The Diphenylether Herbicide Lactofen Induces Cell Death and Expression of Defense-Related Genes in Soybean

Abstract

Lactofen belongs to the diphenylether class of herbicides, which targets protoporphyrinogen oxidase, which in turn causes singlet oxygen generation. In tolerant plants like soybean (Glycine max), the chemical nonetheless causes necrotic patches called “bronzing” in contact areas. Here it is shown that such bronzing is accompanied by cell death, which was quantified from digital microscopic images using Assess Software. Cellular autofluorescence accompanied cell death, and a homolog of the cell death marker gene, Hsr203j, was induced by lactofen in treated soybean tissues. Thus, this form of chemically induced cell death shares some hallmarks of certain types of programmed cell death. In addition to the cell death phenotype, lactofen caused enhanced expressions of chalcone synthase and chalcone reductase genes, mainly in the exposed and immediately adjacent (proximal) cells. Furthermore, isoflavone synthase genes, which are wound inducible in soybean, were up-regulated by lactofen in both proximal and distal cell zones in minimally wounded cotyledons and further enhanced in wounded tissues. Moreover, if the wall glucan elicitor from Phytophthora sojae was present during lactofen treatment, the induction of isoflavone synthase was even more rapid. These results are consistent with the fact that lactofen triggers massive isoflavone accumulations and activates the capacity for glyceollin elicitation competency. In addition, lactofen induces late expression of a selective set of pathogenesis-related (PR) protein genes, including PR-1a, PR-5, and PR-10, mainly in treated proximal tissues. These various results are discussed in the context of singlet oxygen-induced responses and lactofen's potential as a disease resistance-inducing agent.

Glufosinate Ammonium-Induced Pathogen Inhibition and Defense Responses Culminate in Disease Protection in bar-Transgenic Rice

“…These results imply that glufosinate ammonium could induce resistance in the transgenic rice and Arabidopsis. Similar to our results, treatment with lactofen, a herbicide belonging to the diphenylether class, induced robust transcriptions of PR-1a, PR-5, and PR-10 in soybean (Glycine max) leaves (Graham, 2005). In addition, glufosinate ammonium induced systemic transcriptions of three PR genes within the leaves of transgenic plants.…”

RNAi Silencing of Genes for Elicitation or Biosynthesis of 5-Deoxyisoflavonoids Suppresses Race-Specific Resistance and Hypersensitive Cell Death in Phytophthora sojae Infected Tissues

“…HR cell death can be monitored by a number of protocols, including vital stains (Evans blue [Baker et al, 1993;Graham, 2005] or Trypan blue [Meier et al, 1993;Ger et al, 2002]), yellow autofluorescence (YAF; Koga et al, 1988;Essenberg et al, 1992;Wäspi et al, 2001;Gray et al, 2002;Graham, 2005), and the accumulations of hydrogen peroxide and peroxidase. The latter response is commonly followed by staining with diaminobenzidine (Hü ckelhoven et al, 1999;Vanacker et al, 2000) or 3-amino-9-ethylcarbazole (AEC; Ellis and Grant, 2002), which are substrates of peroxidase that are oxidized to colored compounds only in the presence of endogenous hydrogen peroxide.…”

“…A landmark study on P. sojae infected soybean hypocotyls demonstrated the critical importance of carefully analyzing the spatial aspects of phytoalexin accumulation in interpreting the role of the phytoalexins (Yoshikawa et al, 1978). This work provided a foundation for later cellular studies in roots (Hahn et al, 1985) and the development of soybean cotyledon protocols for the cellular delineation of the multiplicity and coordination of responses to infection and WGE treatment (Graham andGraham, 1991b, 1996;Graham, 1994).…”

Pathogenesis Related Protein (PR protein) in Soybean Predicted Through HMMER and BLAST Resources

“…At present, only five PR proteins in soybean were identified. While only PR1 and thaumatin-like protein were reported in the references (Graham, 2005). Therefore, it has a very important significance to predict and investigate PR protein of soybean.…”