Accumulation of 2-C-Methyl-d-erythritol as a Major Osmoticum in Petals During Flower Opening in Phlox drummondii

抄録

Flower opening is associated with the expansion of petal cells. To understand the role played by soluble carbohydrates during cell expansion associated with petal growth, changes in soluble carbohydrate concentrations in petal limbs during flower opening in Phlox drummondii were investigated. The size of adaxial and abaxial epidermal cells in the petal limbs gradually increased during flower opening. 2-C-Methyl-d-erythritol (2-C-ME) was identified using ¹H-NMR in P. drummondii petals. 2-C-ME was the most abundant carbohydrate in the petal limbs at five developmental stages, with the concentration of glucose the second highest, although the concentration of the latter was half of that of the 2-C-ME concentration in all five stages. The concentrations of 2-C-ME and glucose increased during flower opening. In contrast, inorganic ion concentrations did not increase during flower opening. The osmotic potential of petal limbs decreased considerably during the final stage of flower opening; this decrease could in part be attributed to the increasing 2-C-ME concentration. Transmission electron microscopic observations showed that the petal limb cells in open flowers were occupied primarily by the vacuole. The concentration of 2-C-ME in the vacuole was estimated to be 131 mM, which was much higher than the concentrations of the other carbohydrates. We conclude that the accumulation of 2-C-ME in the vacuole at a high concentration acts as an osmoticum, decreasing the osmotic potential of petal limbs and thereby increasing turgor pressure, which is thought to be involved in cell expansion of petal limbs during flower opening.