Azotobacter is a free living bacteria in the soil. It helps some cereal crops like maize (Zea mays) in nitrogen fixation. The farmer adds Azotobacter culture to the maize field for enhancing the nitrogen element in the soil by the process of biological nitrogen-fixation.

Leghaemoglobin is responsible for creating anaerobic conditions in the root nodules of the legume plant. It acts as an oxygen scavenger, protecting enzyme nitrogenase to come in contact with oxygen and help in the proper functioning of enzyme, i.e., conversion of atmospheric nitrogen to ammonia $\left(\mathrm{NH}_3\right)$.

All the above mentioned plants are carnivorous (insectivorous) plants. These trap insects and digest them by proteolytic enzymes and thus, make up their nitrogen deficiency.

Plant with zinc deficiency shows, reduced biosynthesis of auxin. Zinc is the microelement that is absorbed by almost all parts of the plant in the form of $\mathrm{Zn}^{2+}$ ion. It functions as a constituent of carbonic anhydrase and auxin. It also activates various enzymes especially carboxylases and dehydrogenases.

Yellowish edges or chlorosis appears in the leaves, deficient in nitrogen. Nitrogen deficiency also causes delaying of flowering, interference in protein synthesis and dormacy of lateral buds.