This review deals with the effectiveness and mechanism of stress treatments, such as heat and UV treatments (hot air, hot water, and UV-B), on the quality maintenance of postharvest green horticultural crops such as broccoli florets and green sour citrus fruits (lime, Nagato-yuzukichi, and yuzu), in which chlorophyll (Chl) degradation is a main factor in quality deterioration. Postharvest stress treatments effectively suppressed Chl degradation with senescence during storage. In broccoli florets and lime fruit, hydrogen peroxide, which is produced by postharvest stress treatments, could induce the activation of the ascorbate-glutathione (AsA-GSH) cycle, and enhancement of the AsA-GSH cycle might be involved in the suppression of senescence in such produce. The mechanism of peroxidase-mediated Chl degradation and the control of Chl-degrading enzymes by stress treatments were determined using broccoli florets and Nagato-yuzukichi fruit. Peroxidase oxidized phenolic compounds such as apigenin, naringin and p-coumaric acid, which have a hydroxyl group at the p-position, to form phenoxy radicals, and Chl a could be degraded by the formed phenoxy radicals to colorless low-molecular-weight compounds. It was found that the cationic isoperoxidase related to Chl degradation, which is localized in the chloroplast, increased with senescence during storage and enhancement of the activity was effectually inhibited by stress treatments. In addition to peroxidase, the activities and gene expression of other Chl-degrading enzymes were controlled by stress treatments. Thus, stress treatments seem to be a useful method for controlling Chl degradation in stored green fruits and vegetables.

View full abstract

This study was conducted in three consecutive years to determine the appropriate timing of fertilizer application to increase the flower number of the Japanese pepper, Zanthoxylum piperitum (L.) DC. f. inerme Makino (known as ‘Budousanshou’ in Japan) cultivated in Wakayama Prefecture. The timing experiment involved three treatment options: fertilizer application in spring with two equal applications in May and June, a summer/autumn treatment of two equal applications in August and September, or a spring/summer/autumn treatment of four equal applications in May, June, August, and September. Each treatment consisted of an annual application of 300 kg·ha⁻¹ nitrogen. The spring treatment resulted in increased flower number. It was suggested that the application of fertilizer in the May/June spring treatment resulted in a focused accumulation of nutrients prior to the floral evocation period and led to the subsequent increase in flower number and cluster number relative to the summer/autumn and spring/summer/autumn treatments.

View full abstract

Despite recent advances in DNA analysis techniques, the process of acquiring purified DNA is particularly costly and time-consuming in woody plants. The ability to obtain purified DNA is frequently hindered by the presence of secondary compounds, including polyphenols and polysaccharides. In this study, we developed a sample preparation method for direct and non-direct PCR that is highly reproducible and cost-effective. This method entails pricking a leaf sample with a toothpick and dissolving the collected DNA in a PCR mixture or TE0.2 buffer solution. We confirmed the utility of the method using seedlings derived from backcrossed hybrids of Citrus hassaku hort. ex Y. Tanaka × Poncirus trifoliata (Linn.) Raf. Using a direct PCR method, we obtained 99% amplification success rate for the 1200 bp CTg12A region. PCR amplification from DNA extracts, which was also produced by our method, succeeded in 96–100% of samples for five different DNA markers, except for CTg12A, where it was only 86%. We were able to process and commence PCR amplification of 95 leaf samples in 1.5–2.0 h, in contrast to 23 h using conventional methods. We also demonstrated the broader applicability of this method by extending our study to 18 other fruit trees and ornamental woody plants. PCR products were generated for all 18 tested species using chloroplast accD and rbcL markers, and for Japanese chestnut, mango, and Japanese pear using their species-specific SSR markers. Our new method might be suitable for analyses which handle large number of samples, such as marker-assisted selection and cultivar discrimination, and holds promise for use in DNA marker typing in various kinds of woody plants.

