SQDG

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In 1959 A.A.Benson and co-workers discovered a new sulfur containing lipid in plants and identified it as sulfoquinovosyl diacylglycerol (SQDG). The sulpholipid structure was defined as 1,2-di-O-acyl-3-O-(6-deoxy-6-sulpho-a-D-glucopyranosyl)-sn-glycerol (SQDG). The distinctive feature of this substance is carbon bonded directly to sulphur as C-SO3. Sulphonic acids of this type are chemically stable and strong acids over a wide pH range (Barber and Gounaris, 1986). SQDG has been found in all photosynthetic plants, algae, cyanobacteria, purple sulfur and non-sulfur bacteria and is localised in the thylakoid membranes, being the most saturated glycolipid (Janero, Barrnett, 1981). SQDG has been found to be closely associated with certain membrane proteins. In some cases the (electostratic) interactions may be very strong, as suggested by the inability of saturated SQDG molecules associated with purified chloroplast CF0-CF1 ATPase to exchange with other acidic lipids (Pick et al., 1985). It was shown also that SQDG protects CF1 against cold inactivation in the presence of some ATP. CF1 bound to membranes was found to be much more resistant to heat and cold than solubilised protein. Mitochondrial coupling factor F1 is similarly protected by phospholipids and SQDG although, in that case, both were equally effective (Bennun and Racker, 1969; Livn and Racker, 1969). Severe SQDG accumulation was observed in apple shoot bark and wood (Okanenko, 1977) and in pine thylakoid during the autumn hardening (Oquist, 1982), while heat and drought action upon wheat (Okanenko and Taran, 1989; Taran et al., 2000), at NaCl action in the halophyte Aster tripolium (Ramani, Zorn, Papenbrock, 2004). Besides, SQDG inhibits viral development (DNA-polymerase and reverse transcriptase activity, Ohta et al. 1998, 2000).