Isabelle Mary Costa Pereira^1,2, Luan Victor Maia¹, Marjory Lima Holanda Araújo¹, Rômulo Farias Carneiro¹, Humberto Henrique de Carvalho^1,2

In response to increasing global and environmental demands, agriculture increasingly requires inputs with biotechnological properties. Among the main components reported in algal extracts that can act as biostimulants are phytohormones, proteins, and amino acids. It represents a field with great potential for the development of new products, especially those that can be absorbed by the roots or through foliar application, although losses can occur through spraying. The large amount of nutrients and biomolecules that stimulate plant development, seaweed extracts can function as conditioners against biotic and abiotic stresses (exerting a priming effect), positively modulating morphological and biochemical defense mechanisms. A previous work demonstrated the potential of the aqueous extract of Gracilaria birdiae to promote rice growth in hydroponic culture. However, the chemical composition of the extract is complex and may vary due to factors such as seasonality, cultivation location, extraction method, and processing, leading to variations in its properties. This highlights the need for standardization of extraction and application processes in plants. The seaweed was collected in Flecheiras, Ceará (Brazil), washed, and stored in a freezer until extraction. The biomass was weighed and grounded in a food processor, followed by the addition of distilled water (3:1), and homogenized using an industrial homogenizer. The crude extract was filtered through a fine mesh and centrifuged under refrigeration and proteins were extracted. The proteins present in the aqueous extract of G. birdiae were digested using sequencing-grade trypsin and analyzed by capillary liquid chromatography–tandem mass spectrometry with nanoelectrospray ionization (LC-ESI-MS/MS) in a Q-ToF mass spectrometer. Peptides were identified using MASCOT Daemon software by searching against the database for Zea mays, Fusarium oxysporum, Arabidopsis thaliana, Oryza sativa, and Chlamydomonas reinhardtii. A total of 661 peptide fragments identified indicate that the aqueous extract of Gracilaria birdiae may contain regulatory molecules involved in stress response and plant growth promotion. These peptides were grouped into categories related to transport, energy metabolism, lipid metabolism, amino acid metabolism, and responses to stress and defense. Overall, several associated biological processes were observed, including photophosphorylation, translation, and catalytic activity. The peptide fragments were matched to database entries, of which 109 corresponded to uncharacterized proteins. The other 552 peptides were grouped into categories related to transport, energy metabolism, transcription regulation, regulatory factors or signaling, DNA and RNA binding, lipid metabolism, amino acid metabolism, and responses to stress and defense. Additionally, several associated biological processes were observed, including photophosphorylation, translation, signaling, and catalytic activity. These findings suggest that the aqueous extract of G. birdiae may contain regulatory molecules involved in stress responses and plant growth promotion. However, further studies are required to assess its effects under both optimal and stress conditions.

Agradecimentos: ForCe Metabolomics, CAPES, CNPq, INCT AgriS, Associação de Produtores de Algas de Flecheiras e Guajiru (APAFG) and BioMar Lab.