Long- and short-term acclimation of the photosynthetic apparatus to salinity in Chlamydomonas reinhardtii. The role of Stt7 protein kinase.

Salt stress triggers an Stt7-mediated LHCII-phosphorylation signaling mechanism similar to light-induced state transitions. However, phosphorylated LHCII, after detaching from PSII, does not attach to PSI but self-aggregates instead. Salt is a major stress factor in the growth of algae and plants. Here, our study mainly focuses on the organization of the photosynthetic apparatus to the long-term responses of Chlamydomonas reinhardtii to elevated NaCl concentrations. We analyzed the physiological effects of salt treatment at a cellular, membrane, and protein level by microscopy, protein profile analyses, transcripts, circular dichroism spectroscopy, chlorophyll fluorescence transients, and steady-state and time-resolved fluorescence spectroscopy. We have ascertained that cells that were grown in high-salinity medium form palmelloids sphere-shaped colonies, where daughter cells with curtailed flagella are enclosed within the mother cell walls. Palmelloid formation depends on the presence of a cell wall, as it was not observed in a cell-wall-less mutant CC-503. Using the stt7 mutant cells, we show Stt7 kinase-dependent phosphorylation of light-harvesting complex II (LHCII) in both short- and long-term treatments of various NaCl concentrations-demonstrating NaCl-induced state transitions that are similar to light-induced state transitions. The grana thylakoids were less appressed (with higher repeat distances), and cells grown in 150 mM NaCl showed disordered structures that formed diffuse boundaries with the flanking stroma lamellae. PSII core proteins were more prone to damage than PSI. At high salt concentrations (100-150 mM), LHCII aggregates accumulated in the thylakoid membranes. Low-temperature and time-resolved fluorescence spectroscopy indicated that the stt7 mutant was more sensitive to salt stress, suggesting that LHCII phosphorylation has a role in the acclimation and protection of the photosynthetic apparatus.

Alteration of photochemistry and protein degradation of photosystem II from Chlamydomonas reinhardtii under high salt grown cells.

In this study, we evaluated the inhibitory effect of NaCl on cell growth, photochemistry and protein profile of photosystem (PS) II in Chlamydomonas reinhardtii. To study the effect of NaCl on the photosynthetic apparatus, the C. reinhardtii cells were grown at different concentrations (0, 50, 100 and 150 mM). NaCl induced flagellar resorption due to which the cells lost their motility, formation of palmelloids, reduced cell size and slower cell division. Chlorophyll fluorescence transients at different NaCl concentrations had decreased intensities of all peaks (OJIP) indicating the apparent inactivation energies of both donor and acceptor side of PSII. Consequently, inhibition of electron transport occurred particularly at PSII. Further, low temperature emission spectra showed that the rate of damage to the PSII was more when compared to PSI. Also, we have carried out the visible circular dichroism spectra from thylakoids where the major peaks contributed to chlorophyll a and b are equally reduced in different salt grown cells, which may explain the changes at the level of inter pigment-pigment interactions. Furthermore protein profile analysis of PSII revealed that the major subunit of light harvesting complex (LHC)II is more prone to salt stress than core proteins of PSII indicating the light harvesting funnel from LHCII to PSII core is impaired.

Differential degradation of photosystem I subunits under iron deficiency in rice.

Rice (Oryza sativa) is one of the staple foods of the world. Iron (Fe) deficiency is a major abiotic stress factor that contributes world-wide to losses in crop yield and decline in nutritional quality. As cofactor for many enzymes and proteins, iron is an essential element. It plays a pivotal role in chlorophyll (Chl) biosynthesis, and iron deficiency may result in decreased Chl production and, thus, reduced photosynthetic capacity. Photosystem I (PSI) is a prime target of iron deficiency because of its high iron content (12 Fe per PS). To understand the protein level changes in the light-harvesting complex (LHC) of PSI (LHCI) under iron deficiency, rice seedlings were grown in Hoagland's nutrient medium with and without Fe. Chlorophyll content and photosynthetic efficiency decreased under iron deficiency. Protein gel blots probed with antibodies against the PSI core and Lhca 1-4 proteins revealed that the core subunits PsaA and PsaB remained stable under iron deficiency, whereas PsaC and PsaD decreased by about 50%, and PsaE was completely degraded. Among the LHCI subunits, Lhca1 and Lhca2 decreased by 40 and 50%, respectively, whereas Lhca3 and Lhca4 were completely degraded. We propose that the dissociation of LHCI subunits may be due to increased levels of reactive oxygen species, which is suggested by the increased activity of superoxide dismutase.

Interaction studies of coumaroyltyramine with human serum albumin and its biological importance.

N-trans-p-coumaroyltyramine (CT) isolated from Physalis minima is a phenolic substance exhibiting many pharmacological activities like potent inhibition of acetyl cholinesterase, cell proliferation, platelet aggregation, and also antioxidant activity. Here, we have studied the binding of CT with HSA at physiological pH 7.2 by using fluorescence, circular dichroism spectroscopy, mass spectrometry, and molecular docking methods. From the fluorescence emission studies, the number of binding sites and binding constant were calculated to be 2 and (4.5 +/- 0.01) x 10(5) M(-1), respectively. The free energy change was calculated as -7.6 kcal M(-1) at 25 degrees C, which indicates the hydrophobic interactions of CT with HSA and is in well agreement with the computational calculations and molecular docking studies. The changes in the secondary structure of HSA after its complexation with the ligand were studied with CD spectroscopy, which indicated that the protein became partially unfolded. Also, temperature did not affect the HSA-CT complexes. The binding of CT with HSA was detected as 2 molecules bound to HSA was determined using micro TOF-Q mass spectrometry. Further, molecular docking studies revealed that CT was binding at subdomain IIA with hydrophobic interactions and also by hydrogen-bond interactions between the hydroxyl (OH) group of carbon-16 and carbon-2 of CT and Arg222, Ala291, Val293, and Met298 of HSA, with hydrogen-bond distances of 2.488, 2.811, 2.678, and 2.586 A, respectively.