ABSTRACT
At present, heavy metal-contaminated soil is a rapidly growing problem that results in reduction of plant yield and growth, and finally causes huge economic losses and food scarcity. Some heavy metals are beneficial to plants in low concentrations, but in high concentrations, they all are toxic. Chromium is considered the seventh most abundant element on earth; it comes from both natural and anthropogenic resources. Chromium is one of those heavy metals that has high toxic potential to plants and significantly inhibits plant growth and yield. It inhibits plant growth by developing oxidative stress in plants, resulting in many structural and ultrastructural changes, and finally reduces the yield. Silicon is the second most abundant element, after oxygen. Si is not considered essential for higher plants, but in many plants, it is a beneficial nutrient, as it is required for proper growth and development. Many studies have reported its ameliorative effect on plant growth, yield, and biomass production under many environmental stresses, including chromium. Silicon improves the defense system of plants by enhancing their tolerance against chromium toxicity. In this chapter, we briefly
12.1 Introduction .......................................................................................................................... 214 12.2 Occurrence ............................................................................................................................ 215
12.2.1 Chromium in the Environment ................................................................................. 215 12.2.2 Silicon in the Environment ....................................................................................... 215
12.3 Chromium Toxicity in Plants ................................................................................................ 215 12.4 Protective Role of Silicon ..................................................................................................... 216 12.5 Silicon-Mediated Alleviation of Chromium Toxicity in Plants............................................ 216
12.5.1 Reduction in Chromium Uptake ............................................................................... 216 12.5.2 Development in Photosynthetic Pigment and Gas Exchange Attributes .................. 217 12.5.3 Nutrient Uptake, Plant Growth, and Biomass .......................................................... 218
12.6 Mechanisms Involved in Alleviation of Chromium Toxicity ............................................... 218 12.6.1 Immobilization ......................................................................................................... 218 12.6.2 Improvement in Antioxidant Defense System .......................................................... 219 12.6.3 Compartmentation within Plants .............................................................................. 219 12.6.4 Coprecipitation of Silicon with Chromium .............................................................. 219 12.6.5 Structural and Ultrastructural Changes in Plants .....................................................220
12.7 Conclusion and Perspective .................................................................................................. 221 References ...................................................................................................................................... 221
