Ascorbic acid (ASC), a small molecule antioxidant, is commonly found in plant tissues. Antioxidative functions of that compound are implemented in Halliwell – Asada cycle, which comprises a group of biochemical processes, providing detoxification of H₂O₂ and regeneration of the reduced form of ascorbate. Apart from its pivotal role in oxidative stress defense, ASC, taking part in cell cycle regulation and cell growth, plays an important role in morphogenesis of plant organs as well. The most significant ascorbate biosynthesis pathway proceeds via GDP-mannose, L-galactose and L-galactono-γ-lacton that act as key intermediates. Mutations in genes encoding enzymes that catalyze reactions in ascorbate biosynthetic pathway in Arabidopsis cause the decrease in the level of this antioxidant in tissues. Selection of ascorbate-deficient mutants, called vitamin c (vtc), helped to examine ASC significance in various physiological processes. Using mutants it has been shown that changes in ascorbate level play a significant role in the regulation of root morphogenesis and shoot growth. Moreover, it has been observed that ASC takes part in flowering and senescence control. vtc mutants were characterized by increased levels of proteins participating in pathogen defense. Plants accumulating decreased levels of ASC enabled also to characterize role of this compound in the protection of the photosynthetic apparatus during salt stress. Moreover, vtc mutants exposed to drought stress served as an useful tool in the studies on the role of ASC in regulation of plant reactions to that type of stress.