LEAF CARBOHYDRATE STATUS IN LOLIUM-TEMULENTUM DURING THE INDUCTION OFFLOWERING

Unifoliated plants of Lolium temulentum L. cv. Ceres, a qualitative lo ng-day grass, were induced to flower by one 24-h long day (LD) or by o ne 8-h short day (SD) advanced by 12 h in the normal regime, so-called 'displaced short day' (DSD). Standard light for SD and DSD was a mixt ure of fluorescence and incandescence at 400 mu mol m(-2) s(-1) wherea s the extension period of the 24-h LD was solely incandescence at 10-1 5 mu mol m(-2) s(-1). The DSD system first characterized by the timing s of floral induction, stimulus translocation and apical development. Carbohydrates in the blade tissues and in leaf exudate were analysed c omparatively in vegetative and induced plants. Fructans were not detec ted in the leaf tissues whereas sucrose and starch were found to be pr esent in similar amounts. In SD, their contents exhibited a diurnal fl uctuation and were not in large excess. The common change observed dur ing the two inductive treatments was that starch remained at a high le vel during the LD extension, even though the lighting was unsuitable f or photosynthesis, and increased transiently in DSD. Sucrose was the m ajor sugar contained in the leaf exudate. Its content increased when f lowering was induced, but not at the same time in the two systems. In LD, sucrose exudation rose when plants were returned to standard light after the inductive cycle, i.e. after the LD stimulus had left the le af blade. By contrast, during the DSD, sucrose was transported at the same time as the floral stimulus. Results are discussed together with the methods used to time stimulus translocation and their implications .