In vivo and in vitro protective role of proline

Accumulation of proline in response to environmental stresses seems tobe widespread among plants. To elucidate the role of proline in plantresponses,in vivo and in vitro, we studied theeffect of proline on catalase (CAT; EC 1.11.1.6), peroxidase (POD; EC 1.11.1.7)and polyphenol oxidase (PPO; EC 1.14.18.1). In vivo, thesethree enzymes were activated by proline, while CAT and POD were activated andPPO was inactivated by NaCl. In vitro, CAT and POD wereactivated and PPO was inactivated by proline. Proline appeared to protect thesethree enzyme activities. The significance of these findings with regard toenvironmental stress-induced proline accumulation in vivois discussed. The ability of proline to activate the enzymes may suggest alimited conformational change. These results are important for characterisationof metabolic responses to environmental stresses and can be used as a stressindicator.