Mechanisms of chilling-induced oxidative stress injury and tolerance in developing maize seedlings: Changes in antioxidant system, oxidation of proteins and lipids, and protease activities

The mechanisms involved in chilling injury or tolerance in developing maize seedlings subjected to low temperature stress have been investigated. Although acclimation-induced chilling tolerance was developmentally regulated, no tolerance was observed in non-acclimated developing seedlings subjected to 7 days of 4 degrees C stress. Consistent with previous results, chilling induced oxidative stress in the seedlings. Whereas acclimated seedlings had elevated levels (35-120%) of antioxidant enzymes, such as catalase, glutathione reductase and guaiacol peroxidase, nonacclimated seedlings had lower levels of these enzyme activities during chilling conditions. The increase in the activity of mitochondrial catalase3 isozyme, a major antioxidant enzyme in maize, was due to an increase in cat3 transcripts and CATS protein, as indicated by Northern and Western blot analyses. Besides, non-acclimated seedlings had increased levels of oxidized proteins (two to threefold) ana lipids (35-65%) during chilling and recovery compared with control or acclimated seedlings. Low-temperature stress also inhibited two proteases, endopeptidase and aminopeptidase, by 35% in non-acclimated seedlings. Since seedlings treated with prooxidants also promoted the oxidation of proteins and lipids and the inhibition of proteases, it was concluded that in vivo generated oxidative stress was likely responsible for affecting these processes. These results provide a correlative evidence to suggest that: (i) in non-acclimated seedlings, chilling injury was partly due to the build up of reactive oxygen species (ROS) that promoted the oxidation of proteins and lipids and inhibited protease activity; (ii) in acclimated seedlings, chilling tolerance was partly- due to an enhanced antioxidant system that prevented the accumulation of ROS and therefore, prevented the oxidation of proteins and lipids and the inhibition of protease activities during 4 degrees C stress and recovery.