., Japan). Elution was performed at 1 mL·min−1 with 75% acetonitrile and monitored with a charged aerosol detector (Corona Veo; Thermo Fisher Scientific Inc., USA) as described previously (Sugiyama et al., 2016). Standard curves were created using known concentrations of the sugars. Samples obtained before August were diluted 40 times with acetonitrile, and samples after August were diluted 80 times before injection.
The total anthocyanin content in the berry skins was measured as described by Shiraishi et al. (2007), with a slight modification. One skin disc was collected from each berry using a cork borer (Φ = 8 mm) from the berry apex (2014) or equatorial site (2015). Anthocyanins were extracted in 50% (v/v) aqueous acetic acid for 24 h at 4°C in the dark, followed by filtration through a 0.45 μm PVDF filter (EMD Millipore). The absorbance of the extract at 520 nm was measured using a spectrophotometer (Biospec-1600; Shimadzu Corp., Japan). The total anthocyanin content was expressed as nmol·cm−2 skin of equivalent cyanidin 3-glucoside chloride standard (TOKIWA Phytochemical Co., Ltd., Japan).
Determination of endogenous plant hormone contentsA range of endogenous plant hormones in the berry skins was analyzed as described by Gao-Takai et al. (2019) according to the method of Chiwocha et al. (2003) and Gouthu et al. (2013), using liquid chromatography-triple quadrupole mass spectrometry (LC: Waters 2695 Separations Module, MS/MS: Waters micro mass Quattro micro API Mass Spectrometer; Waters Corp., USA), including ABA and ABA-derived compounds, such as ABA glucosyl ester (ABA-GE), dihydrophaseic acid (DPA) and phaseic acid (PA; two ABA catabolites that are produced by ABA 8'-hydroxylation), neophaseic acid (neoPA; an ABA catabolite that is made by ABA 9'-hydroxylation), and 7'-hydroxy ABA (7'-OH-ABA); indole-3-acetic acid (IAA; an auxin) and IAA-amino acid conjugates, such as IAA-aspartate (IAA-Asp), IAA-alanine (IAA-Ala), and IAA methyl ester (IAA-ME); and cytokinins, including trans-zeatin (tZ), isopentenyl adenine (iP), and their sugar conjugates [tZ-riboside (tZR) and iP-riboside (iPR)].
Expression analysis of ABA metabolism-related genesTotal RNA was extracted from the berry skins using the hot borate method (Wan and Wilkins, 1994) and was then treated with DNaseA (Thermo Fisher Scientific) in the presence of RNasin Ribonuclease Inhibitors (Promega Corp., USA). Single-strand cDNAs were then synthesized using SuperScript III Reverse Transcriptase (Thermo Fisher Scientific). The gene expressions encoding ABA metabolism-related genes, including VviNCED3 (VviNCED1 in Gao-Takai et al., 2019) and VviNCED2, which encode a key ABA biosynthesis enzyme, VviCYP707A1 and VviCYP707A4, which are ABA catabolism genes, VviABA-BG1, which encodes β-glucosidases and is associated with the release of free (active) ABA from ABA-GE, VviABA-GT, which encodes glucosyltransferases and is related to the inactivation of ABA to produce ABA-GE, and VviABF2, which encodes ABA-responsive element binding factors and is associated with ABA signal transduction were investigated. Most of primer sequences for quantitative real-time polymerase chain reactions (qRT–PCR) were used as described in Gao-Takai et al. (2019), and the primer pairs were (forward: 5'-AAGGAGAAGAGGTTAGCCGACA-3'; reverse: 5'-GCGATTTGGTCATTGGTCAG-3') for VviCYP707A4 (XM_002282197). PCR was performed on 1 μL cDNA from each sample using a StepOnePlus Real-Time PCR System (Applied Biosystems, USA) and the SYBR Green system with SYBR Pre-mix Ex-Taq II (Takara Bio Inc., Japan). The standard amplification protocol consisted of an initial denaturing step at 95°C for 30 s, followed by 45 cycles at 95°C for five seconds, 60°C for 30 s. Data were calculated from the calibration curve and normalized using a VviGAPDH expression curve (Katayama-Ikegami et al., 2016a). PCR was performed at least in duplicate on each sample of three replicates.
