Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/6/2008
Publication Date: 4/16/2008
Citation: Sobolev, V.S., Sy, A.A., Gloer, J.B. 2008. Spermidine and Flavonoid conjugates from Peanut (Arachis hypogaea) Flowers. Journal of Agricultural and Food Chemistry. 56(9):2960-2969. Interpretive Summary: Peanut is an economically important crop, and yield depends heavily on peanut high resistance to pests and uncompromised plant fertility. Peanut is a self pollinating plant with unusual flowering and fruit formation. The first flowers appear 4 to 6 weeks after planting. Flowering continues for 6 or more weeks. There may be several flowers in an inflorescence on the plant, but only one opens on per morning, and there is an interval from one to several days between the openings of successive flowers. The flower opens at sunrise and pollen shedding takes place. Fertilization occurs 8 to 9 hours after pollination. Then the flower fades and the ovary elongates to become the peg, which pushes into the soil where it matures into the pod with seeds. However, biochemical mechanisms responsible for plant and pollen fertility in peanuts have not been explored. In this research we investigated the production of major chemicals in different organs of the peanut flower that may be responsible for peanut fertility and protection against pests. Four protective flavonoid compounds known from other plants were found in high concentrations in petals, and two spermidine-phenolic acid conjugates were also found in large amounts in the reproductive organ, the keel. Some fundamental functions were attributed to spermidine-like compounds, including influence on cell multiplication, inflorescence and fertility of reproductive organs, as well as protection against bacteria, fungi, viruses, and insects. These substances may also be produced as phytoalexins, defensive compounds that are synthesized by plants in response to exogenous attacks by pests. In addition to diverse functions in plans, three of the spermidine-phenolic acid conjugates appreciably exhibited HIV-1 protease that is essential for the life-cycle of HIV. The same compounds also demonstrated high activity against Helicobacter pylori, a major etiological agent in gastroduodenal disorders. The above compounds were reported in several higher plants, but have never been detected in peanut, a typical representative of the legume family. In this research one new compound that has never been reported in any plant before has also been detected in the keel. The compound was isolated in pure form, and its chemical structure was determined to be a spermidine-phenolic acid and -acetic acid conjugate. This compound exhibited very high sensitivity to sunlight – the original compound was converted into its several structural isomers (compounds with the same chemical formula, but different physical and absorptive spectral properties) within seconds. The dynamics of spermidine conjugate photoisomerization have been investigated. High photosensitivity of the new compound suggests that it might play a role in triggering peanut fertilization within hours after pollination at sunrise. Further investigation may clarify the role of the new compound in peanut reproductive organs.
Technical Abstract: A new triamide has been isolated from peanut flowers and identified as di-p-(EE)-coumaroylacetylspermidine on the basis of detailed analysis of NMR, MS, and UV data. Two other spermidine conjugates, N1, N5, N10-tri-p-(EEE)-coumaroylspermidine and di-p-(EE)-coumaroylspermidine, as well as four flavonoid conjugates (quercetin-3-glucoside, quercetin-3-glucuronide, isorhamnetin-3-glucoside, and isorhamnetin-3-glucuronide) that have been previously reported in plant organs, have been found in this study in peanut (Arachis hypogaea L.), a representative of the Leguminosae family, for the first time. The dynamics of photoisomerization in the spermidine conjugates have been investigated.