Proline but not Glutathione Actively Participates in the Tolerance Mechanism of Young Schizolobium parahyba var. amazonicum Plants Exposed to Boron Toxicity

Glutathione, a peptide frequently associated with the antioxidant mechanism of plants against reactive oxygen species, and proline, an amino acid whose function is related to cellular homeostasis, can both contribute to improve plant tolerance under situations of abiotic stress, such as boron toxicity. Aims of this research were to (i) quantify the oxidant and antioxidant compounds, (ii) evaluate the photosynthetic pigments, (iii) determine amino acids and PRO, and (iv) determine whether GSH and PRO contribute to the tolerance mechanisms in young Schizolobium parahyba var.  amazonicum plants under B toxicity. This experiment tested five boron levels (25, 50, 100, 150 and 250 µM B), being evaluated physiological and biochemical variables. The values reported to proline levels presented significant variation for treatments with 50, 100, 150 and 250 µM B, with increases for the 150 and 250 µM B levels, being 45.2 and 52.4%, respectively. This study found that boron toxicity promoted similar behaviours in both the leaves and root, which included progressive increases in hydrogen peroxide, electrolyte leakage, amino acids and proline, and decreases in total glutathione, chlorophyll a , chlorophyll b and total chlorophyll, confirming that proline but not glutathione actively participates in the tolerance mechanism of young Schizolobium parahyba plants exposed to boron toxicity.