View full abstract

This study was conducted to clarify the ecophysiological traits of high-yielding ‘Benihoppe’ with focus on its dry matter production, plant growth analysis, and leaf photosynthetic rate in comparison with those of ‘Toyonoka’ and ‘Sachinoka’. Total dry matter of ‘Benihoppe’ was higher than that of ‘Toyonoka’, while no difference was found between their harvest indices. In ‘Benihoppe’, the crop growth rate (CGR) and leaf area index (LAI) were higher than those of ‘Toyonoka’ and ‘Sachinoka’. The large LAI of ‘Benihoppe’ was attributed to its ability to bear larger leaves than other cultivars, while ‘Benihoppe’ demonstrated a superior net assimilation rate (NAR) to that of ‘Toyonoka’. NAR is affected by leaf photosynthetic activity; however, no difference was observed between the leaf photosynthetic rates of ‘Benihoppe’ and ‘Toyonoka’. Petioles in ‘Benihoppe’ that supported large leaves were longer and upright, and NAR might be affected by their trait, which allow solar radiation to penetrate the plant canopy. Thus, the outstanding CGR in ‘Benihoppe’ may be a result of the large LAI and upright petioles which allow solar radiation to penetrate the plant canopy.

View full abstract

One of the ways to reduce chemical fertilizer application is the use of cover crops, which improve soil properties and supply nutrition to subsequent crops. The application effect of a legume cover crop, hairy vetch (Vicia villosa R., HV), on N dynamics in fresh market tomatoes (Solanum lycopersicum L.), ‘House Momotaro,’ was investigated using the ¹⁵N-labeling method. Tomato seedlings were transplanted into a 1/2000 a Wagner pot at 0, 80, and 240 kg·ha⁻¹ of N application (N0HV, N80HV, and N240HV) on June 9, 2011. Before transplanting, the labeled HV and chemical fertilizers were incorporated into the soil. Five tomato plants were collected 6 times in each treatment and then separated into leaves, stems, and roots. Fruits were harvested at maturity. HV-derived N uptake was recognized mainly in the first 4 weeks after transplant (WAT). Especially in N240HV, HV-derived N uptake ceased at 4 WAT. The uptake amounts of HV-derived N at 10 WAT were 587, 657, and 729 mg·plant⁻¹ in N240HV, N80HV, and N0HV, respectively, and were increased by decreasing N fertilizer application. The rate of N uptake derived from HV to total N uptake in tomato plants (%N_dfhv) was the highest at 2 WAT, and %N_dfhv in N80HV (52.1%) and N0HV (51.5%) were significantly higher than in N240HV (43.6%). After 2 WAT, %N_dfhv decreased gradually in all N rates as tomatoes grew and decreased to 24.8%, 34.4%, and 37.1% in N240HV, N80HV, and N0HV, respectively, until 12 WAT. Nitrogen use efficiency (NUE) from HV-derived N was the highest at 10 WAT, and N0HV (55.3%) was significantly higher than N240HV (44.5%) and N80HV (49.8%). The partition rate of HV-derived N into fruits was 63.9%, and 39.7% of HV-derived N was distributed into 1st and 2nd fruit clusters. From these results, it was clarified that HV can be expected to be an alternative N fertilizer because HV-derived N was absorbed effectively with a small amount of N fertilizer. Further research on fertilizer management in tomato’s early stage will be needed for an N-reduction system because HV-derived N was mainly absorbed for 4 WAT.

View full abstract

A novel torenia (Torenia fournieri Lind. ex Fourn.) mutant ‘flecked’, which bears variegated flowers, was obtained from ethyl methanesulfonate-treated M₂ plants. The lower lip of this mutant has small violet spots with a pale violet background, while that of the normal type is solid violet. The mutant trait frequently reverted to a semicircular violet sector or solid violet lower lip. Germinal revertant plants with a solid violet lower lip also frequently occurred in S₁ plants derived from self-pollinated mutant flowers. In the lower lip of the mutant type, anthocyanin concentration was much lower than in the normal type. This was attributed to decreased expression of the genes encoding anthocyanin biosynthesis enzymes, i.e. torenia chalcone synthase (TfCHS), flavanone 3-hydroxylase (TfF3H), dihydroflavonol 4-reductase (TfDFR), anthocyanidin synthase (TfANS), and UDP-glucose 3-O-flavonoid glucosyltransferase (TfUFGT). In the lower lip of the mutant, expression of a gene encoding R2R3-MYB transcription factor (TfMYB1, Torenia fournieri MYB1) was much lower than in the normal type and the revertants; this was caused by insertion of a Enhancer/Suppressor-Mutator (En/Spm)-like transposon (Ttf1, Transposon Torenia fournieri 1) in the 2nd intron of TfMYB1. Furthermore, it was found that the reversion of anthocyanin accumulation in the lower lips correlated to excision of Ttf1 from the TfMYB1. Overexpression of TfMYB1 in torenia caused anthocyanins to accumulate in the purple callus as a result of enhanced expression of the five structural genes mentioned above, demonstrating that TfMYB1 regulates these genes. Therefore, we concluded that a homozygous allele of Ttf1-inserted TfMYB1 caused the mutant phenotype. Ttf1 is a non-autonomous element because Ttf1 does not have the DNA sequence encoding transposase. Based on these results, potential uses of the flecked mutant for torenia breeding and transposon tagging are discussed.

