CHANGES IN CARBOHYDRATE CONTENT FOLLOWING OXYGEN DEFICIENCY STRESS INRELATED SENECIO SPECIES WITH DIFFERENT FLOODING TOLERANCES

In the present work we compare responses of the carbohydrate content t o hypoxia of related plant species, which naturally grow on sites pron e to flooding (Senecio aquaticus HILL-flooding tolerant), with plants from habitats with only a low risk of oxygen shortage (Senecio jacobae a L.-flooding sensitive). The sum of water soluble carbohydrates in sh oots of Senecio aquaticus was nearly tripled following one day of hypo xic treatment. While the amounts of glucose and fructose, changed only slightly, those of sucrose and fructans were two-to fourfold. Followi ng oxygen shortage in the root environment the fructans became the mai n pool of water soluble carbohydrates in S. aquaticus. The shoots of t he flooding tolerant species S. aquaticus formed more fructans when gr own under oxygen deficiency, than their flooding intolerant relative S . jacobaea. The substantial increase in sucrose and fructan content oc curred in spite of diminished photosynthetic rates under restricted ox ygen supply. Fructans were found to accumulate as a response to oxygen deficiency in both flooding tolerant and intolerant species but with higher absolute values and ratios between fructan to starch in the flo oding tolerant species. Adding 50 mM sucrose to the nitrogen-flushed n utrient solution did not lead to a further increase of fructan in shoo ts of S. aquaticus but it occurred in S. jacobaea, but the CO2 fixatio n decreased to nearly 50% in both species.