The beneficial roles of trace and ultratrace elements in plants

The optimal elemental nutrition is the key to obtain high quality crop yields, presently and more so in future climate. Plants need a number of elements spanning the periodic table for their overall growth and development, including carbon (C), nitrogen (N), oxygen (O), potassium (K), zinc (Zn), copper (Cu) etc. Some of these elements are required in large amounts and are either easily available or provided to plants via external supply. The elements like Zn, Cu, iron (Fe) etc. are required in lesser amounts ranging from trace to ultratrace levels. Additionally, there are other elements, known as beneficial elements, which are although not essential but improve growth and stress tolerance of plants; for example selenium (Se) and silicon (Si). Various elements take part in plant metabolic activities as constituent of enzymes like Se in glutathione peroxidases and thioredoxin reductase, nickel (Ni) in urease and glyoxalase I, Zn and Cu in superoxide dismutases and molybdenum (Mo) in nitrate reductase. Certain elements participate in electron transport in mitochondria and chloroplasts and allow smooth operation of photosynthetic and respiratory processes. In addition, an optimum supply of beneficial and ultratrace elements help plants' tackle various abiotic as well as biotic stresses. Thus, maintaining a fine balance of plant mineral nutrition is a sustainable approach to ameliorate crop health and yield. The present review presents diverse roles of various essential and beneficial trace and ultratrace elements in planta and discusses future directions of research on these elements in plants.