Potassium ions accumulate in the guard cells and in turn, causes the opening & closing of stomata. Ferredoxin is a protein with clusters of iron and sulphur, also known as capacitors which help in electron transfer in the chloroplasts. The deficiency of zinc in plants leads to decreased plant growth, as zinc plays a role in auxin synthesis. Nitrogenase contains molybdenum which acts as a catalyser in the reduction of atmospheric nitrogen to ammonia.