Stable establishment of organ polarity several plastochrons before primordium outgrowth in Arabidopsis.

In many species, leaves are initiated at the flanks of shoot meristems. Usually, subsequent growth mainly occurs in the plane of the leaf blade, which leads to the formation of a bifacial leaf with dorso-ventral identities. In a classical set of surgical experiments in potato meristems, Sussex provided evidence that dorsoventrality depends on a signal emanating from the meristem centre. Although these results could be reproduced in tomato, this concept has been debated. We revisited these experiments in Arabidopsis where a range of markers are available to target the precise site of ablation. Using specific markers for organ founder cells and dorsoventral identity, we were unable to perturb the polarity of leaves and sepals long before organ outgrowth. While results in Solanaceae suggested that dorsoventral patterning was unstable during early development, we find that in Arabidopsis the local information contained within and around the primordium is able to withstand major invasive perturbations, long before polarity is fully established.