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Stomata, small hydromechanical valves in the leaf epidermis, are fundamental in regulating gas exchange and water loss between plants and the environment. Stomatal development involves a series of coordinated events ranging from the initial cell division that determines the meristemoid mother cells to forming specialized structures such as guard cells. These events are orchestrated by the transcription factors SPEECHLESS, FAMA, and MUTE through signaling networks. The role of plant hormones (e.g., abscisic acid, jasmonic acid, and brassinosteroids) in regulating stomatal development has been elucidated through these signaling cascades. In addition, environmental factors, such as light availability and CO 2 concentration, also regulate the density and distribution of stomata in leaves, ultimately affecting overall water use efficiency. In this review, we highlight the mechanisms underlying stomatal development, connecting key signaling processes that activate or inhibit cell differentiation responsible for forming guard cells in the leaf epidermis. The factors responsible for integrating transcription factors, hormonal responses, and the influence of climatic factors on the signaling network that leads to stomatal development in plants are further discussed. Understanding the intricate connections between these factors, including the metabolic regulation of plant development, may enable us to maximize plant productivity under specific environmental conditions in changing climate scenarios., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier GmbH. All rights reserved.)

Ethylene is a gaseous hormone with a well-established role in the regulation of plant growth and development. However, its role in the modulation of carbon assimilation and central metabolism remains unclear. Here, we investigated the morphophysiological and biochemical responses of tomato plants (Solanum lycopersicum) following the application of ethylene in the form of ethephon (CEPA - 2-chloroethylphosphonic acid), forcing the classical triple response phenotype. CEPA-treated plants were characterized by growth inhibition, as revealed by significant reductions in both shoot and root dry weights, coupled with a reduced number of leaves and lower specific leaf area. Growth inhibition was associated with a reduction in carbon assimilation due to both lower photosynthesis rates and stomatal conductance, coupled with impairments in carbohydrate turnover. Furthermore, exogenous ethylene led to the accumulation of cell wall compounds (i.e., cellulose and lignin) and phenolics, indicating that exposure to exogenous ethylene also led to changes in specialized metabolism. Collectively, our findings demonstrate that exogenous ethylene disrupts plant growth and leaf structure by affecting both central and specialized metabolism, especially that involved in carbohydrate turnover and cell wall biosynthesis, ultimately leading to metabolic responses that mimic stress situations., (Copyright © 2021 Elsevier GmbH. All rights reserved.)