In this paper, the delayed ultra-weak luminescence (UWL), Nitrate reductase activity and reactive oxygen species (ROS)
contents of 3 different maize varieties (Zhengdan958, Jundan20 and Liaoyu18) under 50mg.L<sup>-1</sup> CdCl2 stress were
investigated. The results showed that the UWL intensity of all 3 maize varieties was decreased and the curve attenuating
accelerated under the Cd stress. The total photon number reduced 12.8% (zhengdan958), 20.1% (jundan20) and 13.4%
(liaoyu18), respectively. The activity of Nitrate reductase, which is a key marker reflecting internal physiology status,
decrease 50.12% (zhengdan958), 58.80% (jundan20) and 55.80% (liaoyu18), respectively. The ROS contents increased
remarkably under 50mg.L<sup>-1</sup> Cdstress, ranging from 35.87% (liaoyu18), 40.90% (zhengdan958) to 42.23% (jundan20).
From these results we speculated that UWL decreasing tendency was consisting with the change character of Nitrate
reductase activity, and rather the in vivo metabolism reactions than the ROS contents, was the main resources of ultraweak
photon emitting. Taken together, the UWL and the physiological status are closely related, ultra-weak
luminescence could be used as a time-saving, sensitive method for evaluating cadmium stress resistance of different
varieties of maize.