Soluble carbohydrate concentration and expression of expansin and xyloglucan endotransglucosylase/hydrolase genes in epidermal and parenchyma cells during lily flower opening.

To understand the biochemical mechanism underlying flower opening, the manner of cell expansion, soluble carbohydrate concentration, and expression of expansin and xyloglucan endotransglucosylase/hydrolase (XTH) genes were investigated in the petals of Oriental lily (Lilium 'Sorbonne'). Microscopic observation revealed that petal growth during flower opening mainly depended on cell expansion, which was accompanied by increases in glucose and fructose concentrations in the petals. The adaxial and abaxial sides of the petals grew at different rates during flower opening with petal reflection. To determine the concentration of soluble carbohydrates and the expression of expansin and XTH genes in adaxial and abaxial epidermal cells and parenchyma cells, these cells were separated using tweezers. We confirmed that these cells could be sufficiently separated. Glucose and fructose concentrations were higher in adaxial epidermal cells than in abaxial epidermal cells at the stage immediately preceding flower opening, but these differences diminished during flower opening. Three expansin genes, LhEXPA1, LhEXPA2, and LhEXPA3, and two XTH genes, LhXTH1 and LhXTH2 were isolated. LhXTH1 transcript levels in the petals markedly increased during flower opening and were higher in adaxial epidermal cells than in other types of cells. Conversely, the levels of the three EXPA transcripts decreased during flower opening and there were slight differences in their levels among different cell types, with a few exceptions. In conclusion, differences in glucose and fructose concentrations between adaxial and abaxial epidermal cells, together with the expression of LhXTH1, may contribute to cell expansion associated with flower opening.