Physiological and molecular analyses of black and yellow seeded Brassica napus regulated by 5-aminolivulinic acid under chromium stress.

Brassica napus L. is a promising oilseed crop among the oil producing species. So, it is prime concern to screen the metal tolerant genotypes in order to increase the oilseed rape production through the utilization of pollutant soil regimes. Nowadays, use of plant growth regulators against abiotic stress is one of the major objectives of researchers. In this study, an attempt was carried out to analyze the pivotal role of exogenously applied 5-amenolevulinic acid (ALA) on alleviating chromium (Cr)-toxicity in black and yellow seeded B. napus. Plants of two cultivars (ZS 758 - a black seed type, and Zheda 622 - a yellow seed type) were treated with 400 μM Cr with or without 15 and 30 mg/L ALA. Results showed that exogenously applied ALA improved the plant growth and increased ALA contents; however, it decreased the Cr concentration in B. napus leaves under Cr-toxicity. Moreover, exogenous ALA reduced oxidative stress by up-regulating antioxidant enzyme activities and their related gene expression. Further, results suggested that stress responsive protein's transcript level such as HSP90-1 and MT-1 were increased under Cr stress alone in both cultivars. Exogenously applied ALA further enhanced the expression rate in both genotypes and obviously results were found in favor of cultivar ZS 758. The ultrastructural changes were observed more obvious in yellow seeded than black seeded cultivar; however, exogenously applied ALA helped the plants to recover their cell turgidity under Cr stress. The present study describes a detailed molecular mechanism how ALA regulates the plant growth by improving antioxidant machinery and related transcript levels, cellular modification as well as stress related genes expression under Cr-toxicity.