Brassinosteroids (BRs) play an essential role in plant growth and development, and have been implicated in many physiological responses. However, little is known about the role of BRs in the plant response to oxidative stress. In this study, we identified a novel insertion allele (det2‐9) of the DET2 gene in Arabidopsis based on molecular, physiological and genetic approaches. We found that the det2 mutant exhibited an enhanced resistance to oxidative stress. The enhanced oxidative stress resistance in det2 plants was correlated with a constitutive increase in superoxide dismutase (SOD) activity and increased transcript levels of the defence gene catalase (CAT). To our knowledge, these results demonstrate, for the first time, that loss‐of‐function mutations in the DET2 gene lead to an enhanced oxidative stress resistance in Arabidopsis. A general explanation is that the long‐term BR deficiency in the det2 mutant results in a constant in vivo physiological stress that, in turn, activates the constitutive expression of some defence genes and, consequently, the activities of related enzymes.

In an attempt to screen stay-green mutants in Arabidopsis in the absence of light, a mutant displaying the characteristics of brassinosteroids mutants was isolated. This mutant, dst6, carries a single recessive mutation. Using molecular genetic markers, the mutation was mapped to the bottom of chromosome II , which is around the region of DET2 ,one of the genes known to cause brassinosteroids mutation. The analysis of cDNA and genomic sequence of DET2 in dst6 revealed a frame-shifting insertion. These results suggest that dst6 is a putative new allele of det2.