Cytokinin Oxygenase/Dehydrogenase Inhibitors: An Emerging Tool in Stress Biotechnology Employed for Crop Improvement

Abstract

In order to meet the global challenges of food security, one of the foremost solutions lies in enhancing the crop productivity. This can be attained by considering key plant hormones such as cytokinins as agrochemicals as cytokinins in particular are known to control the essential processes of the plants. Even though, it has already been established since 1980s that the enzyme, cytokinin oxidase/dehydrogenase (CKO/CKX) deactivates cytokinins; the potential applications of manipulating these enzymes have mostly been speculated to have a high potential in the biotechnology industry and spreads to agriculture, horticulture and agroforestry. The enzyme is critical in maintaining a balanced level of cytokinins in plants. However, it is yet to be fully established that inhibiting this enzyme can be the constant source of improvement in the productivity of plants, even though success has been obtained in some economically important plant species. Furthermore, the impact efficiency of this enzyme may vary from plant to plant, which needs to be evaluated employing tissue culture and other extrinsic applications. This review intends to cover the relevant studies addressing any biological activity of this enzyme in the current context and any associated biotechnological applications specific to enhanced grain yield, abiotic stress tolerance, delayed senescence and in vitro organogenesis among various plants and not only cereals. Moreover, our study will identify the present gaps in research with respect to many important food crops, which will be useful for researchers who are actively involved in providing a foundation for a variety of genetically improved plants achieved through this manner. In addition to this, other ways of engineering the amount of cytokinin levels appropriate for signaling also needs to be analyzed in order to extend the benefits of cytokinin biology to other crops too. The application of these inhibitors can be considered among the best alternates as well as addition to genetically modified plants for overcoming the gaps in crop demand.

Grain yield and quality of wheat are improved through post-flowering foliar application of zinc and 6- benzylaminopurine under water deficit condition

“…On the other hand control plants and foliar 6-BAP treated plants had higher expression of CKX, while plants from Zn treatment had lower rate of CKX gene expression. Some studies claimed CKX genes that negatively regulated the levels of cytokinins have been reported to lead to improved crop yield and abiotic stress tolerances ( Arora and Sen, 2022 ). Therefore higher level expression of CKX gene in control plants might be because these plants were more affected by imposed drought relative to those plants treated with Zn.…”

“…Endogenous cytokinins levels can be regulated by the enzyme so called cytokinin oxidase/dehydrogenase, CKO/CKX. Some studies claimed CKX genes that negatively regulated the levels of cytokinins have been reported to lead to improved crop yield and abiotic stresses tolerances ( Arora and Sen, 2022 ). However, there is some evidences that indicate up regulation of this gene has also caused increased yield in rice.…”

Inspired by Nature: Isostere Concepts in Plant Hormone Chemistry

“…These ureas are, however, classified as cytokinines because their cytokinine properties outweigh their CKX inhibitory activities . For example, thidiazuron 234 inhibits CKX only at high micromolar concentrations but exhibits strong cytokinine effects in the low nanomolar range.…”

Killing two birds with a single stone—genetic manipulation of cytokinin oxidase/dehydrogenase (CKX) genes for enhancing crop productivity and amelioration of drought stress response

“…Besides molecular biology-based cytokinin oxidase inhibition through genetic manipulation of CKX genes, exogenous application of chemical-based cytokinin oxidase inhibitors can also be used to suppress CKX enzyme activity and increase endogenous cytokinin levels ( Arora and Sen, 2022 ) Thidiazuron ( TDZ ), diphenylurea and its derivatives like CPPU, DCPPU were the first cytokinin oxidase inhibitors. However, these exhibit cytokinin activity as well which is usually remarkably higher than CKX inhibitory activities ( Kopečný et al, 2010 ).…”