Assessment of stress reactions of monocotyledonous and dicotyledonous plants in the presence of bioavailable lead compounds by the example of lettuce (Lactuca sativa L.) and spring wheat (Triticum aestivum L.)

Relevance. The increasing demand for vegetable crops stimulates the development of their year-round production, including both open and protected ground systems. However, man-made pollution with heavy metals, in particular lead, poses a serious threat to the safety of crop production. Lead is one of the priority pollutants of agricultural soils and substrates, since even at concentrations up to 50 mg/kg it can cause phytotoxicity and accumulate in the commercial part of the crop. Materials and Methods. Lettuce (Lactuca sativa L.) of the Azart variety and wheat (Triticum aestivum L.) of the Ivolga variety were used as model objects of research. The plants were cultivated in a hydroponic system using sterilized peat as a substrate. Lead Acetate (Pb(CH3COO)2) was applied in three con- centrations: 0 (control), 25 and 50 mg/kg. The experiment was carried out in three repetitions. On the 7th and 45th days of cultivation, biometric parameters (wet and dry plant mass), the content of photosynthetic pigments (chlorophylls a, b and carotenoids), the concentration of lead in roots and aboveground organs were determined by atomic emission spectroscopy (ICP-AES), as well as the activity of key antioxidant enzymes, catalase (CAT) and superoxide dismutase (SOD). Results. At the initial stage of the experiment (day 7), no significant differences in biometric parameters were found between the cultures. By day 45, with an average concentration of lead, the decrease in the crude weight of wheat was 4.9 % less than in lettuce, with a maximum concentration (50 mg/kg), the lettuce growth depression reached 29.7 %, while in wheat the indicators were significantly lower. Accumulation analysis showed that wheat mainly localizes lead in the root system, demonstrating a pronounced barrier function, while lettuce has a more uniform distribution of metal between roots and shoots. The study of antioxidant enzymes revealed that, with increased stress, catalase activity increases and superoxide dismutase decreases in both crops, while lettuce is dominated by CAT activity and wheat by SOD, which indicates the preservation of enzymatic balance and adaptive regulation of the level of reactive oxygen species.