Physiological and biochemical studies on carbohydrate accumulation of petals cells in major ornamental plants

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During flower opening, large amount of soluble carbohydrates accumulates, suggesting that soluble carbohydrates play important roles as osmotica in plant cells. In the present study, carbohydrate concentration in cytoplasm, vacuole and apoplast in rose petals was determined and compared with total osmotic potential and osmotic potential derived from carbohydrates. A method for the evaluation of subcellular carbohydrate distributions in petals was developed by combining nonaqueous fractionation method and infiltration-centrifuged method. The volumes of subcellular compartments of petal cells were determined using electron microscope observations. Glucose and fructose concentrations in cytoplasm, vacuole and apoplast were drastically increased with petal opening. With petal opening, total osmotic potentials in symplastic and apoplastic solutions increased. In comparing total osmotic potential with osmotic potential derived from carbohydrates, increase in total osmotic potential with petal opening was mainly attributed to increase in osmotic potential derived from carbohydrates. Thus, accumulation of carbohydrates in the vacuole appears to contribute to cell expansion, leading to the petal opening. To clarify whether carbohydrates accumulate in the vacuole, carbohydrate distributions in cytoplasm, vacuole and apoplast of snapdragon, delphinium, Eustoma grandiflorum, Phlox drummondii, Gentiana triflora var.japonica flowers were investigated. Glucose and fructose in snapdragon, glucose, fructose and mannitol in delphinium, sucrose and glucose in E.grandiflorum, glucose and 2-C-methyl erythritol in P.durmmondii, gentiobiose and sucrose in G.triflora var.japonica increased with petal opening. These carbohydrates distributed mostly in vacuole. In these flowers, accumulation of different carbohydrates depended on species in the vacuole appears to contribute to cell expansion, leading to the flower opening.