Alleviation of cadmium toxicity by improving antioxidant defense mechanism and photosyntetic pigments in Clitoria fairchildiana R.A Howard seedlings through foliar application of 5-ALA

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Abstract
The objective of this work was to evaluate the biometric parameters, photosynthetic pigments and the antioxidant system of Clitoria fairchildiana R.A Howard seedlings subjected to exogenous application of 5-aminolevulinic acid and different concentrations of cadmium (Cd). The experiment was conducted in a greenhouse from May to August 2023. Initially, seedlings were produced from straw seeds. After three months, they were transplanted into 3 kg pots containing previously corrected and fertilized black soil. Ten days after transplanting, the plants received exogenous application of 5-ALA, weekly for 5 weeks, totaling 5 applications. After three days of acclimatization, cadmium concentrations were applied in a single time (42nd DAT), in the form of Cadmium Chloride (CdCl2.H2O): 0 (Control), 15 and 30 mg/L-1. The experimental design was completely randomized blocks (CRB), in a 3x3 factorial scheme, specified as follows: three concentrations of Cd (0, 15 and 30 mg L-1 of CdCl2.H20); and three concentrations of 5-ALA (0, 50 and 100 mg L-1 5-ALA), with 9 replicates. The main biometric and photosynthetic pigment variables showed changes with the application of 5-ALA and little variation in the levels subjected to the presence of cadmium. For the antioxidant system, the activity of the enzymes guaiacol peroxidase (G-POD), ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) suffered oscillations in their levels due to the application of 5-ALA and Cd, varying according to the concentration of the metal and the part of the plant.