INFLUENCE OF LIGHT-INTENSITY ON THE FATTY-ACID COMPOSITION OF ULVA-PERTUSA KJELLMAN (CHLOROPHYTA)

Changes in the fatty acid (FA) composition of the green seaweed, Ulva pertusa, in response to irradiance (15, 30, 45, 90, 135 and 195 muE m- 2 s-1), and to the natural photoperiod were investigated. The levels o f the following FAs increased with increasing light intensity, suggest ing a role as storage products: 15 : 0, palmitic (16 : 0), linolenic ( 18 : 2n-6), arachidonic (20 : 4) and 22 : 4. The level of 16 : 0, a ma jor FA, increased (from 25% to 29% of total FAs) up to 90 muE M-2 s-1, beyond which, levels slightly decreased. Levels of 14 : 1 and the maj or FA, hexadecatetraenoic (16 : 4n-3), were inversely related to light intensity, suggesting a role as components of photosynthetic membrane s. Levels of 16 : 4n-3 at the lowest light intensity (21% of total FAs , 15 muE M-2 S-1) were nearly twice that observed at the highest light intensity (11% of total FAs, 195 muE M-2 s-1). Moisture, crude lipid content and polyunsaturated fatty acid (PUFA) levels did not significa ntly differ between treatments. In thalli exposed to the natural photo period, moisture content increased during the dark, while the level of 22 : 4 increased during the light period. Circadian patterns in the l evel of 18 : 2n-6, observed both in thalli exposed to the natural phot operiod and in thalli kept in total darkness, peaked shortly before mi dnight. Thalli kept in total darkness showed gradual decreases in the levels of crude lipid content, and the major FAs 16 : 4n-3 and 18 : 3n -3; and an increase in the level of 18 : In-9 and 22 : 0; hence, keepi ng Ulva thalli in the dark could not be used as a technique to increas e its PUFA content.