No abstract

Flooding is a major environmental constraint that obliges plants to adopt plastic responses in order to cope with it. When partially submerged, tomato plants undergo profound changes involving rearrangements in their morphology and metabolism. In this work, we observed that partial submergence markedly dampens root respiration and halts root growth. However, the flooded hypocotyl surprisingly enhances oxygen consumption. Previous results demonstrated that aerenchyma formation in the submerged tomato stem re‐establishes internal oxygen tension, making aerobic respiration possible. Indeed, potassium cyanide abruptly stops oxygen uptake, indicating that the cytochrome c pathway is likely to be engaged. Furthermore, we found out that leaf‐derived sugars accumulate in large amounts in hypocotyls of flooded plants. Girdling and feeding experiments point to sucrose as the main carbon source for respiration. Consistently, submerged hypocotyls are characterized by high sucrose synthase activity, indicating that sucrose is cleaved and channelled into respiration. Since inhibition of hypocotyl respiration significantly prevents sugar build‐up, it is suggested that a high respiration rate is required for sucrose unloading from phloem. As substrate availability increases, respiration is fuelled even more, leading to a maintained allocation of sugars to flooded hypocotyls.

With flooding being one of the numerous challenges that ecosystems face throughout the world, plants are therefore obliged to adopt plastic responses in order to cope with this environmental constraint. When flooded, the tomato hypocotyl undergoes profound changes that entail rearrangements in its physiology and metabolism. In this work, we observed that, although soil flooding markedly dampens root respiration, the submerged hypocotyl surprisingly enhances oxygen consumption in spite of hypoxic conditions. Several pieces of evidence indicate that the respiratory pathway is indeed promoted in submerged stems. Besides, underwater hypocotyls are shown to accumulate sugars. Girdling and feeding experiments revealed that leaf-derived sucrose is metabolized and channelled to maintain respiration in underwater hypocotyls. Our data suggest that high respiration is required for sucrose unloading from phloem, since inhibition of hypocotyls respiration significantly prevents sugar build-up. As substrate availability increases, respiration is fuelled even more, leading to a sustained allocation of sugars to flooded hypocotyls.