USE OF THE BIOLISTIC PROCESS FOR THE ANALYSIS OF NITRATE-INDUCIBLE PROMOTERS IN TRANSIENT EXPRESSION ASSAYS

The expression of reporter genes under the control of nitrate reductas e or nitrite reductase promoters measured in bombarded leaf tissues wa s compared to transcript levels expressed from the resident Nia gene o r to that of a reporter gene under the control of nitrite reductase pr omoter stably inserted into the nuclear genome. It was found that tran sient assays do not reflect the expression of the genomic integrated s equences. Particularly striking was the absence of repression of the r eporter genes by ammonium or glutamine in transient assays. The limits of the use of particle bombardment in transient experiments are discu ssed. One of the different hypotheses explaining the data involved a m odel of a negative control mediating the repression of Nia and Nii gen es expression on reduced nitrogen source.