A comparative study on carbohydrate reserves and ethanolic fermentation in the roots of two wetland and non‐wetland species after commencement of hypoxia

Abstract

The problem of availability of storage carbohydrates (fructans and starch) in oxygen‐deficient roots was investigated in wetland species (Senecio aquaticus Hill., Myosotis palustris[L.] L. Em. Rchb.) and compared with related non‐wetland species (Senecio jacobaea L., Myosotis arvensis[L.] Hill.) with respect to ethanolic fermentation (PDC activity, ethanol production).In response to 24 h of hypoxic treatment, the pyruvate decarboxylase (PDC) activity in roots increased 4‐fold in M. arvensis and S. jacobaea, 2‐fold in S. aquaticus and only slightly in M. palustris. The rise in PDC activity was accompanied by an increase in ethanol content in the roots. The increase in ethanolic fermentation in roots of intact plants was associated with a slight increase in fructose and glucose and in a clear rise in sucrose content during the first 24‐48 h after commencement of the hypoxic treatment. Following 24 h of hypoxia, the content of fructans started to increase significantly for the duration of the experiment (9 days) in the four species. Since starch content changed only slightly during this period, the fructan:starch ratio increased under low energy availability. In the roots of flooding‐tolerant Senecio aquaticus, the ratio shifted most clearly from 2:1 in normoxia to 9:1 in hypoxia. For the roots of the two wetland species investigated, the results indicate a stronger accumulation of carbohydrates accompanied by a lower increase in PDC activity under root hypoxia, when compared with the related non‐wetland species respectively.