Toxicity of (+)- and (−)-Gossypol to the Plant Pathogen, Rhizoctonia solani

Abstract

The dimeric sesquiterpene gossypol occurs naturally in cottonseed and other parts of the cotton plant. Gossypol exists as enantiomers because of the restricted rotation around the central binaphthyl bond. The (-)-enantiomer is toxic to nonruminant animals while the (+)-enantiomer exhibits little, if any, toxicity to these animals. Developing cotton plants with low levels of the (-)-gossypol could expand the use of cottonseed as a feed source. Gossypol also may play a role in protecting the plant from pathogens. The relative toxicity of (+)- and (-)-gossypol to plant pathogens has not been reported. We measured the concentration of (+)- and (-)-gossypol in roots from cotton seedlings that were treated with the biocontrol agent Trichoderma virens that induces biosynthesis of gossypol and related terpenoids in cotton roots. (-)-Gossypol was the minor enantiomer in control and treated roots, but levels were slightly higher in roots from T. virens-treated seed. We also determined the toxicity of the gossypol enantiomers and the racemate to the seedling disease pathogen Rhizoctonia solani. The (+)- and (-)-enantiomers of gossypol and the racemate are equally effective in inhibiting growth of this pathogen. The lethal doses of the gossypols required to kill the pathogen appeared to be similar, but their toxicities are significantly less than those of related cotton and kenaf sesquiterpenes. The results indicate that altering the enantiomeric ratio in cotton roots will not adversely affect the resistance of seedlings to the seedling pathogen R. solani.

Characterization of GaWRKY1, a Cotton Transcription Factor That Regulates the Sesquiterpene Synthase Gene (+)-δ-Cadinene Synthase-A

“…In cotton, gossypol and other sesquiterpene phytoalexins not only have fungistatic properties and insecticidal activities but also are toxic to mammals (Bell and Stipanovic, 1977;Davila-Huerta et al, 1995;Puckhaber et al, 2002). In previous studies, we have cloned three enzymes that catalyze consecutive steps from isopentenyl diphosphate and dimethylallyl diphosphate to 8-hydroxy-(1)-d-cadinene of the gossypol pathway: farnesyl diphosphate synthase , CAD1 (Chen et al, 1995(Chen et al, , 1996Tan et al, 2000), and (1)-d-cadinene-8-hydroxylase (CYP706B1; Luo et al, 2001).…”

Evaluating Protective Terpenoid Aldehyde Compounds in Cotton (<i>Gossypium hirsutum</i> L.) Roots

“…A number of studies had demonstrated the efficacy of gossypol against diseases and insects. One study indicated that the (+) and (−) forms were equally effective against black scurf, caused by the plant pathogen Rhizoctonia solani [10]. A second study reported similar results for cotton bollworm (Helicoverpa zea Boddie) larvae [11].…”

Regulation of Specialized Metabolism by WRKY Transcription Factors

“…In Arabidopsis, camalexin has antifungal properties and aids defense against pathogens including Botrytis cinerea, Alternaria brassicicola, and Sclerotinia sclerotiorum (Thomma et al, 1999;Ferrari et al, 2007;Stotz et al, 2011). Berberine, catharanthine, gossypol, momilactones, phytocassanes, and sanguinarine also have antimicrobial properties and confer tolerance to plant pathogens (Stermitz et al, 2000;Puckhaber et al, 2002;Umemura et al, 2003;Fukuta et al, 2007;Roepke et al, 2010;Obiang-Obounou et al, 2011). In addition to the involvement in auxin signaling (Brown et al, 2001;Buer and Muday, 2004), flavonols are protectants against UV light stress (Li et al, 1993;Bieza and Lois, 2001;Emiliani et al, 2013) and herbivores (Wuyts et al, 2006a;Onkokesung et al, 2014).…”