Differential leaf stress responses in young and senescent plants

Responses to low temperature, mechanical wounding and salicylic acid (SA) t reatments were studied in 3-week-old (young) and 6-week-old (senescent) Ara bidopsis thaliana (L.) Heynh. plants by analyzing increases in Pal1 and Pr1 expression and superoxide dismutase (SOD; EC 1.15.1.1) and peroxidase (POX ; EC 1.11.1.7) activities. Young plants showed higher Pal1 transcript accum ulation after low temperature and wounding. In contrast, senescent plants p resented higher accumulation of Pr1 transcripts after SA treatments. Simila r results were obtained with the ethylene-insensitive etr1 mutant, suggesti ng that these differences are not related to increased ethylene content in senescent tissues. SOD activity and inducibility were lower, whereas POX ac tivity and inducibility were higher in senescent plants. A possible relatio nship between senescence-associated changes in responses to stress and in t he metabolism of active oxygen species is discussed.