Reserve lipid accumulation and translocation of 14C in the photosynthetically active and senescent shoot parts of Dicranum elongatum

Lipid metabolism of the subarctic moss Dicranum elongatum was studied by feeding the moss with 2-¹⁴C-acetate and, after extraction of the lipids, counting the ¹⁴C-content of different lipid fractions immediately after feeding or after chase periods. Translocation of ¹⁴C after ¹⁴C-feeding was studied with autoradiography. Both low temperature (+6°C) and drought (at +23°C) resulted in increased incorporation of ¹⁴C into the neutral lipid (NL) fraction and decreased incorporation of ¹⁴C into the glycolipid (GL) fraction of the green shoot part of the moss. The distribution of radioactivity between the NL classes suggests that diacylglycerols (1, 2-DAG) and common triacylglycerols (cTAG) are turned into acetylenic triacylglycerols (aTAG), which are accumulated preferentially. The decrease in the radioactivity of the GL fraction was due to two unknown fractions, whereas ¹⁴C incorporation into the chloroplast membrane lipids, monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG), was very low throughout the experiments. The phospho-lipid (PL) fraction accounted for 48–63% of total lipid radioactivity at both low and high temperatures. 2-¹⁴C-acetate feeding to the senescent moss part resulted in vigorous ¹⁴C incorporation into the lipids, especially into the reserve TAGs. Electron microscopic examination showed the presence of plastids, which explains the capability of the senescent part of the moss for lipid synthesis. The fact that transport of ¹⁴C from 2-¹⁴C-acetate took place upwards and downwards in the moss shoot, together with the capability for lipid synthesis of the senescent moss part, supports the suggestion that the senescent moss part plays a role as an energy store.