Alois A. Bell

Melanins and Their Importance in Pathogenic Fungi

Melanins are generally described as dark brown or black pigments of high molecular weight formed by oxidative polymerization of phenolic compounds. Certain yellow, red, green, purple, or blue pigments have similar chemical structures and occasionally are referred to as types of melanins. Melanins are found in humans and various other warm- and cold-blooded vertebrates; invertebrates, including insects; higher plants; fungi; and bacteria, including actinomycetes. Most animal melanins are synthesized by tyrosinase, whereas a number of less specific polyphenol oxidases may form melanins in various cellular and extracellular environments of other organisms. In some cases melanins are autoxidative products made in the absence of enzymes.

Fungal wilt diseases of plants.

Fungal wilt diseases of plants , Fungal wilt diseases of plants , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Antimicrobial terpenoids of Gossypium: Hemigossypol, 6-methoxyhemigossypol and 6-deoxyhemigossypol

Abstract The sesquiterpenoid aldehydes, hemigossypol ( 1 a), 6-methoxyhemigossypol ( 1 b), and 6-deoxyhemigossypol ( 1 c), were isolated and identified from Verticillium -infected stele tissue of Gossypium barbadense . Structures were established by spectral (UV, IR, NMR, MS) evidence and chemical transformations. This is the first report of ( 1 b) and ( 1 c) in nature, and of NMR and m.p. data for crystalline pure ( 1 a). Compound ( 1 a) occurred in diseased stele tissues of all 21 Gossypium species examined and in the genera, Cienfuegosia , Gossypioides , Hampea , and Thespesia ; it was absent in three Hibiscus spp. Compound ( 1 b) occurred in the same taxa as ( 1 a), except that it was absent in species of two cytogenetic groups (A and B genome) of Gossypium . Compound ( 1 c) occurred in trace quantities, or was not detected, in most species; however, its distribution appeared to besimilar to that

Resistance against various fungal pathogens and reniform nematode in transgenic cotton plants expressing Arabidopsis NPR1

Cotton is an economically important crop worldwide that suffers severe losses due to a wide range of fungal/bacterial pathogens and nematodes. Given its susceptibility to various pathogens, it is important to obtain a broad-spectrum resistance in cotton. Resistance to several fungal and bacterial diseases has been obtained by overexpressing the Non-expressor of Pathogenesis-Related genes-1 (NPR1) in various plant species with apparently minimal or no pleiotropic effects. We examined the efficacy of this approach in cotton by constitutive expression of the Arabidopsis (Arabidopsis thaliana) NPR1 gene. The results show that NPR1-expressing lines exhibited significant resistance to Verticillium dahliae isolate TS2, Fusarium oxysporum f. sp. vasinfectum, Rhizoctonia solani, and Alternaria alternata. Interestingly, the transformants also showed significant resistance to reniform nematodes. Analysis of defense-related, biochemical and molecular responses suggest that when challenged with pathogens or certain systemic acquired resistance-inducing chemicals, the transgenic lines respond to a greater degree compared to the wild-type plants. Importantly, the basal activities of the defense-related genes and enzymes in uninduced transformants were no different than those in their non-transgenic counterparts. The results provide additional evidence supporting the role of NPR1 as an important part of the plant defense system and suggest a means to achieve broad-spectrum resistance to pathogens via genetic engineering.

Sesquiterpenoid aldehyde quinones and derivatives in pigment glands of Gossypium

Abstract The resistance of Gossypium species to insects is enhanced by compounds in their lysigenous pigment glands. In cultivated cottons, glands in achlorophyllous plant parts contained predominately the terpenoid aldehyde gossypol in G. hirsutum , and gossypol and its methyl and dimethyl ethers in G. barbadense . Glands in young green tissues, however, contained hemigossypolone as the predominant terpenoid aldehyde in G. hirsutum , and a new quinone, hemigossypolone-7-methyl ether, in G. barbadense . As glands aged in green tissues, the sesquiterpenoid quinones were replaced by several C 25 -terpenoids formed by the Diels-Alder reaction of the quinones with myrcene or trans -β-ocimene. Two C 25 -terpenoids isolated from G. barbadense , but not G. hirsutum , were the methyl ethers of heliocides H 1 and H 4 and were designated heliocides B 1 and B 4 , respectively. A dark red pigment, gossyrubilone, from glands of young leaves of both species is the isopentylimine of hemigossypolone. Similar red imines, formed from sesquiterpenoid quinones and amino acids, resembled the red coloration of the envelope cells surrounding the gland sac. The terpenoid quinones of Gossypium had physical characteristics different from quinones in Bombax which apparently were incorrectly identified as being the same. A survey of the terpenoid quinones and their heliocide derivates in wild Gossypium species and related genera in the Gossypieae showed considerable diversity which may be used for establishing biochemical and phylogenetic relationships.

