Stress Factors Enhancing Production of Algal Exudates: a Potential Self-Protective Mechanism?

Algae are known to produce extracellular organic substances under optimum conditions and increase their production under stress. The changes in amount and composition of extra­ cellular carbohydrates and proteins of three green algae Scenedesmus quadricauda, Chlorella kessleri and Raphidocelis subcapitata (known as Selenastrum capricornutum) were studied after a 5-days’ cultivation under the influence of different types of stress factors (osmotic, organic, and heavy metal stressors). NaCl enhanced the quantity of carbohydrates more than proteins. A higher increase of proteins than carbohydrates was observed after addition of 3,5-dichlorophenol, glyphosate and cadmium chloride to algal cultures. The production of dissolved organic matter differs from species to species, with the age of a culture and the type of stressor.