Photosynthesis Research (v.132, #1)

David W. Krogmann, 1931–2016 by Jerry J. Brand; Cheryl A. Kerfeld; William A. Cramer; Govindjee (1-12).
We provide here reflections on the life and career of David W. Krogmann (1931–2016), a great scientist, a mentor and an outstanding teacher, who had a remarkable impact on anyone who came in contact with him. Dave was a pillar of photosynthesis at Purdue University, and an international authority on electron transfer intermediates in oxygenic photosynthesis, particularly the soluble cytochromes. The photosynthetic system of his choice was cyanobacteria, and one of his major discoveries was the Orange Carotenoid Protein in these microrganisms.
Keywords: Cytochromes; Cyanobacteria; Orange carotenoid protein; Electron transport; Phosphorylation; Plastocyanin

Frequently asked questions about chlorophyll fluorescence, the sequel by Hazem M. Kalaji; Gert Schansker; Marian Brestic; Filippo Bussotti; Angeles Calatayud; Lorenzo Ferroni; Vasilij Goltsev; Lucia Guidi; Anjana Jajoo; Pengmin Li; Pasquale Losciale; Vinod K. Mishra; Amarendra N. Misra; Sergio G. Nebauer; Simonetta Pancaldi; Consuelo Penella; Martina Pollastrini; Kancherla Suresh; Eduardo Tambussi; Marcos Yanniccari; Marek Zivcak; Magdalena D. Cetner; Izabela A. Samborska; Alexandrina Stirbet; Katarina Olsovska; Kristyna Kunderlikova; Henry Shelonzek; Szymon Rusinowski; Wojciech Bąba (13-66).
Using chlorophyll (Chl) a fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes in the Chl a fluorescence kinetics. Kalaji et al. (Photosynth Res 122:121–158, 2014a) addressed several questions about instruments, methods and applications based on Chl a fluorescence. Here, additional Chl a fluorescence-related topics are discussed again in a question and answer format. Examples are the effect of connectivity on photochemical quenching, the correction of F V /F M values for PSI fluorescence, the energy partitioning concept, the interpretation of the complementary area, probing the donor side of PSII, the assignment of bands of 77 K fluorescence emission spectra to fluorescence emitters, the relationship between prompt and delayed fluorescence, potential problems when sampling tree canopies, the use of fluorescence parameters in QTL studies, the use of Chl a fluorescence in biosensor applications and the application of neural network approaches for the analysis of fluorescence measurements. The answers draw on knowledge from different Chl a fluorescence analysis domains, yielding in several cases new insights.
Keywords: Chl a fluorescence; Delayed fluorescence; Photochemical quenching; Energy partitioning; Area

Erratum to: Frequently asked questions about chlorophyll fluorescence, the sequel by Hazem M. Kalaji; Gert Schansker; Marian Brestic; Filippo Bussotti; Angeles Calatayud; Lorenzo Ferroni; Vasilij Goltsev; Lucia Guidi; Anjana Jajoo; Pengmin Li; Pasquale Losciale; Vinod K. Mishra; Amarendra N. Misra; Sergio G. Nebauer; Simonetta Pancaldi; Consuelo Penella; Martina Pollastrini; Kancherla Suresh; Eduardo Tambussi; Marcos Yanniccari; Marek Zivcak; Magdalena D. Cetner; Izabela A. Samborska; Alexandrina Stirbet; Katarina Olsovska; Kristyna Kunderlikova; Henry Shelonzek; Szymon Rusinowski; Wojciech Bąba (67-68).

