The relationship between changes in lignification and the mechanical strength of rose flower peduncles

The resistance to bending of rose flower peduncle is important to the post-harvest quality of rose flowers. The content and composition of lignin was determined in respectively strong and weak peduncles of Rosa x hybrida cv. Mercedes and Nubia. Xylem tissues of the peduncles of the stronger cv. Mercedes were more lignified than in the weaker cv. Nubia. However, phloem lignin content was increased only in the basal parts of the peduncles of cv. Mercedes. Differences in the monomeric composition of lignins were apparent between cultivars. In both the phloem and xylem fractions, lignin in the peduncles of cv. Mercedes was less condensed than in the weaker cultivar Nubia. Furthermore, lignin rich in syringyl monomeric units occurred in the distal parts of the strong peduncles, accounting for the higher S/G ratio observed in the stronger peduncles compared to the weaker ones. Despite lignin from both phloem and xylem tissue showing a similar S/G ratio, the phloem fraction must synthesize a more condensed lignin network than xylem tissue. Such qualitative and quantitative lignin differences suggest the possible role of lignification in the resistance of rose peduncles to bending.