Circadian rhythms and the induction of flowering in the long‐day grass Lolium temulentum L.

Abstract

ABSTRACTPlants of Lolium temulentum L. strain Ceres were grown in 8‐h short day (SD) for 45 d before being exposed either to a single long day (LD) or to a single 8‐h SD given during an extended dark period. For LD induction, the critical photoperiod was between 12 and 14 h, and more than 16 h were needed for a maximal flowering response. During exposure to a single 24‐h LD, the translocation of the floral stimulus began between the fourteenth and the sixteenth hours after the start of the light period, and was completed by the twenty‐fourth hour. Full flowering was also induced by one 8‐h SD beginning 4 or 28 h after the start of a 40‐h dark period, i.e. by shifting 12 h forward or beyond the usual SD. The effectiveness of a so‐called ‘displaced short day’ (DSD) was not affected by light quality and light intensity. With a mixture of incandescent and fluorescent lights at a total photosynthetic photon flux density of 400 μmol m−2 s−1, a 4‐h light exposure beginning 4 h after the start of a 40‐h dark period was sufficient to induce 100% flowering. The flower‐inducing effect of a single 8‐h DSD was also assessed during a 64‐h dark period. Results revealed two maxima at a 20‐h interval. This fluctuation in light sensitivity suggests that a circadian rhythm is involved in the control of flowering of L. temulentum.