THIDIAZURON - A POTENT REGULATOR OF IN-VITRO PLANT MORPHOGENESIS

TDZ (N-phenyl-N'-1,2,3-thidiazol-5-ylurea) is a substituted phenylurea compound which was developed for mechanized harvesting of cotton bell s and has now emerged as a highly efficacious bioregulant of morphogen esis in the tissue culture of many plant species. Application of TDZ i nduces a diverse array of cultural responses ranging from induction of callus to formation of somatic embryos. TDZ exhibits the unique prope rty of mimicking both auxin and cytokinin effects on growth and differ entiation of cultured explants, although structurally it is different from either auxins or purine-based cytokinins. A number of physiologic al and biochemical events in cells are likely to be influenced by TDZ, but these may or may not be directly related to the induction of morp hogenic responses, and hence, the mode of action of TDZ is unknown. Ho wever, the recent approaches applied to study the morphogenic events i nitiated by TDZ are clearly beginning to reveal the details of a varie ty of underlying mechanisms. Various reports indicate that TDZ may act through modulation of the endogenous plant growth regulators, either directly or as a result of induced stress. The other possibilities inc lude the modification in cell membranes, energy levels, nutrient uptak e, or nutrient assimilation. In this review; several of these possibil ities are presented and discussed in light of recently published studi es on characterization of TDZ-induced morphogenic effects.