One of the following elements, which is not much important to plants is?

Iodine is a micromineral or micronutrient for plants. The micronutrients in plants include iron, cobalt, chromium, copper, iodine, manganese, selenium, zinc and molybdenum. Micronutrients also include vitamins, which are organic compounds required as nutrients in tiny amounts by an organism. However, deficiency of iodine does not cause much effects on plants. Zinc in plants is required for protein formation and as a growth regulator and its deficiency causes less growth. Calcium deficiency leads to necrosis in plants and stunted growth. Sodium helps ion promoting metabolism in plants.