Metabolismo das poliaminas e respostas fisiológicas, bioquímicas e metabolômicas de cultivares de feijão-caupi crescendo sob condições de estresse salino

Abstract

Salinity is one of the most challenging abiotic stresses for plants, causing osmotic, ionic, and oxidative imbalances that lead to reduced growth and development. Plants respond to abiotic stresses, such as salinity, through changes in physiological, metabolic, and biochemical mechanisms in an attempt to acclimate to these adverse conditions. Among the adaptive responses to stress, polyamines (PAs), including putrescine, spermidine, and spermine, stand out as key elements in plant defense against the adverse effects of salinity, contributing to the stabilization of cell membranes, ion regulation, and protection against oxidative damage. In this context, this research evaluated whether salinity tolerance and stress recovery capacity of two cowpea cultivars [Vigna unguiculata (L.) Walp], TVu 2331 and Pitiúba, previously established with different salinity tolerances, are related to the regulation of primary metabolism and endogenous levels of polyamines. To test the established hypothesis, both cowpea cultivars were subjected to saline stress (NaCl 75 mM) under hydroponic conditions for 28 days in a greenhouse. Four assessments were conducted on leaf tissues at 7, 14, 21, and 28 days after sowing (DAS). The recovery treatment involved transferring a group of plants from each cultivar from the saline stress condition to control conditions (absence of NaCl) at 21 DAS for 7 days. The analyses performed encompassed biometric growth parameters, gas exchange, chlorophyll a fluorescence, leaf succulence, osmotic potential, inorganic solutes (Na+ and K+), lipid peroxidation, metabolic profile analysis, diamine oxidase (DAO), and polyamine oxidase (PAO) enzyme activities, as well as determination of free, soluble conjugated, and insoluble polyamines. In both cultivars, the results indicated a significant reduction in leaf area and biomass under saline stress, with Pitiúba being the least affected cultivar, especially at 21 DAS. However, for the other physiological parameters analyzed, the observed changes were generally similar for both cultivars, indicating shared adaptation strategies to stress. Saline treatment altered the metabolic profile of both cultivars on all days analyzed, with sugars, organic acids, and amino acids being the chemical classes with significantly more differentially modulated metabolites. PAO activity increased in response to saline treatment in both cultivars, while DAO activity increased due to salinity only in the Pitiúba cultivar. Remarkably, salinity increased PA levels even after plant removal from the stress condition, suggesting lasting alterations in the regulation of these molecules. In light of the findings, the importance of polyamines in the plant's adaptive response to salinity is evident, not only during stress but also in the subsequent recovery phase.