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.

Boron (B) is a very important nutrient required by forest plants; when supplied in adequate amounts, plants can ameliorate the negative effects of abiotic stresses. The objective of this study was to (i) investigate gas exchange, (ii) measure oxidant and antioxidant compounds, and (iii) respond how B supply acts on tolerance mechanism to water deficit in young Schizolobium parahyba plants. The experiment employed a factorial that was entirely randomised, with two boron levels (25 and 250 µmol L -1 , simulating conditions of sufficient B and high B, respectively) and two water conditions (control and water deficit). Water deficit induced negative modifications on net photosynthetic rate, stomatal conductance and water use efficiency, while B high promoted intensification of the effects on stomatal conductance and water use efficiency. Hydrogen peroxide and electrolyte leakage of both tissues suffered non-significant increases after B high and when applied water deficit. Ascorbate levels presented increases after water deficit and B high to leaf and root. Our results suggested that the tolerance mechanism to water deficit in young Schizolobium parahyba plants is coupled to increases in total glutathione and ascorbate aiming to control the overproduction of hydrogen peroxide and alleviates the negative consequences on electrolyte leakage and gas exchange. In relation to B supply, this study proved that sufficient level promoted better responses under control and water deficit conditions.