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Abstract

Omega-3 fatty acid concentration in purslane (Portulaca oleraceae) is altered by photosynthetic photon flux.

Abstract

Purslane (Portulaca oleracea) 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 h. 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-h 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 h 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 h 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.