Two Distinct Sources of Elicited Reactive Oxygen Species in Tobacco Epidermal Cells.

Abstract

Reactive oxygen species (ROS) play a prominent role in early and later stages of the plant pathogenesis response, putatively acting as both cellular signaling molecules and direct antipathogen agents. A single-cell assay, based on the fluorescent probe dichlorofluorescein, was used to scrutinize the generation and movement of ROS in tobacco epidermal tissue. ROS, generated within cells, quickly moved apoplastically as H202 into neighboring cells. Two classes of rapidly elicited intracellular ROS, originating from distinct sources, were distinguished. Cryptogein, the funga1 elicitor from Phytophthora cryptogea, induced ROS from a flavin-containing oxidase source. ROS accumulation could be inhibited by a number of pharmacological agents, suggesting induction through an active signal transduction pathway. The insensitivity of the increase in ROS to the externa1 addition of enzymes that dissipate ROS suggests that this oxidative increase is primarily intracellular. In contrast, amines and polyamines, compounds that form during wounding and pathogenesis, induced ROS at an apoplastic site from peroxidase-or amine oxidase-type enzyme(s). Salicylic acid, a putative inhibitor of cellular catalases and peroxidases, did not induce cellular ROS, as measured by dichlorofluorescein fluorescence. The physiological relevance of ROS-generated signals was indicated by the rapid alteration of the epidermal cell glutathione pool and the cellular redox state. In addition, induction of ROS by all elicitors was correlated with subsequent cell death.

Early perception responses of Nicotiana tabacum cells in response to lipopolysaccharides from Burkholderia cepacia

“…In the presence of intracellular oxidants, inter alia H 2 O 2 , this compound is oxidized to the highly fluorescent compound 2¢,7¢-dichlorofluorescein (DCF; Keston and Brandt 1965). Treatment of tobacco cells with cryptogein resulted in a fast ROS burst as detected by H 2 DCF (Allan and Fluhr 1997). Here, elicitation of tobacco cells by LPS revealed strong H 2 DCF fluorescence, indicating the presence of ROS (Fig.…”

The sensitivity of ABI2 to hydrogen peroxide links the abscisic acid-response regulator to redox signalling

“…Our figures correspond to an average concentration of 0.1-0.3 mM H 2 O 2 , in agreement with the levels reported for tobacco ), without taking into account different levels in the various cellular and extracellular compartments. The compartment-specific concentrations are still not known and local increases in H 2 O 2 levels probably also occur during signalling and pathogen defence (Allan and Fluhr 1997;Alvarez et al 1998;Rhee et al 2000). Furthermore, H 2 O 2 -consuming enzymes such as catalases and peroxidases, as well as scavenging molecules such as tocopherol and GSH, influence the subcellular H 2 O 2 levels.…”

Are elicitins cryptograms in plant-Oomycete communications?

“…In addition, active oxygen species (AOS) mediate a systemic signal network, and H 2 O 2 orchestrates the plant hypersensitive disease resistance induction [104,105]. In that way, two distinct sources (intra-and extracellular) of AOS in tobacco plants treated by cryptogein have been reported, and correlated with later cell death [106], although these cell responses could be associated with lipid peroxidation [107]. Cryptogein induces lipid peroxidation in tobacco leaves, evaluated by the accumulation of thiobarbituric acid-reactive substances as well as by high-temperature thermoluminescence emission, both indicating a progressive destabilization of the thylakoid membranes [108].…”