Carnivorous pitcher plant uses free radicals in the digestion of prey

Abstract

A study of the involvement of free oxygen radicals in trapping and digestion of insects by carnivorous plants was the main goal of the present investigation. We showed that the generation of oxygen free radicals by pitcher fluid of Nepenthes is the first step of the digestion process, as seen by EPR spin trapping assay and gel-electrophoresis. The EPR spectrum of N. gracilis fluid in the presence of DMPO spin trap showed the superposition of the hydroxyl radical spin adduct signal and of the ascorbyl radical signal. Catalase addition decreased the generation of hydroxyl radicals showing that hydroxyl radicals are generated from hydrogen peroxide, which can be derived from superoxide radicals. Gel-electrophoresis data showed that myosin, an abundant protein component of insects, can be rapidly broken down by free radicals and protease inhibitors do not inhibit this process. Addition of myoglobin to the pitcher plant fluid decreased the concentration of detectable radicals. Based on these observations, we conclude that oxygen free radicals produced by the pitcher plant aid in the digestion of the insect prey.

The Protein Composition of the Digestive Fluid from the Venus Flytrap Sheds Light on Prey Digestion Mechanisms

“…It has been suggested that prey proteins in the Venus flytrap are initially oxidized in order to facilitate their subsequent proteolysis (53), and it has been demonstrated that Nepenthes gracilis uses free radicals during the digestion process (54). Plumbagin, a low-molecular-weight compound present in Venus flytrap digestive fluid, likely facilitates this oxidation (40).…”

Proteomic analysis of secreted protein induced by a component of prey in pitcher fluid of the carnivorous plant Nepenthes alata

“…Class III peroxidases can generate highly reactive oxygen species (ROS) [20][21][22]. Chia et al also reported that ROS were produced in the Nepenthes pitcher fluid, and might aid in degrading proteins derived from the tissues of the prey [23]. Excess ROS cause oxidation reactions in proteins, such as crosslinking, and oxidized proteins are attacked by proteases.…”

A proposed mechanism for nitrogen acquisition by grass seedlings through oxidation of symbiotic bacteria

“…ROS has additionally been shown to be involved in nutritive phagocytosis in starfish and other simple animals (Coteur et al 2002). In carnivorous pitcher plants, plant-secreted ROS plays a nutritional role in digestion of insect proteins (Chia et al 2004). Galek et al (1990) similarly reported that the ‘venus flytrap’ ( Dionaea muscipula ) employs ROS to pre-digest insect proteins prior to protease action on the denatured peptide fragments.…”