Fatty acid and tocopherol accumulation in the seeds of a high oleic acid castor mutant

Abstract

The recent isolation of a natural mutant of castor bean with high oleic acid and low ricinoleic acid concentration opens up new potential uses for castor oil. The objective of the present research was to monitor fatty acid and tocopherol accumulation in developing seeds of the high oleic acid mutant OLE-1 in comparison with seeds of the standard high ricinoleic acid line A74. Seed samples were collected at regular intervals from 6 to 60 days after pollination (DAP) and analyzed for oil content, fatty acid composition, and tocopherol content and composition. Oil accumulation followed a similar pattern in both lines from 12 to 18 DAP, but from this stage oil accumulated much more actively in A74, resulting in a significant difference of about 15% oil content between both lines at maturity. The concentrations of palmitic, linoleic, and linolenic acid were similar in both lines at all stages, whereas stearic acid was about 0.5% higher in A74 during the whole seed filling period. Both lines exhibited contrasting accumulation patterns for oleic and ricinoleic acid. Ricinoleic acid concentration raised rapidly from zero at 9 DAP to above 80% at 21 DAP in A74, whereas its concentration in OLE-1 seeds raised at a much lower rate, from zero at 9 DAP to about 15% at 36 DAP. Conversely, oleic acid concentration remained practically unchanged in A74, whereas it raised drastically from about 10% at 12 DAP to around 75% at 18 DAP. The increase in oleic acid was not accompanied by a concomitant raise of linoleic acid concentration, which suggests that the low linoleic acid concentration in conventional castor oil is not the result of competition between the hydroxylation and desaturation pathways. At 6 DAP, both lines contained very low levels of tocopherols, mainly in the form of alpha-tocopherol. The synthesis of beta-, gamma-, and delta-tocopherol started between 12 and 15 DAP, with a maximum total tocopherol content at 21 DAP for A74 and 24 DAP for OLE-1. The accumulation pattern of gamma-tocopherol content was similar in both lines. However, OLE-1 seeds reached higher levels of beta- and delta-tocopherol, which resulted in a higher total tocopherol content at maturity, about 785 mg kg −1 dry seed weight in comparison with 605 mg kg −1 dry seed weight in A74.