Drought stress tolerance mechanisms and their potential common indicators to salinity, insights from the wild watermelon (Citrullus lanatus): A review

Abstract

Climate change has escalated the effect of drought on crop production as it has negatively altered the environmental condition. Wild watermelon grows abundantly in the Kgalagadi desert even though the environment is characterized by minimal rainfall, high temperatures and intense sunshine during growing season. This area is also characterized by sandy soils with low water holding capacity, thus bringing about drought stress. Drought stress affects crop productivity through its effects on development and physiological functions as dictated by molecular responses. Not only one or two physiological process or genes are responsible for drought tolerance, but a combination of various factors do work together to aid crop tolerance mechanism. Various studies have shown that wild watermelon possess superior qualities that aid its survival in unfavorable conditions. These mechanisms include resilient root growth, timely stomatal closure, chlorophyll fluorescence quenching under water deficit as key physiological responses. At biochemical and molecular level, the crop responds through citrulline accumulation and expression of genes associated with drought tolerance in this species and other plants. Previous salinity stress studies involving other plants have identified citrulline accumulation and expression of some of these genes (chloroplast APX, Type-2 metallothionein), to be associated with tolerance. Emerging evidence indicates that the upstream of functional genes are the transcription factor that regulates drought and salinity stress responses as well as adaptation. In this review we discuss the drought tolerance mechanisms in watermelons and some of its common indicators to salinity at physiological, biochemical and molecular level.

Morphological, Physiological, and Molecular Stomatal Responses in Local Watermelon Landraces as Drought Tolerance Mechanisms

“…Drought stress resulted in reduced stomatal aperture in all watermelon genotypes in this study (Figures 5 and 6), and a highly significant reduction was recorded under extreme drought stress (days 6 and 9). The lowest value for stomatal aperture (14.7) was recorded in Clm-03 on day 9 of drought stress, and this is in line with the drought stress avoidance mechanism reported in [54,55]. Another study [54] reported that both medium and severe droughts led to significant decreases in stomatal aperture in drought-stressed maize (Zea mays) plants compared with well-watered plants.…”

Functional and Transcriptome Analysis Reveal Specific Roles of Dimocarpus longan DlRan3A and DlRan3B in Root Hair Development, Reproductive Growth, and Stress Tolerance

“…A close association between Ran and plant responses to environmental stresses, such as salinity [ 39 ], osmotic stress [ 8 ], drought [ 7 ], low temperatures [ 9 , 40 ], aluminum toxicity [ 41 ], and oxidative stress [ 11 ], has been elucidated in numerous studies. However, the understanding of the underlying mechanisms is slowly improving, and there have been rare reports about the role of longan Ran in defense responses.…”

“…Ras-related nuclear protein (Ran) GTPases, also known as molecular switches, play a universal role in nucleocytoplasmic transport, specifically expressed during embryogenesis, and are essential for cell division in animal development [ 4 , 5 ]. Plant Ran GTPases, along with their cofactors and nucleoporins, are involved in diverse biological processes including plant growth and root development [ 6 , 7 ], regulation of hormone (such as auxin and abscisic acid, ABA) sensitivity [ 6 , 8 , 9 ], enhancement of disease resistance [ 10 ], and stress responses, such as those to drought, salinity, osmotic stress, and cold and oxidative stresses [ 7 , 8 , 11 ]. This indicates that plant Ran may have a remarkable impact on plant growth and, hence, its economic traits when overexpressed.…”

Joint transcriptomic and metabolomic analysis provides new insights into drought resistance in watermelon (Citrullus lanatus)

“…With global warming and increasing water scarcity, drought stress can severely affect the yield and quality of watermelon plants and has become one of the main problems in watermelon cultivation (Malambane et al, 2023). With the development of sequencing technology and molecular biology, analyzing the molecular mechanisms of watermelon drought resistance and identifying functional genes are important for overcoming this problem (Song et al, 2015).…”

“…Watermelon plants produce low-calorie and high-fiber fruits that help control weight, promote digestive health, and contain natural antioxidants (Naz et al, 2014). With global warming and increasing shortages of water resources, drought has become one of the main abiotic stresses that impacts the normal growth of plants and substantially reduces the yield and quality of watermelon plants; thus, drought is one of the main problems faced during watermelon cultivation (Malambane et al, 2023). Therefore, studying the mechanism underlying watermelon drought resistance and identifying key drought resistance genes are highly important for ensuring the sustainable development of the watermelon industry (Malambane et al, 2023).…”