In the two trial years, berry diameter and weight were approximately 35 mm and 30 g for ‘Ruby Roman’ and 30 mm and 18 g for ‘Aki Queen’ at harvest (Fig. 1). The changes in TSS and TA during berry development were not different between the two cultivars. The véraison occurred generally when the TSS was around 8 °Brix and the TA started to reduce (vertical dashed line in Fig. 1). The fructose, glucose and sucrose contents indicated similar changes between the two cultivars, which decreased from the immature stage to the lowest levels at about one week before véraison, then increased. The glucose content around véraison in ‘Aki Queen’ seemed to be higher than in ‘Ruby Roman’ (Fig. 2). Anthocyanin accumulation in ‘Ruby Roman’ skin started at 3–5 days after véraison and continued around the harvest, while that in ‘Aki Queen’ started soon after véraison and gradually proceeded up to approximately 20 days after véraison.
Changes in berry diameter and weight, total soluble solids (Brix) and titratable acidity in berry pulp, and anthocyanin content in the berry skins of ‘Aki Queen’ and ‘Ruby Roman’. Error bars represent SE of the mean in 2014 (n = 3) and 2015 (n = 5) (five berries per replication in both years). Dashed lines indicate the date of véraison. Note that the sample for 2014 is the same as that previously published for anthocyanin accumulation (Katayama-Ikegami et al., 2017).
Changes in sugar content in the berry skins of ‘Aki Queen’ and ‘Ruby Roman’. Error bars represent the SE of the mean in 2014 (n = 3) and 2015 (n = 5). Arrows indicate the date of véraison.
Endogenous ABA contents in both cultivars (Fig. 3) decreased during the immature berry stage until they reached their lowest levels at approximately one week before véraison, and then increased. Interestingly, in ‘Aki Queen’, ABA content stopped increasing on day five (2014) or six (2015) after véraison, and then decreased, whereas in ‘Ruby Roman’, it increased continuously up to 23 days (65 DAFB in 2014) or 13 days (58 DAFB in 2015) after véraison. The ABA content in ‘Ruby Roman’ was four times higher than that of ‘Aki Queen’ at 60–70 DAFB. The DPA content, a catabolite of ABA, was high in immature berries, decreased until véraison and could not be detected after véraison. The ABA-GE content, an inactive form of ABA, was slightly reduced from immature berries and increased after véraison, similar to ABA. ABA-GE content was inconsistent in the two-year trials in ‘Ruby Roman’; it was higher than ABA after 58 DAFB in 2014, but lower than that from véraison in 2015. The total content of ABA metabolites in both cultivars was at the lowest level just before véraison. It continuously increased after véraison in ‘Ruby Roman’, but did not do so in ‘Aki Queen’ (Fig. 3). As for IAA and its metabolites (Fig. 4), the total contents of IAA metabolites were also at the lowest level around véraison in both cultivars. The content of IAA-Asp, an inactive form of IAA, increased from véraison in both cultivars, and the increase was more significant in ‘Ruby Roman’ than in ‘Aki Queen’. In both cultivars, the total cytokinin content (Fig. 5) decreased from the immature stage, reached the lowest level around one week to 10 days before véraison, and then increased. The iP and tZ contents, two active cytokinins, were all observed to increase during the mature stage, especially for iP, for which the content in ‘Aki Queen’ was twice that of ‘Ruby Roman’.
Changes in ABA and its metabolites contents in the berry skins of ‘Aki Queen’ and ‘Ruby Roman’. Error bars represent SE of the mean in 2014 (n = 3) and 2015 (n = 5). Arrows indicate the date of véraison.
Changes in IAA and its metabolites contents in the berry skins of ‘Aki Queen’ and ‘Ruby Roman’ in 2014 (n = 3) and 2015 (n = 5). Arrows indicate the date of véraison.
Changes in cytokinins and their metabolites content in the berry skins of ‘Aki Queen’ and ‘Ruby Roman’ in 2014 (n = 3) and 2015 (n = 5). Arrows indicate the date of véraison.
