Cobalt: An Essential Micronutrient for Plant Growth?

Abstract

Cobalt is a transition metal located in the fourth row of the periodic table and is a neighbor of iron and nickel. It has been considered an essential element for prokaryotes, human beings, and other mammals, but its essentiality for plants remains obscure. In this article, we proposed that cobalt (Co) is a potentially essential micronutrient of plants. Co is essential for the growth of many lower plants, such as marine algal species including diatoms, chrysophytes, and dinoflagellates, as well as for higher plants in the family Fabaceae or Leguminosae. The essentiality to leguminous plants is attributed to its role in nitrogen (N) fixation by symbiotic microbes, primarily rhizobia. Co is an integral component of cobalamin or vitamin B12, which is required by several enzymes involved in N2 fixation. In addition to symbiosis, a group of N2 fixing bacteria known as diazotrophs is able to situate in plant tissue as endophytes or closely associated with roots of plants including economically important crops, such as barley, corn, rice, sugarcane, and wheat. Their action in N2 fixation provides crops with the macronutrient of N. Co is a component of several enzymes and proteins, participating in plant metabolism. Plants may exhibit Co deficiency if there is a severe limitation in Co supply. Conversely, Co is toxic to plants at higher concentrations. High levels of Co result in pale-colored leaves, discolored veins, and the loss of leaves and can also cause iron deficiency in plants. It is anticipated that with the advance of omics, Co as a constitute of enzymes and proteins and its specific role in plant metabolism will be exclusively revealed. The confirmation of Co as an essential micronutrient will enrich our understanding of plant mineral nutrition and improve our practice in crop production.

Dissolution kinetics of citrate coated CoFe2O4nanoparticles in soil solution

“…62 In the case of Co, the specific mechanisms of plant uptake and transport inside the plant system are still unknown to a great extent, 13 but it is known that the Co 2+ form is absorbed by the plant roots. 6,13 Collins et al 5 assessed the Co uptake and translocation in tomato and wheat plants. The authors reported that Co in the roots is complexed with carboxylic acids, suggesting that Co could also be complexed with other organic ligands such as citrate or malate.…”

“…3 Alternatively, Co has been described as a beneficial element, which means that low concentrations (0.01 to 10 mg kg −1 ) stimulate plant growth and yield, improve drought, salt, and heavy metal resistance, inhibit ethylene biosynthesis, and promote nitrogen fixation by increasing the number of nodules in legumes. [4][5][6] Iron and Co may be supplied in soluble chemical compounds to crops. 3 Chemical fertilizers containing these elements can enhance crop yield, but their excessive use in the long term may damage the soil microbial flora, disturb the soil mineral balance, and decrease the soil fertility.…”

“…13 Moreover, there is a scarcity of information about the management, advantages, and limitations of Co in a field level. 6,13 In this context, the challenge is to develop efficient and cheap sources of nutrients for crops. 14 Hence, nano-based fertilizers seem to be an alternative.…”

“…3 Alternatively, Co has been described as a beneficial element, which means that low concentrations (0.01 to 10 mg kg −1 ) stimulate plant growth and yield, improve drought, salt, and heavy metal resistance, inhibit ethylene biosynthesis, and promote nitrogen fixation by increasing the number of nodules in legumes. 4–6…”

“…13 Moreover, there is a scarcity of information about the management, advantages, and limitations of Co in a field level. 6,13…”