High cytokinin activity of TDZ and its physiological mechanism

In 1982, Mok et al. compared the cytokinin activity of 6 thiadiazole urea derivatives with that of 3 pyridine urea derivatives by using the method of callus growth identification from hypocotyls of Phaseolus Lunatus, and found that TDZ was the strongest one. The physiological activity of TDZ was tested with soybean callus, carrot cotyledon and tobacco differentiation material, and compared with purine cytokinins BA, ZT, KT, etc. The results showed that TDZ had high cytokinin activity and plant growth and cell division were sensitive to low concentrations (10-9 ~10-5 mol/ L) of TDZ. The concentration of TDZ was 10-2 times that of BA in carrot bioassay and 10-4 times that of ZT in soybean callus. These results are consistent with reports of activity measurements carried out as early as 1978 in the synthesis of these aromatic urea derivatives. Regarding the physiological mechanism of TDZ, TDZ promotes nucleotide conversion to nucleoside. TDZ caused purine metabolism changes in soybean calli and accelerated the synthesis of cytokinins, so that these calli could continue to grow on medium without exogenous kinetin. This phenomenon has also been observed in other plants. It has also been suggested that TDZ is beneficial to callus growth, bud differentiation and reproduction by promoting the synthesis or accumulation of purine cytokinins in cells. Mok et al. also proposed in tissue culture studies that TDZ has strong cytokinin-like effects due to its benzene ring and another ring structure. However, the molecular mechanism of TDZ high activity cytokinin is still not completely clear, and how it regulates gene expression needs further study. Because TDZ has strong cytokinin action, it shows obvious effect of promoting axillary bud proliferation. Axillary bud induction is an important way of rapid asexual propagation. It can not only maintain the genetic characteristics of species, but also reproduce in large quantities in a short period of time to achieve industrial seedling. It is especially important for rare, rare and difficult to reproduce plants. Some woody plants have poor regeneration ability, purine kinetin used in the past is difficult to start a large number of axillary bud proliferation, after the advent of TDZ, in some difficult to regenerate fruit trees, flowers, trees and other rapid propagation application has obtained ideal results, so that woody plant tissue work opened a new situation.

In tissue culture, high concentration of cytokinin combined with low concentration of auxin or more than two kinds of hormones can promote bud proliferation. TDZ was also used. When BA, IBA or NAA were added to the medium supplemented with TDZ, the proliferation rate of buds could be increased and the shoot tips could be elongated. Similarly, TDZ added to BA medium also increased bud proliferation of maple and grape. It is an interesting question that multiple cytokinins are better used in combination than alone. This indicates that there are differences in the absorption and recognition of different hormones by cells, or differences in the mechanism of action of various hormones. They activate different receptors and regulate the expression of genes. The mechanism of hormone coordination needs further study. (Jiangchengzi)