5-Aminolevolinic acid mitigates the cadmium-induced changes in Brassica napus as revealed by the biochemical and ultra-structural evaluation of roots

In the present study, the ameliorating effects of 5-aminolevulinic acid (ALA) under cadmium (Cd) stress conditions were studied with special emphasis on root morphology and ultra-structure in oilseed rape. For this purpose, plants were treated hydroponically at three different Cd levels (0, 100, 500 μM) and foliar spray of ALA with three concentrations (0, 12.5, 25 mg/l) simultaneously. The results showed that foliar application of ALA improved the plant growth, root morphology and reduced the reactive oxygen species and malondialdehyde contents in roots under Cd stress conditions. The higher concentration of Cd (500 μM) decreased the activities of antioxidants enzymes like catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and glutathione reductase (GR) and also reduced the oxidized glutathione and total glutathione contents in roots. Application of ALA at 25 mg/l dosage significantly enhanced the antioxidant activities e.g. APX, SOD, POD, and GSH contents under Cd stress. The microscopic micrographs showed that application of exogenous ALA improved the cell structure under Cd toxicity. A whole cell with developed nucleus, nuclear membrane, smooth cell wall, continuous endoplasmic reticulum, and well shaped mitochondria was observed under the combine application of ALA and Cd. These results suggest that, application of ALA helped the plants to improve root growth, root antioxidant enzymes, and ultra-structural changes in root tip cells under fifteen days Cd-induced stress.

► ALA alleviated the toxic effect of Cd and improved the morphology of roots.
► Application of ALA decreased the production of reactive oxygen species in roots.
► ALA enhanced the antioxidants activities in roots under Cd stress.
► Cd totally damaged the root ultra-structures shown by electron micrographs.
► Exogenous application of ALA improved the cell structures of roots.