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- Author or Editor: Usha Rani Palaniswamy x
Omega-3 fatty acids (O3FA) are essential for normal human growth, development, and disease prevention. Purslane (Portulaca oleraceae L.) is an excellent source of the O3FA α-linolenic acid (LNA)—with higher concentrations than any green leafy-vegetable examined to date—and is being considered for cultivation (by USDA-ARS) in an effort to improve the balance of essential fatty acids in the western diet. Twenty-fi ve-day-old seedlings of both a green-leafed and a golden-leafed type of purslane were transplanted into a closed hydroponic system. Nitrogen, at 200 ppm, was provided as NO3 and NH4 forms to yield NO3: NH4 ratios of 1:0, 0.25:0.75, 0.5:0.5, and 0.75:0.25. Treatments were arranged in a randomized complete-block design with five replications. The experiment was repeated. Young, fully expanded leaves were harvested 18 days after treatment initiation, frozen (–60°C), and then analyzed for fatty acids using gas chromatography. Although the two types of purslane did not differ in LNA concentration, the green-leafed purslane produced greater total dry mass than the golden-type. On a leaf dry mass basis, plants grown with a NO3:NH4 ratio of 0.5:0.5 produced 241% and 53% greater LNA than plants grown with NO3:NH4 ratios of 1:0 and 0.75:0.25, respectively. Plants grown with NO3:NH4 ratios of 1:0 and 0.25:0.75 produced similar leaf LNA concentrations. Total dry mass was not affected by the nitrogen treatments.
Purslane (Portulaca oleracea L.) has been identified as an exceptionally rich source of α-linolenic acid (LNA), an essential fatty acid that is beneficial in reducing the incidence of coronary heart disease and certain cancers. In general, about two thirds of the LNA in terrestrial plants is associated with chloroplasts. A green-leafed unnamed cultivar of purslane and a golden-leafed cultivar `Goldberg' were grown hydroponically in a complete nutrient solution with 14.3 mm nitrogen provided as nitrate (NO3 -) and ammonium (NH4 +) forms to yield NO3 --N: NH4 +-N ratios of 1:0, 0.75:0.25, 0.5:0.5, and 0.25:0.75. Young leaves, harvested 18 days after treatment initiation, were analyzed to determine the fatty acid composition and concentrations, and thylakoid protein and chlorophyll concentrations. Although the leaves of plants grown with a NO3 --N: NH4 +-N ratio of 0.5:0.5 contained 239% and 114% more LNA than plants grown with ratios 1:0 and 0.75:0.25, respectively, they contained only 41% and 26% more chlorophyll. The green-leafed cultivar had higher (39%) chlorophyll concentrations than `Goldberg', but both cultivars had similar LNA concentrations [per g dry weight (DW)]. These results suggest that the LNA concentration in the fatty acid-rich species P. oleracea may not be as closely associated with chlorophyll concentration as reported earlier for other plants. Leaves of plants grown in solutions with 0.25:0.75 NO3 --N: NH4 +-N ratio contained 35% less LNA per g leaf DW than the leaves of plants grown in nutrient solutions with a 0.5:0.5 ratio. Although total DW production was not affected by the NO3 --N: NH 4 +-N ratios in the nutrient solutions, the green-leafed cultivar produced higher fresh weight, leaf area, total DW, and number of shoots than `Goldberg'.