Production of pectinases and cellulase by six Pythium species isolated from necrotic strawberry roots
Polygalacturonase and polymethylgalacturonase activity was detected in filtrates ofPythium irregulare, P. perniciosum, P. sylvaticum, andP. dissotocum but not in filtrates ofP. rostratum andP. acanthicum. OnlyP. irregulare, P. perniciosum andP. dissotocum elaborated pectin methyl esterase and in trace amounts. None of the species produced detectable pectintrans-eliminase and “macerating enzyme” activity.P. sylvaticum was the only species of four tested which produced cellulase.
Characterisation of the early events in atypical tomato root colonisation by a biocontrol agent, Pythium oligandrum.
The specific oomycete-plant relationship established between a biological agent, Pythium oligandrum, and tomato (Lycopersicon esculentum Mill.) plants was examined over the first 48 h after inoculation of tomato roots with the antagonist. One of the most significant effects was the quick colonisation of cortical and vascular root areas by P. oligandrum (until 9 h post-inoculation); it was similar to invasions by the major pathogens of Pythium genus, and much faster than those by Pythium-minor pathogens. Despite the multiplication of hyphae in the root areas, fungal colonisation was associated with neither host wall disruption nor host cell alterations. The colonising hyphae looked healthy till the ninth hour after inoculation, then, they progressively became highly vacuolated. Cytological observations showed that, over the first 14 h of experiment, oomycete invasion was accompanied with rare host-induced defence reactions. Biochemical analysis evidenced an accumulation of phenolic compounds starting 3 h after inoculation. The 14th hour corresponded to the beginning of rishitin (phytoalexin) synthesis. Accumulation of biochemical host defence compounds was concomitant with early signs of hyphae alterations. During the next 34 h several host reactions were regularly amplified as evidenced by the plugging of invaded host cells with heterogeneous osmiophilic or high electron-dense (ED) materials. Fungal cell decay was accompanied with the formation of oogonia in the cortex, vascular parenchyma and xylem vessels. All these early events suggest a peculiar relationship established between P. oligandrum and the plant.
Studies on Pectic Enzymes
1. Alkali titration method is inquired and employed in the determination of the pectin-es-terase activity. 2. The PE is extracted from tomato pulp by Na2HPO4 at pH 8. It is more influenced by pH than extractant. 3. The PE is precipitated by (NH4)2SO4 at 11_??_70% saturated. The precipitated enzyme is stable at dry state. 4. Pectin solutin is decomposed by PE and produces acid, but this reaction is inhibited at pH 3.8. 5. The PE has opt. pH 6_??_7.5, and decomposes over 80% methoxyl groups in pectin. 6. The opt. temp. is 60°, and loses the activity at 80° 7. CaCl2 and (NH4)2SO4 accelerate the PE activity. 8. The enzyme does not decrasc the viscosity of pectin or pectic acid solution, and does not produce the reducing sugar. 9. The characters of the PE from tomato differs from the PE in mould or bacteria.