Changes in polyamine content, arginine and ornithine decarboxylases and transglutaminase activities during light/dark phases (of initial differentiation) in maize calluses and their chloroplasts

Maize calluses and their isolated chloroplasts were analysed to study the c hanges in polyamine content, arginine and ornithine decarboxylases and tran sglutaminase activities during light/dark phases of the first day after sub culture in maintenance medium (containing 2,4-D) and differentiation medium (without 2,4-D). Free polyamine content changed significantly in both diff erentiating calluses and chloroplasts showing a maximum during light phase and also increasing after mid-dark phase. Acid-insoluble polyamines showed a similar trend. In whole cells from the callus cultured in maintenance med ium, the changes were not significant, except for free putrescine which inc reased in the dark phase. In chloroplasts of both types of calluses, the tr end was similar. Arginine decarboxylase activity in vitro assayed in optima l conditions was not affected by hormone deprivation either in whole cells from the callus or in chloroplasts. The formation of putrescine by arginine decarboxylase activity gradually increased in the light until 9-12 h after subculture, whereas at the onset of the dark phase, a significant decrease was observed. Ornithine decarboxylase activity in vitro always showed slig ht changes, except in growing callus where putrescine synthesis increased a bruptly at 8 h and decreased thereafter. Transglutaminase was immunodetecte d in whole cells from the callus and in isolated chloroplasts by western bl ot. In the entire cells, protein substrates were found which were not prese nt in isolated chloroplast. Transglutaminase activity was light sensitive a nd also affected by hormone deprivation. This enzyme was more active in dif ferentiation than in maintenance medium, in both callus and chloroplasts, i n light and dark phases. These data indicate that, the parameters studied h ere are not only light affected but also regulated by a daily rhythm. (C) 1 999 Editions scientifiques et medicales Elsevier SAS.