HortJ

Three rose varieties, ‘Meivildo’, ‘Meikatana’, and ‘Korcut0122’ were grown using an “arching” method for three years. The relationship between temperature and light intensity, and the yield and quality of cut flowers, were analyzed. Flowering flushes were observed 18 times in ‘Meivildo’ and ‘Meikatana’ and 16 times in ‘Korcut0122’ during the experimental period. In three varieties, significant negative linear regressions between the interval of flowering flush (growth period, GP) and the mean temperature per GP were observed. Significant positive correlations and linear regression were observed between the number of cut flowers per plant and the mean temperature in ‘Meivildo’ and ‘Meikatana’, and the total light integral per GP (TLI) in ‘Korcut0122’. In three varieties, significant positive correlations and linear regressions were observed between the total cut flower weight per plant, and the mean daily light integral per GP (DLI) and TLI. Highly significant positive correlations and linear regressions were observed between the daily gain in flower weight (DGW) of cut flowers per plant (the total cut flower weight divided by the number of days of GP) and the mean DLI in all three varieties. In ‘Meivildo’ and ‘Meikatana’, cut flower weight per stem had significant negative correlations and linear regression with mean temperature and positive ones with TLI, while ‘Korcut0122’ showed no significant correlation with the three environmental factors. Significant positive correlations and linear regressions existed between the specific cut flower weight (the cut flower weight per stem length) and TLI in all three varieties, and negative ones existed between the specific cut flower weight and mean temperature in ‘Meivildo’ and ‘Meikatana’. The relationship between the results in this experiment and previous reports on the relation between the environment and cut flower yield quality are discussed. Finally, we present the significance of the method used in this experiment for 1) prediction of flowering and shipping of cut flowers, 2) evaluation of differences in characteristics among the rose varieties, and 3) contribution to the development of a growth model.

Isolation, purification and identification of anthocyanins and flavonols were carried out on flowers of Ranunculus cultivars. Three anthocyanins and 11 flavonols were characterized by chemical and spectroscopic techniques. The anthocyanins were identified as cyanidin 3-O-sambubioside, cyanidin 3-O-(6''-malonylsambubioside) and delphinidin 3-O-(6''-malonylsambubioside). The flavonols were identified as 3-O-glucosides and 3-O-sophorosides of kaempferol and quercetin, and their acylated compounds with malonic acid. Flower colors were divided into six groups, Red-Purple, White, Yellow-Orange, Orange, Red, and Violet groups using the Royal Horticultural Society Colour Chart. The absorption maxima of buffer solutions containing anthocyanins and flavonols isolated in this study were measured to understand the effect of intermolecular copigmentation between these compounds on flower color. The results showed that by addition of 3-O-(6''-malonylglucoside) of kaempferol or quercetin, the absorption maximum of cyanidin 3-O-(6''-malonylsambubioside) or delphinidin 3-O-(6''-malonylsambubioside) shifted bathochromically and exhibited a closer absorption maximum to fresh flower petals than anthocyanin alone. This indicates that the intermolecular copigment effect between anthocyanins and flavonols is responsible for the flower color expression in Ranunculus cultivars.

Treatment with calcium chloride (CaCl₂) is known to suppress the occurrence of flower stem bending and extend the vase life of cut gerbera. To clarify whether vase life extension by CaCl₂ is improved by combined treatment with gibberellin A₃ (GA₃), the effect of treatment with 50 mg·L⁻¹ GA₃, 5 g·L⁻¹ CaCl₂ or in combination on the vase life of the cut gerbera ʻMinouʼ was investigated. To inhibit bacterial proliferation, which is known to shorten vase life, an isothiazoline antimicrobial compound was included in the vase solution. Treatment with GA₃ alone delayed the opening of tubular florets and increased the area of unopen florets, but stem elongation which led to stem bending shortened vase life. Treatment with GA₃ in combination with CaCl₂ suppressed the occurrence of stem bending. Combined treatment with GA₃ and CaCl₂ extended the vase life of cut gerbera more than treatment with CaCl₂ alone. To clarify whether GA₃ delays petal senescence, the effect of GA₃ at 10 and 50 mg·L⁻¹ on petal senescence was investigated using shortened stems. GA₃ at both concentrations significantly delayed petal senescence. Combined treatment with GA₃ and CaCl₂ also significantly extended the vase life of the cut gerbera ʻKimseyʼ and ʻSandyʼ. It was concluded that combined treatment with GA₃ and CaCl₂ is a suitable treatment for extending the vase life of cut gerbera.

