Respiration in a new tuber crop, Apios americana

The objective of this study was to investigate the respiratory pathways in the underground storage tissues (tubers, fleshy roots, and rhizomes) of Apios americana Medikus (apios). Freshly sliced tubers of experimental breeding lines expressed variable capacities for alternative respiration, depending on genetic background, although the alternative respiratory pathway was not engaged in any of the apios tissues tested. The capacity of the alternative pathway present upon slicing was consistent with genetic line over the 5 years of the study. Respiration patterns of tubers and fleshy roots were comparable within a genetic line; however, substantial differences were found in the respiration of the nonthickened sections of rhizomes compared with the storage tubers. Total respiration of stored rhizomes was high (up to 2.7 microliter O2/g per min) compared to that of tubers (up to 0.9 microliter O2/g per min). Rhizome tissue respiration had a large capacity for alternative respiration (40%-60% of total respiration), while tuber tissue had 0% to 73% alternative respiration, depending on genetic source. Epidermal layers, obtained from tubers that lacked a capacity for alternative respiration after slicing, had alternative respiration rates comparable to those of rhizomes. Furthermore, the alternative pathway could be induced in these tubers through conventional aging techniques. Etiolated shoots and rhizomes growing from these tubers also had an alternative respiration capacity that was half of the total rate. These results demonstrate that, although the capacity for alternative respiration is present in tissues of apios, freshly sliced tubers may or may not exhibit this pathway depending on genetic background. This attribute may be significant as apios undergoes further domestication.