For all living organisms, vitamin B₆ supply is essential to the metabolic function of over two hundred enzymes that require it as a coenzyme. Several structurally related compounds form the vitamin B₆ family and are interchangeable through salvage pathways. In the absence of the salvage pathway enzyme, PDX3, the balance of vitamin B₆ in the model plant Arabidopsis thaliana is disrupted which is paralleled with severe morphological impairments and perturbations in nitrogen metabolism and immunity. The aim of this thesis work is to understand the mechanism behind the various phenotypes associated with the lack of PDX3 as well as provide insight into the metabolic role of the enzyme. The findings in this work support a key role for PDX3 in nitrogen management, particularly serine metabolism and that salicylic acid is partly responsible for the pdx3 morphological phenotype. Perspectives on additional functions, regulation, and molecular partners PDX3 enzyme are also discussed.