Prunus fruit tree species exhibit S-ribonuclease (S-RNase)-based gametophytic self-incompatibility (GSI). This system is also present in the families Plantaginaceae and Solanaceae and the tribe Maleae of the family Rosaceae. In S-RNase-based GSI, self/nonself-recognition between the pistil and pollen is controlled by the pistil S determinant S-ribonuclease gene (S-RNase) and the pollen S determinant F-box gene(s). Accumulated evidence indicates the Prunus pollen S locus contains a single F-box gene, while that of other plants consists of multiple F-box genes. The pollen S F-box genes are called S haplotype-specific F-box (SFB), S-locus F-box brothers (SFBB), and S-locus F-box (SLF) in Prunus, Maleae, and Solanaceae species, respectively. The consequences of pollen S gene mutations and heterodiallelic pollen production differ between Prunus species and other plants, suggesting there are different pollen S functions during self/nonself-recognition. The GSI systems of Prunus and other plants are believed to include the ubiquitin proteasome system for protein degradation. However, Prunus SFB is assumed to facilitate the S-RNase cytotoxic effects during self-recognition, while SLFs and SFBBs are thought to function collaboratively during nonself-recognition to avoid S-RNase cytotoxicity. This review summarizes the distinct features of the S-RNase-based GSI mechanism in Prunus species, with special references to the recent advances in our understanding of S-RNase-based GSI.

Japanese persimmon ‘Totsutanenashi’ (TTN) is a spontaneous small fruit mutant derived from ‘Hiratanenashi’ (HTN). To characterize the small fruit phenotype of TTN, we carried out a histological analysis, plant growth regulator treatments, and a transcriptome analysis using Illumina sequencing. The parenchymal cell number in TTN fruit was significantly less than in HTN fruit, and the parenchymal cell size in TTN fruit was also significantly smaller than that in HTN fruit at the later growing stage. However, the fruit size of TTN recovered by cytokinin treatments [50 or 200 ppm N-(2-chloro-4-pyridyl)-N′-phenylurea]. Thus, diminished cytokinin activity in TTN fruits may lead to less cell division in the early growing stage and less cell enlargement in the later growing stage. A large-scale transcriptome analysis was conducted using Illumina sequencing to determine the differences in gene expressions between TTN and HTN fruits. Illumina sequences were processed, resulting in 21,662,190 read pairs from HTN and 23,195,203 read pairs from TTN. After assembly of all sequences from HTN and TTN, 118,985 contigs (referred to as unigenes hereafter) ranging from 201 to 11,954 bases, with an average length of 915 bases, were obtained. Digital expression analyses revealed that the expression levels of 164 unigenes were significantly higher in HTN than in TTN, while the expression levels of 265 unigenes were significantly higher in TTN. A parametric analysis of gene set enrichment using the expression levels of unigenes showed that the biological process Gene Ontology categories of “cell cycle” and “regulation of cell cycle” were significantly down-regulated in TTN. The cell cycle-related differentially expressed genes included D3-type cyclin and Mitogen-Activated Protein Kinase Kinase Kinase. Based on the obtained results, the possible involvement of cell cycle-related genes in regulating the small fruit phenotype in TTN is discussed.

We aimed to characterize the inheritance of HEPX (heptachlor exo-epoxide) uptake ability in summer squash (Cucurbita pepo L.). Crosses between ‘Patty Green’, a cultivar that cannot take up HEPX, and ‘Toyohira 2’, a cultivar that can take up high levels of HEPX, were evaluated in this study. The pattern of inheritance for F₁ progeny indicated partial dominance since the measured amount of accumulated HEPX was close to that in ‘Toyohira 2’. In the F₂ generation, plants segregated into those that did not take up HEPX and those that did take up HEPX at approximately a ratio of 1:5. This segregation pattern was similar to that for the inhibiting gene (dominant suppression of a dominant allele) in the dihybrid; the expected segregation ratio of 3:13 was supported by a chi-square test. Indeed, the I gene suppresses the N gene (non-transporting gene), but the i gene cannot suppress N (II or Ii suppression of NN or Nn). In this case, the genotype of ‘Patty Green’ is proposed to be iiNN and that of ‘Toyohira 2’ to be IInn. Additionally, we proposed three gene models to explain quantitative variation in HEPX transport. The genotypes of ‘Patty Green’ and ‘Toyohira 2’ are presumed to be ABC and abc, respectively. HEPX cannot be taken up unless two or more different dominant genes are present in a plant. Thus, the genotypes can be divided into HEPX non-transporting (Abc:aBc:abC:abc) and HEPX transporting (ABC:ABc:AbC:aBC) classes. Two or three different dominant genes, irrespective of the gene combination, work together to take up HEPX. In this model, the expected segregation ratio of 10 HEPX non-transporting:54 HEPX transporting was supported by a chi-square test. This pattern of inheritance was also supported by the segregation ratio of self-propagated plants (BC₁-s) derived from a backcross. Although both of these inheritance models were correct phenotypically, the function of these genes should be clarified to explain the quantitative differences in HEPX uptake.

