Gallic acid is found in plant tissues in free form, as well as in the composition of complex esters and hydrolysed tannins. These phenolic compounds have significant antioxidant activity and protect plant cells from damage by free radicals. In the conditions of stress that occurs during the introduction of plants into in vitro culture, the vast majority of explants are characterised by an intensive synthesis of phenols, which quickly oxidise, polymerise, block the explants’ nutrition pathways, and cause tissue necrosis. The addition of gallic acid in millimolar concentrations to the nutrient medium reduces the risk of autointoxication of tissues by secondary metabolic products. The purpose of this study was to investigate the effect of exogenous gallic acid on organogenesis and phenolic synthesis of Salix alba and Corylus avellana plants in vitro. For this purpose, the study used methods of tissue and organ culture in vitro, spectrophotometric determination of total phenols and flavonoids in leaves, methods of dispersion and nonparametric analysis. It was established that gallic acid at a concentration of 1 mmol·l-1 in the composition of the DKW nutrient medium caused the awakening of dormant buds, stimulated the growth of shoots, and also promoted the branching of stems, the development and growth of lateral roots of Salix alba in vitro. It also inhibited the synthesis of phenols in Corylus avellana plants of the varieties ‘Tonda Romana’, ‘Tonda Gentile Dele Lange’, ‘Barcelona’, while contributing to an increase in the content of phenolic compounds in the leaves of the varieties ‘Tonda Di Giffoni’, ‘Mortarella’, and ‘Epsilon’. It was established that the varieties recommended for fruiting have a higher content of phenolic compounds (‘Tonda Gentile Dele Lange’ and ‘Tonda Di Giffoni’) compared to pollinator varieties (‘Mortarella’). Therefore, exogenous gallic acid at a concentration of 1 mmol·l-1 has the properties of a non-specific regulator of phenol synthesis in regenerating plants of hazel (Corylus avellana), which is relevant for plants with a high content of phenols, especially at the stage of their introduction into in vitro culture
