Different regulation of leaf respiration between Spinacia oleracea, a sun species, and Alocasia odora, a shade species

Abstract

Mature leaves of shade species exhibit lower respiratory rates than those of sun species. To elucidate the mechanism underlying different respiratory rates between sun and shade species, we examined respiratory properties of leaves in Spinacia oleracea L., a sun species, and Alocasia odora (Lodd.) Spach, a shade species, with special reference to changes in the respiratory rate throughout the night. In S. oleracea, rates of both CO2 efflux and O2 uptake decreased with time during the night, whereas in A. odora both rates were virtually constant at lower levels. The rates of O2 uptake in S. oleracea increased upon addition of sucrose, and the rates attained were virtually identical throughout the night. However, the addition of an uncoupler [carbonyl cyanide p‐(trifluoromethoxy)‐phenylhydrazone; FCCP] did not alter the rates. In contrast, the rates of O2 uptake in A. odora were enhanced by the addition of FCCP, but not by sucrose. The concentrations of carbohydrates in the tissue decreased throughout the night in both species and the ATP/ADP ratio was always greater in A. odora. These results indicate that, in S. oleracea, the availability of respiratory substrate determines the respiratory rate, while the low respiratory rate in A. odora is ascribed to its low demand for ATP.