Summary: Drought is a major abiotic stress that impairs plant growth and development. Despite this, a comprehensive understanding of drought effects on the photosynthetic apparatus is lacking. In this work, we studied the consequences of 14‐d drought treatment on Arabidopsis thaliana. We used biochemical and spectroscopic methods to examine photosynthetic membrane composition and functionality. Drought led to the disassembly of PSII supercomplexes and the degradation of PSII core. The light‐harvesting complexes (LHCII) instead remain in the membrane but cannot act as an antenna for active PSII, thus representing a potential source of photodamage. This effect can also be observed during nonphotochemical quenching (NPQ) induction when even short pulses of saturating light can lead to photoinhibition. At a later stage, under severe drought stress, the PSI antenna size is also reduced and the PSI‐LHCI supercomplexes disassemble. Surprisingly, although we did not observe changes in the PSI core protein content, the functionality of PSI is severely affected, suggesting the accumulation of nonfunctional PSI complexes. We conclude that drought affects both photosystems, although at a different stage, and that the operative quantum efficiency of PSII (Φ_PSII) is very sensitive to drought and can thus be used as a parameter for early detection of drought stress.

Damaged photosystem II reaction centers are the site of photoinhibition-related energy dissipation.

Nontarget impacts of six transgenic Bt rice lines (expressing the Cry1Ab or Cry1Ab/Cry1Ac protein) on the thrips, Stenchaetothrips biformis (Bagnall)

CAM plants are superior to C3 plants in drought resistance because of their peculiar photosynthesis pathway and morphological features. While those aspects have been studied for decades, little is known about the photosynthetic machinery of CAM plants. Here, we used a combination of biochemical and biophysical methods to study the photosynthetic apparatus of Tillandsia flabellate, an obligatory CAM plant. Most of the Photosystems super- and sub-complexes have properties very similar to those of Arabidopsis, with the main difference that in Tillandsia PSI-LHCI complexes bind extra LHCI. Functional measurements show that the PSI/PSII ratio is rather low compared to other plants and that the antenna size of both PSI and PSII is small. Upon 30-day water deficiency, the composition of the photosystems does not change significantly, PSII efficiency remains high and no Photosystem II photoinhibition was detected despite a reduction of non-photochemical quenching (NPQ).

Guanosine tetraphosphate (ppGpp) is a hyperphosphorylated nucleotide originally discovered in prokaryotes and found in the chloroplasts of plants and algae. In plants, ppGpp regulates photosynthetic activity, which is important in acclimation to environmental stresses such as nitrogen limitation. However, the full range of stresses involving ppGpp signalling is not yet known. Here, we investigated the role of ppGpp accumulation in the acclimation of plants to excess light. We found that the over-accumulation of ppGpp in transgenic lines that overexpress RSH3 (OX:RSH3) increases tolerance to excess light. Although ppGpp leads to higher non-photochemical energy dissipation (NPQ) than in wild-type plants, we show that NPQ is not critical for the enhanced excess light tolerance. Rather, our results show that ppGpp accumulation leads to broad changes in plant physiology that prime plants to resist and subsequently recover from excess light exposure. ppGpp levels themselves also increase in response to excess light exposure, suggesting that ppGpp may play a physiological role in excess light acclimation. Our work adds to a growing body of evidence for the importance of ppGpp in plant stress acclimation.

Once-Through Steam Generator (OTSG) is the key equipment of nuclear power plant. Thermal hydraulic characteristic of OTSG is very important for the safety of nuclear reactor. Based on proper thermal hydraulic model, an analysis program is established to compute the response of reactor primary loop parameters against the time delay of control rods insertion in the case of loss-of flow accident. The results show that the longer insertion time delay will lead to more intensive variations of OTSG thermal parameters. When the time delay of the control rods insertion exceeds 2s, transient boiling will appear at the core outlet region. To ensure the safety of nuclear reactor, in the case of half the designed flow rate in the core, the time delay of the control rods insertion must be strictly limited to less than 2s.