A cytokinin analog Thidiazuron suppresses shoot growth in potted rose plants via the gibberellic acid pathway

Authors: CELIKEL, FISUN - Ondokuz Mayis University; ZHANG, QING-CHUN - Northwest Agricultural & Forestry University; ZHANG, YANLONG - Northwest Agricultural & Forestry University; REID, MICHAEL - University Of California, Davis; Jiang, Cai-Zhong

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2021
Publication Date: 7/15/2021
Citation: Celikel, F., Zhang, Q., Zhang, Y., Reid, M., Jiang, C. 2021. A cytokinin analog Thidiazuron suppresses shoot growth in potted rose plants via the gibberellic acid pathway. Frontiers in Plant Science. 12. Article 639717. https://doi.org/10.3389/fpls.2021.639717.
DOI: https://doi.org/10.3389/fpls.2021.639717

Interpretive Summary: Potted miniature roses are popular year-round potted plants, with increases in production for special days such as Mother’s Day and Easter in the United States. However, the leaves of potted roses yellow and abscise after pinching (a technique intends to stimulate branching), as well as under low-light conditions after production. Plant height control is important in maintaining the compactness and quality of pot plants during, and after production. The lower light conditions in homes and offices could result in an increase in plant height and a reduction of postharvest quality. To provide compact plants, growers apply plant growth regulators, such as ethylene (released from ethephon) or, more commonly, inhibitors of gibberellin biosynthesis (such as flurprimidol, ancymidol, paclobutrazol), to suppress extension growth after production. The main commercial use of the non-metabolized cytokinin TDZ is as a defoliant in cotton, an activity that results from stimulation of ethylene production and accelerated abscission when the plants are sprayed with relatively low concentrations of the regulator. In a previous study, we used TDZ as a tool for preventing leaf yellowing after pinching of potted miniature roses. In addition to effective prevention of leaf yellowing, we found that application of TDZ inhibited shoot growth, resulting in plants with shorter and thicker stems. Our observation that the anti-yellowing effect of TDZ was accompanied by marked reduction of elongation growth is therefore of considerable practical interest.

Technical Abstract: Application of thidiazuron (N-phenyl-N’-1, 2, 3-thiadiazol-5-ylurea, TDZ), a non-metabolized cytokinin analog, to inhibit the leaf yellowing that occurs after pinching potted rose plants, resulted in compact plants with shorter shoots and thicker internodes. Two weeks after treatment with 100 µM TDZ, new shoots were half as long as those in control plants, and stem diameters were about 40% greater. This effect of TDZ is associated with changes in cell architecture. Although TDZ treatment stimulated ethylene production by the plants, inhibitors of ethylene biosynthesis (2-aminoethoxyvinyl glycine - AVG) or action (silver thiosulfate - STS) did not affect the plants’ response to TDZ. We found TDZ treatment significantly suppressed expression of bioactive GA biosynthesis genes encoding GA3 and GA20 oxidases and slightly increased expression of GA catabolism genes encoding GA2 oxidase. Application of gibberellic acid (GA3) and TDZ together resulted in normal elongation growth, although stem diameters were still somewhat thicker. Our results suggest that TDZ regulates shoot elongation and stem enlargement in potted rose plants through modulation of bioactive GA biosynthesis.