To clarify a strong possibility of performing cross breeding between diploid (2x) and triploid (3x) apple cultivars, flowering and fruit bearing of 2x × 3x seedlings were compared with those of 3x × 2x and 2x × 2x. Rates of flowering and fruiting in seedlings, and number of fruits per fruiting tree, were highest for 2x × 2x and lowest for 3x × 2x. Ten years after sowing, the fruiting rate of seedlings was 49.5 to 65.8% for 2x × 3x, but only 10.9% for 3x × 2x. The trunk circumference of 2x × 3x seedlings was estimated as the circumference relative to the average circumference of 2x × 2x seedlings at 6 years after sowing. These values were used as a circumference index. The seedling fruiting rate and number of fruits per fruiting tree, 10 years after sowing, were highest in seedlings with an index of more than 75, and lowest in those with an index of less than 50. These results show that seedlings from 2x × 3x can be used in apple breeding, and that the trunk circumference index can probably be used as an indicator for judging and selecting at an early stage whether or not the seedlings will flower and bear many fruits. Seedlings from 3x × 2x are considered unsuitable for breeding new apple cultivars, based on a much lower fruiting rate and number of fruits per fruiting tree 9 to 10 years after sowing.
To elucidate the mechanism of the high level of β-cryptoxanthin (β-cry) accumulation in ‘Tamami,’ the relationship between carotenoid accumulation and the expression of carotenoid-related genes during fruit maturation was investigated in the juice sacs of ‘Tamami,’ a hybrid between ‘Kiyomi’ tangor (Citrus unshiu Marc. × Citrus sinensis Osbeck) and ‘Wilking’ mandarin (Citrus nobilis Lour. × Citrus deliciosa Ten.), and its parental varieties, ‘Kiyomi’ tangor and ‘Wilking’ mandarin. In mature fruit, ‘Tamami’ predominantly accumulated a high level of β-cry. ‘Kiyomi’ tangor also accumulated β-cry. However, the level of β-cry in ‘Kiyomi’ tangor was lower than that in ‘Tamami.’ ‘Wilking’ mandarin accumulated a high level of 9-cis-violaxanthin predominantly. To analyze the expression of carotenoid-related genes, cDNA fragments for their genes were cloned from the three varieties, and the TaqMan MGB probe and a set of primers were designed for the respective genes on the basis of the common sequence of cDNA fragments among the three varieties. In ‘Tamami’ and ‘Wilking’ mandarin, the expression of genes that produce β,β-xanthophylls (CitPSY, CitPDS, CitZDS, CitLCYb, CitHYb, and CitZEP) increased simultaneously during the massive accumulation of β,β-xanthophylls (β-cry, zeaxanthin, all-trans-violaxanthin, and 9-cis-violaxanthin). In addition, higher levels of upstream synthesis genes (CitPSY, CitPDS, CitZDS, and CitLCYb) and lower levels of downstream synthesis genes (CitHYb and CitZEP) were observed in ‘Tamami’ than in ‘Wilking’ mandarin. In ‘Kiyomi’ tangor, simultaneous increases in the expression of genes that produce β,β-xanthophylls were observed in the early maturation stage. During the β,β-xanthophyll accumulation, the gene expression of carotenoid cleavage dioxygenases (CitCCD1, CitNCED2, and CitNCED3) increased in the three varieties. The results suggest that the simultaneous increases in gene expression under a balance of high expression of upstream synthesis genes and low expression of downstream synthesis genes led to a high level of β-cry accumulation in the juice sacs of ‘Tamami.’
Proanthocyanidins, which are oligomers and polymers of flavan-3-ol units (e.g., (+)-catechin and (−)-epicatechin), are important components of grapes for red winemaking. Flavan-3-ols are biosynthesized by the catalysis of anthocyanidin reductase (ANR) and leucoanthocyanidin reductase (LAR). In this study, we investigated the effect of shading on proanthocyanidin biosynthesis in berries of Vitis vinifera ‘Cabernet Sauvignon’. Shading of the berries reduced the accumulation of proanthocyanidins and the transcription of ANR and LAR genes in the skins during berry development, while no significant effect was observed in the seeds. Because the proanthocyanidins significantly decreased in the skins and seeds of the control berries during ripening, the levels of proanthocyanidins were similar in the shaded and control berries at the harvest stage.
