A review on regulatory control of chromium stress in plants

Chromium (Cr) is a non-biodegradable heavy metal that persists long in aquatic and terrestrial ecosystems and enters the food chain. It is cytotoxic even at low concentrations and reduces the yield of plants. Plants also have cellular mechanisms to manage the accumulation of metal ions inside the cell to diminish the possible injury from non-essential metal ions. This paper reviews current information on plant response to Cr, a key environmental pollutant. The harmful effects together with absorption, transfer, and aggregation of Cr are discussed. The roles of the cell wall, plasma membrane, and plant microbes as the primary hindrances for Cr ingression into the cell, along with sequestration and compartmentalization process, have also been discussed. Cr-generated oxidative injury is also regarded as the main deliberated effect of Cr toxicity.  It interferes with NADPH oxidases (plasma membrane) and the electron transport chains, which develop electron leakage. Some genes related to Cr stress in plants get expressed, and suppression produces protective effects by activating the signal transduction pathways. The expression of genes like BnaCnng69940D and BnaC08g49360D is increased, which is involved in protein kinase activity, signal transduction, and oxidoreductase activity. The increased mRNA levels of Cr stress response proteins, including HSP90-1 and MT-1, have been reported in the Brassica napus plant. The stressed environment around the plants may stimulate the biosynthesis of phytochelatins and metal-binding proteins, which have a protective role in plant’s growth and development. 