Expression Of Enzyme Activities And Transcripts Required For Nitrate Assimilation In Maize (Zea Mays L A188 X Bms) Suspension Cell Cultures

The response of a rapidly growing, transformable maize suspension cell culture line (Zea mays L. A188 x BMS) to changes in media N and NO3- treatment was examined. Growth, N content, enzyme activities and transcript levels were measured in cells transferred to N-rich media (N6) or to media lacking N (N-free). Transferring cells to N-free media had little impact on cell growth (fresh and dry weight). However, reduced N, soluble protein, and total RNA per g dry weight were about 50% lower than in cells transferred to N6 media. Cellular NO3- nitrate reductase (NR) and nitrite reductase (NiR) activity declined rapidly when cells were transferred to N-free media. Within 24 h after transfer to N-free media, treatment with 1 mM KNO3 increased NADH: NR, NAD(P)H: NR, and NiR activities, and NR transcript levels. Cells transferred to N6 media did not respond to KNO3 treatment. Three days after transfer to N-free media, NR transcript levels increased rapidly and transiently in response to low concentrations of NO3-(.) This response was not prevented by the cytoplasmic protein synthesis inhibitor, cycloheximide. The similarity between the response of the N-starved A188 x EMS cell culture and maize roots to environmental NO3- indicated that the cell cultures provide a uniform, easily manipulable system for the study of NO3- signal transduction processes.