Further Investigations on the Occurrence and the Effects of Abscisic Acid in Algae

Summary After abscisic acid (ABA) had been detected in the green alga Stigeoclonium a much wider occurrence of the hormone in other green algae e.g. Dunaliella parva, Chlamydomonas reinhardii, Ulva lactuca, Draparnaldia mutabilis and Chara foetida could be demonstrated by combined GC-MS. The effect of exogenously applied ABA in the concentration range of 10 -7 -10 -5 M on batch cultures of Stigeoclonium cf. tenue was rather small. 3 weeks after application, a slight reduction of growth was caused by ABA, and in some cases, senescence was promoted. In order to investigate the effects of salt stress on endogenous ABA levels batch cultures of Dunaliella parva (halotolerant ecotype) and Draparnaldia mutabilis (halophobe ecotype) were treated with various NaCl-concentrations. When 85.5 mM NaCl were added to the culture medium the ABA concentration of Draparnaldia cultures increased to the tenfold within a week. On the contrary, in Dunaliella the ABA level is lowest at 1.5 M NaCl. This salt concentration is regarded optimal for e.g. photosynthesis of Dunaliella .