Expression of mRNAs and Proteins Associated with Cell-wall-loosening during Eustoma Flower Opening

Flower opening is important for floricultural crops. The mechanisms flower opening associated with the expansion of petal cells were investigated in Eustoma grandiflorum (Raf.) Shinn. Eustoma petals showed marked changes in their fresh weight, shape, and color during flower opening. Concurrently, petal cell-wall extensibility increased. This suggests that petal growth through flower opening is mainly caused by cell expansion. Expansin and xyloglucan endotransglycosylase/hydrolase (XTH) are known as representative proteins that loosen cell walls in plants. Three expansins and one XTH gene were isolated from opening Eustoma petals. We monitored for the first changes in their protein abundance in growing petals by Western blot analysis using antibodies to specifically detect expansin or XTH. The accumulation of these proteins marked the highest amount in petals when the flower was blooming and the petals were bending outwards. Thus, we showed that expansins participate in continuous petal growth from bud to opening flower and XTH plays a role in rapid petal growth accompanied by dynamic changes in petal fresh weight and petal shape.