In plants, zinc plays a key role as a structural constituent or regulatory co-factor of a wide range of different enzymes
in many important biochemical pathways and these are mainly concerned with:
a) carbohydrate metabolism, both in photosynthesis and in the conversion of sugars to starch,
b) protein metabolism,
c) auxin (growth regulator) metabolism,
d) pollen formation,
e) the maintenance of the integrity of biological membranes,
f) the resistance to infection by certain pathogens.
When the supply of zinc to the plant is inadequate, i.e. there is a deficiency of zinc, one or more of the many important physiological functions of zinc is unable to operate normally and the growth of the plant is adversely affected. The changes in plant physiological mechanisms brought about by a deficiency of zinc result in the plant developing visible symptoms of stress which might include one or more of the following: interveinal chlorosis (yellowing of the leaves between the veins), bronzing of chlorotic leaves, small and abnormally shaped leaves, stunting and rosetting (leaves form a whorl on shortened stems).