Cell Wall Extensibility and Effect of Cell-Wall-Loosening Proteins during Rose Flower Opening

As flower opening involves the expansion of petal cells, the mechanisms of expansion growth were investigated in Rosa hybrida L. ‘FEbesa’ (syn. ‘Pretty Woman’) petals. Petal cell-wall extensibility was analyzed by creep extension analysis. Walls of the petal cells became loose at developing stage IV of completely separated sepals on an opening flower. Furthermore, cell-wall proteins extracted from rose petals at stage IV were suggested to have a positive effect on cell-wall loosening of stage III petals. Expansin and xyloglucan endotransglycosylase/hydrolase (XTH) proteins, which are located on apoplasts, are probably involved in cell-wall loosening in plants. Transcripts of these cell-wall proteins were extracted from rose petals with a view to elucidating their potential role in rose flower opening. Expansin and XTH transcript levels changed markedly during petal development. In particular, transcript levels of RhEXPA1 and RhXTH1 increased markedly during petal growth and were relevant to the typical growth in different part of the petals. Based on the present findings, we suggest that RhEXPA1 and RhXTH1 are the major paralogs involved in expansion growth of rose petals.