Phototrophic microorganisms like cyanobacteria show growth curves in batch culture that differ from the corresponding growth curves of chemotrophic bacteria. Instead of the usual three phases, i.e., lag-, log-, and stationary phase, phototrophs display four distinct phases. The extra growth phase is a phase of linear, light-limited growth that follows the exponential phase and is often ignored as being different. Results of this study demonstrate marked growth phase-dependent alterations in the photophysiology of the cyanobacterium Synechocystis sp. PCC 6803 between cells harvested from the exponential and the linear growth phase. Notable differences are a gradual shift in the energy transfer of the light-harvesting phycobilisomes to the photosystems and a distinct change in the redox state of the plastoquinone pool. These differences will likely affect the result of physiological studies and the efficiency of product formation of Synechocystis in biotechnological applications. Our study also demonstrates that the length of the period of exponential growth can be extended by a gradually stronger incident light intensity that matches the increase of the cell density of the culture.
Keywords: Batch culture; Cyanobacteria; Molecular physiology; PSI/PSII ratio; State transition

The effects of pH and pCO2 on photosynthesis and respiration in the diatom Thalassiosira weissflogii by Johanna A. L. Goldman; Michael L. Bender; François M. M. Morel (83-93).
The response of marine phytoplankton to the ongoing increase in atmospheric pCO2 reflects the consequences of both increased CO2 concentration and decreased pH in surface seawater. In the model diatom Thalassiosira weissflogii, we explored the effects of varying pCO2 and pH, independently and in concert, on photosynthesis and respiration by incubating samples in water enriched in H2 18O. In long-term experiments (~6-h) at saturating light intensity, we observed no effects of pH or pCO2 on growth rate, photosynthesis or respiration. This absence of a measurable response reflects the very small change in energy used by the carbon concentrating mechanism (CCM) compared to the energy used in carbon fixation. In short-term experiments (~3 min), we also observed no effects of pCO2 or pH, even under limiting light intensity. We surmise that in T. weissflogii, it is the photosynthetic production of NADPH and ATP, rather than the CO2-saturation of Rubisco that controls the rate of photosynthesis at low irradiance. In short-term experiments, we observed a slightly higher respiration rate at low pH at the onset of the dark period, possibly reflecting the energy used for exporting H+ and maintaining pH homeostasis. Based on what is known of the biochemistry of marine phytoplankton, our results are likely generalizable to other diatoms and a number of other eukaryotic species. The direct effects of ocean acidification on growth, photosynthesis and respiration in these organisms should be small over the range of atmospheric pCO2 predicted for the twenty-first century.
Keywords: Ocean acidification; Photosynthesis; Respiration; Carbon concentrating mechanism; Diatoms; Light limitation

The proteolysis adaptor, NblA, binds to the N-terminus of β-phycocyanin: Implications for the mechanism of phycobilisome degradation by Amelia Y. Nguyen; William P. Bricker; Hao Zhang; Daniel A. Weisz; Michael L. Gross; Himadri B. Pakrasi (95-106).
Phycobilisome (PBS) complexes are massive light-harvesting apparati in cyanobacteria that capture and funnel light energy to the photosystem. PBS complexes are dynamically degraded during nutrient deprivation, which causes severe chlorosis, and resynthesized during nutrient repletion. PBS degradation occurs rapidly after nutrient step down, and is specifically triggered by non-bleaching protein A (NblA), a small proteolysis adaptor that facilitates interactions between a Clp chaperone and phycobiliproteins. Little is known about the mode of action of NblA during PBS degradation. In this study, we used chemical cross-linking coupled with LC-MS/MS to investigate the interactions between NblA and phycobiliproteins. An isotopically coded BS3 cross-linker captured a protein interaction between NblA and β-phycocyanin (PC). LC-MS/MS analysis identified the amino acid residues participating in the binding reaction, and demonstrated that K52 in NblA is cross-linked to T2 in β-PC. These results were modeled onto the existing crystal structures of NblA and PC by protein docking simulations. Our data indicate that the C-terminus of NblA fits in an open groove of β-PC, a region located inside the central hollow cavity of a PC rod. NblA may mediate PBS degradation by disrupting the structural integrity of the PC rod from within the rod. In addition, M1-K44 and M1-K52 cross-links between the N-terminus of NblA and the C-terminus of NblA are consistent with the NblA crystal structure, confirming that the purified NblA is structurally and biologically relevant. These findings provide direct evidence that NblA physically interacts with β-PC.
Keywords: Cyanobacteria; Phycobilisome proteolysis; Nitrogen starvation; Cross-linking; Mass spectrometry; Protein docking