Carotenoid accumulation during grain development in durum wheat (Triticum turgidum L. var. durum)

Abstract

Yellow pigment (YP) concentration is an important quality trait in durum wheat (Triticum turgidum L. var durum) 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 cultivars and breeding genotypes with large variation in total YP concentration (<16 µg⁻¹ to >15 µg g⁻¹) were studied. Spikes were sampled from replicated field plots in 2007 and 2008 near Saskatoon and Swift Current, Saskatchewan, Canada, at 14, 21, 28 and 35 days after heading (DAH). The remainder of each plot was combined at grain maturity for YP and carotenoid analysis. Carotenoids were extracted with 1:1 methanol:dichloromethane (0.1% BHT) and quantified with HPLC. Trans (E)-lutein was the predominant carotenoid at maturity and was detected at 14 DAH in all genotypes. The rate and duration of E-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. E-zeaxanthin concentrations were highest in mature grain, but no significant differences were detected among genotypes. However, the ratio of E-zeaxanthin to E-lutein was inversely correlated with total YP, suggesting that the β,ε branch of lycopene cyclization is favoured over the β,β branch in high-YP genotypes. These results provide insights to the regulation of the carotenoid biosynthetic pathway during grain fill stage in durum wheat and will facilitate breeding for higher carotenoid concentration.