Source. It is absorbed by plants in the form of MoO³⁺ or MoO⁴⁺ ions. It is also absorbed in the forms of di, tri, or pentoxides. It is found relatively in higher concentration in mineral oil and coal ashes.

Regions. It is required all over the plant particularly by roots in the form of MoO³⁺ ions.

Functions. The most important role of molybdenum is in nitrate reduction and nitrogen fixation, and its deficiency, particularly in plant that have symbiotic nitrogen fixation, results in a reduced organic nitrogen content. Thus, it activates enzymes of nitrogen metabolism.

Deficiency symptoms.

(i) Slight retardation of growth.
(ii) Deficiency of molybdenum leads to mottling and marginal wilting of leaves, producing disease "yellow spot" of citrus fruits.
(iii) "Whiptail" is a very characteristic molybdenum deficiency disease of cabbages and related plants. In such cases, young leaves are distorted, having a long mid-rib and narrow poorly developed ragged blades.