CAM-related changes in chloroplastic metabolism of Mesembryanthemum crystallinum L.

Crassulacean acid metabolism (CAM) is an intriguing metabolic strategy to maintain photosynthesis under conditions of closed stomata. A shift from C3 photosynthesis to CAM in Mesembryanthemum crystallinum plants was induced by high salinity (0.4 M NaCl). In CAM-performing plants, the quantum efficiencies of photosystem II and I were observed to undergo distinct diurnal fluctuations that were characterized by a strong decline at the onset of the day, midday recovery, and an evening drop. The temporal recovery of both photosystems’ efficiency at midday was associated with a more rapid induction of the electron transport rate at PSII. This recovery of the photosynthetic apparatus at midday was observed to be accompanied by extreme swelling of thylakoids. Despite these fluctuations, a persistent effect of CAM was the acceptor side limitation of PSI during the day, which was accompanied by a strongly decreased level of Rubisco protein. Diurnal changes in the efficiency of photosystems were parallel to corresponding changes in the levels of mRNAs for proteins of PSII and PSI reaction centers and for rbcL, reaching a maximum in CAM plants at midday. This might reflect a high demand for new protein synthesis at this time of the day. Hybridization of run-on transcripts with specific probes for plastid genes of M. crystallinum revealed that the changes in plastidic mRNA levels were regulated at the level of transcription

Tester of the TRT front-end electronics for the ATLAS-experiment

The VME based tester for front-end electronics of the TRT (Transition Radiation Tracker) detector of the ATLAS-LHC experiment at CERN, Geneva, is described. The TRT read-out electronics for 424576 proportional tubes grouped on many thousands of cards requires stringent quality control after assembly and during installation. The tester provides all required data, pulses, timing and power supplies for tested cards. The essential part of the tester is its software that allows for device handling as well as facilitates functional and statistical tests. The prototype, present design as well as the new design for mass production tests are discussed. (17 refs)