Chapter 10 - Cobalt and molybdenum: deficiency, toxicity, and nutritional role in plant growth and development

Abstract

The role of cobalt (Co) and molybdenum (Mo) in the growth and development of plants is disproportionate with respect to the minimal amounts needed by the plants. Both Co and Mo serve as beneficial micronutrients for the plant system. Co is essential for vitamin B12 synthesis and is also associated with drought tolerance in plants. The addition of Co in growth medium of leguminous plants such as soybean, demonstrated an increase in overall dry weight of the plants and inhibition of nitrogen deficiency in these plants, which is common in leguminous plants deprived of this essential micronutrient. However, an excessive supply of Co can lead to marked decline in photosynthetic pigments like chlorophyll and carotenoids, along with increased activities of antioxidative enzymes like superoxide dismutase, peroxidase, etc. On the other hand, Mo serves as a part of nitrogenase and a number of essential enzymes involved in redox reactions in plants including nitrate reductase, aldehyde oxidase, sulfite oxidase, etc. Mo deficiencies in plants have adverse impacts on plant development due to disrupted nitrogen metabolism and decline in the biosynthesis of important phytohormones like abscisic acid and some auxins. However, toxicity due to Mo is quite rare and is usually subject to misdiagnosis, due to symptoms associated with the altered activities of many redox enzymes.