An Arabidopsis mutant,alr1, was isolated and characterized. The alr1 mutant exhibited downward curling and asymmetric rosette leaves. Moreover,it showed an enhanced apical dominance in shoots, agravitropism in roots, shortened hypocotyl and extended life span. It also exhibited a significant higher SOD activity in the leaves of mutant plants. Genetic analysis revealed that the mutant was due to a single recessive mutation,which was mapped to a region about 7.89 cM from nag111 on Chromosome 1 using SSLPs markers.

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.

Genetic analyses of lifespan in model animals have revealed that extended lifespans are closely associated to increased resistance to oxidative stress. In the model plant Arabidopsis, late-flowering mutants are also found to be more tolerant to oxidative stress. However, Arabidopsis mutants with extended lifespans are poorly studied so far. In this study, a screening system for mutants with extended lifespans in Arabidopsis was established using paraquat, a potent herbicide that exacerbates O2-. radical production. The relationship between lifespan and resistance to oxidative stress was examined with one of the mutants, SFNA-9-4. Compared to that of wild type, the lifespan of SFNA-9-4 is significantly extended, and its resistance to oxidative stress is also significantly elevated. These results suggest that, as in Drosophila, paraquat can also be used to screen for mutants with extended lifespans in Arabidopsis.