TDZ-Induced Morphogenesis Pathways in Woody Plant Culture

Thidiazuron (TDZ) possesses a unique property to stimulate both the auxin- and cytokinin-like activities to induce in vitro morphogenesis pathways in the different explants of many species. An additional advantage of TDZ in low concentrations for many recalcitrant woody species in comparison to common amino purine cytokinins is a higher efficiency in overcoming monopodial growth habits by stimulating the axillary shoot development in in vitro culture. The application of TDZ for in vitro woody tissue culture inducts the wide range of morphological reactions including somatic embryogenesis and shoot organogenesis followed by root organogenesis, which occurs directly or through callus formation. These responses suggested that TDZ-induced regeneration systems could be used as the models for studying the fundamental aspects of plant biology and better understanding the developmental pathways. Despite the progress of recent biochemical, physiological, and molecular researches of TDZ effect on plant regeneration through organogenesis and somatic embryogenesis, the data on chronological sequences of morphological events are still limited. The abnormality formation of de novo structures is known to be undesirable side effect of TDZ. Therefore, the morpho-histological approach based on the observation of developmental route under TDZ at microscopic level and detailed histological analysis is necessary to reveal the type of morphogenic response (organogenic or embryogenic), improve the regeneration efficiency, and create systems of large-scale propagation for woody species. The chapter discusses the data on TDZ-induced regeneration systems in various woody tissue cultures analyzed by morpho-histological approach as a valuable tool to perform morphogenesis studies.