Author:

Abstract:

Although a lot of important crops such as tomato, potato and tobacco have the tendency to respond to unfavorable conditions such as root hypoxia by bending down their leaves, the regulation of this epinastic response remains elusive. We have discovered a strong link between epinasty and the ontogeny of the plant, which in this case means that younger leaves are less prone to stress induced epinasty compared to older leaves. This indicates a developmental regulatory pathway, which is determined by a shift in the ethylene metabolism of the different leaves. We found that young leaves convert 1-aminocyclopropone-1-carboxylic acid (ACC), which is the precursor of ethylene and acts as a root-borne signal during hypoxia, to the conjugate MACC, while in older leaves the conversion of ACC to ethylene predominates. Furthermore, the expression pattern of ACO1 is stimulated in older leaves, indicating that ethylene production itself is also enhanced by the elevated ACC transport from the roots. We have also quantified in real-time important physiological changes to study the dynamic epinastic response during hypoxia. Leaf angle and canopy cover rapidly change in response to root hypoxia, reducing foliar transpiration. There is a close relationship between transpiration and the regulation of stomatal conductance through ABA signaling and the regulation of ACC transport from the roots to the shoot. Notabilis, an ABA deficient tomato mutant, showed elevated ACC levels in the roots and in the older leaves after a 24h hypoxia treatment, suggesting that both signaling pathways are closely intertwined. In order to further unravel the molecular regulation of this signaling mechanism and the ontogenetic differences, were are currently performing a genome wide association study of 400 sequenced tomato accessions. So far, we have observed a large variation in the timing and the magnitude of the epinastic response as well as in its ontogenetic differentiation during root hypoxia-induced epinasty.