Activity of Host-derived Attractants and Their Related Compounds toward the Zoospores of PhytopathogenicAphanomyces cochlioides

Abstract

Eleven flavones, including cochliophilin A and a chromone, were chemically prepared to determine the attracting activity for zoospores of Aphanomyces cochlioides, a causative fungus of spinach root rot. Analyses of the structure-activity relationship of each revealed a significant correlation between the zoospore attracting activity and the A-ring oxygenation at C-5 and C-7 in the flavone skeleton. The relative attractancy of four regio-isomers of N-trans-feruloyl 4-0-methyldopamine, which was identified as a zoospore attractant specific to another host plant Chenopodium album, was also examined.Aphanomyces cochlioides Drechsler (Saprolegniales) is a causal fungus of root rot disease to spinach (Spinacia oleracea L.) and infects some other species of Chenopodiaceae. It is considered that when zoospores of the Aphanomyces spp. infest the host, they are initially attracted to an exudate from the roots. 1 -3) Cochliophilin A (5-hydroxy-6,7-methylenedioxyflavone, 1) has been isolated from spinach roots as a highly potent attractant for the zoospores of A. cochlioides. 4) A second attractant has recently been isolated from Chenopodium album, one of the host plants, and was characterized to be N-trans-feruloyl 4-0-methyldopamine (17) by chemical and spectroscopic methods. S ) In this study, we synthesized cochliophilin A analogs and regio-isomers of the phenolic amide attractant to analyze the relationship between the zoospore attracting activity and the chemical structure. We anticipate that the results would provide some knowledge which would be available for the eco-chemical regulation of those soil-borne phytopathogens that are usually very difficult to control by agrochemicals. Materials and MethodsChemicals. Cochliophilin A (1) and 5-hydroxy-7-methoxychromone (12) were prepared by the method of Horio et at. 4) and Jain,6) respectively. 6,7-Methylenedioxyflavone (2), 7-hydroxyflavone (6), 5,7-dihydroxyflavone (7), 5, 6,7-trihydroxyflavone (10), and 5,7-dihydroxy-4'-methoxyflavone (16) were synthesized according to the method of Agasimundin and Siddapa. 7 ) Flavone (4) and 5-hydroxyflavone (5) were obtained by the method ofJain et al. 8) Compounds 7,10 and 5,7,4'-trihydroxyisoflavone (genistein, 14) were methylated to 5-hydroxy-7-methoxyflavone (8), 5-hydroxy-6,7-dimethoxyflavone (11), and 5,4'-dihydroxy-7-methoxyisoflavone (prunetin, 15) with diazomethane, respectively. 9) 5-Methoxy-6,7-methylenedioxyflavone (3) and 5-hydroxy-7,4'-dimethoxyflavone (13) were converted from 1 and 16 by methylating with dimethyl sulfate in a mixture of K 1 C0 3 and acetone, respectively. Ethylation of 7 with diethyl sulfate gave 5-hydroxy-7-ethoxyflavone (9). Genistein (14) was isolated from the leaves of white lupin. 10 ) N-trans-Feruloyl 4-0-methyldopamine (17) was prepared by the method of Horio et al.,5) and N-trans-isoferuloyl 4-0-methyldopamine (18), N-trans-feruloyl 3-0-methyldopamine (19) and N-trans-isoferuloyl 3-0-methyldopamine (20) were prepared by almost the same method.All compounds were identified on the basis of th...

Phenolic Constituents ofCelosia cristataL. Susceptible to Spinach Root Rot PathogenAphanomyces cochlioides

“…The other Celosia compounds were practically inactive. The relationship between the structure and attractant activity has been reported in our earlier papers, 14,16) The content of cochliophilin A (1) in C. cristata seedlings grown for 4 days was quantified by NMR by using the internal standard method to be at least 1.4 mg (¼ 4:9 Â 10 À9 mol)/g fresh weight. The content of 1 in spinach roots has been reported to be 5.3 mg/g fresh root, ca.…”

“…The known flavonoids (3-7) isolated for the first time from C. cristata were identified by comparing their physicochemical data with those reported for 3 from Polygonum lapathifolium, 11) 4 from Daphne oleoides, 12) 5 from Leptospermum scoparium, 13) 6 from Polemonium viscosum, 14) and 7 from Celosia argentea.…”

Effects of different classes of attractants, cochliophilin A and <i>N</i>-(<i>E</i>)-feruloyl-4-<i>O</i>-methyldopamine, on the response of <i>Aphanomyces cochlioides</i> zoospores in their chemoattraction and activation of motility linked with intracellular cAMP

“…3,5,15) A tyrosine kinase inhibitor, tyrphostin B56 (6) 17) and methyl ferulate (7) were purchased from Funakoshi (Tokyo, Japan) and TCI (Tokyo, Japan), respectively ( Fig. 1).…”

“…As shown in Table 1, the zoospores were all inactive toward the carrier particles when applying 1×10 −4 M 1 to any of the 1×10 −6 M aqueous solutions of agonistic flavonoid compounds that showed relatively high attractant activities toward A. cochlioides zoospores, 15) while the zoospores were clearly attracted to compound 2 (Table 2). Therefore, these flavonoid-type agonists likely share the flavonoid sensor with 1.…”

“…Therefore, many analogous compounds of 1, including 5-hydroxy-6,7-dimethoxyflavone (3), 5,7-dihydroxyflavone (chrysin, 4), and 5,6,7-trihydroxyflavone (5), showed agonistic activity toward A. cochlioides zoospores. 15) Conversely, a structural variation of compound 2, which is widely distributed throughout several plant families other than the Amaranthaceae, suggests a relatively narrow attracting activity toward zoospores.…”