Aplicação exógena de ácido 5-aminolevulínico em plantas de jatobá (Hymenaea courbaril L.) submetidas a diferentes doses de cádmio

Abstract

Heavy metals are high molecular weight elements that, in high quantities, contaminate the environment causing a series of environmental damages. One of the most toxic heavy metals is cadmium, which causes lower productivity, mutations, decreased chlorophyll levels and oxidative stress in plants. 5-aminolevulinic acid is a growth regulator that is involved in the formation of the heme group and chlorophylls in plants, being a possible attenuator of cadmium toxicity. Therefore, the objective of the research was the exogenous application of 5-aminolevulinic acid in order to mitigate the harmful effects of cadmium contamination in Jatobá plants (Hyminaea courbaril L.), considered a rustic plant and tolerant to unfavorable environments, such as a possible strategy for cadmium contaminated areas. The experiment was carried out in the greenhouse of the Institute of Agricultural Sciences with an experimental design in randomized blocks, with five blocks in a 3x2 factorial scheme, with 3 concentrations of cadmium: control, 15 mg. L-1 Cd and 30mg.L-1 Cd; and 2 concentrations of 5-aminolevulinic acid: 0 and 100 mg. L-1, totaling 6 treatments with 30 experimental units. The Jatobá seedlings underwent a period of 43 days of acclimatization, shortly after this period, a solution of 5-aminolevulinic acid was applied with sprayers on the leaves in spaced periods, after 5 days of application of the acid, a solution of Cadmium Chloride was applied to each vessel according to its respective treatment. After three months of evaluation, the plants had their chlorophyll a, b and total levels measured by chlorophyllometer and subsequently, the plant material was removed for freeze-drying and analysis of the enzymes APX, SOD, CAT and GPOD. Statistical analyzes were carried out using the AgroStat statistical program, using the F test for analysis of variance and the Tukey test for comparing treatment means at 5% probability. Cadmium contamination promoted a decrease in the levels of chlorophyll a, b and total in the leaves, APX and GPOD in the root, and an increase in the levels of SOD (root and leaf); APX in leaf (15 mg. L-1 Cd); CAT and GPOD in the leaves. The application of 5-aminolevulinic acid increased the levels of chlorophyll a, b (30 mg. L-1 Cd) and total, CAT in the leaves (0 and 30 mg. L-1 Cd) and APX in the roots; and decreased the levels of leaf SOD (15 mg. L-1 Cd), root SOD (0 and 30 mg. L-1 Cd), leaf APX (15 mg.L-1 Cd), root CAT (30 mg.L-1 Cd), leaf GPOD (0 mg.L1 Cd) and root GPOD (0 mg.L-1 Cd). The results obtained show that cadmium was harmful to Jatobá plants and promoted different responses in the leaves and roots. The application of 5-aminolevulinic acid increased chlorophyll levels, in addition to promoting changes in antioxidant enzyme levels.