Abstract
Using plant growth regulators to alter cytokinin homeostasis with the aim of enhancing endogenous cytokinin levels has been proposed as a strategy to increase yields in wheat and barley. The plant growth regulators INCYDE and CPPU inhibit the cytokinin degrading enzyme cytokinin oxidase/dehydrogenase (CKX), while TD-K inhibits the process of senescence. We report that the application of these plant growth regulators in wheat and barley field trials failed to enhance yields, or change the components of yields. Analyses of the endogenous cytokinin content showed a high concentration of trans-zeatin (tZ) in both wheat and barley grains at four days after anthesis, and statistically significant, but probably biologically insignificant, increases in cisZ-O-glucoside, along with small decreases in cZ riboside (cZR), dihydro Z (DHZ), and DHZR and DHZOG cytokinins, following INCYDE application to barley at anthesis. We discuss possible reasons for the lack of efficacy of the three plant growth regulators under field conditions and comment on future approaches to manipulating yield in the light of the strong homeostatic mechanisms controlling endogenous cytokinin levels.
Highlights
Food producers face a range of challenges in addressing global food security in the 21st century
INCYDE (2-chloro-6-(3-methoxyphenyl)aminopurine) is a substituted 6-anilinopurine derivative (Figure 1d). It is a stronger inhibitor of cytokinin oxidase/dehydrogenase than
It is a stronger inhibitor of cytokinin oxidase/dehydrogenase than TDZ, while more weakly activating cytokinin receptors compared to TDZ and tZ
Summary
Food producers face a range of challenges in addressing global food security in the 21st century. These include continuing growth in food consumption in developing nations [1]. Increasing the yield of cereal crops, including wheat and barley, is fundamental to ensuring food security. In the 2019/2020 season, global production of wheat was more than 770 million tonnes, while for barley it was more than 150 million tonnes [5]. Several traits in cereals have been identified as important components of, and contributors to, overall yields, including having more productive tillers [6,7,8], a greater proportion of fertile grain-containing florets, larger grains, and leaf senescence occurring at an optimal time [9]. The production of more tillers is not necessarily beneficial, as small, unproductive tillers could direct resources away from productive tillers and negatively impact yield [15,16]
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