Involvement of arginine decarboxylase in the response of Arabidopsis thaliana to osmotic stress

The polyamines putrescine, spermidine and spermine have roles in the growth and development of nearly all organisms studied. Elevated levels of polyamines are correlated with increased rates of cell division, embryo development and stress responses of plants. Activities of the enzymes leading to the biosynthesis of putrescine, arginine decarboxylase (ADC) and ornithine decarboxylase (ODC), were both detectable in Arabidopsis. Specific inhibitors of ADC and ODC were used to confirm the identity of the enzymes. Leaves from Arabidopsis plants were osmotically stressed by incubation in buffers containing sorbitol. The efficacy of the stress treatment was confirmed by measuring water loss from the leaves. This osmotic stress led to dramatic elevations of ADC activity, and elevated levels of the putrescine accompanied the rise in ADC activity. This stress-related ADC response was blocked by cycloheximide. Elevated ADC levels in stressed leaves returned to control levels upon removal of leaves from the stress condition, verifying the correlation between ADC activity and osmotic stress. This report demonstrates that the dicot species Arabidopsis, a widely used model organism, responds to osmotic stress in a fashion similar to monocot species.