Fermentation and Adenylate Metabolism of Hedychium coronarium J. G. Koenig (Zingiberaceae) and Acorus calamus L. (Araceae) under Hypoxia and Anoxia

Abstract

Rhizomes of wetland plants are subjected to periods of hypoxia and/or anoxia by the seasonal or permanent waterlogging of their growing sites. Hedychium coronarium, the White Ginger, and Acorus calamus, the Sweet Flag, have their origin in India and were introduced into Latin America and Europe, respectively, more than three centuries ago. The White Ginger grows in humus-rich, shaded or semi-shaded areas subjected to waterlogging but it is never totally submersed, while the Sweet Flag grows at lake margins and is totally submersed during winter. Winter rhizomes of both species were cultivated in water culture in a greenhouse. The end products of fermentation (ethanol, lactic acid, malic acid), overall rhizome pH, the adenylate pool of nucleotides, the energy charge and their capacity to resume growth, were measured after periods of 1, 2, 4, 8 and 16 days of anoxia and hypoxia. In all cases metabolic responses were also determined in rhizomes allowed to recover for 24 h in air. Ethanol was the main fermentation end product in both species, reaching higher concentrations in the anoxia-treated rhizomes. In H. coronarium, there was also a significant increase in the levels of lactic acid, with a considerable drop in overall rhizome pH. Anoxia and hypoxia induced, in both species, a significant drop in the energy charge values. Control plant rhizomes and rhizomes allowed to recover in air for 24 h had energy charge values of around 0.8. In rhizomes subjected to stress these values were lower, around 0.50 in A. calamus and as low as 0.3 in H. coronarium. Although in both species there is also a decrease in the amount of total nucleotides, it was much more drastic in the case of anoxia treated rhizomes of H. coronarium. The pH drop was most probably the underlying cause of the metabolic disarray that lead to a depletion of the adenylate pool and, finally, failure to regenerate after 16 days of anoxia. The results also show that energy charge values without measurements of the total adenylate pool may give a misleading impression of fitness. Thus, the anaerobic metabolism of H. coronarium is less efficient and more harmful than that of A. calamus and, although considerably tolerant to hypoxia, it does not tolerate strict anoxia as the latter species does.