Formation of gossypol and related substances in glandless cotton after inoculation with Xanthomonas campestris pv. malvacearum

Both in glanded and glandless cotyledons of cotton, the occurrence of gossypol (G), hemigossypolone (HGQ), hemigossypol (HG) and deoxyhemigossypol (dHG) was determined after inoculation with Xanthomonas campestris pv. malvacearum. The cultivars Tamcot GCNH (glandless) and Tamcot CAMD-E (glanded) are both resistant to the inoculated strain. One, 3 and 5 days after inoculation the cotyledons were harvested, extracted and the extract were analyzed by chromatography. In glandless plants, gossypol was found only in very small concentrations up to a maximum of 0.19 mg/g dry weight, while in the glanded cultivar gossypol varied considerably between 0.6 and 2.8 mg/g dry weight. Bacterial inoculation or water injection had very little effect on the content of gossypol. HGQ was present in the glandless plants only in traces, whereas in the glanded cotyledones it increased to 0.3 mg/g dry weight. The increase of this substance was evident very clearly 3 and 5 days after inoculation in both cultivars. HG and dHG were analyzed together. In untreated plants and in those injected with water, these substances were not found or were present only in concentrations of up to 0.09 mg/g dry weight. Three days after inoculation, both cultivars reacted with a very strong increase of HG and dHG reaching 0.8-1.0 mg/g dry weight. Evidently, glandless plants are also able to synthesize gossypol-related sesquiterpenes. This is consistent with the assumption, that HG and dHG may be involved as phytoalexins in the defence of cotton against the pathogen Xanthomonas campestris pv. malvacearum.