Growth and DMSP response to airborne DMS in the alga Ulva lactuca

Abstract

Ulva lactuca , a green alga, produces the volatile compound dimethylsulfide (DMS), a breakdown product of dimethylsulfionopropionate (DMSP), as a chemical defense to protect itself from physiological stress or herbivore grazing. Terrestrial plants can use volatile chemicals that are released by neighboring plants when they are grazed as a signal to produce increased levels of defenses. I hypothesized that algae producing DMSP would respond similarly to airborne DMS; therefore, higher levels of DMSP and lower growth rates would occur in U. lactuca exposed to DMS than in control U. lactuca not exposed to DMS. To test this hypothesis, I exposed U. lactuca to DMS for 6 hours and measured algal size and DMSP concentration over 2 weeks. The results of my experiment showed that U. lactuca exposed to DMS initially had higher concentrations of DMSP, but then had reduced DMSP concentrations 12 to 15 days following exposure. At the end of the experiment, algae exposed to DMS were significantly larger than the unexposed control algae.

Introduction

Algal communication is a largely unexplored area among scientists. Terrestrial plants, which have similar characteristics as algae have been proven to communicate to neighboring species. Work on terrestrial plants show that poplar trees increased concentration of phenolic compounds occur when they are damaged, which provides a mode of evidence that when they are in distress, they release chemicals that communicate and warn neighboring plants, because the neighboring plants concentration of phenolics also increased. (Baldwin and Schultz 1983). The increased concentrations prevent predators from grazing on the plants. We wonder if the same theory applies to algae.

The species that we chose to test this theory on is in alga called Ulva lactuca. The reason we chose this species is because it is one of the most abundant algae in the Puget Sound area and local beaches on this region and because it is interesting chemically. Work from our lab has shown that the chemical releases might be anti-herbivore. The chemical that is thought to be utilized in this green alga that is there is form of deterrence, is a chemical called dimethysulfoniopropionate (DMSP). DMSP is well known as an osmolyte that helps U. lactuca deal with changes in salinity is found in many green algae.

Methodology