## 1 Introduction  
Drought, among other abiotic stresses, is the most challenging threat to plant growth, yield, and development, which is envisaged to worsen primarily due to human-caused climate changes [1]. Moreover, the shortfall of drought monitoring systems used to quantify the direct impact of agricultural drought on crop yield has further exposed the vulnerability of global food security [2, 3]. Drought has caused grave impairment in plants' morphological, biochemical, physiological, and molecular traits [4]. Therefore, an urgent need is to improve environmentally friendly, time-saving, and cost-effective strategies to mitigate this impact on food availability to feed the ever-increasing human population. Knowledge about the resistance of various crop plants to drought is still limited; although, many studies are being conducted [5]. For this reason, exogenous application of plant protective osmolytes, like organic acids, has proven to be a better alternative for improving plant tolerance to environmental stresses. It is known that organic acids are present in all plants. Moreover, they play a multifaceted role in plants, including their tolerance to stress more than other acids [6], and are pivotal in cellular metabolism [7]. In addition, these acids are involved in the regulation of pH and have organoleptic properties. The level and type of the organic acids to which they accumulate are variable between species, tissues, and developmental stages. Malate and citrate are frequently the most accumulated in plants [8]. Natural low-molecular-weight organic acids, a vital group of plant metabolites, such as salicylic acid (SA), citric acid (CA), and malic acid (MA), have a high degradability and low toxicity, making them environmentally friendly [9]. However, they may confer varied responses among plants when applied exogenously due to the different metabolic pathways. Numerous studies have elaborated on the importance of organic acids in respiration and photosynthesis, nutrient uptake, tricarboxylic acid cycle metabolism [10; 11], and the mitigation of plant abiotic stress [12]. Citric acid (CA) is a three-carboxylic acid (COOH). Salicylic acid (2-hydroxybenzoic acid), a vital plant hormone, has proven to significantly improve the physiological, yield, and growth parameters of rubber [13] and mustard plants [14] under drought stress by improving stomatal aperture, photosynthetic functionality, membrane permeability, and the activities of antioxidants. Similar results have been observed in plants under cold stress [15] and metal toxicity [16]. Studies have shown that exudates of malate and citrate in the roots of plants growing in stressed conditions promote the uptake of nutrients by decreasing pH in the soil [17]. Under drought-stress conditions, the exogenous application of citric acid improved the photosynthetic rate by increasing the volume of chloroplasts in mesophyll cells while malic acid significantly enhanced biomass by accelerating the activities of antioxidants in scavenging reactive oxygen species. However, studies relating to the efficacy of malic acids in drought-stress plants have been relatively scarcely investigated. This study aimed to determine the influence of the exogenous application of three varied organic acids (malic, salicylic and citric) on the response of lettuce plants grown under induced PEG-drought stress. The quality of the plants was evaluated based on several parameters: fresh weight, nutrient content, chlorophyll and carotenoid content, and chlorophyll fluorescence. In addition, the present investigation aimed to study the effects of tested organic acids on oxidative stress (O\({}_{2}\)\({}^{\bullet-}\), H\({}_{2}\)O\({}_{2}\)) and antioxidant potential by evaluating ascorbate, phenolic contents, and lipid peroxidation. Drought stress conditions also altered proline levels, which regulate cellular osmotic potential.