The Effect of Light Intensity, Day Length, and Temperature on Fatty Acid Synthesis and Desaturation inVicia fabaL.

Some effects of light intensity, day length, and temperature on the fatty acid composition of the major glycerolipids of leaves of Vicia faba L. (cv. Giant Windsor) were observed. Increasing light intensity caused an increase in the relative concentrations of 16 : 1 in PG and 18 : 3 in MGDG and DGDG. Increasing day length during growth (and continuous illumination of leaf tissue) had no effect on 16 : 1 in PG but caused a decrease in the 18 : 3 content of PG, PC, MGDG, and DGDG. Since the quantities of these lipids increased under these conditions, the decrease was not due to photodestruction but to the differences in the relative rates of biosynthesis and desaturation of fatty acids. Incubation of leaf tissue in the dark for 4 d had little effect on the fatty acid composition of MGDG, DGDG, and PG. Temperature also controls fatty acid synthesis and desaturation. Above the optimum growth temperature (20 °C), the 18 : 3 content of MGDG, DGDG, PG, and PC decreased. In mature leaf tissue, the degree of unsaturation of MGDG may be modified upward in response to temperature changes. When plants were grown at 30 °C and transferred to 20 °C the level of 18 : 3 in MGDG of the leaf tissue increased to levels found in plants grown only at 20 °C. The level of 18 : 3 in MGDG does not decrease as rapidly when plants grown at 20 °C were transferred to 30 °C. This suggests that the lower temperature induced desaturation of 18 : 2 to 18 : 3.