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 l ignin was determined in respectively strong and weak peduncles of Rosa x hybrida cv. Mercedes and Nubia. Xylem tissues of the peduncles of t he stronger cv. Mercedes were more lignified than in the weaker cv. Nu bia. However, phloem lignin content was increased only in the basal pa rts of the peduncles of cv. Mercedes. Differences in the monomeric com position of lignins were apparent between cultivars. In both the phloe m and xylem fractions, lignin in the peduncles of cv. Mercedes was les s condensed than in the weaker cultivar Nubia. Furthermore, lignin ric h in syringyl monomeric units occurred in the distal parts of the stro ng peduncles, accounting for the higher S/G ratio observed in the stro nger peduncles compared to the weaker ones. Despite lignin from both p hloem and xylem tissue showing a similar S/G ratio, the phloem fractio n must synthesize a more condensed lignin network than xylem tissue. S uch qualitative and quantitative lignin differences suggest the possib le role of lignification in the resistance of rose peduncles to bendin g.