Qualitative and Quantitative Analysis of Carbohydrates in Leaf Exudate of the Short-day Plant, Xanthium strumarium L. during Floral Transition

Abstract

Intact plants of Xanthium were induced to flower by a single 16-h long night (LN) or were kept vegetative either by continuous 18-h long days (LD) or by a 5-min night break (NB) in the middle of a single LN of 16 h. We first established that intact Xanthium plants behave as unifoliated plants with regard to sensitivity to the inductive night, translocation of the floral stimulus and rate of development of the terminal staminate inflorescence. Using HPLC and refractometry, carbohydrates in the leaf exudate, obtained by the EDTA-method, were analysed in response to the 3 photoperiodic treatments either inducing flowering or keeping the plants at the vegetative stage. Sucrose was the major sugar detected. Its content in the phloem sap increased in LN induced and NB vegetative control plants as compared with LD vegetative control plants. These results suggest that while the increase of sucrose export out of the leaves could be related to floral transition, it does not suffice to trigger the complete sequence of floral evocation.