Abscisic acid, gibberellins and brassinosteroids in Kelpak®, a commercial seaweed extract made from Ecklonia maxima

The seaweed extract Kelpak(A (R)) made from the kelp Ecklonia maxima is registered as a biostimulant for use in agriculture. It elicits many beneficial responses including improved root and shoot growth, higher yields and greater resistance to abiotic and biotic stresses. Previously, cytokinins, auxins and polyamines were identified in Kelpak(A (R)). The aim of the present study was to quantify other groups of plant growth regulators (PGRs)-abscisic acid (ABA), gibberellins (GAs) and brassinosteroids-that may be present in E. maxima and Kelpak(A (R)). Kelpak(A (R)) samples harvested between 2008 and 2010 and stored for up to 26 months were analysed using ultra performance liquid chromatography tandem mass spectrometry. ABA levels were below the limits of detection in E. maxima but were detected in low concentrations in Kelpak(A (R)), ranging from 0.31 to 20.70 pg mL(-1) Kelpak(A (R)). Eighteen GAs were found in E. maxima and Kelpak(A (R)) with concentrations from 187.54 to 565.96 pg mL(-1) Kelpak(A (R)). The biologically active GAs (GA(1), GA(3), GA(4), GA(5), GA(6) and GA(7)) comprised less than 3 % in Kelpak(A (R)). Although GA(13) (a final product in the metabolic pathway) was present in low concentrations in E. maxima, very high concentrations were present in Kelpak(A (R)). The brassinosteroids brassinolide (BL) and castasterone (CS) were identified in E. maxima and Kelpak(A (R)). Concentrations varied with harvest and storage time, ranging from 384.72 to 793.23 pg BL mL(-1) Kelpak(A (R)) and 62.84 to 567.51 pg CS mL(-1) Kelpak(A (R)). It is likely that this cocktail of natural PGRs present in Kelpak(A (R)) may act individually or in concert and thus contribute to the numerous favourable physiological responses elicited by Kelpak(A (R)) application to plants.