Oxidative-Burst-Associated Responses

VHOCs was also observed in response to grazing pressure in Ascophyllum nodosum beds (Nightingale et al. 1995). Their biogenesis involves vanadium haloperoxi-dases (vHPO), which catalyse the oxidation of halides (X ) and generate X+ to yield hypohalous acid (XIO) and other forms of oxidized halides (X2, X2 ). Marine organisms and especially seaweeds have been known for a long time to concentrate halides from their environment (for a recent review, see Leblanc et al. 2006). 

More recently, a novel type of halogenating enzyme, named hydroperoxide halolyase, which generates halogenated aldehydes, has been described in the marine diatom Stephanopyxis turris (Wichard and Pohnert 2006). In other microalgae, halogenation of organic compounds was shown to mainly involve methyl halide transferases (Moore et al. 1996 Manley 2002), and no vHPO has yet been identified on genomic data obtained from diatoms (Scala et al. 2002 Armbrust et al. 2004). Clearly, these emissions are not directly associated with an oxidative burst. 

Lipids can be oxidized by some ROS such as hydroxyl ( OH). but not by H202, NO, or 02 - (Halliwell and Gutteridge 1999). However, both enzymatic and nonenzymatic cellular mechanisms can oxidize fatty acids. Challenging L. digitata sporophytes with lipopolysaccharides from various sources resulted in a rapid release of free fatty acids (FFAs) with a concomitant accumulation of oxidized derivatives of linolenic (08 2) and eicosapentaenoic acid (C20 5) (Kiipper et al. 2006). Other strong inducers of the oxidative burst, such as oligoguluronates, in Laminaria could induce neither the release of FFAs nor the oxylipin production. These results 

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Toward New Approaches to Test the Ecological Relevance of Oxidative-Burst-Associated Responses... 

From the previously discussed studies, the oxidative burst response appears to integrate and/or orchestrate several defense responses. These provide an adaptive mechanism to counteract attacks on or injury to algal cells and thalli. As shown in Fig. 12.2, the occurrence of an oxidative burst associated with the perception of cell-free extracts of A. operculata was shown to play a crucial role in the natural resistance of C. crispus gametophytes (Bouarab et al. 1999). 

Oxidative burst, and all associated responses in Chondrus crispus, including oxylipin pathway and VHOCs... 

Transfer from the water column to the atmosphere may also occur by the formation of droplets formed as breaking waves create a spray. This is responsible for the transmission of sodium chloride into coastal areas. Bursting of bubbles at the water surface may cause very small water droplets to be propelled into the atmosphere, whereupon they become permanently incorporated into the atmosphere by turbulent eddies. This is most likely to occur in water bodies where there is significant anaerobic methane formation, or in biological oxidation units in which there is deliberate mechanical aeration of the water. It is noteworthy that such droplets may be enriched in solutes which preferentially associate with surface organic microlayers. 

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