Hideo Imanishi’s research while affiliated with Tokyo University of Agriculture and other places

Lily bulbs of Oriental hybrid ‘Casa Blanca’ produced in Hokkaido or Niigata were packed in polyethylene bags with wet peat moss and subjected to pre-chilling at various temperatures for various durations from 0 to 20 weeks before storing at –2.0°C. On moving to –2.0°C, bulbs were dissected and the shoot length and Brix of shoot tip juice were measured. Soluble carbohydrate concentrations of the shoot tip were analyzed by a conventional extraction method using hot ethanol with HPLC. After storage at –2.0°C for more than 7 months, they were grown in a glass house kept at a minimum temperature of 15°C to check for the occurrence of black shoots, non-flowering plants, and damaged leaves, which might be caused by long-term storage at –2.0°C. Rates of black shoots, non-flowered plants, and damaged leaves became high when bulbs were subjected to pre-chilling at 1°C for more than 12 weeks. The rise in rates and decrease of the sucrose content occurred simultaneously. Furthermore, changes in the sucrose content were closely related to changes of Brix. When bulbs were pre-chilled at 1, 6, 8, or 12°C for 8 weeks followed by 1°C for 10 weeks, those pre-chilled at 1 or 6°C showed a decreased sucrose content or Brix at the end of pre-chilling and higher rates of non-flowering plants and damaged leaves after storage at –2.0°C for 24 weeks. An extended duration of storage at –2.0°C for 8 weeks induced black shoots and non-flowering plants when bulbs were pre-chilled at 1°C for 18 weeks before moving to –2.0°C. From these results, it was concluded that excessively long pre-chilling of bulbs at low temperatures below 6°C induces black shoots and leaf damage after long-term storage at a subzero temperature.

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.

To compare the effect of lowering solution temperature and the application of germicides at higher temperatures, cut rose flowers were placed in vases containing distilled water (DW) or isothiazolinonic germicides, a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (CMIT/MIT) solution. Vase solutions were kept at 10 and 23°C under an air temperature of 23°C or at 10 and 30°C under an air temperature of 30°C. Lowering the vase so-lution temperature significantly extended the vase life of cut roses at an air temperature of 30°C but not at an air temperature of 23°C. Treatment with CMIT/MIT significantly extended the vase life of cut roses at both air temperatures. CMIT/MIT treatment delayed the time to the start of the decrease in fresh weight more than did lowering vase solution temperature at both air tem-peratures. Stem hydraulic conductance of cut flowers held in DW at 23 and 30°C decreased with time. The decrease in hydraulic conductance was suppressed by CMIT/MIT treatment more than by lowering the vase solution temperatures at both air temperatures. These results show that CMIT/MIT treatment is more effective than lowering the temperature of vase water for extending the vase life of cut roses.

Petal growth associated with flower opening depends on cell expansion. To understand the role of soluble carbohydrates in petal cell expansion during flower opening, changes in soluble carbohydrate concentrations in vacuole, cytoplasm and apoplast of petal cells during flower opening in rose (Rosa hybrida L.) were investigated. We determined the subcellular distribution of soluble carbohydrates by combining nonaqueous fractionation method and infiltration-centrifugation method. During petal growth, fructose and glucose rapidly accumulated in the vacuole, reaching a maximum when petals almost reflected. Transmission electron microscopy showed that the volume of vacuole and air space drastically increased with petal growth. Carbohydrate concentration was calculated for each compartment of the petal cells and in petals that almost reflected, glucose and fructose concentrations increased to higher than 100 mM in the vacuole. Osmotic pressure increased in apoplast and symplast during flower opening, and this increase was mainly attributed to increases in fructose and glucose concentrations. No large difference in osmotic pressure due to soluble carbohydrates was observed between the apoplast and symplast before flower opening, but total osmotic pressure was much higher in the symplast than in the apoplast, a difference that was partially attributed to inorganic ions. An increase in osmotic pressure due to the continued accumulation of glucose and fructose in the symplast may facilitate water influx into cells, contributing to cell expansion associated with flower opening under conditions where osmotic pressure is higher in the symplast than in the apoplast.

