We studied changes in the chlorophyll (Chl) fluorescence components in chilling-stressed sweet potato (Ipomoea batatas L. Lam) cv. Tainting 57 (TN57, chilling-tolerant) and cv. Tainting 66 (TN66, chilling-susceptible). Plants under 12-h photoperiod and 400 mu mol m(-2) s(-1) irradiance at 24/20 degrees C (day/night) were treated by a 5-d chilling period at 7/7 degrees C. Compared to TN66, TN57 exhibited a significantly greater basic Chl fluorescence (170), maximum fluorescence (F.), maximum fluorescence yield during actinic irradiation (F-m'), and the quantum efficiency of electron transport through photosystem 2, PS2 ((Phi(PS2)). Chilling stress resulted in decrease in the potential efficiency of PS2 (F-v/F-m), Phi(PS2), non-photochemical fluorescence quenching (NPQ), non-photochemical quenching (q(N)), and the occurrence of chilling injury in TN66. Chilling increased the likelihood of photoinhibition, characterized by a decline in the Chl fluorescence of both cultivars, and photoinhibition during low temperature stress generally occurred more rapidly in TN66.
