EFFECT OF NICOTINAMIDE ON GENE-EXPRESSION AND GLUTATHIONE LEVELS IN TISSUE-CULTURES OF PISUM-SATIVUM

Nicotinamide (NIC; 8.2 mM) caused increased abundance of mRNA for chal cone synthase in shoot and root cultures of Pisum sativum. Increased g ene expression was observed from 3.5 h after NIC addition in shoot cul tures in light (PS-S) and root cultures in light (PS-R-L) and darkness (PS-R-D). Twelve h after NIC addition to the cultures, the amount of mRNA for chs 2 was increased 10-fold in PS-R-L, 6-fold in PS-R-D and 2 -fold in PS-S. The expression of the glutathione reductase (GR) gene a nd the photosynthetic cab gene was also studied. Increased GR expressi on was clearly seen 3.5 h after NIC addition in PS-S and PS-R-L and af ter 12 h in PS-R-D cultures, while the amount of mRNA for cab initiall y (2 - 3.5 h) increased and later (6 - 12 h) decreased in PS-S. Glutat hione content was determined in the cultures. After a decrease in glut athione content during the first 2 - 3.5 h following NIC addition, the level of glutathione increased. In light-grown cultures, an increase in the content of the oxidised (disulfide) form of glutathione (GSSG) was an earlier event than the rise in reduced glutathione (GSH) levels , after 12 h for PS-R-L and after 3.5 - 6 h for PS-S. Five days after NIC addition, the GSSG contents in the root and shoot cultures in ligh t were increased by up to 150 and 500 %, respectively, whereas the amo unts of GSH doubled in both cultures. In dark grown cultures, an early increase in the content of GSH, but not GSSG, was observed.