There have been few reports on the morphology of flower opening, despite its horticultural significance. It is not clear when cell division stops during rose petal development or what changes occur in cell morphology. This study aims to clarify the details of cell morphological changes during rose petal development. Rose (Rosa hybrida L. 'Sonia') petals were sampled in six flower bud stages. Cell morphological changes were observed by light microscopy, transmission and scanning electron microscopy using cross sections of the petals, and the number of epidermal cells was measured using Nomarski differential interference contrast microscopy. The number of epidermal cells increased with flower opening, but the rate of increase in the number of abaxial epidermal cells slowed down at an earlier stage than in adaxial epidermal cells. The increase in the epidermal cell area was much more rapid in later stages compared with the increase in cell number, suggesting that petal growth in later stages is mainly due to cell expansion. During flower opening, the unique expansion of spongy parenchyma cells produced large air spaces. Epidermal cells of the upper part showed obvious lateral expansion. In particular, marked expansion of adaxial epidermal cells with enlargement of the central vacuole was observed. Differences in the patterns of cell expansion among cell types and locations would contribute to the reflex of petals during rose flower opening. JSHS

Perennial pea (Lathyrus latifolius L.) is a perennial new florist crop introduced to Japan in the 1990s. Flowering behavior and pretreatment method to extend the vase life of this plant is unknown. This study was carried out to develop a useful and practical pretreatment method using an STS solution to extend the vase life of cut perennial pea flowers. Cut flowers were treated with 1) 100gL-1 sucrose for 2h, 2) 0.05% surfactant for 2h, 3) 0.2 mM silver thiosulfate complex (STS) for 2h, 4) 0.2mM STS + 10% sucrose + 0.05% surfactant for 2h, and 5) water (control). To evaluate effects of the treatments on vase life they were transferred to vessels containing distilled water and kept at 22°C, 70% relative humidity, under 10 μmol m-2 s -1 light intensity and a 12-h photoperiod. Compared to the control, all treatments extended longevity. In particular the vase life of cut flowers treated with 0.2mM STS + 10% sucrose + 0.05% surfactant for 2h was extended by 3 times compared with that of control. This pretreatment is recommended to extend the vase life of cut perennial pea flowers.

To establish a simple and rapid extraction method for soluble carbohydrate for determination of osmolar concentration in petals by HPLC analysis, a method using a centrifugal filter device with microwave heating was developed. Rose 'Sonia' petals were placed in a centrifugal filter device and heated in a microwave oven to boiling. The centrifugal filter device was centrifuged with the petals at 12,000 g for 10 min. The resulting leached solution was subjected to HPLC analysis. No significant difference in soluble carbohydrate composition was observed between the solution obtained from this method and that obtained from a conventional extraction method in which tissues are homogenized using hot ethanol solution. Changes in soluble carbohydrate concentration with flower opening in 'Rote Rose' roses were investigated using the new method. The osmolar concentrations of glucose and fructose in the petals increased during flower opening. This increase was roughly comparable to the increase in osmotic pressure in the petals. The results suggest that the method using the centrifugal filter device with microwave heating is a simple and rapid way to determine osmolar concentration of soluble carbohydrates of rose petals.

We developed a simple and rapid extraction method of soluble carbohydrates from petals for analysis by high performance liquid chromatography (HPLC), using a centrifugal filter device in a test tube without homogenization. Rose 'Sonia' petals were immersed in 99.5% ethanol solution in a test tube and kept at 75 degrees C for 20 min. Sorbitol was then added to the solution as an internal standard, and the petals were transferred to the centrifugal filter device and centrifuged at 12000 x g for 10 min. Following removal of the filtrate, 99.5% ethanol was added to the filter device and a second round of centrifugation performed. Filtrated solution obtained from both centrifugations was combined with the ethanol solution remaining in the test tube, heated to dryness at 80 degrees C, and used for HPLC analysis. Few differences in soluble carbohydrate content were observed between the new method and a conventional method in which soluble carbohydrates are extracted by homogenization. We confirmed that most carbohydrate was extracted by the new method. Moreover, the soluble carbohydrate content of samples extracted from 'Sonia' petals using the new method did not change during one week of storage at -30 degrees C, indicating the stability of the samples. Marked differences in soluble carbohydrate content were not observed among 'Chanel', 'New Bridal', 'Rote Rose', or 'Saturn' rose petals, carnations or Tweedia caerulea petals or Delphinium sepals, using either the new or conventional method. Marked differences in soluble carbohydrate content were also not observed among leaves and stems in carnations, Delphinium or rose 'Sonia' using either the new or conventional method. These results suggest that the new method, which does not require homogenization, appears to be a more simple and rapid method of extraction of soluble carbohydrates from various organs of floricultural plants.