The Effects of Pectin and Plant Root Surface Carbohydrates on Encystment and Development of Phytophthora cinnamomi Zoospores

Abstract

Citrus pectin induces highly synchronous differentiation in populations of Phytophthora cinnamomizoospores in the absence of a host plant. This action is independent of the presence of Ca2 + in the zoospore suspension medium. Water-soluble, ethanol-insoluble material present on the surface of the plant roots also induces differentiation of P. cinnamomi zoospore populations with the same time course iis pectin. It is proposed that this material provides the natural recognition signal which induces P. cinnamomi zoospores to differentiate, and that pectin is sufficiently similar in structure for it to mimic its action.

Role of phosphatide acid during differentiation of Phytophthora palmivora zoospores

“…Exogenous cAMP and cGMP both induced P. palmivora spore differentiation and the associated Ca2+ efflux (Irving et al, 1984), but only at m~ concentrations, as might be expected from the known low permeability of nucleotides. There is no evidence for cyclic nucleotide receptors on the P. palmivora spore surface, such as have been demonstrated on the surface of Dictyostelium discoideum (Schaap & Wang, 1985).…”

“…palmivora zoospores is very rapid, and in the presence of pectate is normally followed by germination. The earliest response previously recorded, an increase in the rate of Ca2+ exchange, had a t l 1 2 of 30 s or less (Irving et al, 1984). Although many intracellular messengers may be involved in the regulation of spore germination, any compound involved in the direct transmission of the external signal to encyst must respond within a time scale of seconds, which is also the time scale within which spores become committed to germination (Paktitis et al, 1986).…”

“…Differentiation is dependent upon low concentrations of Ca2+ (Griffith el al., 1988) and is accompanied by increases in the transmembrane fluxes of both this ion (Irving et al, 1984) and Na+ . Zoospore differentiation is also sensitive to external pH (Griffith et al, 1988).…”

“…This transition from zoospore to germling takes less than 30min at 25 "C, while encystment is completed in less than 5 min. Encystment and germination are induced by contact with polysaccharides at the host surface (Hinch & Clarke, 1980;Irving & Grant, 1984;Longman & Callow, 1987;Estrada-Garcia et al, 1990). They may also be induced by localized concentrations of Ca2+, which have been shown to occur on root surfaces (Miller & Gow, 1989).…”

Root exudate ofSolanum tuberosumis enriched in galactose-containing molecules and impacts the growth ofPectobacterium atrosepticum

“…Based on the glycosidic linkage patterns established from exudates of different plants, it appears that polysaccharides are highly diverse and often unique within a plant species. Moreover, the nature of the polysaccharides and other glycan-containing molecules of root exudates plays a major role in mediating root-microbe interactions (Hinch and Clarke, 1980;Irving and Grant, 1984;Ray and Callow, 1988;Cannesan et al, 2012, Nguema-Ona et al, 2013. Although hydroxyproline has been reported to be a minor component in maize and cress exudates (Ray and Callow, 1988), glycoproteins such as arabinogalactan proteins (AGPs), which belong to the hydroxyproline-rich glycoprotein (HRGP) family, have been found to occur in root secretions of many plant species, such as pea, arabidopsis and Brassica napus (Knee et al, 2001;Durand et al, 2009;Cannesan et al, 2012).…”