Cumulative potential of Lactuca sativa L. and physiological and anatomical damage when exposed to lead

The objective of this study was to investigate the effect of lead on the cultivation of Lactuca sativa L. in a hydroponic system, elucidating the effects of lead on physiological processes, anatomy, and its bioaccumulation capacity. Lettuce plants were grown in a greenhouse under a hydroponic system containing lead nitrate (50, 100, 250, 500 μM), with Hoagland solution as a negative control, for a period of 42 to 70 days. Plant height, number of leaves, fresh and dry matter, leaf area, chloroplastic pigments, chlorophyll fluorescence, anatomical parameters, and lead content were evaluated. The results demonstrated that growth parameters were affected according to lead concentration. The 500-μM concentration caused the greatest reduction in stem height (30.28%) and leaf area (88.07%). A significant decrease in the number of leaves, ranging from 20 to 90.47%, was observed at all concentrations on the 70th day. Chloroplastic pigment content was statistically reduced at all concentrations, reflecting a sharp decline of 58.82% in the photochemical quenching and 45.22% in the vitality index. The root morpho-anatomy was also altered, with the proportion of vascular bundle area decreasing by 43.50% and a 501.47% increase in aerenchyma formation. Lead accumulation in the roots was 21.54 times higher at the highest concentration compared to the lowest, highlighting the cumulative potential of this organ, while the metal was not detected in the aerial part, indicating the absence of translocation. Despite the negative effects on biomass and physiological parameters, Lactuca sativa L. demonstrated tolerance to lead and potential for rhizofiltration, making it a promising candidate for application in hydroponic systems aimed at treating contaminated wastewater.