Genetic Variation of Beta-carotene and Lutein Contents in Lettuce

Abstract

<jats:p>There is increasing medical evidence for the health benefits derived from dietary intake of carotenoid antioxidants, such as β-carotene and lutein. Enhancing the nutritional levels of vegetables would improve the nutrient intake without requiring an increase in consumption. A breeding program to improve the nutritional quality of lettuce (<jats:italic>Lactuca sativa</jats:italic> L.) must start with an assessment of the existing genetic variation. To assess the genetic variability in carotenoid contents, 52 genotypes including crisphead, leaf, romaine, butterhead, primitive, Latin, and stem lettuces, and wild species were planted in the field in Salinas, Calif., in the Summer and Fall of 2003 with four replications. Duplicate samples from each plot were analyzed for chlorophyll (<jats:italic>a</jats:italic> and <jats:italic>b</jats:italic>), β-carotene, and lutein concentrations by high-performance liquid chromatography (HPLC). Wild accessions (<jats:italic>L. serriola</jats:italic> L., <jats:italic>L. saligna</jats:italic> L., <jats:italic>L. virosa</jats:italic> L., and primitive form) had higher β-carotene and lutein concentrations than cultivated lettuces, mainly due to the lower moisture content of wild lettuces. Among major types of cultivated lettuce, carotenoid concentration followed the order of: green leaf or romaine &gt; red leaf &gt; butterhead &gt; crisphead. There was significant genetic variation in carotenoid concentration within each of these lettuce types. Crisphead lettuce accumulated more lutein than β-carotene, while other lettuce types had more β-carotene than lutein. Carotenoid concentration was higher in summer than in the fall, but was not affected by the position of the plant on the raised bed. Beta-carotene and lutein concentrations were highly correlated, suggesting that their levels could be enhanced simultaneously. Beta-carotene and lutein concentrations were both highly correlated with chlorophyll <jats:italic>a</jats:italic>, chlorophyll <jats:italic>b</jats:italic>, and total chlorophyll concentrations, suggesting that carotenoid content could be selected indirectly through chlorophyll or color measurement. These results suggest that genetic improvement of carotenoid levels in lettuce is feasible.</jats:p>

Mapping QTL, epistasis and genotype × environment interaction of antioxidant activity, chlorophyll content and head formation in domesticated lettuce (Lactuca sativa)

“…This association is likely due to the fact that chlorophyll and carotenoids are intricately intertwined as the core antennae of photosystems I and II (Fromme et al 2003), and the C40 isoprenoid backbone for carotenoids synthesis occurs in plastids. In lettuce, direct positive correlations between phenolic content and antioxidant content and between chlorophyll content and b-carotene at market maturity were reported (Kang and Saltveit 2002;Mou 2005). Given these observations, it might be expected that RIL families with high chlorophyll content also have high ORAC values in the D 9 M RIL population.…”

“…Of these different antioxidants, dicaffeoyl tartaric acid accounted for about 55% of the total antioxidant content in the lettuce cultivars tested (Nicolle et al 2004). Mou (2005) reported very high correlations between chlorophyll (Chl a, Chl b, and tChl) and b-carotene in lettuce. Because chlorophyll assays are simpler than b-carotene assays, chlorophyll could be used as a proxy for improving b-carotene content in lettuce.…”

“…The supernatant was transferred to a new tube and stored at -80°C until assayed for chlorophyll and antioxidant content. We measured chlorophyll content as a proxy of b-carotene, as Mou (2005) reported that b-carotene and lutein concentrations were highly correlated with chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (tChl) content. Chlorophyll content was determined by diluting an aliquot of the acetone-extracted samples into 80% acetone, mixed, and added to a 96-well microplate, and the absorbance at 649 and 665 nm were obtained using a BioTek lQuant Microplate Spectrophotometer (Bio-Tek Instruments, Winooski, VT).…”

“…Depending on type (butterhead, romaine, iceberg, red or green leaf), lettuce contains 20-80% of the antioxidant content of red cabbage and 30-160% of that of spinach (USDA 2010b). Iceberg lettuce shows the least amount of antioxidant activity of the four main lettuce types (Cao et al 1996;Llorach et al 2008;Mou 2005;Wu et al 2004). However, because of its high per capita consumption, lettuce is the fourth highest contributor of antioxidants of all vegetables consumed in the USA (Song et al 2010).…”

“…Given the broad range of variation in antioxidant content across lettuce types reported (Cao et al 1996;Llorach et al 2008;Mou 2005;Wu et al 2004), a potentially large environmental influence and the possibility of epistasis, elucidating the genetic basis of antioxidant content in lettuce is required to understand and improve this trait. In this study, a lettuce recombinant inbred line (RIL) population was grown in two different production sites in three consecutive years.…”