Long Term Survival of Rhizomatous Species Under Oxygen Deprivation

The underground organs of geophytes, such as rhizomes and tubers, are usually not the most sensitive to flooding and anoxia stress. However, they do show considerable variability. Prolonged flooding resistance is dependent on efficient oxygen transport and release through porous tissues, as well as metabolic adaptations. The mechanism for maintaining a sufficient oxygen supply and its underlying components are well understood. Similarly, details of anaerobic energy metabolism are well known. Some very general information is available concerning the synthesis of essential gene products, proteins and other macromolecules. On the other hand, our knowledge of the extent of lipid and membrane integrity in wetland and dryland rhizomes under oxygen deprivation and re-aeration is rather limited. The lipid composition of rhizomes from Acorus calamus, Iris germanica and Schoenoplectus lacustris, kept under strict anoxia but retaining 25–50% regeneration capacity, shows a saturation of the linolenic acid (CI8:3) component of most individual polar lipids. The saturation gradually increases in the order A. calamus < S. lacustris < I. germanica. The total quantity of polar lipids decreases only slightly in A. calamus and S. lacustris, whereas in I. germanica a rapid loss of glyco- and phospholipids can be observed under prolonged oxygen deprivation. Free fatty acids increase markedly in I. germanica, but only to a limited extent in the other species. Re-exposure to air induces a marked formation of peroxidation products (malondialdehyde and ethane) in I. germanica, less so in S. lacustris and only to a limited extent in A. calamus, which is able to reconstitute the previous lipid desaturation state under these conditions. A. calamus proved to be the most anoxia-tolerant species, followed by the other wetland species, S. lacustris. The dryland species I. germanica, with its unstable lipids, is the most anoxia-intolerant species of the three.