Antimicrobial terpenoids of Gossypium: 6-methoxygossypol and 6,6′-dimethoxygossypol☆

Abstract The triterpenoid aldehydes, gossypol ( 1 ), 6-methoxygossypol ( 2 ) and 6,6′-dimethoxygossypol ( 3 ); and the sesquiterpenoid aldehydes, hemigossypol ( 4 ) and methoxyhemigossypol ( 5 ), were isolated from 1-week-old roots of Gossypium hirsutum and G. barbadense and identified. This is the first report of 2 and 3 in nature and of 4 and 5 from healthy roots. Compounds 2 and 3 also constituted 30% of the total terpenoid aldehydes in the seeds of 1 cultivar of G. barbadense , but occurred only in trace quantities in those of G. hirsutum . Spectral data (UV, IR, NMR, MS) and proof of structure for 2 and 3 are presented.

Transmission of cotton seed and boll rotting bacteria by the southern green stink bug (Nezara viridula L.).

Aims:  To determine the ability of the southern green stink bug (SGSB) (Nezara viridula L.) to transmit Pantoea agglomerans into cotton (Gossypium hirsutum) bolls.

Toxicity and role of terpenoid phytoalexins in verticillium wilt resistance in cotton

Abstract Hemigossypol (HG), methoxyhemigossypol (MHG), desoxyhemigossypol (dHG) and desoxymethoxyhemigossypol (dMHG), the four major terpenoids formed in the stem stele of Verticillium dahliae -infected, wilt-resistant Seabrook Sea Island (SBSI) cotton, were tested at pH 6·3–7·5 in liquid nutrient media for toxicity to V. dahliae . The terpenoids dHG, HG, dMHG, and MHG at 25 °C killed all conidia after 18–40 h at 10, 45, 25 and 60 μg ml −1 , respectively; and all mycelia after 48 h at 15, 32, 25 and 45 μg ml −1 , respectively. Inhibition of conidia germination also occurred at concentrations well below the fungicidal concentrations. Dimethylsulfoxide at 2 or 5% was required to solubilize HG, MHG and dMHG at fungicidal concentrations. Only dHG had the water solubility apparently required to reach fingicidal concentration in the aqueous medium of infected xylem vessels and thus account for the death of V. dahliae conidia and mycelia in most infected vessels in the stem stele of SBSI cotton 10 days after inoculation. The dHG in the stem stele at 10 days after inoculation was in excess of fungicidal concentration.

Effect of aging on flavonoid content and resistance of cotton leaves to verticillium wilt

Abstract Young (1 to 3 nodes from the apex) leaves of Acala 4–42 cotton plants resist infection by Verticillium dahliae , but become susceptible with increased age. This phenomenon is due to inhibition of fungal growth in young leaves. Resistant young leaves contain (+)-catechin, (+)-gallocatechin, isoquercitrin and condensed tannins in higher concentration than do older, susceptible leaves. Infection increases the concentrations of these compounds, especially in young leaves. (+)-Catechin prevents conidiation by V. dahliae at 5 × 10 −5 m and strongly inhibits mycelial growth above 1 × 10 −3 m . The concentration of (+)-catechin and (+)-gallocatechin found in resistant leaves is consistent with that required to strongly inhibit mycelial growth, whereas the concentrations found in older, susceptible leaves is much less inhibitory.

Stereoselective coupling of hemigossypol to form (+)-gossypol in moco cotton is mediated by a dirigent protein

The terpenoid gossypol, a secondary metabolite found in the cotton plant, is synthesized by a free radical dimerization of hemigossypol. Gossypol exists as an atropisomeric mixture because of restricted rotation around the central binaphthyl bond. The dimerization of hemigossypol is regiospecific in cotton. In the case of some moco cotton, the dimerization also exhibits a high level of stereoselectivity. The mechanism that controls this stereoselective dimerization is poorly understood. In this paper, we demonstrate that a dirigent protein controls this stereoselective dimerization process. A partially purified protein preparation from cotton flower petals, which by itself is unable to convert hemigossypol to gossypol, converts hemigossypol with a 30% atropisomeric excess into (+)-gossypol when combined with an exogenous laccase, which by itself produces racemic gossypol.