Photosynthetic efficiency and transcriptome analysis of Dunaliella salina under hypersaline: a retrograde signaling mechanism in the chloroplast.

Understanding the molecular mechanisms of environmental salinity stress tolerance and acclimation strategies by photosynthetic organisms facilitates accelerating the genetic improvement of tolerant economically important crops. In this study, we have chosen the marine algae Dunaliella (D.) salina, a high-potential and unique organism that shows superior tolerance against abiotic stresses, especially hypersaline conditions. We have grown the cells in three different salt concentrations 1.5M NaCl (control), 2M NaCl, and 3M NaCl (hypersaline). Fast chlorophyll fluorescence analysis showed increased initial fluorescence (Fo) and decreased photosynthetic efficiency, indicating hampered photosystem II utilization capacity under hypersaline conditions. Also, the reactive oxygen species (ROS) localization studies and quantification revealed elevated accumulation of ROS was observed in the chloroplast in the 3M condition. Pigment analysis shows a deficit in chlorophyll content and increased carotenoid accumulation, especially lutein and zeaxanthin content. This study majorly explored the chloroplast transcripts of the D. salina cell as it is the major environmental sensor. Even though most of the photosystem transcripts showed moderate upregulation in hypersaline conditions in the transcriptome study, the western blot analysis showed degradation of the core as well as antenna proteins of both the photosystems. Among the upregulated chloroplast transcripts, chloroplast Tidi, flavodoxin IsiB, and carotenoid biosynthesis-related protein transcripts strongly proposed photosynthetic apparatus remodeling. Also, the transcriptomic study revealed the upregulation of the tetrapyrrole biosynthesis pathway (TPB) and identified the presence of a negative regulator of this pathway, called the s-FLP splicing variant. These observations point towards the accumulation of TPB pathway intermediates PROTO-IX, Mg-PROTO-IX, and P-Chlide, those earlier reported as retrograde signaling molecules. Our comparative transcriptomic approach along with biophysical and biochemical studies in D. salina grown under control (1.5 M NaCl) and hypersaline (3M NaCl) conditions, unveil an efficient retrograde signaling mechanism mediated remodeling of photosynthetic apparatus.

Temperature-induced reversible changes in photosynthesis efficiency and organization of thylakoid membranes from pea (Pisum sativum).

High temperature can induce a substantial adverse effect on plant photosynthesis. This study addressed the impact of moderately high temperature (35 °C) on photosynthetic efficiency and thylakoid membrane organization in Pisum sativum. The Chl a fluorescence curves showed a significant change, indicating a reduction in photosynthetic efficiency when pea plants were exposed to moderate high-temperature stress. The pulse-amplitude modulation measurements showed decreased non-photochemical quenching while the non-regulated energy dissipation increased in treated compared to control and recovery plants. Both parameters indicated that the photosystem (PS)II was prone to temperature stress. The PSI donor side limitation increased in treated and recovery plants compared to control, suggesting the donor side of PSI is hampered in moderate-high temperature. Further, the PSI acceptor side increased in recovery plants compared to control, suggesting that the cyclic electron transport is repressed after temperature treatment but revert back to normal in recovery conditions. Also, the content of photoprotective carotenoid pigments like lutein and xanthophylls increased in temperature-treated leaves. These results indicate the alteration of macro-organization of thylakoid membranes under moderately elevated temperature, whereas supercomplexes restored to the control levels under recovery conditions. Further, the light harvesting complex (LHC)II trimers, and monomers were significantly decreased in temperature-treated plants. Furthermore, the amount of PSII reaction center proteins D1, D2, PsbO, and Cyt b6 was reduced under moderate temperature, whereas the content of LHC proteins of PSI was stable. These observations suggest that moderately high temperature can alter supercomplexes, which leads to change in the pigment-protein organization.

Change in the photochemical and structural organization of thylakoids from pea (Pisum sativum) under salt stress.

Salt can induce adverse effects, primarily on the photosynthetic process, ultimately influencing plant productivity. Still, the impact of salt on the photosynthesis process in terms of supercomplexes organization of thylakoid structure and function is not understood in Pea (Pisum sativum). To understand the structure and function in the leaves and thylakoids under salt (NaCl) treatment, we used various biophysical and biochemical techniques like infrared gas analyzer, chlorophyll a fluorescence, circular dichroism, electron microscopy, blue native gels, and western blots. The net photosynthetic rate, transpiration rate, and stomatal conductance were reduced significantly, whereas the water use efficiency was enhanced remarkably under high salt conditions (200 mM NaCl). The photochemical efficiency of both photosystem (PS) I and II was reduced in high salt by inhibiting their donor and acceptor sides. Interestingly the non-photochemical quenching (NPQ) is reduced in high salt; however, the non-regulated energy dissipation (NO) of PSII increased, leading to inactivation of PSII. The obtained results exhibit inhibition of NAD(P)H dehydrogenase (NDH) mediated pathway-dependent cyclic electron transport under salinity caused a decrease in proton motive force of ΔpH and Δψ. Further, the electron micrographs show the disorganization of grana thylakoids under salt stress. Furthermore, the macro-organization and supercomplexes of thylakoids were significantly affected by high salt. Specifically, the mega complexes, PSII-LHCII, PSI-LHCI, and NDH complexes were notably reduced, ultimately altering the electron transport. The reaction center proteins of oxygen-evolving complexes, D1 and D2 proteins were affected to high salt indicating changes in photochemical activities.

Effects of Dried Apple Consumption on Body Composition, Serum Lipid Profile, Glucose Regulation, and Inflammatory Markers in Overweight and Obese Children.

Consumption of fruits reduces the risk of chronic diseases such as cardiovascular disease; however, very few studies have investigated the effect of fruit consumption in overweight and obese children. We examined whether consuming dried apple as a snack is a practical solution for weight loss and improves body composition and metabolic markers. Thirty-eight overweight or obese children aged 10 to 16 years were randomly assigned to one of two groups consuming twice daily 120 kcal serving per day of either dried apple or a control snack (muffin) for 8 weeks. Body weight, height, waist circumference, and body composition were determined during an initial visit and after 8 weeks of intervention. Blood samples were collected to measure serum concentrations of blood lipids, glucose, insulin, proinsulin, total adiponectin, and C-reactive protein, as well as total antioxidant capacity and activity of glutathione peroxidase. Body weight increased in the muffin group (P = .01). BodPod and dual-energy X-ray absorptiometry showed that fat-free mass increased (P < .05) only in the muffin group. High-density lipoprotein cholesterol concentration increased (P = .04) after the 8-week treatment within the apple group. Overall, minor differences were detected in growing children who consumed snacks of either dried apples or muffins with similar macronutrient profiles for 8 weeks. Future research should evaluate the effects of consuming fresh apples that include the peel.