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.

Cut rose (Rosa hybrida L.) cv. Rote Rose was treated with glucose, fructose or sucrose at 10 g L -1 in combination with a commercial preparation of isothiazolinonic germicide (a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one; CMI/MI; Legend MK) at 0.25, 0.5 or 1 mL L -1 . To stabilize germicidal activity, the solution was acidified by the addition of citric acid to a final concentration at 30 mg L -1 . Of the sugars, glucose was the most effective in extending the vase life, followed by fructose. CMI/MI was most optimal at 0.5 mL L -1 . The addition of aluminum sulphate at 50 mg L -1 to glucose plus CMI/MI considerably extended the vase life of cut roses more than glucose plus CMI/MI. Based on these results, a formulation comprising 10 g L -1 glucose, 0.5 mL L 8-hydroxyquinoline sulphate (HQS). Treatment with GLCA extended the vase life of all the tested cultivars more than glucose plus HQS. Hydraulic conductance of stem segments in the control 'Rote Rose' roses decreased rapidly after harvest, but those for GLCA and glucose plus HQS were maintained at near their initial levels. The extension of vase life in cut roses by the addition of GLCA is attributed to the supply of sugars and the suppression of vascular occlusion without toxicity to cut flowers.

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.

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.

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We conclude that petal growth in Eustoma is divided into four phases, based on the activities of cell division and expansion, and that petal growth in the final phase is mainly due to cell expansion with marked enlargement of vacuoles.

Petal growth associated with flower opening is due to cell expansion. To elucidate the role of soluble carbohydrates in expansion of petal cells in Eustoma grandiflorum, its soluble carbohydrates were identified, and changes in their subcellular concentrations during flower opening were investigated. In addition to glucose, fructose, sucrose, and myo-inositol, D-bornesitol was identified using 1 H-NMR. D-Bornesitol was the major soluble carbohydrate in leaves and stems. Given that cyclitols are known to be the translocated carbohydrates in alfalfa, phloem exudate was analyzed. However, the translocated carbohydrate was suggested to be sucrose, and not D-bornesitol. In the petals, glucose and sucrose content increased whereas D-bornesitol and myo-inositol contents were almost constant during flower opening. The fructose content in petals was very low. Glucose, sucrose, myo-inositol, and D-bornesitol were found mainly in the vacuole, although sucrose was also found in the cytoplasm. In the petals of open flowers, glucose and sucrose concentrations in the vacuole increased to 60 and 53 mM. Inorganic ion concentrations in the symplast and apoplast did not increase during flower opening. The osmotic potential of the symplast and apoplast in the petals was lower at the open stage than the potential of those at the bud stage, and this difference was mainly attributed to increases in glucose and sucrose concentrations. The results suggest that the accumulation of glucose and sucrose in the vacuole reduces the symplastic osmotic potential, which appears to be involved in the cell expansion associated with flower opening, but that the contribution of D-bornesitol as an osmoticum to cell expansion is limited in Eustoma.

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