Modulation of host pH during the wheat–Fusarium culmorum interaction and its influence on the production and activity of pectolytic enzymes

Abstract

The effect on ambient pH of Fusarium culmorum during its growth on mineral medium and in apoplastic fluids from infected wheat seedlings, and the effect on the production and activity of the enzymes pectin lyase (PNL) and polygalacturonase (PG), were investigated. Fungal development on a weakly buffered mineral medium in the pH range 5·0 -8·0, with pectin as the sole carbon source, led to pronounced alkalinization, reaching values above 8·0. The increase in ambient pH was accompanied by enhancement of total PNL activity. Pectin lyase secretion was detected at pH 5·0 as a single isoenzyme. An additional isoenzyme was apparent during the increase in medium pH. Polygalacturonase was detected as a single isoenzyme only during early growth on medium buffered at pH 5·0. At this stage, the initial medium pH of 5·0, corresponding to the optimum pH for PG activity, appeared to be the most suitable for the activation of early production of this enzyme. During growth in acidified yeast extract medium the fungus secreted ammonia and increased medium pH. Similarly, in apoplastic fluids from inoculated seedlings the concomitant ammonia accumulation and rise in pH were recorded. This trend was accompanied by an increase in PNL, which could therefore function at close to its optimal pH. The results suggest that during infection of wheat seedlings by F. culmorum , pH modulation can lead to PNL production and activity, thus promoting colonization of host tissue.

Low pH regulates the production of deoxynivalenol by Fusarium graminearum

“…Sclerotinia sclerotiorum and Botrytis cinerea both secrete oxalic acid, which has both pH-lowering and elicitor activities during pathogenesis (Kim et al, 2008;Williamson et al, 2007). Although an in planta requirement of an acidic pH for induction of DON production is unknown, the pH optimum of between 2.4 and 3.1 observed here for maximal DON induction is at the extreme end of the previously reported pH of plant apoplastic fluid (Yu et al, 2000), and considerably different from the pH rise from 6 to 7.3 observed in wheat seedlings during crown rot disease caused by Fusarium culmorum (Aleandri et al, 2007). However, accurate measurement of extracellular pH in complex tissues is difficult (Yu et al, 2000), and the pH may not necessarily be homogeneous.…”

Effect of salicylic acid on Fusarium graminearum, the major causal agent of fusarium head blight in wheat

“…Letters indicate steps supported by gene expression analysis (see Table 2). polygalacturonase by secreting ammonia to increase alkalinisation of the growing media or of the apoplastic fluids of wheat seedlings (Aleandri et al 2007). Merhej et al (2011) have recently shown that Pac1 is a homologue of PacC in F. graminearum.…”

An Impedance-Based Mold Sensor with on-Chip Optical Reference

“…This change in the pH of the medium is caused by the metabolic activity of the mold. As the mold grows, it utilizes the organic matter present in the culture medium and releases some secondary metabolites as by-products that change the pH of the medium [27]. …”