This paper reports on morphophysiological and biochemical characteristics of control and potato plants (Solarium tuberosum L., Skoroplodnyi cultivar) transformed with the Δ12 acyl-lipid desaturase gene (desA) grown long-term in vitro. The transformed plants showed faster growth and faster ontogenesis as compared to controls, which was accompanied with changes in the accumulation of photosynthetic pigments (chlorophylls a and b, carotenoids) and phenolic compounds, including flavonoids in the leaves. These characteristics were pronounced to a high degree in Line II plants with high expression rates of the desA gene, whereas Line I plants (moderate expression rate) were similar to control plants in many parameters.