Biology subjects

Subramanyam, R.

Publications and source records attributed to Subramanyam, R..

5 recordsLinked to original sources

bioRxiv2023

Mitigation of the effect of high light on the photosynthetic apparatus of Rhodobacter alkalitolerans when grown in an alkaline environment

In the phototrophic alphaproteobacteria, photosynthesis is performed by pigment-protein complexes, including the light-harvesting complexes known as LH1 and LH2. The photosystem also encompasses carotenoids to assist in well-functioning of photosynthesis. Most photosynthetic bacteria are exposed to various abiotic stresses, and here, the Rhodobacter (R.) alkalitolerans were extracted from the alkaline pond. We report the comparative study of the photosynthetic apparatus of R. alkalitolerans in various light intensities in relation to this bacteriums high pH tolerance ability. We found that as the light intensity increased, the stability of photosystem complexes decreased in normal pH (npH pH 6.8{+/-}0.05) conditions, whereas in high pH (hpH pH 8.6{+/-}0.05) acclimation was observed to high light. The content of bacteriochlorophyll a, absorbance spectra, and circular dichroism data shows that the integrity of photosystem complexes is less affected in hpH compared to npH conditions. LP-BN of photosystem complexes also shows that LH2 is more affected in npH than hpH, whereas RC-LH1 monomer or dimer has shown interplay between monomer and dimer in hpH although the dimer and monomer both increased in npH. The sucrose density gradient of {beta}-DM solubilized intracytoplasmic membranes, further evidences the pattern of monomer-dimer conversion. Additionally, thin layer chromatographic separation of isolated membrane lipids shows that phosphatidylcholine (PC) levels have increased in hpH conditions which further confirms the integrity of photosystem complexes in hpH conditions. Moreover, qPCR data showed that the subunit -c of ATPase levels was overexpressed in hpH. Consequently, the P515 measurement shows that more ATP production is required in hpH, which dissipates the protons from the chromatophore lumen. This could be the reason the photosystem protein complex destabilized due to more lumen acidification. To maintain homeostasis in hpH, the antiporter NhaD expressed more than in the npH condition. IMPORTANCER. alkalitolerans is an alkaline tolerant species discovered from an alkaline pond in Gujrat India. Being a photoautotrophic photosynthetic organism, it serves as a good model organism to study the photosynthetic apparatus among phototrophic alphaproteobacteria. In nature organisms not only tackle a single abiotic stress but many including temperature, light, salinity, and many other abiotic stresses. Here we investigate how two different abiotic factors light and alkaline conditions modulate the growth and photosynthetic apparatus in a phototrophic alphaproteobacterium, R. alkalitolerans. Our results of this study will give leads in developing alkali-tolerant algae and higher plants.

cell biology↗

bioRxiv2023

Distinctive mechanism of LHCSR3 expression and function under osmotic stress in Chlamydomonas reinhardtii

Light-harvesting complex stress-related protein 3 (LHCSR3) expression is observed in various protoxidizing conditions like high light and nutrient starvation. LHCSR3 expression is essential for energy-dependent quenching (qE), whereas its role under nutrient starvation is elusive. It is also unclear how nutrient starvation can induce LHCSR3 expression under subsaturating light intensities. To study the role of LHCSR3 under nutrient starvation, the C. reinhardtii cells are grown under osmotic stress that would prevent water uptake; therefore same holds true for soluble nutrients in the medium. In this work, we have shown that LHCSR3 expression can occur under osmotic stress and subsaturating light intensities, whereas it does not elicit qE. Further examination of thylakoid membrane architecture from wild-type and npq4 mutant grown under nutrient starvation revealed that LHCSR3 expression affects the interaction between the PSII core with its peripheral LHCII antenna and possibly can prevent excitation energy transfer. Thylakoid lumen acidification is essential for the expression and function of LHCSR3. Under saturating light intensities, this is achieved by the increased rate of photosynthetic electron flow coupled with proton translocation into the thylakoid lumen. Whereas, under nutrient starvation, the reports of LHCSR3 expression also showed reduced photosynthetic electron flow. Therefore, an alternative mechanism should exist for developing the proton gradient. We observed the downregulation of chloroplast (cp) ATP synthase activity and its abundance under osmotic stress, suggesting the role of (cp) ATP synthase in thylakoid lumen acidification under reduced photosynthetic electron flow. This observation is supported by the expression of LHCSR3 in (cp) ATP-synthase mutant atpF upon exposure to moderate light intensity. This study proposes that the mechanism of LHCSR3 expression and its functionality can vary with the type of photooxidizing stress.

plant biology↗

bioRxiv2022

Low polyethylene glycol (PEG) concentration contributes to photoprotection in Chlamydomonas reinhardtii under highlight stress.

