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Ethylene, a plant hormone that significantly influences both plant growth and response to stress, plays a well-established role in stress signaling. However, its impact on stomatal opening and closure during dehydration and rehydration remains relatively unexplored and is still debated. Exogenous ethylene has been proven to induce stomatal closure through a series of signaling pathways, including the accumulation of reactive oxygen species, subsequent synthesis of nitric oxide and hydrogen sulfide, and SLOW ANION CHANNEL-ASSOCIATED 1 activation. Thus, it has been suggested that ethylene might function to induce stomatal closure synergistically with abscisic acid (ABA). Furthermore, it has also been shown that increased ethylene can inhibit ABA- and jasmonic acid-induced stomatal closure, thus hindering drought-induced closure during dehydration. Simultaneously, other stresses, such as chilling, ozone pollution, and K+ deficiency, inhibit drought- and ABA-induced stomatal closure in an ethylene synthesis-dependent manner. However, ethylene has been shown to take on an opposing role during rehydration, preventing stomatal opening in the absence of ABA through its own signaling pathway. These findings offer novel insights into the function of ethylene in stomatal regulation during dehydration and rehydration, giving a better understanding of the mechanisms underlying ethylene-induced stomatal movement in seed plants. [ABSTRACT FROM AUTHOR]

Clarifying the mechanisms underlying the recovery of gas exchange following drought is the key to providing insights into plant drought adaptation and habitat distribution. However, the mechanisms are still largely unknown. Targeting processes known to inhibit gas exchange during drought recovery, we measured leaf water potential, the leaf hydraulic conductance, stomatal reopening, abscisic acid (ABA) and the ethylene emission rate (EER) following moderate drought stress in seedlings of the globally pervasive woody tree Fraxinus chinensis. We found strong evidence that the slow stomatal reopening after rehydration is regulated by a slow decrease in EER, rather than changes in leaf hydraulics or foliar ABA levels. This was supported by evidence of rapid gas exchange recovery in plants after treatment with the ethylene antagonist 1-methylcyclopropene. These findings provide evidence to rigorously support ethylene as a key factor constraining stomatal reopening from moderate drought directly, thereby potentially opening new windows for understanding species drought adaptation. [ABSTRACT FROM AUTHOR]

γ-aminobutyric acid (GABA) is a non-protein amino acid involved in various physiological processes; it aids in the protection of plants against abiotic stresses, such as drought, heavy metals, and salinity. GABA tends to have a protective effect against drought stress in plants by increasing osmolytes and leaf turgor and reducing oxidative damage via antioxidant regulation. Guard cell GABA production is essential, as it may provide the benefits of reducing stomatal opening and transpiration and controlling the release of tonoplast-localized anion transporter, thus resulting in increased water-use efficiency and drought tolerance. We summarized a number of scientific reports on the role and mechanism of GABA-induced drought tolerance in plants. We also discussed existing insights regarding GABA's metabolic and signaling functions used to increase plant tolerance to drought stress. [ABSTRACT FROM AUTHOR]

Ozone (O3) is a gaseous environmental pollutant that can enter leaves through stomatal pores and cause damage to foliage. It can induce oxidative stress through the generation of reactive oxygen species (ROS) like hydrogen peroxide (H2O2) that can actively participate in stomatal closing or opening in plants. A number of phytohormones, including abscisic acid (ABA), ethylene (ET), salicylic acid (SA), and jasmonic acid (JA) are involved in stomatal regulation in plants. The effects of ozone on these phytohormones' ability to regulate the guard cells of stomata have been little studied, however, and the goal of this paper is to explore and understand the effects of ozone on stomatal regulation through guard cell signaling by phytohormones. In this review, we updated the existing knowledge by considering several physiological mechanisms related to stomatal regulation after response to ozone. The collected information should deepen our understanding of the molecular pathways associated with response to ozone stress, in particular, how it influences stomatal regulation, mitogen-activated protein kinase (MAPK) activity, and phytohormone signaling. After summarizing the findings and noting the gaps in the literature, we present some ideas for future research on ozone stress in plants [ABSTRACT FROM AUTHOR]

In recent years, research on spermine (Spm) has turned up a lot of new information about this essential polyamine, especially as it is able to counteract damage from abiotic stresses. Spm has been shown to protect plants from a variety of environmental insults, but whether it can prevent the adverse effects of drought has not yet been reported. Drought stress increases endogenous Spm in plants and exogenous application of Spm improves the plants' ability to tolerate drought stress. Spm's role in enhancing antioxidant defense mechanisms, glyoxalase systems, methylglyoxal (MG) detoxification, and creating tolerance for drought-induced oxidative stress is well documented in plants. However, the influences of enzyme activity and osmoregulation on Spm biosynthesis and metabolism are variable. Spm interacts with other molecules like nitric oxide (NO) and phytohormones such as abscisic acid, salicylic acid, brassinosteroids, and ethylene, to coordinate the reactions necessary for developing drought tolerance. This review focuses on the role of Spm in plants under severe drought stress. We have proposed models to explain how Spm interacts with existing defense mechanisms in plants to improve drought tolerance. [ABSTRACT FROM AUTHOR]

Plants secreted phytocytokine SMALL PHYTOCYTOKINES REGULATING DEFENSE AND WATER LOSS (SCREWs) and its receptor PLANT SCREW UNRESPONSIVE RECEPTOR (NUT) to counter abscisic acid (ABA)- and pathogen-induced stomatal closure (Liu et al.). This novel signaling process provides plants with a new strategy to increase immunity through disrupting an aqueous habitat for pathogen colonization. [ABSTRACT FROM AUTHOR]