FLIM-based detection of early wound-response signatures suggesting rooting hotspots in Argania spinosa.

Root regeneration from stems requires cells to reprogram their developmental trajectories. This reprogramming becomes possible when multiple factors converge at specific sites, ultimately giving rise to adventitious roots in what often appears to be a random pattern. Here, we asked whether such rooting `hotspots' could be detected by fluorescence-lifetime imaging microscopy. Using stem cuttings from a difficult-to-root Argan tree (Argania spinosa) clone, we examined wounded tissues by microscopy. Upon 440 nm illumination, discrete and asymmetric regions emerged in which fluorescence events with lifetimes below 2 ns increased within 3 h. Further, we show that similar lifetime signal appeared both around newly initiating root primordia and along what seemed to be their outward pathway through the stem tissues. These observations suggest that early, localized modifications in cell wall composition occur prior to visible root formation and may mark sites with the competence to initiate adventitious roots.