The function of polyamines in Arabidopsis thaliana
To evaluate the importance of polyamines under stress conditions, mutants in the polyamine pathway were grown under salt and osmotic stress. Two types of mutant were chosen, methionine-overproducing (mto) mutants (may increase polyamine production) and arginine decarboxylase (spe) mutants (may decrease polyamine production). Initial experiments were done to determine how polyamines were to be extracted from the plant. Under normal growth conditions, the polyamine content of each mutant was similar to wild type contents. Polyamines varied in different organs of Arabidopsis with flowers having higher polyamine contents than green organs. To determine the effect of stress on the mutants, Fv/Fm (maximum photo synthetic efficiency), fresh weight, chlorophyll and polyamine contents were determined. Under salt stress, polyamine contents increased in wild type plants, but only when they were germinated on salt-containing medium, spe mutants showed a decreased tolerance to saline conditions, and the spe2-1 mutant plants also showed a decrease in polyamine accumulation compared to its wild type. Under severe salt stress, spe mutants bleached more rapidly than their wild types. Results for the effect of salt stress on the mto mutants were inconsistent. Under osmotic stress (treatment with polyethylene glycol), polyamine content decreased and no clear difference was found between the effect on mto mutants and their wild types. To isolate mutants in polyamine signalling, activation-tagged lines were screened on Murashige-Skoog (MS) medium supplemented with 5 mM spermidine. Mutants that stayed green under these conditions and/or had longer roots than the wild type were isolated. The mutants were crossed to the wild type and the F2 generation was analysed for segregation on BASTA and on spermidine-containing medium. Adaptor PCR, inverse PCR and plasmid rescue were used to determine the insertion sites of the enhancer tag. One of the mutants had several T-DNA inserts, one next to a 5S rRNA gene and one in either a gene for a chloroplast nucleoid DNA-binding protein or a U2 small nuclear ribonucleoprotein. It is therefore unclear what caused the mutant phenotype. Publication: Kasinathan, V., Wingler, A. (2004) Effect of reduced arginine decarboxylase activity on salt tolerance and on polyamine formation during salt stress in Arabidopsis thaliana. Physiologia Plantarum: 121 101-107.