**Identification and Quantification of Plant Growth Regulators and Antioxidant Compounds in Aqueous Extracts of** *Padina durvillaei* **and** *Ulva lactuca*

**Israel Benítez García <sup>1</sup> , Ana Karen Dueñas Ledezma 1, Emmanuel Martínez Montaño 1,2 , Jesús Aarón Salazar Leyva <sup>1</sup> , Esther Carrera <sup>3</sup> and Idalia Osuna Ruiz 1,\***


Received: 15 May 2020; Accepted: 15 June 2020; Published: 18 June 2020

**Abstract:** Aqueous seaweed extracts have diverse compounds such as Plant-Growth Regulators (PGRs) which have been utilized in agricultural practices for increasing crop productivity. Algal biomass of *Padina durvillaei* and *Ulva lactuca* have been suggested for use as biofertilizers because of plant growth-enhancing properties. This work aimed to identify the main PGRs and antioxidant properties in *P. durvillaei* and *U. lactuca* extracts, such as abscisic acid, auxins, cytokinins, gibberellins, jasmonates, and salicylates, to assess their potential use as biofertilizers that improve plant growth and crop yield. Phytochemical analyses of two seaweed extracts showed a significantly higher content of sulfates, flavonoids, and phenolic compounds in *P. durvillaei* extract, which could be linked to its higher antioxidant activity (DPPH, ABTS, and FRAP) compared to *U. lactuca* extract. The identification and quantification of PGRs showed two gibberellins (GA1 and GA4), abscisic acid (ABA), indoleacetic acid (IAA), three cytokinins (tZ, IP, and DHZ), jasmonic acid (JA), and salicylic acid (SA) in two seaweed extracts. However, GA4, tZ, and DHZ contents were significantly higher in *P. durvillaei* compared to *U. lactuca* extracts. These findings evidence that *P. durvillaei* and *U. lactuca* extracts are suitable candidates for use as biofertilizers.

**Keywords:** seaweed extract; phytohormone profiling; fertilizers; antioxidant; plant growth regulators; brown seaweed; green algae
