Osmotic responses of unicellular blue-green algae (cyanobacteria): changes in cell volume and intracellular solute levels in response to hyperosmotic treatment

Abstract Changes in cell volume and solute content upon hyperosmotic shock have been studied for six unicellular blue-green algae (cyanobacteria): Synechococcus PCC 6301, PCC 6311; Synechocystis PCC 6702, PCC 6714, PCC 6803 and PCC 7008. The extent of change in volume was shown to be dependent upon the solute used to establish the osmotic gradient, with cells in NaCl showing a reduced shrinkage when compared to cells in media containing added sorbitol and sucrose. Uptake of extracellular solutes during hyperosmotic shock was observed in Synechocystis PCC 6714, with maximum accumulation of external solutes in NaCl and minimum solute uptake in sucrose solutions. Conversely, solute loss from the cells (K⁺ and amino acids) was greatest in sucrose-containing media and least in NaCl. The results show that these blue-green algae do not behave as ‘ideal osmometers’ in media of high osmotic strength. It is proposed that short-term changes in plasmalemma permeability in these organisms may be due to transient membrane instability resulting from osmotic imbalance between the cell and its surrounding fluid at the onset of hyperosmotic shock.     

Carbonic Anhydrase and the Regulation of Photosynthesis

THE role of CO₂ in the regulation of photosynthetic and respiratory metabolism in plants is little understood in the unicellular alga Chlorella pyrenoidosa; for example, after autotrophic growth in high CO₂ (5·5% by volume), transfer to a CO₂ concentration about ten times less than the concentration in air results initially in low rates of photosynthesis characterized by the virtual absence of the Calvin cycle¹ of CO₂ fixation². An induction period of about 2 h is necessary before normal photosynthetic rates are established. Cells grown in air (0.03% CO₂) do not show this effect and photosynthesize at comparatively high rates even in very low concentrations of CO₂.     

Synthesis,characterization, and electrocatalytic behaviour of hydrothermally grown nanostructured La2O3 and La2O3/K-complex

Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium–potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2–4-N,N-dimethylaminobenzoate-κO)(μ2–4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La₂O₃ nanomaterials to obtain a nanohybrid La₂O₃/K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and ¹H and ¹³C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La₂O₃/K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La₂O₃/K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour.     

The Effects of Salinity upon Galactosyl-Glycerol Content and Concentration of the Marine Red Alga Porphyra purpurea (Roth) C.Ag.

Changes in the major alcohol-soluble, low molecular weight carbohydratesof P. purpurea, O--D-galactopyranosyl-(1-2)-glycerol (‘floridoside’)and O--D-galactopyranosyl-(1-1)-glycerol (‘isofloridoside’),have been examined in response to salinity variation. ‘Floridoside’is shown to vary in absolute amount, increasing in hypersalineand decreasing in hyposaline media. ‘Isofloridoside’content per cell does not change in a similar manner. Responsesare almost identical under light or dark conditions, ‘floridoside’changes being complete within 24 h. Decreasing the externalwater potential using ionic and non-ionic solutes has the sameeffect upon galactosyl-glycerol content. The amount of ‘floridoside’synthesized, and degraded under hypersaline and hyposaline conditionsrespectively is shown to be insufficient to restore cell volumeto its original value. It is therefore suggested that the primaryfunction of ‘floridoside’ increases in concentratedsea-waters is that of a compatible solute, serving to protectthe cell during periods when the external salt content is increaseddramatically.