Omega-3 Fatty Acid Concentration in Purslane (Portulaca oleraceae) is Altered by Photosynthetic Photon Flux

Purslane ( Portulaca oleracea L.) is an excellent source of the essential fatty acid α-linolenic acid (LNA) but little is known of the effects of cultural conditions on LNA concentration. Purslane seedlings were grown under an instantaneous photosynthetic photon flux [ PPF (400 to 700 nm)] of 299 or 455 μmol·m -2 ·s -1 for a daily duration of either 8, 12, 16, or 20 hours. Thus, plants were exposed to a daily PPF of 8.6, 12.9, 17.2, or 21.5 mol·m -2 ·d -1 in the low PPF treatment (299 μmol . m -2. s -1 ) and 13.1, 19.7, 26.2, or 32.8 mol·m -2 ·d -1 in the high PPF treatment (455 μmol·m -2 ·s -1 ). Plants in all treatments received a 20-hour photoperiod by providing ≈5 μmol·m -2 ·s -1 from incandescent lamps starting at the end of the photosynthetic light period. At low PPF , purslane grown under a 16 hour PPF duration produced the highest concentrations of total fatty acids (TFA) and LNA per unit leaf dry weight (DW), but at high PPF , concentrations of these compounds were highest under 8 and 12 hour PPF duration. Trend analysis indicated that maximum TFA and LNA concentrations occurred with a daily PPF of 14.1 and 17.2 mol·m -2 ·d -1 , respectively; and in the thylakoids, protein, chlorophyll, and LNA concentrations peaked at a PPF of 21.8, 19.9, and 16.1 mol·m -2 ·d -1 , respectively. LNA as a percentage of TFA was unaffected by treatment. Shoot DW increased with PPF up to the highest PPF exposure of 32.8 mol·m -2 ·d -1 .