Identification and quantification of indole-3-acetic acid in the kelp Laminaria japonica Areschoug and its effect on growth of marine microalgae

Abstract

A method was established for the identification and quantification of indole-3-acetic acid (IAA) in extracts of the kelp Laminaria japonica. An IAA content of 90–95 μg kg−1 fresh weight in kelp extract was determined by high performance liquid chromatography (HPLC). IAA identification was based on a combination of co-chromatography and comparative chromatography with a standard, analysis of UV spectra, and atmospheric pressure electrospray mass spectrometry (APESI-MS). IAA was isolated by silica gel chromatography and HPLC. The effect on the growth of four marine microalgae of the pure IAA isolated from kelp extract was investigated. Exogenously added IAA from kelp enhanced the growth of Chlorella sp., Dunaliella salina and Porphyridium cruentum, but not that of Chaetoceros muelleri. IAA from kelp significantly inhibited the accumulation of soluble cellular proteins in Chlorella sp. and P. cruentum, and had a very significant effect on chlorophyll biosynthesis in Chlorella sp. However, there was no obvious effect of IAA on the regulation of biosynthesis of cellular polysaccharides in these four marine microalgae.