Anthocyanins are ubiquitously accumulated in diverse plant species and play crucial roles in plant development. In addition, anthocyanin pigmentation is associated with significant characteristics in the flowers and fruits of horticultural products. Notably, anthocyanin biosynthesis and storage are known to be affected by environmental factors. High ambient temperatures often suppress anthocyanin accumulation in flowers and fruits, raising concerns regarding the increase in atmospheric temperatures caused by global warming. Therefore, a comprehensive understanding of the mechanisms underlying the effects of high ambient temperatures on the regulation of anthocyanin biosynthesis and storage is necessary to maintain pigment quality and quantity of the products. In this review, we provide comprehensive information on the role of high-temperature-related signaling pathways in the regulation of anthocyanin biosynthesis. The expression of genes involved in anthocyanin biosynthesis is mainly regulated by R2R3-MYB activators, R2R3-MYB repressors, and R3-MYB negative regulators. The expression levels of R2R3-MYB activators decrease under high-temperature conditions, as observed in many flowers and fruits. The upregulation of R2R3-MYB repressors and R3-MYB negative regulators has also been demonstrated in some plant species under high-temperature conditions. The high-temperature-related signaling pathways have been evaluated mainly in the vegetative organs of Arabidopsis and apple fruits. In these organs, light strongly influences anthocyanin biosynthesis in addition to ambient temperatures. The CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1)-ELONGATED HYPOCOTYL 5 (HY5) module and B-box proteins upregulate the R2R3-MYB activators under light conditions, while they downregulate the R2R3-MYB activators under high-temperature conditions. However, the pathways that transduce high-temperature signals in flowers are poorly understood. Unlike in fruits and vegetative organs, light exerts relatively small effects on anthocyanin pigmentation in flowers, suggesting that the COP1-HY5 module-independent pathway could be responsible for the regulation of R2R3-MYB regulators in many flowers. Further research to clarify the related signaling pathways in flowers is needed to find solutions to overcome the problem of color fading caused by high ambient temperatures. In addition, exceptional cases have been reported in which high temperatures do not inhibit or enhance the anthocyanin pigmentation of flowers. Such species can prove helpful in elucidating the mechanisms underlying temperature-mediated regulation of anthocyanin pigmentation and as parental materials for crossbreeding.

In the most popular fragrant rose cultivar in Japan, ‘Yves Piaget’, the petal edges are frequently malformed, curving toward the adaxial side. These malformed petals prevent normal flowering and weaken the flower fragrance, which significantly decreases the quality of this cultivar and increases financial losses of cut flowers. We refer to such malformed flowers as ‘incurved flowers’. It has been reported that jasmonic acid (JA) affects petal growth. Therefore, we attempted to control the number of incurved flowers by applying exogenous JA, methyl jasmonate (MeJA), during flower development before harvest. Two types of spray treatment were applied to the flower buds before flower opening; (1) 100 μM MeJA or (2) deionized water as a control. The 100 μM MeJA spray treatment before harvest reduced the incurved flower rate, with fewer incurved petals, and resulted in a significantly larger maximum flower diameter and longer stamen length. In addition, the 100 μM MeJA spray treatment before harvest tended to increase the number of days from the commercial harvest stage to full bloom and also significantly increased the maximum flower diameter of fully-bloomed flowers. We also analyzed the endogenous phytohormone content in the petals of normal and incurved flowers at each flower developmental stage. The results showed that at the beginning of the flower opening stage the petals of incurved flowers had higher indoleacetic acid (IAA) content and lower JA/jasmonoyl isoleucine (JA-Ile) content than those of normal flowers. In particular, the JA and JA-Ile contents in incurved petals were approximately one quarter of those in normal flowers. These results suggest that IAA, JA, and JA-Ile may be involved in the development of incurved flowers.

