Lignification in Scots Pine Callus as Reaction to Cultivation Conditions and Nutrient Medium

The effect of nutrient medium composition and of the conditions of cultivation of Scots pine (Pinus sylvestris L.) callus on the morphology of its cells, the degree of their differentiation and lignification was studied. The morphological characteristics of callus cells, the content and macromolecular structure of lignin considerably vary in the dependence on the duration of callus cultivation, the degree of illumination and on the content of sucrose, polyvinylpyrollidon (PVP), ferulic and ascorbic acids in nutrient medium. The increase in the duration of callus cultivation from 21 to 60 days promotes the differentiation of cells, the homogeneity of morphological cell wall structure and intensification of lignification. The cultivation of callus in the darkness suppresses its growth and lignification, whereas under the conditions «light- darkness» leads to the growth of the callus and the accumulation of lignin. The callus grown in the darkness contains more low-molecular lignin and less high-molecular lignin than that cultivated in the light. The increase in sucrose concentration in nutrient medium to 5 % leads to the growth of callus mass and its lignification, to heightened content of high-molecular fraction in lignin and influences the composition of lignin structural units, especially under such conditions as «light- darkness». The effect of PVP on lignification depends on the development stage of callus cells, the conditions of illumination and the time of cultivation. With the cultivation in the darkness during 21 days PVP suppresses the lignification of callus, but it contributes to appearance of siringyl units in the composition of lignin. The increase in the duration of cultivation with PVP to 60 days promotes the condensation of lignin precursors that increases the quantity of high-molecular fraction. The ferulic acid, added in the medium, contributes to the development of the secondary wall thickening of callus cells as matrix for deposition of lignin, increases the content of low-molecular fraction and decreases the high-molecular fraction. The addition of ascorbic acid to nutrient medium favourably affects the proliferation of cells and the growth of the callus mass, but it impedes its lignification.