Figure 4.

Effect of irradiance and nitrogen availability on the mRNA levels of the zeaxanthin epoxidase gene (zep) and cellular content of violaxanthin and zeaxanthin in Chlorella zofingiensis. (a) Low irradiance (20 µmol photons m⁻² s⁻¹) and constant nitrate concentration (LL +N); (b) low irradiance and nitrate deprivation (LL −N); (c) high irradiance (300 µmol photons m⁻² s⁻¹) and constant nitrate concentration (HL +N); and (d) high irradiance and nitrate deprivation (HL −N). Columns indicate mRNA levels of the zep gene; (♦), violaxanthin content (mg g⁻¹ DW); (□), zeaxanthin content (mg g⁻¹ DW). Error bars indicate the standard deviations of four independent measurements. DW, dry weight.