Study of the in vitro glucose release from spinach petioles (Spinacia oleracea cv. Nobel) before and after the photoperiodic induction of flowering.- The kinetics of the in vitro glucose release from isolated spinach petioles show the presence of two main pools of glucose. When spinach plants are submitted to a photoperiodic induction of flowering, the great increase in glucose content takes place in only one of the two pools. We suggest that it corresponds to the vacuolar compartment.