Assessment of Castor Plant (Ricinus communis L.) Tolerance to Heavy Metal Stress-A Review

Increased urbanization and industrialization have greatly contributed to the emission of higher amount of heavy metals such as cadmium, nickel, and lead into the environment. These metals are non-biodegradable and toxic, causing much effects on plants and by extension to animals and humans, which have become a major global concern. The inherent ability of plants to resist heavy metal toxicity seems to be the most sustainable and cost-effective strategy. Castor plant is widely studied due to its tolerance to the effects of heavy metal contaminated soils, owing to its large biomass content and high accumulating capacity. Castor plants to some extent can tolerate elevated levels of heavy metals through several developed mechanisms, such as activation of antioxidant enzymes, exclusion, accumulation of proline, compartmentalization, organic acid exudation, and phytochelatins. Molecular studies have identified some stress-responsive to aid the tolerance of heavy metals in castor. Stress caused by heavy metal toxicity affects seedling growth, biomass, photosynthetic pigments, protein level, and nutrient uptake of castor plant. The response of castor, however, to these stresses differs among cultivars, metal type and concentration, and time of metal applied. This review aims to summarize the physiological responses and various defense mechanisms of castor to tolerate and eradicate heavy metal toxicity and some stress-responsive genes identified at transcriptional and post-transcriptional levels that confer metal tolerance in this plant.