Zoospore attractants

HOST-SPECIFIC ZOOSPORE ATTRACTANTS OF THE FUNGUS APHANOMYCES COCHLIOIDES, THE CAUSE OF SPINACH ROOT ROT... 

Table 7. Results of a Preliminary Screening Test for Zoospore Attractants in Roots of Species Compatible and Incompatible with Aphanomyces cochlioides...

The fractionation stages, which were monitored by bioassays using zoospores of A. cochlioides AK-1, are illustrated in Scheme 3. The relative activity of each fraction, as determined by the particle method, is shown in Isolation and Identification of Zoospore Attractants from the Table 9. 

Table 9. Purification Procedures for the Zoospore Attractant in Roots of Spinacia oleracea...

A comparison of the attractant activity of 55 (5-OH, 7-OMe, tectochrysin), with that of 57 (5,7-di-OH, chrysin), and that of 77 (5-OH, 6,7-diOMe) with that of 54 (5,6,7-triOH) revealed that 7-0-methylation significantly increased activity. However, the 7-0-ethyl derivative (79) was of considerably lower activity when compared with the 7-0-methyl derivative (55), probably as a result of steric effects. Although 6-hydroxylation had a negative effect on activity (compare 54 with 57), it was found that 6-methoxylation markedly increased activity (compare 55 with 77). Based on the high activity of the 6,7-methylenedioxy-substituted flavone (6) and the 6,7-dimethoxy derivative (77), the presence of small alkoxy groups at C-6 and C-7 would seem to be effective in enhancing the zoospore attractant properties (Table 12) [83]. 

We thank Professors R. Yokosawa, F. Tomita, and M. Fujimura for kindly supplying the fungal strains, Aphanomyces cochlioides, Cladosporium herbarum, and Neurospora crassa, respectively. Much of the research on which this review is based, has been carried out by the following students, Masters Y. Matsukura, N. Toda, and H. Katsuta (benzimidazole antidotes), and by Dr. T. Horio Masters T. Takayama, H. Kikuchi, K. Ohkawa, and M. Mizutani (zoospore attractants). 

Here we review our research results concerning zoospore attractants, repellents, cytotoxins and inhibitors of zoospore motility together with bioassay systems to survey chemical regulators toward zoospores. The first part of this review described some new findings on the effects of host-specific plant signals on chemotaxis and differentiation of oomycete zoospores. The potential role and mode of action of nonhost secondary... 

Tait K, Joint I, Daykin M, Milton DL, Williams P, Camara M (2005) Disruption of quorum sensing in seawater abolishes attraction of zoospores of the green alga Ulva to bacterial biofilms. Environ Microbiol 7 229-240... 

Cancellieri PJ, Burkholder JM, Deamer-Melia NJ, Glasgow HB (2001) Chemosensory attraction of zoospores of the estuarine dinoflagellates, Pflesteria piscicida and P. shumwayae, to finfish mucus and excreta. J Exp Mar Biol Ecol 264 29 15 Carde RT, Millar JG (2004) Advances in Insect Chemical Ecology. Cambridge University Press, New York... 

Flavonoids exuded from plants play an important role in the symbiosis between legumes and leguminous bacteria. At the same time, they attract zoospores and induce spore germination of phytopathogenic fungi. 

Table 8. Chemical Attractants of Phytopathogenic Zoospores Isolated from Plant Species...

Two bioassay techniques, the capillary method [58], and the drop method [63], have already been developed to study the chemotaxis of phytopathogenic zoospores and gametes of marine brown algae. We have devised a new procedure (the "particle method") which is a qualitative, rather than a quantitative, method of detecting an attractant after it has been absorbed on to an inorganic particle. This method has been used to study attractants of A. cochlioides zoospores in the roots of both spinach and pigweed (Chenopodium album). 

Fig. (12). Attractant effect of treated and untreated particles on zoospores of Aphanomyces...

The figure shows dark field microscopic photographs of a zoospore suspension containing Chromosorb W AW particles (ca 150 x 200 pm) with and without the attractant, cochliophilin A (6). [A] a particle soaked in 1.0 x 10-8 M cochliophilin A, [B] a control particle treated with solvent alone. The zoospore density around the particle [A] containing the attractant is clearly higher than around the control particle [B],... 

A second flavone attractant for zoospores of A. cochlioides has also now been isolated from the leaves of spinach [65] and identified as 5,4 -dihydroxy-3,3 -dimethoxy-6,7-methylenedioxyflavone (71). Although this compound has already been found as a glucuronide derivative in spinach [66], the role of the aglycone 71 in the interaction between the host plant and its fungal pathogens has still to be determined. 

The attractant activity of cochliophilin A towards zoospores of A. cochlioides (strains AC-5 and AK-1) was tested over the range 10-M0-" M by the particle method (Table 10). Zoospores of AC-5 were more sensitive to the attractant at all concentrations, when compared with the closely related strain AK-1. Zoospores of both AK-1 and AC-5 began to... 

Attractant activity was determined I min after dropping Chromosorb W AW particles treated with cochliophilin A (6), into the zoospore suspension. ++ indicates activity which is approximately equal to, or stronger than, that shown in Fig. 12 [A]. + indicates activity which is weaker than that shown in Fig. 12 [A], no observed activity. 

The attractant activity of the ferulamide derivatives (70 and 69) towards zoospores of A. cochlioides (AK-1 and AC-4) was also tested. As shown in Table 11, 70 exhibited clear chemo-attraction at lxlO 8 M, whilst its regio isomer 69 was only active around 10-5 M. 

Table 11. Attractant Effect of the Ferulamide Derivatives (69 and 70) on Zoospores of Aphanomyces cochlioides...

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