Acyl‐lipid desaturases introduce double bonds (unsaturated bonds) at specifically defined positions in fatty acids that are esterified to the glycerol backbone of membrane glycerolipids. The desA, desB and desD genes of Synechocystis sp. PCC 6803 encode acyl‐lipid desaturases that introduce double bonds at the delta12, omega3 and delta6 positions of C18 fatty acids respectively. The mutation of each of these genes by insertion of an antibiotic resistance gene cartridge completely eliminated the corresponding desaturation reaction. This system allowed us to manipulate the number of unsaturated bonds in membrane glycerolipids in this organism in a step‐wise manner. Comparisons of the variously mutated cells revealed that the replacement of all polyunsaturated fatty acids by a monounsaturated fatty acid suppressed growth of the cells at low temperature and, moreover, it decreased the tolerance of the cells to photoinhibition of photosynthesis at low temperature by suppressing recovery of the photosystem II protein complex from photoinhibitory damage. However, the replacement of tri‐ and tetraunsaturated fatty acids by a diunsaturated fatty acid did not have such effects. These findings indicate that polyunsaturated fatty acids are important in protecting the photosynthetic machinery from photoinhibition at low temperatures.

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Far-infrared absorption coefficients of silicon crystals grown by the Czochralski method (CZ) and by the floating-zone method (FZ) in the range of 20–200 cm−1 were obtained from transmission measurements at two different thicknesses, allowing for the effect of the multiple internal reflection. The CZ and FZ specimens used were not intentionally doped and had dc resistivities of 9.4±0.3 Ω cm and (5±2)×104 Ω cm, respectively. The impurity-induced absorption of the CZ crystal is well explained by the Drude model, while the FZ crystal showed only a weak absorption which is attributed to a wing of the intrinsic lattice band of silicon.