View full abstract

The number of epidermal cells, osmotic potential, and carbohydrate and inorganic ion concentrations in petals during development and opening of Tweedia caerulea D. Don flowers was studied. The number of adaxial epidermal cells was greater than that of abaxial epidermal cells at all stages. The increase in cell number stopped at the stage just before flower opening. The size of adaxial and abaxial epidermal cells increased during flower development and opening. The results indicate that petal growth before flower opening depended on cell division and expansion, and petal growth during flower opening was attributable to petal cell expansion. Osmotic potential decreased and fructose, glucose and sucrose concentrations in the petals gradually increased during flower opening. Starch content and total inorganic ion concentration were almost constant during flower opening. Decreased osmotic potential is mainly attributed to increased glucose, fructose and sucrose concentrations. It is concluded that an increase in these sugar concentrations largely contributes to the decrease in osmotic potential. This decrease may facilitate water influx to cells, thereby maintaining pressure potential, which is apparently involved in petal cell expansion associated with flower opening.

View full abstract

Lychnis belongs to Caryophyllaceae and contains a number of horticulturally attractive species. In order to widen their variations in horticultural traits, interspecific cross-pollination and subsequent immature seed culture were carried out using 8 Lychnis species, L. chalcedonica, L. coronata, L. fulgens, L. gracillima, L. kiusiana, L. miqueliana, L. sieboldii, and L. wilfordii. Enlarged fruits containing immature seeds were obtained in the 26 cross-combinations 4 weeks after pollination. Immature seeds were isolated from the fruits and cultured on half-strength Murashige and Skoog medium without plant growth regulators, on which germination occurred in 11 cross-combinations and seedlings were produced in 8 cross-combinations. However, green seedlings were obtained only in L. fulgens × L. sieboldii, and seedlings obtained from the other 7 cross-combinations, L. coronata × L. gracillima, L. gracillima × L. coronata, L. kiusiana × L. fulgens, L. kiusiana × L. sieboldii, L. kiusiana × L. wilfordii, L. wilfordii × L. kiusiana, and L. wilfordii × L. sieboldii, were albino and died during acclimatization. The hybridity of all 55 green seedlings obtained from L. fulgens × L. sieboldii was confirmed by random amplified polymorphic DNA analysis. Although some morphological variations were observed among hybrids, hybrid plants generally showed intermediate morphologies between the parents. Hybrids showed high pollen fertility and their self-pollination yielded viable seeds. The present study shows the possibility of interspecific cross-breeding in Lychnis. Further studies are necessary to improve the culture conditions of immature seeds and to examine interspecific cross-compatibility using a wide range of Lychnis species.

View full abstract

The role of temperature in bulb dormancy induction and release was investigated in one-year-old seedlings of three populations of Lilium longiflorum, i.e., Yakushima (LYA) and Kikaijima (LKI) in the Ryukyu Archipelago, Japan and Pitouchiao (LPI), Taiwan, and two populations of L. formosanum, Wulai (FWU), Taiwan and domesticated Fukuoka population (FFU), Japan. LYA and LKI undergo deep summer dormancy, while LPI, FWU and FFU do not. Four weeks of high temperature induced dormancy in LYA and LKI, whereas two weeks of high temperature was insufficient. Dormancy was not induced in LPI and FFU even after eight weeks of high temperature. Re-growth after dormancy was initiated in LKI and LYA six to eight weeks after shifting to 15°C. In the temperature-controlled experiment, all the populations continued developing new leaves at 15°C for 22 weeks, and stopped leaf production at 20 and 25°C in winter, while FFU produced new leaves at 30°C. It is considered that summer dormancy induction and release in one-year-old seedlings of northern ecotypes of L. longiflorum is determined by the duration of high and low temperature, respectively. It was proved that development of non- or weakly dormant ecotypes of L. longiflorum and L. formosanum is associated with the lack or reduction of sensitiveness to high temperature.

