Effects of Silicon Deficiency on Lipid Composition and Metabolism in the Diatom Cyclotella Cryptica

The effects of silicon deficiency on the metabolism and composition of lipids in Cyclotella cryptica T13L Reimann, Lewin, and Guillard were examined Silicon-deficient cells had higher levels of neutral lipids (primarily triacylglycerols) and higher proportions of saturated and monounsaturated fatty acids than silicon-replete cells. After 4 h of silicon deficiency, the percentage of newly assimilated NaH{sup 14}CO{sub 3} partitioned into lipids increased from 27.6% to 54.1%, whereas the percentage partitioned into chrysolaminarin decreased from 21.6% to 54.1%, whereas the percentage partitioned into chrysolaminarin decreased from 21.6% to 10.6%. In addition, pulse-chase experiments with NaH{sup 14}CO{sub 3} indicated that the amount of {sup 14}C in the total cellular lipid fraction increased by 32% after 12 h of silicon deficiency despite the absence of additional photoassimilable {sup 14}C. Therefore, the accumulation of lipids in response to silicon deficiency appears to be due to two distinct processes: (1) an increase in the proportion of newly assimilated carbon partitioned into lipids, and (2) a slow conversion of previously assimilated carbon from non-lipid compounds into lipids.