The effect of cadmium on HMA4 gene expression in some brassica species and the role of effect on germination

In terms of soil pollution, heavy metals are among the most important sources of pollutants. Around 450 plant species in Brassicacea, Asteraceae, Fabaceae, Scrophulariaceae, Lamiaceae and Euphorbiaceae families have been identified as metal hyper accumulators. Among them, majority of the accumulator plants have been discovered in Brassicacea family. Brassica juncea (brown mustard) in Brassicaceae is a major oilseed crop and is also identified as a metal tolerant and metal accumulator plant. This plant species is able to produce more biomass than other hyperaccumulative species, due to its rapid growth. Another plant species Brassica rapa (fodder turnip) has elaborated root system and is reported to be a hyper accumulator for certain heavy metals. In this study, four varieties of B. juncea, B. rapa, B. campestris var. toria were studied. The aim of this study was to investigate the seed germination rate and plant growth and development in Brassica rapa, Brassica juncea early raya and Brassica juncea sind raya grown at different levels of Cd (0, 5, 10, 20, 50 and 100 uM Cd). Leaf samples were dried at 72oC for 72 hrs and then digested with HNO3 acid and HClO4 acid mixture (3:1). Cd content in this diluted acid mixture was analyzed by Atomic Absorption Spectrophometry. Gene expression pattern of metal ATPases HMA2 and HMA4 in the leaves of these Brassica spp. grown at different Cd levels were analyzed by R-T qPCR. The data was anlaysed in order to understand the role of these heavy metal ATPases in Cd accumulation and their role in phytoremediation. When the expression of HMA2 gene was examined, it was found that HMA2 expression was increased in the leaves of B. rapa and B. juncea var sind raya grown at 20 µM Cd compared to control. B. juncea early raya leaves showed no any increase in gene expresseion at 20 uM Cd compared to control. For the HMA4 gene, expression was increased in the leaves of B. juncea var early raya and B. rapa when grown at 10 uM Cd but B. juncea var sind raya showed high expression when plants were treated with 20 uM Cd. The results of atomic absorption spectrometry (ASS) and HMA4 gene expression correlated with each other. It is concluded that B. rapa, B. juncea var sind raya and B. juncea var early raya plants accumulated Cd and this accumulation pattern was correlated with high HMA4 gene expression.