When cut gerbera flowers absorb water after dry transport, some cultivars often exhibit petal curling, a phenomenon known as “Ben-sori” in Japanese. This study showed that the occurrence rate differed among gerbera cultivars, with ‘Aloha’, ‘Prime Time’ and ‘Kimsey’ being categorized as sensitive cultivars, while ‘Pinta’ and ‘Vivid’ were insensitive. In ‘Aloha’, petal curling caused the abaxial length and adaxial width of epidermal cells to be significantly shorter than in normal petals. ‘Aloha’ flowers harvested at later developmental stages were less affected by petal curling compared with those harvested at earlier stages. The petal length and width increased sharply at stage 4 (anthesis), and the development ray florets finished at stage 6 (flowers with anthers visible in three outermost rings in disk florets). Therefore, cut gerbera flowers that still have petal elongation potential may exhibit increased occurrence of petal curling symptoms. Lower absorption temperatures accelerated petal curling, and the most severe symptoms were observed at 5°C. Interestingly, when cut flowers absorbed water at 15°C, no symptoms were detected. We propose two ways to prevent the occurrence of petal curling in cut gerbera flowers: first, harvest flowers of sensitive cultivars at later developmental stages when anthers are visible in the two or three outermost rings of disk florets and second, allow water absorption at around 15°C after dry transport. These prevention strategies can resolve issues associated with petal curling for both flower retailers and customers and will improve the quality of cut gerberas.

Malformed flowers similar to super-double-flowers were observed in potted ‘Cherie’ carnation (Dianthus caryophyllus L.) plants. In the malformed flower (mlf) lines, most flowers were malformed at 15°C, but not at 20°C. Thus, we hypothesized that the malformation was due to a mutation associated with morphological responses to temperature. In this study, RNA-sequencing analysis of young flower buds and whole-genome re-sequencing of leaves were performed using wild-type (WT) and mlf plants to identify malformation-related candidate genes. The RNA-sequencing analysis revealed 691 significant differentially expressed genes (DEGs) between WT flower buds at 15 or 20°C and mlf flower buds at 15°C. The Gene Ontology (GO) analysis indicated that metal ion binding, transmembrane transport, and anaphase-promoting complex enriched GO terms in mlf, whereas translation and ribosome enriched GO in terms of WT. The Kyoto Encyclopedia of Genes and Genomes analysis revealed an increase in the expression of 9-cis-epoxycarotenoid dioxygenase (NCED), Pyrabactin Resistance 1-Like (PYL), and Calmodulin (CAM), but a decrease in the expression of Histone H4, in mlf. The fragments per kilobase per million reads (FPKM) values were used to select candidate malformation-related DEGs. Transcription factor genes, including WUSCHEL (WUS) and STERILE APETALA, were upregulated in mlf, whereas PISTILLATA-like protein, MADS-box protein CMB2, and F-box UNUSUAL FLORAL ORGANS were downregulated. Heat Shock Cognate 70 kDa (HSC70) and Temperature-induced lipocalin-1 were upregulated in mlf, but genes encoding histones and ribosomal proteins were downregulated. Moreover, NCED1, PYL8 and 9, and cytokinin-related genes were upregulated in mlf. Using whole-genome re-sequencing data, sequence variants were detected in the upstream regions and exons of WUS, HSC70-1 and 2, CAM7, and ribosomal protein-encoding genes. Furthermore, examination of the F1 progeny derived from WT and mlf crosses with cultivars producing fertile pollen revealed a significant difference in the proportion of malformed flower phenotypes between WT and mlf regardless of temperature, suggesting that the malformed flower phenotypes of mlf can be inherited. Candidate genes associated with the temperature-dependent super-double-flower phenotypes were examined.

Dahlia (Dahlia variabilis) flower colors are diverse and are determined by the accumulation of flavonoids. Cultivars with dark red flowers accumulate more anthocyanins in their petals. Flower color changes such as color fading often occur in some cultivars. In this study, low minimum temperature regulated flower color fading and flavonoid synthesis in dahlia ‘Nessho’ were investigated. The pigment contents and expression levels of flavonoid biosynthesis genes were investigated in detail under several growing environments in which color fading occurs. Flavones accumulate more in color-faded orange flowers than in dark red ray florets. The expression analysis of the anthocyanin synthesis pathway genes indicated that the upregulation of flavone synthase (DvFNS) gene expression correlated with the high accumulation of flavones in color-faded petals. DvFNS expression was also detected in young leaves, and the expression level was higher in winter than in summer. Seasonal changes in DvFNS expression in young leaves significantly correlated with color fading in petals. The change in DvFNS expression in young unexpanded leaves of relatively high-sensitive plants was significantly higher than that of low-sensitive plants before and after treatment under inductive conditions. In conclusion, low-temperature-inducible changes in the flavonoid accumulation in petals was suggested to reflect a change in DvFNS expression occurring in the meristem prior to flower bud formation. This temporal DvFNS expression in young unexpanded leaves of ‘Nessho’ dahlia could be an insight for the selection and breeding of non-color fading plants.