Lipid Synthesis During Sporulation of

Lipid synthesis was studied inbothsporulating (diploid) andnonsporulating (haploid) cells ofSaccharomyces cerevisiae. Twophases oflipid synthesis occur indiploid cells transferred tosporulation medium.PhaseI,which occursduring thefirst 12hofexposuretosporulation medium, was also observed inthehaploid strains. PhaseII,occurring fromthe20thtothe25thh,coincided withthe appearance ofmatureasciandwas observed onlyinthediploid cells. The majority ofphospholipid synthesis tookplace during period I,whereas neutral lipid synthesis occurred during bothperiods. Phospholipid synthesis was virtually identical inbothtypeandquantity inthesporulating andnonsporulat- ingstrains. Lipidaccumulation insporulating cells of Saccharomyces cerevisiae hasbeenwelldocu- mented. Pontefract andMiller (14) reported an increase inlipid-containing vacuoles during sporulation. Esposito etal.(3), inexamining theuptake of'IC-acetate into total lipids during sporulation, observed oneperiod ofsynthesis during thefirst 10handasecond from24to30h ofsporulation. Recently, Illingworth etal.(6) alsofoundtwoperiods oflipid synthesis. In addition, theydemonstrated insporulating cells increases inphospholipids, neutral lipids, and unsaturated fatty acids. Sporulation inyeastinvolves twomeiotic divisions inwhichrearrangements ofnuclear andplasma membranes occur. Therefore, the possibility exists thatsignificant changes in membranecomponents suchaslipids might accompany themeiotic divisions andsubse- quentspore formation. However, anyanalysis of synthetic activity occurring insporulating cells musttakeintoaccounttheenvironmental changes associated withtheshift tosporulation medium.Sporulation mediumisdeficient in nitrogen andutilizes acetate asa sourceof energy. Thus, itisimportant todetermine what metabolic processes areinitiated asaresponse tothealteration ingrowth conditions, evenin theabsence ofsporulation. Thepresent report deals primarily withtwo questions. First, whatlipids aresynthesized duringsporulation? Particular emphasis is