Drought stress represents an immense global environmental challenge, disturbing plant growth and survival. Thiamine and salicylic acid (SA) have been frequently exhibited to boost drought tolerance in plants, but their precise role in improving citrus resistance to drought stress remains unclear. The current study assessed the effect of different treatments of thiamine (0, 50, and 100 µM) and SA (0, 10, and 20 µM) on drought stress (5% PEG) in three important citrus rootstocks, ‘sour orange’, ‘volcamariana’, and ‘lime’, under in vitro conditions. Results revealed that drought stress negatively altered citrus growth and performance; however, the supplementation of thiamine and SA, particularly at 100 and 20 µM, respectively, modulated these adverse effects, with variable responses among the tested rootstocks. Notably, thiamine and SA promoted the germination percentage as well as several growth parameters, including shoot length, root length, leaf area, fresh weight, dry weight, and water content. Moreover, thiamine and SA modulated the negative effect induced by PEG through increasing chlorophyll a, chlorophyll b, and carotenoids and regulating proline and phenolic levels. The activities of antioxidant enzymes i.e., PAL, PPO, CAT, and POD were also modified by thiamine and SA, resulting in an activation of defensive machinery against drought stress. This framework provides a valuable strategy for the development of citrus adaptation in three rootstocks to drought stress, highlighting the contribution role of thiamine and SA in achieving sustainability in water-limited environments.

Background

The expansive usage of metal oxide nanoparticles (NPs) as a potential constituent in modern nano-enabled products raises threats to environmental safety and crop production. Key lime is an economic plant enriched with secondary metabolites and imperative bioactive compounds. NPs can alter lime’s essential components, making it an ideal model for monitoring NPs’ toxicity. Hence, a comparative analysis of two synthesized metallic NPs, aluminum (Al2O3) and copper (CuO) at concentrations of 0, 100, 200, and 500 mg/L, was conducted to assess their impact on the growth and quality attributes of lime plants under controlled micro-conditions.

Results

Observations from germination, growth, physiological, biochemical, and ionomic attributes showed that Al2O3-NPs had variable effects in a concentration-dependent manner, while CuO-NPs were toxic at all concentrations. Heatmap and principal component analysis revealed that CuO-NPs instigated more pronounced toxic effects compared with Al2O3-NPs at each applied concentration, as evidenced by heightened oxidative stress symptoms. CuO-NPs exerted their toxicity by over-accumulating reactive oxygen radicals and methylglyoxal and elevating lipoxygenase activity, causing peroxidation of membrane lipids and attenuation of photosynthetic pigments. Al2O3-NPs-treated plants relatively up-regulated the pool of phenolics, flavonoids, anthocyanins, ascorbic acid, and α-tocopherol as well as stimulated the activity of enzymatic antioxidants. Ionomics analysis showed excessive copper accumulation in toxic levels (~ 15-fold), which triggered nutritional imbalance (Mg, Si, P, S, Cl, K, Ca, Fe, Cu, and Zn) and disruption of chelating molecules, nitric oxide, and hydrogen sulfide.

Conclusions

This work provides precious insights into the differential impacts of metallic NPs on the development and quality of lime plants and the underlying mechanisms involved in NPs accumulation, highlighting the possible hazards of manufactured NPs in the environment, especially for valuable plant species. However, the controlled use of NPs—particularly aluminum oxide—may offer agronomic benefits, but their application must be carefully handled to prevent toxicity.

Aluminum (Al) toxicity exhibits a challenge for growing strawberries (Fragaria x ananassa Duch), impacting their growth and nutritional value. Considerably in this study, we explored how melatonin, an endogenous plant hormone, can help alleviate Al stress in strawberry plants. The current research examined the effects of foliar spraying melatonin (0,50, and 100 ppm) on growth indicators, photosynthetic pigment levels, carbon and nitrogen assimilation, oxidative stress markers, and fruit quality attributes under Al stress (100 µM) in a controlled pot experiment conducted in a greenhouse. The results revealed that exposure to Al stress significantly reduced the adequate growth, as well as the yield and quality of fruits. Melatonin application improved plant growth parameters, especially at a concentration of 100 ppm, enhancing the levels of photosynthetic pigments and boosting carbohydrate and nitrogen metabolism. Moreover, melatonin played a role in reducing stress markers while increasing enzymatic antioxidant activities (catalase, superoxide dismutase, ascorbate peroxidase, glutathione peroxide, glutathione-S-transferase, and phenylalanine ammonia-lyase) and secondary metabolites (proline, ascorbic acid, flavonoids, reduced glutathione, and phytochelatins), while decreasing polyphenol oxidase activity as well as phenolics content, implying a role in ROS scavenging. The results underscore the promise of melatonin as a method to enhance the ability of strawberries to withstand Al toxicity and promote friendly agricultural practices in polluted soils.