This study analyzes the first large-scale asparagus experiment in Japan to examine the productive differences between male and female plants using the rootstock-planting forcing culture technique. This technique has recently been developed in Japan and uses dug-up rootstocks for one-season harvests during the off-crop season. As larger spears and early sprouting are especially favored in this culture for higher yield, it is important to clarify and evaluate the productive traits of the male and female plants. We conducted collaborative research among eight institutes from Hokkaido to Kyushu to examine plants grown at different cultivation sites. There were two digging-up months and different low-temperature backgrounds. Plant rootstocks sourced from the eight different sites used in the experiment were cultured in an abandoned tunnel in Nagano Prefecture, Japan, in a large area with uniform temperature and high humidity throughout the year, and their white spears were harvested. The results of this study show that the female plants had a significantly higher rootstock weight, weight per spear per plant, and weight per early spear per plant, whereas the male plants had a significantly higher total spear number per plant, early spear number per plant, and significantly fewer days to first harvest. No significant differences were observed in soluble solid contents of roots, total spear weight per plant, or early spear weight per plant. It seems that male plants have a tendency to sprout earlier than female plants in response to reduced accumulated low temperature hours, and also to produce a higher total spear number per rootstock weight and total spear weight per rootstock weight. The ranges of most of the productive traits analyzed in this study completely overlapped between the sexes. However, female plants showed higher variation in weight per spear per plant and weight per early spear per plant.

Flowers of wild Camellia japonica L. are usually red, but infrequently the flowering trees of this species may have purple flowers. Such purple flowers are a highly desired horticultural property, but the color expression is not fixed. Even if a tree has splendid purple flowers in the spring, they may revert back to the red color of a wild C. japonica flower the next year. We investigated the factors responsible for the purple coloration using red, purplish-red, and purple flowers of the cultivar ‘Sennen-fujimurasaki’. The epidermal cells of purplish-red and purple petals were composed of both red and purple colored cells, whereas those of the red petals were uniformly red. Many of the purple cells contained blue-black granules. Cyanidin 3-glucoside and cyanidin 3-p-coumaroylglucoside, major pigments of red-flowered C. japonica, were the major anthocyanins of ‘Sennen-fujimurasaki’. The anthocyanin contents were not noticeably different among flowers of these different colors. Potential co-pigments such as flavones, flavonols, and cinnamic acid derivatives were negligibly detected. No significant differences were found in the Ca, Mg, Mn, Fe, Cu, and Zn ion contents or in the pH of petal homogenates; however, a significant difference was found in the Al ion content. The Al content of the purplish-red and the purple petals was 4–10 times higher and 14–21 times higher than that of red petals, respectively. A cyanidin 3-glucoside solution prepared at pH 4.8 was pale red with no precipitates. When Al ions were added to the cyanidin 3-glucoside solution, the solution became purple and produced blue-black precipitates similar to the blue-black granules observed in the purple colored cells. Differences in the spectral properties of the petals from those of the prepared solution could be caused by the co-occurrence of red and purple cells and may be influenced by other Al-chelating compounds and/or substantial Al concentrations in the vacuoles. We conclude that the purple flower color of ‘Sennen-fujimurasaki’ is generated by chelation of Al ions by anthocyanins. In other purple-flowered C. japonica exhibiting unstable flower coloration similar to that of ‘Sennen-fujimurasaki’, Al-anthocyanin chelation is also likely associated with the purple flower color.