The highlight is one of the major problems encountered by all the autotrophs in the natural environment, as it affects the photosynthetic performance of these organisms, they were equipped themself with the diverse photoprotective mechanism. However, the drastic climate change in recent years had a more lethal effect on these organisms as it is beyond their threshold to withstand. In the past decade, scientists have unravelled many photoprotective mechanisms like qE, qZ, qT and qI (NPQ) used by autotrophs to combat highlight stress and the thirst for discovering such a new mechanism remains constant. In this regard, we studied the effect of mild osmotic stress (2%PEG) in alleviating high-light stress using Chlamydomonas (C) reinhardtii as a model system. The cells were grown in low Polyethylene glycol (PEG)-induced osmotic stress at varying light intensities; their response to these treatments had been examined via biochemical and biophysical approaches. The PEG-treated cells showed better growth and photosynthetic efficiency even at highlight than control, but their NPQ level is lesser than control, suggesting a unique or novel photoprotective mechanism is operating in PEG-treated samples. The Circular dichroism and ATG8 localization assay suggest that supercomplexes organization is not much disturbed in PEG-treated samples irrespective of light intensity. Also, the latter indicates that PEG-treated cells were healthier than the control at the highlight. This result is promising as we can improve the algal biomass under natural environmental conditions with fluctuating light intensity. As algal biomass has immense commercial importance in biofuel production, cosmetics and pharmaceutical application. This mechanism can be exploited to promote the socio-economic status of our nation. HighlightsO_LIPEG application triggers ROS accumulations, stimulating signalling cascade and overcoming highlight-induced compromise in biomass. C_LIO_LIUnder highlight, the photosynthetic pigment (chlorophyll and carotenoid) constantly increased with PEG except for C-250. Specifically, the photoprotective pigment like violaxanthin and lutein has been increased. C_LIO_LIPEG shielding stabilizes pigment-protein interaction, confirming that the supercomplex organization is in its native state. C_LIO_LIPEG keeps low ATG8 accumulation, preventing cells and enabling it to combat highlights more effectively. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=129 SRC="FIGDIR/small/505872v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@1bef077org.highwire.dtl.DTLVardef@9d45bcorg.highwire.dtl.DTLVardef@14d7366org.highwire.dtl.DTLVardef@1d3617f_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗

bioRxiv2020

Autophagy induced accumulation of lipids in pgrl1 and pgr5 of Chlamydomonas reinhardtii under high light

Chlamydomonas (C) reinhardtii cells (wild-type CC125 and 137AH, and cyclic electron transport dependant mutants pgrl1 and pgr5) were grown in high light 500 {micro}mol photons m-2 s-1 where the growth was significantly enhanced after three days. The starch and lipid contents were also increased; however, starch content was decreased in pgr5. Further, the Nile Red fluorescence shows that a significant amount of lipid bodies were observed in pgr5 cells under high light. Similarly, the electron micrographs show that large vacuoles were formed in high light stress despite the change in stacks of grana structure. We also observed increased production of reactive oxygen species (ROS) that could lead to autophagy. Inline, a significant increase of ATG8 protein was noticed in pgr5, which is a hallmark characteristic for autophagy formation. Consequently, the triacylglycerol (TAG) content was increased due to DGAT and PDAT enzymes expression, especially in pgr5. Here, the TAG synthesis would have been obtained from degraded membrane lipids in pgr5. Additionally, mono, polyunsaturated, and saturated fatty acids were identified more in the high light condition. Our study shows that the high light induces ROS, leads to autophagy and TAGs accumulation, which is stored as an energy source to acclimatize the algae.

plant biology↗

bioRxiv2018

Elucidating the active interaction mechanism of phytochemicals withanolide and withanoside derivatives with human serum albumin

Withania somnifera (Ashwagandha) is an efficient plant known in Ayurveda and Chinese medicine since ancient times, whose extracts are consumed orally as food supplement or as a health tonic owing to its several restorative properties for various CNS disorders, inflammation, tumour, stress and rheumatism. In this study, we have analyzed the binding interaction of four derivatives of Withania somnifera (Withanolide A, Withanolide B, Withanoside IV and Withanoside V) with HSA because of their important pharmacological properties. To unravel the binding between derivatives of Withania somnifera and HSA, fluorescence spectroscopy was used. Binding studies were further studied by molecular docking and dynamics studies and results confirmed greater stability upon binding of derivatives with HSA. Circular dichroism data illustrated change in the secondary structure of protein upon interaction with these derivatives, particularly the helical structure was increased and {beta}-sheets and random coils were decreased. Furthermore, morphological and topological changes were observed using AFM and TEM upon binding of ligands with HSA indicating that HSA-withnoside/withanolide complexes were formed. All the results cumulatively demonstrate strong binding of withanosides and withanolides derivatives with serum albumin, which should further be explored to study the pharmacokinetics and pharmacodynamics of these derivatives.

biophysics↗