Fig. 9.

Temperature-dependency of the cell communication network during the dormancy cycle at the shoot apical meristem. a At moderate growth temperatures (dark green line, 18 °C), exposure to short photoperiod (SD) for 6 weeks (numbers on left) switches cells from an ‘online’ to an ‘offline’ state. Both terminal (TB) and axillary buds (AXB) have by then a complete embryonic shoot and a SAM that has established dormancy (red dot). At high ambient temperatures (orange line, 24 °C), buds may flush repetitively after reaching a hypothetical checkpoint (at 3–4 weeks; open orange dot). A 6- week exposure to low temperature (LT) (blue line, numbers on the right, 5-12 °C) releases dormancy and switches the meristem to a connected ‘standby’ state. A rise in temperature (light green line, 18 °C) induces burst, unfolding of preformed leaves, and production of neoformed leaves. AXBs of mature trees can produce flowers. Chilling characteristically regulates meristem-specific as well as floral and gibberellin pathway genes (light blue box). b Exposure to short photoperiod at low temperature (blue line, 12 °C) hampers bud ontogeny and all subsequent events in the bud dormancy cycle. It promotes a premature‘stand-by’ state and loss of vernalization by perturbing the expression of central genes (light blue box). Key: closed colored dots indicate dormant buds; open dots indicate nondormant buds; arrowheads indicate meristem proliferation; arrows in the light blue boxes indicate up- or downregulation of genes; horizontal double arrow indicates absence of clear effects