Unifoliated plants of Lolium temulentum L.
cv. Ceres, a qualitative long-day grass, were induced to
flower by one 24-h long day (LD) or by one 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 mixture
of fluorescence and incandescence at 400 μmol m−2
s−1 whereas the extension period of the 24-h LD was
solely incandescence at 10–15 μmol m−2
s−1. The DSD system was first characterized by the
timings of floral induction, stimulus translocation and apical
development. Carbohydrates in the blade tissues and in leaf exudate
were analysed comparatively in vegetative and induced plants.
Fructans were not detected in the leaf tissues whereas sucrose and
starch were found to be present in similar amounts. In SD, their
contents exhibited a diurnal fluctuation and were not in large
excess. The common change observed during the two inductive
treatments was that starch remained at a high level during the LD
extension, even though the lighting was unsuitable for
photosynthesis, and increased transiently in DSD.
Sucrose was the major sugar contained in the leaf exudate. Its
content increased when flowering 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 leaf 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.