Histochemical Study of Xylem Cells in In Vitro Culture of Iris sibirica L

In this study, lignin content data are presented for annual regenerant Iris sibirica plants, comparable to those in six-year-old intact plants. The structure of the shoots of Iris sibirica grown on artificial nutrient media was studied by the histochemical method. Features of the formation of the xylem in Iris sibirica on artificial nutrient media were revealed. Regenerants very quickly developed a complex system consisting of vascular bundles containing sieve tubes, vessels and tracheids, and hydrocyte systems. Hydrocytes of Iris sibirica were tracheids with lignified thickening, but, in contrast to tracheids and vessels of xylem (they are formed based on procambium or cambium—special lateral primary or secondary meristem), hydrocytes differentiated from the cells of permanent tissues (like phellogen), which probably possessed meristematic activity at the time of differentiation. In Iris sibirica hydrocytes covered the vascular bundle by the thick layer and strung along it up to a certain height. High lignin content in young regenerant Iris sibirica plants was due to the formation of the dense tissue from lignified tracheal elements. The study of the differentiation of xylem elements under controlled conditions can serve as a model for our understanding of wood formation processes.