Evolution of PS IIα and PS IIβ centers during the greening of Euglena gracilis Z: Correlations with changes in lipid content.

The building up of the two types of reaction centers, PS IIα and PS IIβ, was investigated during the greening of Euglena gracilis Z cells in resting medium. The maximal values in the proportion of PS IIα centers (55%) and in the oxygen evolved per chlorophyll were reached at the outbreak of greening, when accumulation of galactolipids (MGDG and DGDG) rich in unsaturated fatty acids occurred, and when anionic lipids (SQDG and PG) emerged. As the greening progressed, the chlorophyll accumulation corresponded to a secondary enrichment in PS IIβ centers, which built up more rapidly than PS IIα centers; correlatively, a general saturation of the fatty acids constitutive of all lipid classes took place.