M. Friedlander et al., Gracilaria and its epiphytes: 4. The response of two Gracilaria species toUlva lactuca in a bacteria-limited environment, J APPL PHYC, 13(6), 2001, pp. 501-507
The responses of Gracilaria lemaneiformis, an easily epiphytized host, and
the relatively resistant G. cornea mutant, to the green alga Ulva lactuca w
ere studied using biculture experiments with and without antibiotics. Both
Gracilaria species grown with and without U. lactuca showed different level
s of growth rate, release of hydrogen peroxide and of halogenated hydrocarb
ons. These quantitative differences led to a successful response against Ul
va lactuca in the case of G. cornea mutant and to a failure in response in
the case of G. lemaneiformis. The response of each Gracilaria species to U.
lactuca was qualitatively similar to its response to bacteria. This sugges
ts the involvement of oligosaccharide elicitors produced in the presence of
epiphytes and bacteria. A clear Gracilaria inhibition was demonstrated wit
h extracts of the culture medium. It appears that hydrogen peroxide, haloge
nated hydrocarbons and oligosaccharides may be components of the inhibitory
activity of the extracts. The responses of Gracilaria species to the prese
nce of U. lactuca suggest the characterization of a defence response.