Photosynthetic characteristics and protective mechanisms against oxidativestress during chilling and subsequent recovery in two maize varieties differing in chilling sensitivity

Plants of two maize varieties differing in chilling sensitivity (Z7, tolera nt and Penjalinan, sensitive) were subjected to 5 degreesC, 300 mu mol m(-2 ) s(-1) PPFD and 12-h photoperiod during 5 days and recovered during 3 days at 25 degreesC at the same light regime. Gas exchange and chlorophyll fluo rescence analyses showed the same degree of photoinhibition during chilling period in both varieties. However, chlorophyll fluorescence analysis showe d an increase in the process of energy dissipation mainly in Z7 leaves. Bes ides, Z7 leaves showed higher carotenoids/total chlorophyll ratio than Penj alinan, On the other hand, Z7 leaves showed a marked increase in antioxidan t enzyme activities (superoxide dismutase, SOD; ascorbate peroxidase, APX; glutathione reductase, GR), while in Penjalinan decreased the cytoplasmatic and chloroplastic CuZn and Fe SODs activities and increased the APX and GR activities in less extent than in Z7. Such antioxidant enzyme behaviour co uld be responsible for chloroplast damage caused by superoxide anion (O-2(- )) during chilling in Penjalinan. When plants were returned to 25 degreesC, Z7 leaves quickly recovered photosynthetic activity thus diminishing the p otential power for reactive oxygen species generation. On the contrary, Pen jalinan leaves only recovered photosynthetic activity after 3 days at 25 de greesC. Moreover, during chilling recovery, Penjalinan leaves increased SOD and GR activity, while APX activity decreased. As a consequence, oxidation damage due to H2O2 accumulation could occur in Penjalinan leaves. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.