Total and Percent Atropisomers of Gossypol and Gossypol-6-methyl Ether in Seeds from Pima Cottons and Accessions of Gossypium barbadense L.

Authors: Stipanovic, Robert - Bob; Puckhaber, Lorraine; Liu, Jinggao; Bell, Alois - Al

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2008
Publication Date: 1/28/2009
Citation: Stipanovic, R.D., Puckhaber, L.S., Liu, J., Bell, A.A. 2009. Total and percent atropisomers of gossypol and gossypol-6-methyl ether in seeds from Pima cottons and accessions of Gossypium barbadense L. Journal of Agricultural and Food Chemistry. 57:566-571.

Interpretive Summary: Cottonseed is utilized as a feed by the dairy industry, but the seed cannot be consumed by non-ruminant animals such as chickens because it contains a toxic compound called gossypol. In the seed, gossypol exists as a mixture of two forms termed R-gossypol and S-gossypol; only R-gossypol is toxic. Interestingly, R-gossypol exhibits anti-cancer activity. Extra long staple type cottons, called barbadense cottons, are known to contain high levels of R-gossypol in the seed (seed from traditional commercial cottons contain more S-gossypol than R-gossypol). The U.S.D.A. collections of barbadense cottonseeds have never been fully scrutinized to determine if any contain very high levels of R-gossypol. The seed of plants which contain very high levels of R-gossypol could be of interest to the pharmaceutical industry. We have completed an analysis of the cottonseed in the barbadense collection, and no seed contained more than 70% R-gossypol. However, seed with very high levels of S-gossypol were identified. Plants derived from these seed could be used in a breeding program to decrease the levels of R-gossypol in commercial barbadense seed. This would make the seed more acceptable as a feed by dairy farmers who currently tend to avoid feeding barbadense cottonseed because they fear poisoning their herds.

Technical Abstract: Gossypol occurs naturally in the seed, foliage and roots of the cotton plant (Gossypium) as atropisomers due to restricted rotation around the binaphthyl bond. The atropisomers differ in their biological activity. ( ) (R)-Gossypol is more toxic and exhibits significantly greater anti-cancer activity than the (+)-(S)-atropisomer. Most commercial Upland (Gossypium hirsutum) cottonseed have an (R)- to (S)-gossypol ratio of ~2:3, but some Pima (G. barbadense) seed have an excess of (R)-gossypol. There is no known source of cottonseed with a (R)- to (S)-gossypol ratio greater than ~70:30. Cottonseed with a high percent of (R)-gossypol would be of value to the pharmaceutical industry. It was theorized that G. barbadense cotton might be a source of this desirable high (R) gossypol seed trait. There are 671 different accessions of G. barbadense in the U.S. Cotton Germplasm Collection, few of which had been characterized with respect to their (R)- to (S)-gossypol ratio. We have completed that analysis and found considerable variation in the atropisomer ratio. Approximately half of the accessions have an excess of (R)-gossypol and 52 accessions have essentially a 1:1 ratio. The highest percentage of (R)-gossypol was found in accessions GB26 (68.2%) and GB 283 (67.3%). Surprisingly, five accessions had 5% or less of (R)-gossypol: GB516 (5.0%), GB761 (4.5%), GB577 (4.3%), GB719 (3.7%) and GB476 (2.3%). These accessions may be useful in a breeding program to reduce (R)-gossypol in Pima seed, which is a concern to the dairy industry because of the toxicity and male antifertility activity of this atropisomer. Also, GB710 was devoid of gossypol.