Plant hormone cytokinin at the crossroads of stress priming and control of photosynthesis

Abstract

To cope with biotic and abiotic stress conditions, land plants have evolved several levels of protection, including delicate defense mechanisms to respond to changes in the environment. The benefits of inducible defense responses can be further augmented by defense priming, which allows plants to respond to a mild stimulus faster and more robustly than plants in the naïve (non-primed) state. Priming provides a low-cost protection of agriculturally important plants in a relatively safe and effective manner. Many different organic and inorganic compounds have been successfully tested to induce resistance in plants. Among the plethora of commonly used physicochemical techniques, priming by plant growth regulators (phytohormones and their derivatives) appears to be a viable approach with a wide range of applications. While several classes of plant hormones have been exploited in agriculture with promising results, much less attention has been paid to cytokinin, a major plant hormone involved in many biological processes including the regulation of photosynthesis. Cytokinins have been long known to be involved in the regulation of chlorophyll metabolism, among other functions, and are responsible for delaying the onset of senescence. A comprehensive overview of the possible mechanisms of the cytokinin-primed defense or stress-related responses, especially those related to photosynthesis, should provide better insight into some of the less understood aspects of this important group of plant growth regulators.

Integrative regulatory mechanisms of stomatal movements under changing climate

“…Cytokinins (CKs) are essential growth‐promoting phytohormones with various molecular structures (Sakakibara, 2006) that play significant roles in diverse physiological processes in plants, including plant growth and development, leaf senescence and plant response to biotic or abiotic stresses (Pavlů et al, 2018; Nedvěd et al, 2021). Regarding the roles in regulating stomatal movements, CKs are often considered an ABA antagonist and function in promoting stomatal opening (Song et al, 2006; Tanaka et al, 2006; Veselova et al, 2006; Hudeček et al, 2023). The mechanisms of CKs function in guard cells mainly include membrane hyperpolarization via stimulating electrogenic H + ‐pump, mediating the interaction between CKs and ABA via [Ca 2+ ] cyt concentration and scavenging H 2 O 2 in guard cells (Pospíšilová, 2003; Hudeček et al, 2023).…”

“…Regarding the roles in regulating stomatal movements, CKs are often considered an ABA antagonist and function in promoting stomatal opening (Song et al, 2006; Tanaka et al, 2006; Veselova et al, 2006; Hudeček et al, 2023). The mechanisms of CKs function in guard cells mainly include membrane hyperpolarization via stimulating electrogenic H + ‐pump, mediating the interaction between CKs and ABA via [Ca 2+ ] cyt concentration and scavenging H 2 O 2 in guard cells (Pospíšilová, 2003; Hudeček et al, 2023). At the molecular level, CK receptors AHK2/3 (ARABIDOPSIS HISTIDINE KINASEs) are negative regulators, while AHK1 is a positive regulator in drought stress (Tran et al, 2007; Figure 2).…”

Effects of Lactone- and Ketone-Brassinosteroids of the 28-Homobrassinolide Series on Barley Plants under Water Deficit

“…Priming is defined as the process by which an organism acquires the ability to increase stress tolerance in response to some damaging factor in the future. Factors of different natures, including BRs, can serve as inducers of the plant transition to the priming state [17][18][19][20].…”

Phytohormones mitigate salt stress damage in radish

“…Precise control of leaf gas exchange plays a pivotal role in enhancing tolerance to abiotic stresses, such as salt exposure (Montanaro et al, 2022). Amongst the myriad of biochemical processes, photosynthesis stands out as highly susceptible to environmental stress, with the photosynthetic apparatus ranking among the most stresssensitive components in plants (Hudeček et al, 2023).…”

“…Phytohormones play a vital role in how plants respond to salt stress, as they oversee the regulation of plant growth and facilitate adaptations in development because they contribute to perceiving salt stress signals and mediating the plant's defense system (Zhao et al, 2021). Jasmonic acid, salicylic acid, cytokinin, and polyamine have been reported as mitigators of damage caused by salt stress in plants (Naeem et al, 2020;Azzam et al, 2022;Silva et al, 2022a;Hudeček et al, 2023;Henschel et al, 2023).…”