Search for an endotherm in chloroplast lamellar membranes associated with chilling-inhibition of photosynthesis.
The phase transition of chloroplast lamellar membrane lipids has been proposed to be the underlying cause of chilling-induced inhibition of photosynthesis in sensitive plants. Differential scanning calorimetry has been used to search for any endotherms arising from lipid state changes in chloroplast lamellar membranes of the chilling-sensitive plants cantaloupe , kidney bean, domestic tomato, and soybean. For comparison, calorimetric scans of chloroplast lamellar membranes from the chilling-insensitive plants spinach, pea, and wild tomato were made. A large reversible endotherm, extending from below 10 degrees to nearly 40 degrees C, was observed in chloroplast membranes from tomatoes of both chilling-sensitive (Lycopersicon esculentum Mill. cv. Floramerica ) and chilling-insensitive (L. hirsutum LA 1361) species. A much smaller endotherm, approximately 5 to 10% of the area of that seen in the two tomato species, and extending over a similar temperature range, was detected in chloroplasts from chilling-insensitive spinach and peas, and also was generally observed in chloroplasts from chilling-sensitive cantaloupe , kidney bean, and soybean. The enthalpy of these smaller endotherms indicates that, if the endotherm arose entirely from a lipid transition, then it corresponded to the melting of less than about 10% of the total membrane polar lipid. On the basis of these data it is concluded that there is no correlation between chilling sensitivity of photosynthesis and the presence or absence of a phase transition of bulk membrane lipids of the chloroplast lamellar membrane at temperatures above 5 degrees C.
D002736:Chloroplasts / Q000378:metabolism*; D003080:Cold Temperature; D007887:Fabaceae / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008563:Membrane Lipids / Q000502:physiology*; D010084:Oxidation-Reduction; D010788:Photosynthesis; D010944:Plants / Q000378:metabolism; D010946:Plants, Medicinal; D013816:Thermodynamics
D008563:Membrane Lipids