In plants,flowering was triggered by endogenous and environmental signals.CONSTANS (CO) promotes flowering of Arabidopsis in response to long-day conditions.In a screening for stay-green mutants in Arabidopsis thaliana,a late-flowering mutant in Columbia background was isolated and tentatively named fnc25.It was later testified a new constans allele,co-9.When grown in the long-day conditions,the mutant showed a tall stature and dark-green leaves,bearing more rosettes leaves,flowering late and extending its lifespan.As far as the flowering time is concerned,the co-9 was insensitive to vernalization,flowering slightly earlier under short days.The late-flowering phenotype was not resumed by applying exogenous gibberellin.A 10 nt fragment deletion was found in the coding region of CO gene,resulting in premature termination of CO protein and the absence of the 92 amino acids of C-terminal domain.These phenotypes were most likely caused by a reduction in the function of CONSTANS.It is remarkable that the mRNA level of FT,one of the direct target genes of CO,is dramatically reduced,whereas mRNA levels of SOC1,the other direct target gene of CO is almost not changed.CO maybe promotes the target genes through difference domains of its protein.One domain is altered but the other is intact maybe only influence promoting of one of the target genes,and thereby lead to a late-flowering phenotype.

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.

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.