Studies on the role of glycine betaine and pathogenesis-related protiens in cold and drought tolerance of plants

The present study was conducted to investigate the role of glycine betaine and pathogenesis-related proteins in cold and drought tolerance of plants.; Increase of endogenous glycine betaine level in both bean and Arabidopsis plants was observed in response to water stress. Bean plants treated with exogenous glycine betaine maintained better water status during water stress treatment than did the untreated plants. Exogenously applied glycine betaine slightly offset the reductions in the leaf CO{dollar}sb2{dollar} absorption rate and in the decline of {dollar}rm Fsb{lcub}v{rcub}/Fsb{lcub}o{rcub}{dollar} caused by water stress. Exogenous glycine betaine also improved the plant growth under well-watered conditions.; All the plant species (barley, blackberry, spinach and Arabidopsis thaliana) investigated in this study accumulated glycine betaine in response to low temperature (2/4{dollar}spcirc{dollar}C) treatment. The increase of endogenous glycine betaine in Arabidopsis plants was rapid. A three-fold increase was observed after one day cold acclimation. Exogenous glycine betaine (10 mM) increased the cold tolerance (1.5{dollar}spcirc{dollar}C) of plants. Exogenous ABA (1 mM) increased the cold tolerance and the endogenous glycine betaine level in Arabidopsis plants, suggesting that ABA may induce cold tolerance via glycine betaine synthesis.; Pathogenesis-related protein ({dollar}beta{dollar}-1,3-glucanase, chitinase and thaumatin-like protein) were induced during cold acclimation in barley plants. However, PR-proteins were not induced in Arabidopsis plants in response to the cold acclimation treatment. Transgenic Arabidopsis plants, which constitutively expressed thaumatin-like protein gene, did not show significant increases in cold tolerance as well as in drought tolerance. The results suggest that PR-proteins are a part of plants' response to low temperature, but may not be involved in conferring cold tolerance in Arabidopsis plants. In addition, PR-proteins also were induced by exogenous glycine betaine in bean plants under both greenhouse and aseptic conditions. In spinach plants, water stress increased the levels of PR-proteins in leaves. These results further support the involvement of PR-proteins in the plants' response to abiotic stress.