Two photosystems, I and II, absorb and convert light energy in photosynthesis in chloroplasts of green plants. The genes psbA and psaAB of the cytoplasmic chloroplast genome encode core components of photosystem II and photosystem I, respectively. Here we show that the absolute amounts of photosystem I and photosystem II respond, in a complementary manner, to changes in light quality that preferentially excite each photosystem in mustard seedlings. We also show that the initial response to altered energy distribution is a change in the rates of transcription of psbA and psaAB. Changes in chlorophyll fluorescence emission in vivo suggest that the signal initiating this change is the oxidation-reduction state of plastoquinone, a component of the photosynthetic electron transport chain that connects photosystem I and photosystem II. The results are consistent with transcriptional effects observed previously with chloroplasts isolated in vitro and demonstrate that redox control of chloroplast transcription initiates long-term adjustments that compensate for imbalance in energy distribution and adapt the whole plant to altered light environments.

Plants respond to changing light conditions by altering the stoichiometry between components of the photosynthetic electron transport chain of chloroplast thylakoids. We measured specific run-on transcription of the chloroplast genes psaB, psbA and rbcL in pea (Pisum sativum L.) seedlings grown under three different conditions of illumination: light selective for photosystem I (PSI-light); light selective for photosystem II (PSII-light); and a combination of PSI- and PSII-light (mixed light, ML). The transcriptional rate of the psaB gene increased under PSII-light and decreased under PSI-light, while the transcriptional rates of the psbA and rbcL genes were affected only in a non-specific way. Similar effects also occurred in plants grown under ML and switched to either PSI- or PSII-light for 4 h. Addition of the inhibitors of photosynthetic electron transport 3-(3,4 dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) influenced psaB transcription in isolated, illuminated chloroplasts: DCMU addition resulted in oxidation of the plastoquinone pool and decreased transcription of psaB; DBMIB addition resulted in reduction of the plastoquinone pool and increased transcription of psaB. The experimental results obtained in vivo and in vitro provide evidence for coupling between the redox state of plastoquinone and the rate of transcription of the psaB gene in pea.

SummaryTwo photosystems, I and II, absorb and convert light energy in photosynthesis in chloroplasts of green plants. The genes psbA and psaAB of the cytoplasmic chloroplast genome encode core components of photosystem II and photosystem I, respectively. Here we show that the absolute amounts of photosystem I and photosystem II respond, in a complementary manner, to changes in light quality that preferentially excite each photosystem in mustard seedlings. We also show that the initial response to altered energy distribution is a change in the rates of transcription of psbA and psaAB. Changes in chlorophyll uorescence emission in vivo suggest that the signal initiating this change is the oxidation-reduction state of plastoquinone, a component of the photosynthetic electron transport chain that connects photosystem I and photosystem II. The results are consistent with transcriptional effects observed previously with chloroplasts isolated in vitro and demonstrate that redox control of chloroplast transcription initiates long-term adjustments that compensate for imbalance in energy distribution and adapt the whole plant to altered light environments. IUBMB Life, 48: 271-276, 1999

No abstract

Helicopter landing and take-off in degraded visibility caused by blowing sand or dust (brown-out) may distort the pilot's comprehension of the helicopter's position. This is a serious problem that may lead to unattended lateral drift or descending rate. We have previously shown advantages of redundant tactile and multimodal information a simulated combat vehicle. In order to investigate if lateral drift in a helicopter can be reduced by use of a drift display an experiment with a simulated helicopter was performed. Three types of drift displays were tested: visual, tactile, and bimodal display and compared with the primary display that did not present lateral drift. Compared with the primary display lateral drift was reduced with all three drift display configurations. This indicates the value of a drift display in the helicopter and the possibilities of disengaging the pilot's vision for parallel tasks by the use of tactile or bimodal drift displays.