Expression analysis of transcription factor (CBF/DREB) gene and biochemical response of Cannabis sativa to cadmium toxicity and foliar application of molybdenum

Abstract

Plants respond to heavy metals stress by the activation of stress responsive genes to establish biochemical defense mechanisms against the stress. We have investigated the molecular and biochemical response of Cannabis sativa to cadmium (Cd) stress in the presence of molybdenum (Mo) foliar treatments. For this purpose, C. sativa plants were allowed to grow in pots containing Cd polluted soil, for two month duration. Aqueous solutions of ammonium molybdate pentahydrate (0.5, 1.0 and 2.0 ppm) were foliarly sprayed on the plants, at two weeks intervals. Various parameters were inter-correlated i.e., Plant biomass, Cd phyto-accumulation, transcript level/expression of CBF/DREB genes, concentrations of free proline, polyphenolics, and chlorophyll contents. Phenolic compounds were analyzed by High Performance Liquid Chromatography Diode Array Detector (HPLC-DAD) and Cd contents were analyzed by Atomic Absorption Spectrophotometer. Biomass and chlorophyll contents decreased while the concentrations of free proline and polyphenolics increased under Cd stress. Dry biomass of the all the plant parts (roots (1.87 ± 0.22 g), stem (3.28 ± 0.39 g) and leaves (3.54 ± 0.87 g) and free proline in roots (69.00 ± 8.28 µg/g) and leaves (40.56 ± 4.87 µg/g) were most significantly increased with foliar spray of 2.00 ppm Mo. Nineteen (19) different polyphenolic compounds were identified and quantified in leaves and most of them were highly increased in concentration under Cd stress. The highest concentration was noted in Caffeoyl tyramine (1111 µg/g) in plants treated with 2.00 ppm Mo. Transcript level of CBF/DREB genes in control plants were less as compared to Mo treated plants, where a high increase in transcript level of these genes were found. Expression of CBF /DREB genes showed significant positive correlations with Cd accumulation (R2= 0.751) and concentrations of free proline (R2 = 0.62) and polyphenolics (R2 = 0.65) in leaves. The results suggested that Mo increased the expression of CBF/DREB genes and subsequently the concentration of phenolic compounds and free proline to combat plant against the toxicity of high concentration of Cd on plants.