The black flower color of dahlias (Dahlia variabilis) has been suggested to be attributed to a high accumulation of cyanidin (Cy)-based anthocyanins. A possible explanation for this effect is that Cy-based anthocyanins in dahlias contribute more to the black flower color than pelargonidin (Pg)-based anthocyanins by lowering petal lightness (L*) and chroma (C*), but no obvious evidence has been reported. In this study, four major anthocyanins accumulated in dahlia petals, 3,5-diglucoside (3,5diG) and 3-(6''-malonylglucoside)-5-glucoside (3MG5G) of Pg and Cy, were purified and their colors were evaluated in vitro at various pHs (3.0, 4.0, 4.5, 5.0, 5.5, 6.0, or 7.0) and various concentrations (0.25, 0.5, 1.0, 2.0, or 3.0 mg·mL⁻¹ at pH 5.0 or pH 3.0). The color of solution of purified anthocyanins varied depending on pH. At pH 5.0, which is approximately the same as pH of dahlia petals, and at pH 3.0, at which anthocyanins are relatively stable, the L* and C* of Cy 3,5diG were similar to or higher than those of Pg 3,5diG, suggesting that Cy 3,5diG did not contribute more to the black flower coloring than Pg 3,5diG. On the other hand, the L* and C* of Cy 3MG5G were significantly lower than those of Pg 3MG5G, particularly above 2.0 mg·mL⁻¹, suggesting that Cy 3MG5G contributed more than Pg 3MG5G. A similar tendency was observed in the color measurement of mixed anthocyanins in various proportion of Pg and Cy. The L* and C* of Pg 3MG5G were much higher than those of the other three anthocyanins; therefore, its color was considered to be the farthest from black among the four anthocyanins. The accumulated amount of 3MG5G-type anthocyanins was much higher than that of 3,5diG-type anthocyanins in all nine cultivars, although the proportion of Pg- and Cy-based anthocyanins varied among the cultivars. Considering these results, it was suggested that because 3MG5G-type anthocyanins predominantly accumulate in petals, and Cy 3MG5G has a significantly higher contribution to lowering L* and C* than Pg 3MG5G, the high accumulation of Cy-based anthocyanins is critical for the black flower coloring of dahlias. The contribution of each anthocyanin is considered to depend on the structure; therefore, identifying the anthocyanin with the highest contribution to lowering L* and C* may enable the production of black flowers in various species through the high accumulation of the anthocyanin in petals.

We isolated a torenia mutant “Begonia” from selfed progeny of the mutable line “Flecked,” in which the ventral petal of the flower was converted into dorsal petal. In normal-type (NT) flowers, dorsal petals were pale violet and limbs of lateral and ventral petals were violet, whereas the ventral petal had a yellow nectar guide. In contrast, the ventral petal of mutant-type (MT) flowers changed to pale violet, and the nectar guide disappeared. These altered pigmentation patterns were observed from the early stage of corolla pigmentation. Expression analyses of the floral symmetry genes CYCLOIDEA (CYC), RADIALIS (RAD), and DIVARICATA (DIV) showed that TfCYC1, TfCYC2, TfCYC3, and TfRAD1 were mainly expressed in dorsal petals of NT flowers, but in the mutant, these genes were expressed in the ventral petal similar to dorsal ones. These results suggest that conversion of ventral to dorsal petal in the “Begonia” mutant is caused by high expression of TfCYC1, TfCYC2, TfCYC3, and TfRAD1 in the ventral petal, comparable to their expression in dorsal petals.

To assess the growth and flowering of the Doritaenopsis orchid in alternative substrates, Doritaenopsis Queen Beer ‘Mantefon’ was grown for 15 months in four different substrates; a commercial 100% Chilean sphagnum moss (S), peat moss (P), medium-grade Douglas fir bark mixed with P with a 3:7 ratio (v/v) (BP), and S and P mixes (SP) with a 4:6 ratio (v/v). Physical (porosity and water holding capacity) and chemical (pH and EC) properties of the four substrates were investigated. SP substrate had significantly higher substrate volumetric water content (VWC) than the other three substrates only for the first 3 days after fertigation, and only the BP substrate maintained lower air space than the other substrates. Although there was no relevant growth responses to VWC and air space changes, a better growth in shoots and fastened flowering of Doritaenopsis ‘Mantefon’ occurred in plants grown in the P substrate, which could be attributed to providing better contact of terrestrial roots to the substrate enabling enough water and nutrient supply, along with a proper pH range of 6.15. At 15 months after transplanting, plants grown in the P and BP substrates had larger leaves and a greater shoot dry weight than the plants grown in the S and SP substrates. Plants grown in the P substrate produced 2.75 flower spikes, whereas the plants grown in the S, BP, and SP substrates produced 2.00 to 2.33 flower spikes. Plants grown in the P, BP, S, and SP substrates produced a third flower spike, being 67%, 33%, 17%, and 8%, respectively. There was no significant difference in the total number of flowers, while the total numbers of buds were 32.3, 23.4, 23.0, and 19.7 in plants grown in the P, S, BP, and SP substrates, respectively. Time to visible flower spike was shortened in plants grown in the P substrate compared to the plants grown in other substrates. With these results, using alternative substrates including peat moss for Doritaenopsis cultivation, growers may be able to promote leaf growth and flower spike induction with lower expenses on substrate costs, resulting in a high quality production of Doritaenopsis ‘Mantefon’ with more profit.

