Structure-Activity Relationship Study of Host-Specific Phytotoxins (AM-Toxin Analogs) Using a New Assay Method with Leaves from Apple Meristem Culture

Abstract

AM -toxins are host-specific phytotoxins of the Alternaria alternata apple pathotype, which induce necrosis on apple leaves. In this study, we developed a new assay to measure the necrotic activity of AM -toxin analogs using cultured leaves from meristem cells. This method was not only more sensitive to AM -toxin I, but also more reliable than the previous one that used tree leaves due to the homogeneous nature of cultured leaves and to the method of application of toxins. U sing this assay method we investigated a structure-activity relationship of AM -toxin analogs synthesized in this study. Most residues and the macrocyclic ring structure were strictly recognized by AM -toxin putative receptor, whereas the L-Ala binding subsite of the receptor allowed for side chain structures with various stereoelectronic properties. These findings are important for designing ligands for further experimental probing of the nature of the receptor.

Phytotoxins produced by microbial plant pathogens

“…19 Some authors have used tissue cultures: apple leaves cultured from meristem cells were more sensitive to AM-toxin 30, the host-selective toxin of the apple pathotype of Alternaria alternata, and gave more reproducible results than an assay using leaves from trees. 20 The toxicity of this host-selective toxin and some of its analogues was also evaluated using inhibition of the photosynthetic evolution of oxygen, measured with an oxygen electrode: the results obtained correlated with the ability of the compounds to induce necrosis. 21 Fluorescence imaging is a method which allows comparison of toxin-damaged and healthy tissue in the same leaf, 22 and has been used to examine the response of canola (Brassica napus) and white mustard (Sinapis alba) to destruxins A 31 and B 32: the limits of detection were 50 ng ml −1 and 10 lg ml −1 , respectively.…”

Fungicide-free management of Alternaria leaf blotch and fruit spot on apple indicates Alternaria spp. as secondary colonizer

“…We believe that a critical examination of this method is necessary to ensure accurate interpretation of the infection biology of Alternaria spp. In “detached-leaf bioassays” or “pathogenicity bioassays” this direct toxin effect is used to infer the pathogenicity (pathotype vs. non-pathotype) of Alternaria strains 9 , 55 , 56 . Nevertheless, these assays can pose some challenges, because they (a) do not trace the biological process of infection, i.e.…”

Effect of a nonhost‐selective toxin from Alternaria alternata on chloroplast‐electron transfer activity in Eupatorium adenophorum

“…AK‐ and AF‐toxin (Chelkowski & Visconti, 1992); (v) interrupting membrane lipid biosynthesis and osmosis, inducing rapid depolarization of membrane potential and increasing electrolyte efflux, e.g. AM‐toxin, AB‐toxin (Miyashita et al ., 2001); (vi) inducing programmed cell death, e.g. AAL‐toxin (Spassieva et al ., 2002); and (vii) increasing transformation of C3H/10T1/2 cells and inducing expression of EBV‐EA in Raji cells, indicating tumour‐promoting activity, e.g.…”