Lead is one of the major environmental pollutants which is highly toxic to plants and living beings. The current investigation thoroughly evaluated the synergistic effects of oxalic acid (OA) and salicylic acid (SA) on Zea mays L. plants subjected to varying durations (15, 30, 30, and 45 days) of lead (Pb) stress. Besides, the effects of oxalic acid (OA) combined with salicylic acid (SA) for different amino acids at various periods of Pb stress were also investigated on Zea mays L. The soil was treated with lead nitrate Pb (NO3)(2) (0.5 mM) to induce Pb stress while the stressed plants were further treated using oxalic acid (25 mg/L), salicylic acid (25 mg/L), and their combination OA + SA (25 mg/L each). Measurements of protein content, malondialdehyde (MDA) levels, guaiacol peroxidase (GPOX) activity, catalase (CAT) activity, GSH content, and Pb concentration in maize leaves were done during this study. MDA levels increased by 71% under Pb stress, while protein content decreased by 56%, GSH content by 35%, and CAT activity by 46%. After treatment with SA, OA, and OA+SA, there was a significant reversal of these damages, with the OA+SA combination showing the highest improvement. Specifically, OA+SA treatment led to a 45% increase in protein content and a 39% reduction in MDA levels compared to Pb treatment alone. Moreover, amino acid concentrations increased by 68% under the Pb+OA+SA treatment, reflecting the most significant recovery (p < 0.0001).

Background and aimsA better understanding of plant carbon assimilation, water status and photosystem performance responses to combined heat and drought stress would help to optimize grapevine management under such limiting conditions.MethodsGas exchange and chlorophyll fluorescence parameters were measured in potted grapevines, cv Sauvignon Blanc, before, during and after simulated six-day heat (Tmax = 40 degrees C) wave using heated well-watered (HW), heated drought-stressed (HD), non-heated well-watered (CW) and non-heated dry (CD) vines.ResultsPhotosynthesis and stomatal conductance in HW vines increased during the morning and dropped in the afternoon with respect to CW vines. Daily plant transpiration in HW almost doubled that of CW vines. When grapevines were already exposed to drought, the effects of the heat wave were negligible, with HD plants showing similar leaf photosynthesis and transpiration to their CD counterparts. Heat, but not drought stress, decreased the maximum (Fv/Fm) and effective photochemical quantum yield of PSII (phi PSII), and also affected the use of absorbed energy. HW plants dissipated more radiative energy as heat, a protective mechanism of the photosystem, while HD vines increased the energy dissipated by non-regulated non-photochemical pathways, which might lead to photoinhibition damages. The different behavior could be due to the enhanced transpiration rate and consequent decrease in leaf temperature in HW as compared to HD vines. After the heat wave, only HW vines recovered the afternoon values of photosynthesis, stomatal conductance and phi PSII to similar levels as those in CW vines.ConclusionDrought had a more significant effect than heat stress on photosynthesis, stomatal conductance and transpiration. The combined heat and drought stress, however, increased the proportion of energy lost by the leaves through harmful non-regulated dissipative pathways. With adequate soil water availability, grapevines withstood the heat wave period through an increase in leaf transpiration, which decreased leaf temperature and protected the PSII from heat damage. Drought had a stronger impact on gas exchange parameters than elevated temperature during a simulated heatwave, while heat stress was the main driver of PSII functionality and absorbed energy partitioning. Well-watered grapevines were able to recover their physiological function after a six-day heatwave (Tmax 40 degrees C), while plants under heat and drought stress were unable to resume PSII performance after one day of recovery.