Carotenoid accumulation during grain development in durum wheat

Yellow pigment (YP) concentration is an important quality trait in durum wheat and is comprised primarily of carotenoids. The main objective of our study was to measure the accumulation of carotenoids during the grain fill period to improve our understanding of the physiological basis for differences among durum wheat cultivars. Thirteen genotypes with large variation in total YP concentration were studied. Spikes were sampled from replicated field plots in 2007 and 2008 at 14, 21, 28 and 35 days after heading (DAH). The remainder of each plot was harvested at grain maturity for analysis. trans-Lutein was the predominant carotenoid at maturity and was detected at 14 DAH in all genotypes. The rate and duration of lutein accumulation was variable among genotypes expressing high, intermediate and low YP. The accumulation of all carotenoids was lowest in genotypes expressing low YP, and suggests rate limitations early in the carotenoid biosynthetic pathway. The ratio of trans-zeaxanthin to trans-lutein was inversely correlated with total YP and suggests that the β,ɛ branch of lycopene cyclization leading to α-carotene and thus lutein, synthesis may also be limiting in low-YP genotypes. These results provide insights into the regulation of the carotenoid biosynthetic pathway in durum wheat grain.