The expressions of VviNCED3 and VviNCED2 were high in the immature berries (23 DAFB) in both cultivars in 2014, then decreased with berry development before véraison. However, in ‘Ruby Roman’, the expression of VviNCED3 increased again after véraison and was maintained at a relatively high level until around 51 DAFB, while that in ‘Aki Queen’ was maintained at a low level after 45 DAFB (Fig. 6). In 2015, the expressions of VviNCEDs at 25 and 27 DAFB in both cultivars were lower than those in 2014. In ‘Aki Queen’, the expression of VviNCED3 tended to increase just before véraison (38 DAFB) and then decreased, and was hard to detect after 46 DAFB (six days after véraison). However, in ‘Ruby Roman’, it tended to increase after véraison (48DAFB) and was maintained at a relatively high level until 63 DAFB (18 days after véraison). The expression of VviABABG1, which is associated with the release of free (active form) ABA from ABA-GE, gradually increased from véraison to the harvest stage in both cultivars. The expression level was lower in ‘Aki Queen’ at the late mature stage in 2014, compared to the other cultivars. As for VviABAGT, which is thought to encode glucosyltransferases and produce the inactive form of ABA, ABA-GE, the expression level was different between the two-year’s trials; the level in 2014 was higher than that in 2015 in both cultivars. The expression of VviCYP707A1 and VviCYP707A4, which are thought to be ABA catabolism genes, was high at the immature stage and decreased before véraison. The expression of VviCYP707A1 increased again around véraison in ‘Ruby Roman’, but not in ‘Aki Queen’, and was detected in ‘Ruby Roman’ at a relatively higher level than that in ‘Aki Queen’. There was no noticeable difference in the expression of VviABF2, a responsive ABA gene, between the two cultivars, although it appeared to remain relatively higher in ‘Ruby Roman’ than in ‘Aki Queen’ after véraison especially in 2014.
Changes in gene expression involved in ABA metabolism in the berry skins of ‘Aki Queen’ and ‘Ruby Roman’. Error bars represent SE of the mean in 2014 (n = 3) and 2015 (n = 3). Dashed lines indicate the date of véraison.
In cultivation practice, the problem of poor coloring in ‘Aki Queen’ and its parent ‘Kyoho’ is usually significant, especially under high temperatures, while it is not very serious in ‘Ruby Roman’, a seedling of ‘Fujiminori’. ‘Aki Queen’ and ‘Ruby Roman’ have the same haplotypes at the coloring locus, and their berries express red skin. However, the difference in color development between the two cultivars may indicate another genetic basis in addition to the coloring locus. In this study, the three endogenous plant hormones (ABA, auxin [IAA], and cytokinin), and their metabolites were compared with the two cultivars to characterize their functions in coloration at the late mature stage. Some differences in the number of metabolites, such as ABA, IAA-Asp, and iP were detected between the two cultivars (Figs. 3, 4, and 5).
The endogenous ABA content at the late mature stage in ‘Ruby Roman’ was higher than that in ‘Aki Queen’ in the two-year’s trials (Fig. 3) and this may be associated with the good coloration in ‘Ruby Roman’. In previous studies, the accumulation pattern of endogenous ABA in the berry skin was not affected by different cultivation methods, i.e., each shoot bears one cluster, or three shoots bear one cluster in ‘Ruby Roman’, and long cane pruning or short cane pruning in ‘Aki Queen’ (unpublished). Also, we reported that the ABA content in ‘Ruby Roman’ was almost the same in 2016 and 2017 (Gao-Takai et al., 2019). Therefore, the difference in the endogenous ABA level is not likely dependent on the cultivation method or environmental factors, but rather on the cultivar’s features. The high level of DPA in immature berries observed in both cultivars in this study (Fig. 3) was previously reported in ‘Shiraz’, ‘Merlot’, and ‘Muscat Hamburg’ berries (Böttcher et al., 2013; Owen et al., 2009; Sun et al., 2010). The high expression of VviNCEDs and VviCYP707As, and DPA content in the immature stage may indicate that active biosynthesis and catabolization of ABA simultaneously occurred during the early stage of berry development. Castellarin et al. (2016) mentioned that the initial increases in ABA at véraison may largely result from decreased catabolism in 8' hydroxylation. However, in this study, the expression of VviCYP707As in ‘Ruby Roman’ was higher than those in ‘Aki Queen’ after véraison, although the ABA content was higher in ‘Ruby Roman’ than in ‘Aki Queen’. Alternatively, the higher expression of VviNCED3 in ‘Ruby Roman’ until around 60 DAF (Fig. 6) may partly account for the higher ABA in this cultivar at the late mature stage. Possible reasons for the high level of ABA metabolites in ‘Ruby Roman’ after 60 DAFB are; i) the enzyme for ABA biosynthesis remaining active in berry skins during the late mature stage, and ABA accumulation from immature stage and that is not easily degraded ii) the translocation of ABA from other organs, and iii) other VviNCEDs, such as VviNCED5 or VviNCED6 being involved in ABA biosynthesis in grape berries as reported by Pilati et al. (2017) and Cramer et al. (2020). Additionally, VviABAGT and VviABABG1 may contribute to maintaining the amount of ABA at a constant level each year during the mature stage. The difference in the expression of VviABAGT between the two years (Fig. 6) may have been affected by the environment. The ambient temperature during the berry development period in 2014 was higher than that in 2015, resulting in elevated expression of VviABAGT and accumulation of inactive ABA-GE.
