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.