Relationship between Chloroplast Membrane Fatty Acid Composition and Photosynthetic Response to a Chilling Temperature in Four Alfalfa Cultivars

Abstract

The photosynthetic responses of four alfalfa (Medicago sadva L.) cultivars to 10 and 22 C air temperatures were examined and the relationship between the photosynthetic response at 10 C and the fatty acid composition of the chloroplast membranes was determined. Chilling-resistant cultivars exhibited moderate reductions in photosynthesis at 10 C, compared to 22 C, and contained a significantly greater percentage of polyunsaturated fatty acids in the chloroplast membrane and a greater double bond index than the chilling-sensitive cultivars. The chiiUng-sensitive cultivars exhibited severe reductions in photosyntbesis at 10 C, compared to 22 C. The reduction in pbotosynthesis at 10 C is shown to be negatively correlated (r --0.94) with the double bond index of the chloroplast membranes of the cultivars observed.The results support the hypothesis that reduced photosynthesis due to chiling temperatures is influenced by the unsaturated fatty acid composition of the chloroplast membrane which affect temperature-induced phase changes in chloroplast membrane lipids.The inability of chilling-sensitive plants to maintain physiological activity at chilling temperatures has been correlated with a marked increase in the activation energy of respiratory enzymes (5, 10) and a marked increase in the activation energy of photoreduction of NADP+ (7, 1 1). The observed increase in activation energy of these systems is related to temperature-induced phase changes in the lipids of the respective membranes (9-11). This phase change has been detected by a change in the mobility of spin labels and occurs at precisely the same temperature as the change in activation energy (8,9). No change in activation energy was detected in respiratory enzymes (5, 10) or NADP+ photoreduction (8, 11) of chilling-resistant plants, nor was a phase change in the lipids detected by spin labeling (8,9 Chloroplast Extraction. Chloroplasts were isolated from depetiolated leaves of each plant, three replications, in extraction buffer (0.4 M sucrose, 0.05 M Tricine, 0.01 M NaCl, pH 7.8) (1). The leaves were homogenized in a VirTis "23" homogenizer for 10 sec at maximum speed and 30 sec at 0.5-speed in 40 ml of extraction buffer. The suspension was filtered through four layers of cheesecloth and the filtrate centrifuged for 90 sec at 500g. The pellet was discarded and the supernatant recentrifuged for 7 min at 1,000g. The resulting pellet was resuspended in 20 ml of extraction buffer, centrifuged for 90 sec at 500g, and the pellet discarded. The supernatant was recentrifuged for 10 min at 2,000g and the resulting pellet dissolved in 25 ml of methanol and 5 ml of methylene chloride. This solution was directly analyzed for fatty acid composition. The chloroplast pellet was found to contain 90%o intact chloroplasts, as judged by light microscopy.Chloroplast Fatty Acid Assay. Methyl esters were prepared by direct micromethanolysis using boron trichloride gas (3). Qualitative and quantitative analyses were performed according to established gas-liquid chromato...

Glycerolipid and Fatty Acid Changes in Eastern White Pine Chloroplast Lamellae during the Onset of Winter

“…This has been demonstrated repeatedly in tissues sensitive to low temperatures, which exhibit a lipid phase transition in the 8 to 12 C range (16 controls (6). This suggests that the increase in 18:3 representation during temperature decline was, in part, responsible for maintenance of an optimal winter range of lamellar viscosity for structural and functional stability of lamellae (4,21,22). Similar changes in unsaturation of fatty acids assocated with the membrane have been shown in plants at different growth temperatures, the degree of unsaturation responding inversely to low (5,18) (4,27).…”

Role of Potassium in Carbon Dioxide Assimilation in Medicago sativa L

“…(24) as a measure of PSI and PSII activity. Chloroplasts were isolated from 10 g depetiolated leaves from each plant in 25 ml extraction buffer (15 (400-700 nm). The Petri plates were gently swirled during incubation.…”

Age and temperature effects on saturation of leaf fatty acids of Saxifraga cernua, an arctic herb

“…A low temperature induced accumulation of linolenic acid could be masked by the accelerated chloroplast accumulation at 10°C when younger plants of the same age were compared. (13) analyzed the fatty acid cotr. It seems that plants of the same age which have been raised at different temperatures are difficult to compare: growth temperature affects plant development, the stages of which are often associated with the synthesis or degradation of specific lipid components.…”