Induction of Lycopene and Lycopene Precursors in Germinating Cottonseed with the Substituted Triethylamine Compound MPTA

Treatment of dark germinating cottonseed (Gossypium hirsutum Acala cultivar) with 0.72 mM 2(4-methylphenoxy) triethylamine (MPTA) resulted in a 18-fold increase in carotenoid biosynthesis. In comparison to H₂O treated control seed germinating in the dark that formed 8.4 μg/g fr wt of lutein and 1.6 μg/g fr wt of b-carotene, the MPTA treated germinating seed formed 74.9 μg/g fr wt phytoene, 4.8 μg/g fr wt phytofluene, 96.7 μg/g fr wt lycopene and 1.0 μg/g fr wt lutein. The accumulation of lycopene and lycopene precursors resulted from an increased biosynthesis of the carotenes and a partial blockage of phytoene desaturase (PDS) and blockage of lycopene-β and -e cyclase. The loss of lutein and β-carotene would not account for the increase in lycopene and lycopene precursors although these losses may lead to an end-product regulation of phytoene synthase (PSY) and carotene biosynthesis.            Treatment of the germinating cottonseed with MPTA, actinomycin D, α-amanitin, cordycepin, and cycloheximide demonstrated that the increased biosynthesis of carotenes with MPTA was dependent on gene expression, polyadenylation of gene transcripts, and translation of the mRNA on 80S ribosomes. The effect of MPTA on the transcript levels of PSY and LYCb and LYCe were determined by qPCR. The levels of the PSY1 and PSY2 transcripts of MPTA treated germinating seeds increased 6.2- and 2.1-fold, respectively, compared to the water treated control sample. The up-regulation of PSY may play a major role in the increased biosynthesis of carotenes by MPTA. Treatment with MPTA also increased the transcript levels of LYCb1 and LYCe by 2.8- and 3.5-fold, while decreased the transcript level of LYCb2 by 0.4-fold, respectively, compared to the water treated control sample. Therefore, the blockage of lycopene cyclization is due to the inhibition of LYC, not the reduced transcript level.