Limonium bellidifolium (2n = 2x = 18), a perennial statice belonging to the family Plumbaginaceae, is cultivated as a garden plant or for cut flowers and is an important breeding material for the production of hybrid cultivars in the genus. In this study, chromosome doubling in L. bellidifolium was attempted to increase the variability in horticultural traits. Seeds of this species were treated with an antimitotic agent, colchicine, at different concentrations and exposure periods. The treated seeds were sown in soil in a cell tray and the seedlings were grown in a greenhouse. More than 50% of the seedlings treated with colchicine for 24 or 48 h, irrespective of the concentration, survived for 4 months after treatment. Most of the seedlings treated for 72 h at any concentration showed very poor growth and abnormal thickening of the hypocotyl, and ultimately died. The surviving seedlings were grown in 9-cm pots. Flow cytometry analysis of leaf tissues showed that 2.5%–5% of plants that received 0.05% colchicine for 72 h, 0.25% colchicine for 24 h, 0.25% colchicine for 48 h, or 0.5% colchicine for 48 h were tetraploid (4x) or mixoploid (2x + 4x). The highest frequencies of tetraploids and mixoploids occurred following treatment with 0.05% colchicine for 72 h. These results showed that colchicine treatment of seeds is effective for chromosome doubling in L. bellidifolium. After 3 years of cultivation, the morphological characteristics of diploid and tetraploid L. bellidifolium plants at the flowering stage were investigated. The stomatal density was lower in all investigated tetraploid and mixoploid plants than in the control diploid plant. The stomatal length was 1.1- to 1.5-fold higher in all tetraploid and mixoploid plants than in the control. Tetraploid plants tended to have wider and thicker leaves than the control and also produced larger flowers.

In many Hydrangea cultivars, sepal color depends on soil conditions. The traditional concept is that different levels of absorption of aluminum ions from soil and its accumulation in sepal vacuoles changes Hydrangea sepal color. To investigate how sepal coloration can be stabilized, we examined the components that may contribute to color variability according to the traditional concept. Using 10 cultivars and lines with sepals of stable red or stable blue color plants or with sepals of variable color (red or purple) plants grown in acid soils and alkaline soils, we analyzed sepal pH and sepal contents of anthocyanin, aluminum ion, 5-O-caffeoylquinic acid, and 3-O-caffeoylquinic acid. Sepals of all cultivars became bluer when plants were grown in acid soil than when they were grown in alkaline soil, even if the change in stable color plants was milder than that of variable color plants. The same component changes probably happen in sepals of both stable and variable color plants in response to different soil conditions to cause the coloration change. When the two soil conditions were compared, a statistically significant difference was detected for delphinidin 3-glucoside, which is a major anthocyanin of Hydrangea, in the variable-color line ‘HH2’ and for 3-O-caffeoylquinic acid in the stable red line ‘HH19’, but not for any other compound examined, including aluminum ions. Although there is possibility that localization of aluminum ions in vacuoles of the colored cells changes, it is assumed that changes in contents of aluminum ion chelaters such as phosphoric acid affect the sepal color change in response to different soil conditions, as well as the coloration stability or variability. When cultivars were compared in terms of properties of sepal coloration, although contents of aluminum ions and 5-O-caffeoylquinic acid tended to be higher in stable blue cultivars than in other cultivars, these differences were not statistically significant. In agreement with previous reports, our data indicate that a lower content of 3-O-caffeoylquinic acid is essential for blue Hydrangea sepals.

To analyze hose-in-hose flowers of Kurume azaleas, floral morphologies and homeotic MADS genes were investigated in single and hose-in-hose cultivars. In floral morphological analysis, single flowers are comprised of four whorls of floral organs: sepals, petals, stamens, and carpels. Hose-in-hose flowers, in contrast, produced petaloid sepals instead of sepals in the first whorl. Based on molecular analysis, we isolated PISTILLATA (PI)/GLOBOSA (GLO) homologs in the hose-in-hose flower cultivar ‘Kirin’ and analyzed their expression in single flower and hose-in-hose flower cultivars. The mRNA sequences of two RoPI genes, RoPI-1 and RoPI-2, differed in terms of a 6 bp deletion. Based on genomic analysis, an insertion sequence was found in the second intron of RoPI-1 in hose-in-hose flowers. These RoPI genes were mainly expressed in the second and third whorls of single flowers, whereas these genes were expressed in all whorls of hose-in-hose flowers. These results suggest that the up-regulation of RoPI-1 expression contributed to the petaloid sepal formation of hose-in-hose flowers of Kurume azaleas.