We characterized the pollen germination and longevity in durian (Durio zibethinus Murr.) under in vitro conditions and observed the morphological changes during anther dehiscence. Approximately 10 anthers aggregate on a filament; these merge with others at the base to form five phalanges in the flower. Anther dehiscence occurred at 19:00, at the same time as floral anthesis. Observation with a low-vacuum scanning electron microscope revealed pollen grains clinging to the anther even after the anther had dehisced. In vitro pollen germination was highest at a sucrose concentration of 10%. In the test of pollen germination on Brewbaker and Kwack (BK) medium, the germination rate was highest (59.1%). The germination rate was decreased (5.0% to 46.0%) when any of the minerals of B, Ca, Mg, and K was removed. The pollen germination rate at anthesis was 40.4 to 50.6% in four cultivars (‘Mon Thong’, ‘Chanee’, ‘Kradum Thong’, and ‘Phaung Manee’), and the rate was maintained at more than 40% until 24 h after anthesis and then decreased gradually. When pollen was stored under desiccating conditions with silica gel, pollen following 120-h storage could germinate after rehydration. Rehydration for 12 h achieved the best results, with 47.0% germination occurring after this rehydration period.
Some cultivars of apple (Malus × domestica Borkh.) show parthenocarpy. In these cultivars, the MdPISTILLATA (MdPI) gene, which is homologue of the PISTILLATA (PI) gene of Arabidopsis thaliana, does not function by the insertion of a retrotransposon into MdPI. MdPI is a class B floral organ identity gene belonging to the MADS-box gene family. When MdPI was overexpressed in Arabidopsis Columbia ecotype under the control of the cauliflower mosaic virus (CaMV) 35S promoter, the sepals showed petaloid changes. In the case of the pi-1 mutant of Arabidopsis Landsberg erecta, apple MdPI overexpression led the pi-1 mutant to recover normal petals and carpeloid stamens. In detailed observations with a scanning electron microscope, we observed that the filaments were also normally recovered. However, the anthers were not. We isolated the MdPI promoter from the apple cultivar ‘Jonathan’, and the uidA gene which encodes β-glucuronidase (GUS) was fused as a reporter gene. The MdPI promoter fused with GUS was designated p1MDPI.1G. Just petals and stamens of Arabidopsis plants transformed with p1MDPI.1G had GUS activity. These results indicated that the MdPI gene was related to the development of petals and stamens, and formed petals and filaments. Therefore, the MdPI gene had a function equal to PI, although the relation between MdPI and parthenocarpy in the apple is unknown.
This study investigated ploidy levels of endosperm and embryos in seeds of the hexaploid (2n = 6x = 90) Diospyros kaki ‘Fujiwaragosho’ to determine the possible origin of unusual ploidy levels observed in seedlings of this cultivar. Female flowers of ‘Fujiwaragosho’ were pollinated with sorted reduced (3x) and unreduced (6x) pollen grains of ‘Zenjimaru’ in 2004 and 2005. Embryo rescue culture was conducted with normally developing seeds that were excised from immature fruit harvested in August. Ploidy levels of the endosperm and plantlets from the embryos in the seeds were determined by flow cytometry. In some cases, chromosomes of root tip cells of the plantlets were also counted to determine ploidy levels of the embryos. It appeared that seeds obtained with reduced pollen pollination contained a normal hexaploid embryo and nonaploid (9x) endosperm, while those obtained with unreduced pollen pollination mostly contained a dodecaploid (12x) embryo and octadecaploid (18x) endosperm. These results indicated unreduced embryo sac formation in ‘Fujiwaragosho’. We discuss the possible cause of the occurrence of only nonaploid and octadecaploid endosperm, respectively, with reduced and unreduced pollen pollinations.
We investigated the effects of bottom-heat treatment (BHT) during low-air-temperature storage on the rooting and growth of squash cuttings after planting following storage. Rooting of cuttings was much improved with BHT temperatures ranging from 27 to 32°C, and the root fresh weight after planting increased linearly with increasing BHT duration from 0 to 24 h. Rooting during storage was observed 30 h after starting BHT, but was not observed at 26 h. BHT should end just before rooting begins to avoid the inhibition of root growth caused by root damage during planting; therefore, the optimum BHT duration is thought to be 26 to 30 h (approximately 1 day). To test the practicality of BHT in transplant production, we used cuttings obtained by grafting cucumber (Cucumis sativus L.) scions onto squash rootstock. The squash cuttings used for the rootstock were either exposed or unexposed to BHT (30°C) during storage at 9°C for 24 h, and were then grafted with the cucumber scions. One portion of the grafted cuttings was planted in growing medium immediately after grafting. Six days after planting, total and root fresh weights of the BHT cuttings were 1.3 and 4.0 times higher compared to those of the non-BHT cuttings, respectively. Another portion of the grafted cuttings was stored at an air temperature of 9°C for 7 days. The root-promoting effects of BHT were maintained during the low-temperature storage.
