RESPONSES OF THE TRANSCRIPTIONAL APPARATUS OF BARLEY CHLOROPLASTS TO A PROLONGED DARK PERIOD AND TO SUBSEQUENT REILLUMINATION

In this study the responses of the chloroplast transcriptional apparat us in barley (Hordeum vulgare L. cv. Carina) primary foliage leaves we re examined during and after interruption of the light/dark growth reg ime by a two-day period of light deprivation on days 10 and 11 after s awing. Run-on transcript assays and northern blot analyses showed that transcripts in chloroplasts can be divided into at least three groups that differ in their levels during the dark period and in the kinetic s of their resynthesis during the reillumination phase. Group I transc ripts (rbcL, psaA,B, atpB) show decreased expression as well as reduce d transcript accumulation during the dark period both of which are res tored within 32 h after reillumination of the plants. Group II (psbA, psbD) and group III (16S rRNA, trnE) transcripts show a delayed or no detectable response to prolonged darkness at the transcript level. Whi le group II transcription does not change significantly upon reillumin ation, transcription of group III genes increases substantially above the initial value within a very short time after retransfer into light . Changes in gene specificity of the transcriptional apparatus are acc ompanied by a changing sensitivity of the chloroplast transcriptional apparatus towards the transcription inhibitor tagetitoxin. The stronge st inhibitory effect of tagetitoxin could be observed in leaves recove ring from the dark-induced stress situation.