Physiological, Morphological, and Biochemical Responses of Soybean [Glycine max (L.) Merr.] to Loquat (Eriobotrya japonica Lindl.) Leaf Extract Application on Pb-Contaminated Soil

Abstract

Lead (Pb) is a non-essential element; however, plants uptake it from soils rich in Pb. Soybean [Glycine max (L.) Merr.] is an important legume crop, and Pb toxicity exerts negative impacts on its growth and yield. This study investigated the role of foliar-applied loquat (Eriobotrya japonica Lindl.) leaf extract in improving the morphological, physiological, and biochemical traits of soybean plants under Pb toxicity. Soybean plants were exposed to four Pb concentrations (0, 200, 400, and 800 µg/L) and supplemented with 0% or 5% loquat leaf aqueous extract (EJLE). Data relating to pigments, proline, total soluble sugars, malondialdehyde (MDA), hydrogen peroxide (H2O2), non-enzymatic antioxidant, i.e., [ascorbic acid (AsA), glutathione (GSH), total phenolic contents (TPC), and total flavonoids content (TFC)] and enzymatic antioxidant, i.e., [superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR)] were recorded. Total chlorophyll contents and carotenoids were significantly decreased by Pb stress, while lycopene and anthocyanin contents were increased. Similarly, proline, total soluble sugars, MDA, H2O2, AsA, GSH, TPC, TFC, SOD, CAT, POD, APX, and GR were increased under Pb stress. Foliar spray of EJLE lowered MDA and H2O2 accumulation and increased the contents of chlorophylls, carotenoids, lycopene, anthocyanins, proline, total soluble sugars, and the antioxidant system. The increase in the activities of antioxidant enzymes lowered the adverse effects of Pb stress in soybean. Similarly, the application of EJLE lowered Pb accumulation in different plant parts compared to those receiving no EJLE. It is concluded that EJLE can improve the Pb tolerance of soybean plants by enhancing morphological, physiological, and biochemical traits. However, the actual mechanisms behind these improvements warrant further investigation.