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W.Y.L. Poon and I.L. Goldman

Carotenoids have been shown to be important both nutritionally and medicinally. Carotenoid accumulation was compared during growth and storage of four carrot genotypes: YY y1y1y2y2RPRP, yyY1 Y1Y2Y2 RPRP, YY Y1 Y1Y2Y2 RPRP, and rprp. These genotypes exhibit orange, yellow, white, and pale-orange roots respectively. The orange and pale-orange genotypes are near-isogenic for rp, a gene that reduces total carotenoid content by 93%. Genotypes were grown in replicated field plots during 1996 and stored for 8 months at 4°C. Samples of root tissue were removed at 7-day intervals during vegetative growth and 4-week intervals during the postharvest period. Total carotenoid content were quantified using HPLC and spectrophotometric analyses. Increases in carotenoid content of 119% and 79% in rprp and YY y1y1y2y2RPRP and decreases of 6% and 64% in YYY1 Y1Y2Y2RPRP and yyY1 Y1Y2Y2RPRP, respectively, were measured between 62 and 100 days after planting. At 100 days after planting, YY y1y1y2y2RPRP exhibited 10-fold greater carotenoid content than rprp. Carotenoid content in yyY1 Y1Y2Y2RPRP and YY y1y1y2y2RPRP increased during the first 28 days of storage and decreased subsequently. Meanwhile, rprp began to decrease in carotenoid content at day 14 of storage. HPLC analysis at l = 445 nm revealed two large unique peaks in rprp with elution times of 27 and 28.7 minutes that were of lesser abundance in YY y1y1y2y2RPRP, suggesting that the rate of β- and α-carotene accumulation is not the only difference between YY y1y1y2y2RPRP and rprp.

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W.Y.L. Poon and I.L. Goldman

The rp allele causes a significant reduction in total carotenoid pigmentation in carrot (Daucus carota L.) roots. The objective was to investigate the effect of rp on the composition, accumulation, and retention of carotenoids in two near-isolines of carrot, W266RPRP and W266rprp, during vegetative growth and postharvest storage. Field experiments were conducted during 1996 and 1997 in which roots were sampled weekly from 62 to 100 days after seed-sowing and biweekly during postharvest storage at 4 °C up to 386 days after sowing. Linear increases in total carotenoid concentration were observed for W266RPRP and W266rprp during vegetative growth. The average daily rate of increase in total carotenoid concentration in W266RPRP and in W266rprp was 12.7 and 1.3 mg·g-1 dry weight, respectively. A linear decrease in carotenoid concentration was measured for W266RPRP but not for W266rprp during postharvest storage. At 100 days after sowing, high-performance liquid chromatography analyses showed W266rprp had 20-fold lower concentrations of a-carotene and 50-fold lower concentrations of β-carotene in root tissue compared to W266RPRP. Levels of β-carotene and lutein in the first true leaves were reduced by ≈50% in W266rprp compared to W266RPRP. Results from this investigation suggest that the rp allele affects the concentration of root and foliage carotenoids, as well as the rate of carotenoid accumulation and degradation in carrot roots. The impact of the rp allele is far greater in root tissue than in foliage, suggesting it may act as a transcription factor or structural gene affecting primarily root carotenoid biosynthesis.