VviABABG has been shown to act as a functional enzyme in ABA metabolism (Sun et al., 2015). However, the functions of other enzymes possibly involved in ABA metabolism, encoded by homologous genes of other plants such as Arabidopsis, including VviCYP707As and VviNCEDs, have not yet been elucidated. Therefore, it cannot yet be said that these genes are involved in the control of the ABA level. Further analysis is required for functional characterization of the enzymes encoded by these genes and ABA transport to clarify the different ABA accumulation patterns in the late stage of maturation of these cultivars.
Endogenous IAA, thought to be an inhibitor of berry maturation, decreased before véraison. Meanwhile, inactive IAA-Asp increased during berry maturation (Böttcher et al., 2010; Gouthu and Deluc, 2015). Active auxin is inactivated by IAA-amido synthetase, known as GH3-1, producing IAA-Asp from IAA (Böttcher et al., 2010). The content of IAA-Asp increased after véraison in both cultivars, and the final content was higher in ‘Ruby Roman’ (Fig. 4). These results were consistent with our previous study (Gao-Takai et al., 2019). Although the content of IAA remained low after véraison, the increase in IAA-Asp indicated that the biosynthesis and catabolization (inactivation) of IAA may occur simultaneously during maturation. Another possibility is that IAA-Asp (or IAA) may be transported to berries from other organs.
It has been proposed that iP, an active cytokinin, affects the accumulation of sugars by maintaining sink strength in ripening berries that is related to the expansion driven growth after véraison (Böttcher et al., 2015). In this study, the iP content started to increase a few days before véraison and continued until harvest. The iP content in ‘Ruby Roman’ was two times lower than that in ‘Aki Queen’ around 70 DAFB (Fig. 5). The changes in ABA, IAA-Asp, and iP content during berry development were different between the two cultivars. Several reports have described the hormonal interactions. Griesser et al. (2020) reported that they detected a high content of ABA-GE, and low IAA-Asp and iP contents in shriveling disorder berries that were artificially induced by exogenous application of ACC (aminocyclopropene-1-carboxylic acid). Li et al. (2021) reported that exogenous ABA treatment at véraison reduced the IAA and increased the iP content, and mentioned a close relationship between iP and berry enlargement. In our study, however, berry enlargement of ‘Ruby Roman’ was still ongoing at the late stage of maturation, while iP content was lower than of ‘Aki Queen’. The results suggested that there is some interplay between these phytohormones in terms of fruit ripening at the later stage of maturation. Further analysis is needed to clarify the interaction in the berry maturation process. In subsequent studies, transcriptomic analysis, including IAA inactivation and response, and iP biosynthesis, may reveal the reason for the different accumulation levels of phytohormones or their metabolites between the two cultivars and provide some information on berry maturation.
In conclusion, the coloration pattern and contents of endogenous ABA, IAA, and cytokinins in two red hybrid grape cultivars, which had the same haplotypes at the coloring locus was investigated. The results showed that the accumulation pattern of anthocyanins in the two cultivar skins were different. Also, the phytohormone contents at different developmental stages were not similar. Further clarification of the traits found in ‘Ruby Roman’ may be useful in breeding grapes and for a deeper understanding of grape berry ripening in the future.
We thank Mariko Esaki and the other technicians of Experimental Farm of Ishikawa Prefectural University, for their assistance in experimentation and cultivation.
