|Stipanovic, Robert - Bob|
|Frelichowski, James - Jim|
|O Neil, Thomas - Mike|
|Bell, Alois - Al|
|HAKE, KATER - Cotton, Inc|
Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2015
Publication Date: 12/22/2015
Citation: Stipanovic, R.D., Puckhaber, L.S., Frelichowski, J.E., Esquivel, J.F., Westbrook, J.K., O Neil, T.M., Bell, A.A., Dowd, M.K., Hake, K., Duke, S.E. 2015. Gossypolhemiquinone, a dimeric sesquiterpenoid identified in cotton (Gossypium). Phytochemistry. 122:165-171.
Interpretive Summary: Wild species of cotton may exhibit unusual resistance to herbivorous insect feeding. A report that a wild cotton, Gossypium thurberi, appeared to exhibit such resistance prompted an investigation of chemicals that occur naturally in the plant’s foliage. We identified a chemical called gossypol in the leaves of this plant together with an unidentified compound. Gossypol has previously been identified in this species of cotton and is known to protect the plant from insect herbivores. The new chemical, which we call gossypolhemiquinone (GHQ) that has a structure closely related to gossypol, was identified in small amounts in the leaves of G. thurberi. To test the ability of GHQ to deter insect feeding, it was incorporated into an artificial diet and fed to the larvae of the corn earworm. Some commercial cotton cultivars were also found to contain low concentrations of GHQ. To determine its relative effectiveness, gossypol was also fed to the larvae as well as a mixture of gossypol and GHQ. Days for larvae to reach pupation, pupal weight and survival were ascertained. GHQ produced effects similar to or less than gossypol as gauged by these factors. Thus, by itself GHQ did not appear to offer any enhanced resistance capabilities. However, a mixture of 85.5% gossypol and 14.5% gossypolhemiquinone at the highest concentration tested (0.18%) showed a significant increase in the days to pupation compared to either of the pure compounds, as well as a reduction in survival. Thus, breeding plants to produce high levels of gossypolhemiquinone together with gossypol may offer cotton a new source of resistance to herbivorous insects.
Technical Abstract: The report that the cotton leaf perforator, Bucculatrix thurberiella, is one of the few insect herbivores to attack Gossypium thurberi prompted an investigation of the terpenoids present in the leaves of this wild species of cotton. Members of Gossypium produce subepidermal pigment glands in their leaves that contain the dimeric sesquiterpenoid gossypol as well as other biosynthetically related terpenoids. In addition to gossypol, a new dimeric sesquiterpenoid, gossypolhemiquinone (GHQ), was identified in G. thurberi, a member of the D genome. Other members of the D genome of Gossypium were subsequently found to contain this compound, as well as some commercial cotton cultivars in concentrations similar to that found in G. thurberi. When fed to Helicoverpa zea in an artificial diet, GHQ delayed days-to-pupation, reduced pupal weights, and survival compared to those on a control diet, at a lesser or equal extent than gossypol. However, it had a synergistic effect on survival when combined with gossypol at the highest dosage tested (0.18%; 85.5:14.5 gossypol:GHQ). Because gossypol exhibits anti-cancer activity, GHQ was also evaluated for its anti-cancer activity against the National Cancer Institute’s 60-Human Tumor Cell Line Screen. Significant inhibitory activity against these cell lines was not observed.