View full abstract

Several morphological changes in flowers can be induced in torenia (Torenia fournieri L.) by applying forchlorfenuron (CPPU) to flower buds. We investigated the temporal and spatial distributions of the cytokinin response in CPPU-treated flower buds, which is indicated by type-A response regulator (RR) and cytokinin oxidase (CKX) gene expression. The quantitative real-time PCR analysis showed that the expression of both T. fournieri RR1 (TfRR1) and TfCKX5 was induced from 1 day after CPPU treatment in the sepal, petal, stamen, and pistil, and maintained at a high level until 5 days after the treatment, when the earliest morphological changes due to CPPU treatment were observed. In situ hybridization analysis showed weak expression of both genes in the stamen and pistil through all floral stages of non-treated flower buds. However, when CPPU was applied at the sepal development stage, expression of both genes was strongly induced in the abaxial side of the stamen primordia, which is the site of initiation of the wide paracorolla. When CPPU was applied during the early stage of corolla development, high expression of those genes was observed in the stamen, basal, and middle part of the petal, which is the site of initiation of the narrow paracorolla. Those high levels of expression became more strongly localized to the paracorolla initiation site once the paracorolla primordia formed. When CPPU was applied during the middle corolla development stage, strong expression of those genes was detected in the middle to apical parts of the petal, which is the site of changes in the distribution pattern of the vascular bundles and the resultant serrated margin. These results suggest that long-term elevation of cytokinin signaling caused by CPPU treatment induces changes in flower morphology, and the paracorolla and serrated margin of the petal are induced by localized high levels of cytokinin signaling at the site of those morphological changes within flower buds.

View full abstract

It has been attempted to develop multiple resistant rootstock against rose root rot (Pythium helicoides Drechsler) and crown gall disease (Rhizobium radiobacter (Beijerinck and van Delden, 1902) Young et al., 2001) using tetraploid Rosa multiflora ‘Matsushima No.3’ and R. ‘PEKcougel’. However, hybrid identification based on conventional morphological characteristics is difficult, and establishment of hybrid diagnosis by DNA markers is desired. In this study, we attempted to develop specific DNA markers of R. multiflora. Three hundred 10 mer random oligonucleotide primers were screened, and a unique polymorphic fragment in R. multiflora amplified by OPAK16 primer was identified. This fragment could distinguish between roses with cross-fertilization genealogy with R. multiflora and roses with no relationship with R. multiflora. This specific fragment was cloned, sequenced and converted into a sequence characterized amplified region (SCAR) marker–SCAK16, which can amplify a 583 base pair (bp) fragment only in roses with relatedness to R. multiflora. This result indicated that SCAK16₅₈₃ was a species-specific marker of R. multiflora that could be used in a marker-assisted breeding program for hybrid identification of R. multiflora.

View full abstract

After fruit development has been triggered by pollination, the abscission zone (AZ) in the pedicel strengthens its adhesion to retain the fruit. In tobacco, unpollinated flowers are shed from the AZ, while enlargement of the same tissue occurs in pollinated flowers. The abscission rate depends on effective pollination. In this study, we focused on pectin and boron (B) distribution and their functions in the AZ. B is an essential micronutrient that forms cross-links in pectin, which are important for organ differentiation and maturation. B content and the formation rate of the borate-ester cross-linked rhamnogalacturonan II dimer (dRG-II-B) were measured in tobacco. Expression of NtGUT1, which is important for the formation of dRG-II-B, and the B transporter NtNIP3;1 were analyzed in the peduncle and AZ. To determine B content and dRG-II-B formation rate, the following samples were collected: bud peduncle, bud AZ, fruit peduncle, fruit AZ, and flower AZs, which were treated to prevent pollination or were artificially pollinated. Samples treated in HNO₃ were assayed for total B content with ICP-MS. Endo-polygalacturonase (EPG)-treated alcohol-insoluble residues were assayed for formation rates of dRG-II-B with HPLC. Although there was more total B in fruit AZs than in branches, no differences in total B, water-soluble B, and B relevant to cross-linking with RG-II were found between buds and fruits. The formation rates of dRG-II-B were also the same in peduncles and AZs in both buds and fruits. These have the same characteristics of variation with or without pollination. Expression of both NtGUT1 and NtNIP3;1 was highest in AZs of flowers before opening, however, expression of NtGUT1 in flower AZs without pollination was not significantly different from after artificial pollination. These results suggest that the presence of relatively large amounts of B and pectin is important in structural enhancement of AZs after anthesis, but is not related to abscission with or without pollination.

View full abstract