Phytoalexin

About: Phytoalexin is a research topic. Over the lifetime, 1161 publications have been published within this topic receiving 63405 citations. The topic is also known as: phytoalexins.

Sesquiterpene cyclase is not a determining factor for elicitor- and pathogen-induced capsidiol accumulation in tobacco

Abstract: The induction of sesquiterpene cyclase, a key phytoalexin biosynthetic enzyme, and the accumulation of phytoalexins in relation to the induction of a hypersensitive response (HR) and cell necrosis in tobacco (Nicotiana tabacum L.) were investigated. When tobacco leaves were inoculated with virulent or avirulent isolates of Ralstonia solanacearum, steady-state levels of mRNA complementary to cDNA of the sensitivity-related (sts) gene str319 were dramatically induced. This cDNA clone is greater than 90% homologous with a gene coding for 5-epi-aristolochene synthase (EAS), previously described as a branch-point enzyme regulating the synthesis of capsidiol, the major sesquiterpenoid phytoalexin found in tobacco. Accumulation of EAS transcripts in leaves after inoculation with virulent and avirulent strains of R. solanacearum, or after treatment with necrotizing or non-necrotizing elicitins was rapid but transient, and restricted to the site of infiltration. Two highly similar sesquiterpene cyclase activities, 5-epi-aristolochene synthase and a vetispiradiene synthase-like activity, were found in extracts of elicitin-challenged and R. solanacearum-inoculated tobacco. Under all conditions tested, the induction of cyclase activity was closely correlated with induction of the cyclase mRNA level. In contrast, high levels of capsidiol were found only after treatment with the necrosis-inducing elicitin cryptogein, or after infiltration with HR-inducing bacterial strains. Low levels of capsidiol did accumulate after application of capsicein, an elicitin that induces little or no necrosis on tobacco, or after infection with a virulent bacterium. Hence, capsidiol accumulation, not 5-epi-aristolochene synthase gene expression or total sesquiterpene cyclase enzyme activity, appears to be a good marker for the HR of tobacco.

İnduction of phytoalexin accumulation in broad bean (Vicia faba L.) cotyledons following treatments with biotic and abiotic elicitors

Abstract: Broad bean (Vicia faba) cotyledons that were inoculated artificially with fungal pathogens or exposed to various abiotic agents were analysed for phytoalexin production. Biotic elicitors, such as Botrytis cinerea and B. allii, and abiotic elicitors, such as ultraviolet (UV) radiation (254 nm) and freezing-thawing, were used to induce phytoalexin accumulation. Wyerone and other wyerone derivatives were the major phytoalexins responding in broad bean cotyledons. The quantities of wyerone within elicitor-treated tissues were examined by thin layer chromatography. The highest amount of wyerone was induced by B. cinerea (943 mg/g fresh weight). Treatment of cotyledons with UV radiation (452 mg/g f.wt), B. alli (325 mg/g f.wt) and freezing-thawing (288 mg/g f.wt) also caused considerable activation of the phytoalexin synthesis. Cell necrosis and wyerone accumulation were closely associated, and the highest concentration of wyerone was in tissue bearing brown lesions. Only very low concentrations of wyerone accumulated at sites of mechanical damage. The results indicate that the presence of both damaged and healthy tissues is necessary for phytoalexin production.

Resveratrol impaired the morphological transition of Candida albicans under various hyphae-inducing conditions.

Abstract: The ability of the human fungal pathogen Candida albicans to undergo the morphological transition from a single yeast form to pseudohyphal and hyphal forms in response to various conditions is known to be important for its virulence. Many studies have shown the pharmacological effects of resveratrol, a phytoalexin polyphenolic compound. In this study, we investigated the antifungal activity of resveratrol against C. albicans. Both yeast-form and mycelial growth of C. albicans were inhibited by resveratrol. In addition, normal filamentation of C. albicans was affected and yeast-to-hypha transition under serum-, pH-, and nutrient-induced hyphal growth conditions was impaired by resveratrol.

The effect of salicylic acid on phenylalanine ammonia-lyase and stilbene synthase gene expression in Vitis amurensis Cell Culture

Abstract: Resveratrol is a phytoalexin with antibacterial, antiviral and cancer-preventing effects. The objective of the study was to identify PAL and STS genes of Vitis amurensis Rupr. encoding the phenylalanine ammonia-lyases (PAL) and stilbene synthases (STS), the key enzymes involved in the resveratrol biosynthesis. A V. amurensis Rupr. cell culture characterized by low resveratrol level was chosen as a model object. Salicylic acid (SA), a known secondary metabolism inducing agent, was used for enhancement of resveratrol production in this culture. PAL and STS gene expression was analyzed using the reverse transcription PCR and real-time PCR techniques. SA was originally found to specifically enhance the expression of VaPAL3, VaSTS2, VaSTS3, VaSTS4, VaSTS5, VaSTS6, and VaSTS8 of multigene families VaPAL and VaSTS. The results obtained were compared with the earlier published data on PAL and STS gene expression in the rolB transformed V. amurensis cell cultures characterized by high levels of resveratrol. The effects of SA treatment and the rolB transformation on VaPAL and VaSTS gene expression were found to be considerably different.

Sucrose: a constitutive elicitor of phytoalexin synthesis.

Abstract: Extracts of seeds and leaves of the tropical legume Cajanus cajan (L.) Millsp. (the pigeon pea) elicited the accumulation of three phytoalexins when applied as droplets to superficially wounded leaves of the plant. The active component was purified and identified as sucrose. Phytoalexin accumulation was proportional to the logarithm of the concentration of sucrose applied, with maxima ranging from 338 to 455 micrograms per gram (fresh weight) of leaf tissue. The sucrose concentrations required to elicit half these amounts ranged from 20 to 35 micrograms per milliliter, but other sugars had little effect even at 1000 micrograms per milliliter. The elicitor activity of sucrose was abolished by actinomycin D, puromycin, and cycloheximide at a concentration of 10 micrograms per milliliter or greater, suggesting that gene derepression is required for expression of the phytoalexin response.