RESPIRATION IN A NEW TUBER CROP, APIOS-AMERICANA

The objective of this study was to investigate the respiratory pathway s in the underground storage tissues (tubers, fleshy roots, and rhizom es) of Apios americana Medikus (apios). Freshly sliced tubers of exper imental breeding lines expressed variable capacities for alternative r espiration, 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 con sistent with genetic line over the 5 years of the study. Respiration p atterns of tubers and fleshy roots were comparable within a genetic li ne; 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 mu l O-2/g per min) compared to that of tubers (up to 0.9 mu l O-2/g per min). Rh izome tissue respiration had a large capacity for alternative respirat ion (40%-60% of total respiration), white tuber tissue had 0% to 73% a lternative respiration, depending on genetic source. Epidermal layers, obtained from tubers that lacked a capacity for alternative respirati on after slicing, had alternative respiration rates comparable to thos e of rhizomes. Furthermore, the alternative pathway could be induced i n these tubers through conventional aging techniques. Etiolated shoots and rhizomes growing from these tubers also had an alternative respir ation capacity that was half of the total rate. These results demonstr ate that, although the capacity for alternative respiration is present in tissues of apios, freshly sliced tubers may or may not exhibit thi s pathway depending on genetic background. This attribute may be signi ficant as apios undergoes further domestication.