Submitted to: American Journal of Agricultural and Biological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2010
Publication Date: January 1, 2011
Citation: Liu, J., Puckhaber, L.S. 2011. The induction of lycopene in germinating cottonseed with 2-(4-methylphenoxy)triethylamine (MPTA). American Journal of Agricultural and Biological Science. 6(1):1-6. Interpretive Summary: Carotenoids are fat soluble pigments that perform a wide variety of biological functions. In plants, they constitute light-harvesting complexes, impart structural integrity, function as photoprotectants and antioxidants, confer colors to many flowers and fruits, and serve as precursors to the plant hormone abscisic acid. We studied the effect of a chemical called MPTA on the production of carotenoids in developing cottonseed. Our understanding of how this chemical works is poorly understood. We found that MPTA stimulates the production of critical genes involved in the synthesis of carotenoids. This provides additional understanding as to how MPTA affects production of carotenoids.
Technical Abstract: Cottonseed (Gossypium hirsutum Acala cultivar) were imbibed in H2O for 6 hr and seed coats removed. The seeds were imbibed for an additional 3 hr in H2O or 7.2x10**-4M 2-(4-methylphenoxy) triethylamine (MPTA) and germinated in the dark for 72 hr. The carotenoids were extracted and analyzed by HPLC. In comparison to the H2O control seedlings that formed 8.4ug/g fr. wt. lutein and 1.6ug/g fr. wt. beta-carotene, the MPTA-treated germinated seedlings formed 74.9ug/g fr. wt. phytoene, 4.8ug/g fr. wt. phytofluene, 96.7ug/g fr. wt. lycopene and reduced lutein to 1.0ug/g fr. wt. and beta-carotene to 0.0ug/g fr. wt. The partial blockage of lycopene cyclase-beta (LYC-beta) and lycopene cyclase-epsilon (LYC-epsilon) with MPTA and the reduction of beta-carotene and lutein account for 5.4% of the increase in lycopene and lycopene precursors. The remaining 94.6% increase is due to an increase in the rate of biosynthesis of these carotenes. Treatment of the germinating cottonseed with MPTA and actinomycin-D, alpha-amanitin, cordycepin or cycloheximide reduced the stimulatory effect of MPTA and demonstrated that the increased biosynthesis of carotene with MPTA was dependent on gene expression, polyadenylation of the gene transcripts, and translation of the mRNA on 80 S ribosomes. The relative transcript levels of phytoene synthase (psy) and lyc genes were determined in the germinating seedlings using Step One Real-Time PCR System. The G. hirsutum EST database was searched with a number of psy genes and a number of lyc genes from plant species. Alignment of the resulting sequences gave two groups of psy genes (psy-1 and psy-2) and lyc-beta and lyc-epsilon genes. Primer pairs were designed with the consensus sequences, and the sequences of the amplified products were verified through sequencing. The relative expression levels of psy-1 and psy-2 transcripts in the MPTA germinating seedlings increased 6.5 and 2.2 fold, respectively, compared with the transcript levels in the H2O controls. The relative levels of lyc-beta and lyc-epsilon transcripts in the MPTA-treated seedlings compared with the H2O controls increased 3.7 and 3.6 fold, respectively. The results support the conclusion that the accumulation of lycopene and lycopene precursors in the MPTA-treated germinating cottonseed was dependent on the partial blockage of LYC-beta and LYC-epsilon and the increased expression and translation of the psy genes leading to an increased carotenogenesis.