RESPONSE OF GRACILARIA CONFERTA (RHODOPHYTA) TO OLIGOAGARS RESULTS IN DEFENSE AGAINST AGAR‐DEGRADING EPIPHYTES

Abstract

Elicitation of Gracilaria conferta (Schousboe ex Montagne) J. et G. Feldmann with oligoagars resulted in a defense response that was strong enough to kill epiphytic bacteria associated with the alga. Up to 60% of the resident bacterial flora of healthy plants was eliminated within 60 min after addition of neoagarohexaose to the algal medium. Single isolates of agar‐degrading bacteria that had been isolated previously from healthy or decaying algal tissues proved to be more sensitive. Some of them were generally unable to survive on healthy G. conferta. Others survived on unelicited plants. Approximately 90% of these more resistant agar degraders were eliminated within 15 min after elicitation. The bacterial degradation of dead tissue of G. conferta resulted in a release of elicitors. The elicitors accumulated in the medium and reached high enough concentrations within 24 h to induce a hypersensitive response in healthy algae. The eliciting agent could be destroyed with β‐agarase and was thus probably oligoagar. Application of antibiotics prevented the accumulation of the elicitor, which indicated that bacteria were responsible for its release from the algal biomass. The hypersensitive response of G. conferta after contact with oligoagars is thus a true defense response, because it enables the plant to protect itself efficiently from enzymatic attacks on its cell wall.

Herbivore-induced defence response in the brown seaweedFucus vesiculosus(Phaeophyceae): temporal pattern and gene expression

“…The cell wall peroxidase 34 (PRX34), which was also found to be up-regulated in this study, is involved in accumulation of reactive oxygen species (ROS) in Arabidopsis thaliana (O'Brien et al, 2012), and plays a role in plant defence against herbivores (Leitner et al, 2005). Production of ROS has also been reported in response to pathogen elicitors in marine macroalgae (Bouarab et al, 1999;Weinberger & Friedlander, 2000;Küpper et al, 2001) and may play a role in resistance of F. vesiculosus against pathogens which could enter at wounding sites caused by herbivore attack. However, since ROS production can also harm host plant cells, the activation of protective mechanisms is necessary (Apel & Hirt, 2004).…”

Chemical inhibition of bacterial colonization by the red alga Bonnemaisonia hamifera

“…Seaweeds may defend themselves against bacterial fouling by physical means, such as sloughing of the outermost cell layers (Johnson & Mann 1986, Keats et al 1997, Nylund & Pavia 2005, by physiological responses, such as oxidative bursts (Collen et al 1995, Weinberger & Friedlander 2000, or by production of secondary metabolites, that prevent attachment and growth of bacteria (Maximilien et al 1998). Seaweeds are rich in secondary metabolites (see Tringali 1997), and earlier (summarized by Aubert et al 1979, Sridhar & Vidyavathi 1991 as well as more recent studies (e.g.…”

Defense responses in female gametophytes of Saccharina japonica (Phaeophyta) induced by flg22-derived peptides

“…It is widely accepted that the initiation of defense responses largely depends on the successful recognition of the pathogens based on specific elicitors produced by the pathogens (Potin et al 2002;Jones and Takemoto 2004;Zipfel 2009). Elicitors can be divided into endogenous and exogenous elicitors based on their origins (Weinberger and Friedlander 2000;Küpper et al 2001, Küpper et al 2006Cosse et al 2007). Endogenous elicitors originate from structural compounds of host, such as the oligosaccharides, which are released from the host cell walls during enzymatic degradation of wall components caused by the pathogens, as it has been described in the brown alga Laminaria digitata (Küpper et al 2001) and in the red alga Gracilaria conferta (Weinberger et al 1999).…”

“…Additionally, liposaccharides and lipoteichoic acids isolated from the cell envelope of bacteria were found to modify gene expression of C. crispus, indicating that PAMP elicitors are present in these cell-free extracts (Weinberger 2007). Similarly, the red alga G. conferta reacts on the presence oligosaccharides with the production of ROS, which controls the growth of epiphytic bacteria (Weinberger and Friedlander 2000). LPS extracted from the Gram-negative bacterium Salmonella arbortus equi was shown to be an efficient elicitor triggering an oxidative burst in L. digitata (Küpper et al 2006).…”