The present study was carried out to compare the differences in peroxide-scavenging metabolism between radish cultivars which are susceptible to internal browning (IB) colorization upon increased temperature and cultivars which are resistant to browning. The induction of IB in the susceptible cultivars was progressively intensified with high temperature treatment during the later growth period, resulting in significant increases of glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), L-phenylalanine ammonia-lyase (PAL), and polyphenol oxidase (PPO) at the central stele. Conversely, in the IB-resistant ones, neither the accumulation of IB nor induction of these enzymes occurred regardless of the treatment during this period. No correlation was found between the isothiocyanate (ITC) content and the development of IB. The ascorbic acid (AsA) content, however, was closely correlated with the development of IB. These results strongly suggest that intervarietal differences with respect to susceptibility to IB formation are closely correlated with differences in the polyphenol biosynthesis ability under high temperature conditions and largely dependent on AsA metabolism in the root.
A convenient method was devised for the fractionation of aliphatic polyamines (PAs), 1-aminocyclopropane-1-carboxylic acid (ACC), and their conjugated forms using a cation exchange resin, and applied to the floral organs of Hibiscus syriacus L. ‘Diana’. A batch-wise use of the cation exchange resin to the acid extracts of the Hibiscus flower effectively separated the ACC-conjugate from free ACC, free PAs, and PA-conjugates. Good recovery rates, showing over 90% for PAs and 76–97% for ACC, were obtained when known amounts of ACC and PAs were added to the tissue extract. The amounts of these cellular compounds were determined in the petal, sepal, ovary, and style with stigma (+ stamen) collected at two different stages (flower opening and flower senescence showing complete petal in-rolling). Both ACC and ACC-conjugate, which are generally associated with tissue senescence, were consistently detected in all organs even immediately after flower opening, but their concentrations, especially that of the ACC-conjugate in the ovary, greatly increased in the senescent flowers. As regards the free PA levels, a high concentration of spermidine was found in the ovary, and its level was maintained even when the petals wilted. PA-conjugates bound to small molecules decreased in the ovaries of senescent flowers, while the PA-conjugates bound to macromolecules remained very low in all organs at the two different flower stages. The present method seems applicable to a quantitative analysis of these physiologically important compounds in a variety of plant tissues, despite the fact that their extracts contain highly viscous materials that generally reduce the recovery rate of ACC.
We studied the effects of the type of leaf cuttings, 6-benzylaminopurine (BA) application, and the section position and orientation of leaf pieces on adventitious bud formation in leaf cuttings inserted in rockwool beds, using expanded young leaf blades of Begonia Tuberhybrida Group ‘Tenella’. In BA absence, 73% of whole leaf blades with petioles formed adventitious buds, whereas none of the 2 × 1.5 cm leaf pieces did at all. The percentages of surviving and adventitious bud formation of 2 × 1.5 cm leaf pieces without petioles were 47% and 0%, respectively. When these small leaf pieces were inserted in rockwool beds containing 0.25–2 ppm BA, the percentages of surviving and adventitious bud formation were 100% and 80%, respectively. In BA presence, the percentage of adventitious bud formation became lower from the base towards the tip of the leaf, and the leaf pieces at positions 2 cm away from the leaf bases did not form adventitious buds at all. When they were placed horizontally and vertically inverted, the percentages of adventitious bud formation were 60% and 80%, respectively.
Rosa multiflora ‘Matsushima No. 3’ shows tolerance to root rot disease caused by Pythium helicoides Drechsler. However, there has been no report on the tolerance mechanism of ‘Matsushima No. 3’. The infection process of Pythium in diseased plants was divided broadly into two stages, as early and later infection processes. This study focused on the early infection process: chemotaxis, attachment, and encystment of zoospores and germ tube germination on the root surface, in order to clarify the tolerance of ‘Matsushima No. 3’ in comparison with a susceptible rose. ‘Matsushima No. 3’ and R. ‘Fashion Parade’, which were estimated as showing tolerance and susceptibility to root rot disease in the field, respectively, were used as plant materials. Rooted cuttings of ‘Matsushima No. 3’ and ‘Fashion Parade’ were inoculated by zoospore suspension of P. helicoides, and root rot symptoms of these roses were evaluated at 7 days after inoculation. From the results of inoculation, we concluded that ‘Matsushima No. 3’ was tolerant, and ‘Fashion Parade’ was susceptible to root rot disease. Visual observation showed that zoospores of P. helicoides aggregated at the end of capillaries filled with root extract agar of ‘Matsushima No. 3’ as well as ‘Fashion Parade’, and zoospores encysted on the root surface of ‘Matsushima No. 3’ too. Therefore, ‘Matsushima No. 3’ didn’t inhibit the chemotaxis and encystment of zoospores. From SEM observations, most cystospores germinated on the root surface in ‘Matsushima No. 3’ and ‘Fashion Parade’, and the percentages of germ tube penetration to the epidermis in ‘Matsushima No. 3’ and ‘Fashion Parade’ were 55.0 and 71.2, respectively. The result that no differences were recognized between the two roses during the early infection process indicated that the tolerance mechanism in ‘Matsushima No. 3’ was not active in the early but in the latter infection process, that is, some tolerance mechanism might inhibit hyphae from expanding to the cortical tissue.