Histochemistry and identification of disease-induced terpenoid aldehydes in Verticillium-wilt-resistant and -susceptible cottons

Abstract

Hemigossypol (HG) and 6-methoxyhemigossypol (MHG) were the major terpenoid aldehydes isolated from stem stele tissue of 6-week-old verticillium-wilt-susceptible Rowden and verticillium-wilt-resistant Seabrook Sea Island 12B2 (SBSI) cotton plants infected for 14 days with Verticillium dahliae. HG constituted 90 and 45 mol % and MHG 6 and 41 mol % of the induced terpenoid in the steles of Rowden and SBSI, respectively. No terpenoids were detected in extracts of noninfected steles.The cellular localization of terpenoids in infected and noninfected stems was studied histochemically with a SbCl3 reagent. Terpenoids first occurred in both SBSI and Rowden in scattered, usually solitary, paratracheal parenchyma cells appressed to infected xylem vessels. After extensive fungal colonization, diffusion of induced terpenoids obscured the initial, discrete sites of localization.