EFFECT OF GROWTH AND LIGHT DARK CYCLES ON DIATOM LIPID-CONTENT AND COMPOSITION

Total extractable lipid (TEL) and lipid composition were studied throughout the growth cycle in three fresh-water diatoms-Cyclotella meneghiniana Kutz., Melosira varians C. A. Ag., and Stephanodiscus binderanus (Kutz.) Krieg.-under three light regimes (16:8 h LD, 20:4 h LD, and 12:12 h LD) at 20-degrees-C. Two of the diatoms demonstrated strong daylength preferences for growth; C. meneghiniana grew best under long-day (20: 4-h LD) conditions, whereas S. binderanus grew best under short-day (12:12-h LD) conditions. The lipid composition of the diatoms was similar throughout the growth cycle. Aged (2-month-old) cells were high in total lipid and triacylglycerols. Before the onset of active growth and during the early part of active growth, there was a reduction in total neutral lipids, primarily triacylglycerols, and an increase in all polar lipids, including chlorophyll a, acetone-mobile polar lipids, and phospholipids. While cell numbers were still increasing, triacylglycerols increased and polar lipids decreased to levels near those found in aged cultures. Results suggest that increased triacylglycerol content of freshwater diatoms is not necessarily indicative of senescent populations.