Plant cell wall degrading enzymes, pectinase and cellulase, in the digestive system of the red palm weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae)

Abstract

In digestion, the red palm weevil, Rhynchophorus ferrugineus, has been adapted to overcome the plant cell wall barrier, specially lignocellulosic and pectic compounds, by producing cellulase and pectinase enzymes. Partial biochemical characterisations of cellulase and pectinase were determined in the larval digestive system of the pest. Larval midgut extract showed an optimum activity for cellulase and pectinase against carboxyl methyl cellulose and pectin at pH 6.0 and 7.0, respectively. Larval midgut cellulase and pectinase were more stable at pH 4.0–8.0 and pH 6.0–8.0 than in highly acidic and alkaline condition, respectively. However, cellulase and pectinase showed to be more stable at pH 6.0 and 7.0, respectively, when the incubation time increased. Maximum activity for cellulase and pectinase incubated at different temperatures was observed at 50°C. Cellulase and pectinase activity significantly decreased in the presence of EDTA and SDS. On the contrary, Ca<sup>2+</sup>, Mg<sup>2+</sup>,and Na<sup>+</sup> significantly affect pectinase activity and K<sup>+</sup> did not affect the enzyme activities. Ca<sup>2+</sup> and Mg<sup>2+</sup> increased cellulase activity as well. K<sub>M </sub>and V<sub>max</sub> for pectinase activity were 0.92 mg/ml and 290 units/mg. Zymogram analyses revealed the presence of one form of pectin methyl esterase and one form of cellulase in the larval digestive system.