Oligoguluronates elicit an oxidative burst in the brown algal kelp Laminaria digitata

Oligomeric degradation products of alginate elicited a respiratory and oxid ative burst in the sporophytes of the kelp Laminaria digitata. The generati on of activated oxygen species (AOS),O-2(-), and H2O2 was detected at the s ingle cell level, using nitroblue tetrazolium precipitation and a redox-sen sitive fluorescent probe, respectively. The oxidative burst involved diphen yleneiodonium-sensitive AOS-generating machinery and its amplitude depended on the type of tissue. After a first elicitation plants were desensitized for about 3 h. The activity of alginate oligosaccharides was dose dependent , saturating around 40 muM. It was also structure-dependent, with homopolym eric blocks of alpha -1,4-L-guluronic acid, i.e. the functional analogs of oligogalacturonic blocks in pectins, being the most active signals. The per ception of oligoguluronate signals resulted in a strong efflux of potassium . Pharmacological dissection of the early events preceding the emission of AOS indicated that the transduction chain of oligoguluronate signals in L. digitata is likely to feature protein kinases, phospholipase A(2), as well. as K+, Ca2+, and anion channels.