Molecular Soil Biology 2024, Vol.15, No.5, 205-215 http://bioscipublisher.com/index.php/msb 206 physiological, biochemical, and molecular adaptations that enable plants to survive and thrive under drought conditions (Mullet and Whitsitt, 1996; Farooq et al., 2009; Yang et al., 2021). These adaptations include stomatal closure, morphological and structural changes, synthesis of hormones, osmotic regulatory substances and expression of drought-resistant genes to alleviate drought stress (Bray, 1997; Kaur et al., 2021). Secondly, understanding these mechanisms can inform the development of drought-resistant crop varieties through breeding and genetic engineering, thereby enhancing agricultural resilience to climate change (Chaves, 2004). Additionally, knowledge of plant responses to water deficit can guide the implementation of sustainable agricultural practices and water management strategies, ensuring efficient use of water resources (Shao et al., 2009). Ultimately, such studies contribute to the broader goal of maintaining ecosystem stability and productivity in the face of increasing water scarcity. By integrating physiological, biochemical, molecular, and ecological perspectives, this review aims to provide a comprehensive understanding of plant responses to water deficit, highlight the importance of interdisciplinary approaches in addressing this critical environmental challenge. 2 Physiological Adaptation Mechanisms 2.1 Stomatal regulation and transpiration Stomatal regulation, such as increase stomatal length, stomatal width, stomatal density, and stomatal opening is a critical physiological adaptation mechanism that plants employ to manage water loss and maintain water use efficiency (WUE) under water deficit conditions. Stomata are microscopic pores on the leaf surface that control gas exchange, including the uptake of CO2 for photosynthesis and the release of water vapor through transpiration. Under drought conditions, plants often close their stomata to reduce water loss, which can also limit CO2 uptake and affect photosynthesis (Buckley, 2019; Kaur et al., 2021; Lobato et al., 2021). The plant hormone of abscisic acid (ABA) is a crucial signal molecule in stomatal closure. ABA is synthesized in response to water deficit and signals the guard cells to close the stomata, thereby reducing transpiration rates (Giorio et al., 2018; Kaur et al., 2021; Yari Kamrani et al., 2022). This response is part of a complex signaling network that includes secondary messengers and mitogen-activated protein kinases, which help in the rapid adjustment of stomatal aperture (Kaur et al., 2021; Lawson and Vialet-Chabrand, 2019). Additionally, circadian clocks regulate the diurnal opening and closing of stomata, optimizing WUE day-night (Yari Kamrani et al., 2022). 2.2 Water transport and root structure adjustment Water transport within the plant and adjustments in root structure are essential for maintaining water uptake during periods of water deficit. The morphological changes of plant roots to enhance water absorption from deeper soil layers. Root system configurations involve root length and root density, root hair, root branches can significantly affect the water deficiency of plants (Gupta et al., 2020; Wu et al., 2022). Hydraulic conductance within the plant, particularly in the roots and leaves, is also adjusted to optimize water transport. This involves changes in the expression of aquaporins, which are water channel proteins that facilitate water movement across cell membranes (Kaur et al., 2021). The root, stems, leaves system have ability to produce aerenchyma, a tissue with air spaces, helps in maintaining oxygen supply from the stem to the root in plants under waterlogged conditions, which can also be beneficial during drought stress by improving root function and water uptake (Sou et al., 2021; Wu et al., 2022). 2.3 Leaf morphology changes and water conservation strategies Leaf morphology changes are another crucial adaptation mechanism that helps plants conserve water. Under water deficit conditions, plants may exhibit leaf wilting, crimping, and reduce leaf number and area to minimize water loss through transpiration (Lobato et al., 2021; Wu et al., 2022). These morphological changes are often accompanied by alterations in leaf anatomy, such as a reduction in leaf angle and size, stomatal position, deposition of the cuticle and epidermal thickness, which further contribute to water conservation on the leaf surface (Yavas et al; 2023).
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