The global agricultural productivity has been significantly impaired due to the extensive use of heavy metal. Cadmium (Cd) is now recognized as a significant soil and environmental contaminant that is primarily spread by human activity. This study investigates the possible impact of melatonin (ME) in mitigating the toxicity caused by Cd in pepper (Capsicum annuum L.) seedlings. There were three groups of plants used in the experiment: control (CK) plants, Cd-stressed plants and ME-pretreated + Cd-stressed plants. The concentration of ME and Cd was 1 mu M and 0.1 mM, respectively, and applied as root application. The results described that Cd treatment remarkably reduced growth parameters, impaired pigment concentration, hindered gas exchange traits. In contrast, ME supplementation significantly recovered these parameters by increase in growth and biomass production of pepper seedlings under Cd toxicity. In addition, ME application considerably increased osmolyte production and protein level in pepper leaves and roots. Furthermore, ME positively upregulated the antioxidant enzymes activity and effectively decreased the oxidative damage in pepper leaves and roots. The enhanced antioxidant enzymes activity performed a significant role in the reduction of H2O2 and MDA concentration in plants under Cd stress. The findings indicated that the application of ME to plants effectively alleviates the stress caused by Cd exposure. Moreover, ME demonstrates significant efficacy in mitigating the adverse impacts of Cd on pepper plants.

To uncover the regulatory metabolism of poly-glutamic acid (PGA) in protecting wheat crops against salt stress (SS) at the physiological level, we utilised hydroponic experiments to explore the roles of PGA in regulating the photosynthetic performance, water physiology, antioxidant metabolism and ion homeostasis of wheat seedlings exposed to SS for 10 days. The findings demonstrated that SS inhibited the photosynthetic performance of wheat seedlings. In contrast, different doses of PGA all improved the photosynthetic performance, especially for 0.3% PGA. Compared with SS, 0.3% PGA plus SS decreased nonphotochemical quenching (qN) by 26.3% and respectively increased photosynthetic rate (Pn), soil and plant analyser development (SPAD) value, maximum photochemical efficiency of photosystem II (PSII) (Fv/Fm), photochemical quenching (qP) and actual photochemical efficiency of PSII (Y(II)) by 54.0, 27.8, 34.6, 42.4 and 25.8%. For water metabolism, SS destroyed the water balance of wheat seedlings. In contrast, different doses of PGA enhanced water balance, especially for 0.3% PGA. Compared with SS, 0.3% PGA plus SS decreased leaf water saturation deficit (LWSD) by 35.5% and respectively increased leaf relative water content (LRWC), transpiration rate (Tr), stomatal conductance (gs) and the contents of soluble sugars (SSS) and proline (Pro) by 15.9, 94.7, 37.5, 44.6 and 62.3%. For antioxidant metabolism, SS induced the peroxide damage to wheat seedlings. In contrast, different doses of PGA all mitigated the SS-induced peroxide damage, especially for 0.3% PGA. Compared with SS, 0.3% PGA plus SS respectively decreased superoxide anion (O2-), hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents and electrolyte leakage (EL) by 39.1, 29.6, 46.2 and 36.3%, and respectively increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductases (DHAR) and monodehydroascorbate reductase (MDHAR) activities, and antioxidants ascorbic acid (AsA) and glutathione (GSH) contents by 69.2, 49.2, 77.8, 80.6, 109.5, 121.7, 104.5, 63.8 and 39.6%. Besides, SS destroyed the ion homeostasis of wheat seedlings. In contrast, different doses of PGA all maintained ion homeostasis, especially for 0.3% PGA. Compared with SS, 0.3% PGA plus SS reduced Na+ content creasing K+/Na+, Ca2+/Na+ and Mg2+/Na+ ratios by 177.6, 209.4 and 244.8%. In the above ways, SS inhibited wheat height and biomass. In contrast, different doses of PGA all improved wheat height and biomass under SS, especially for 0.3% PGA. Compared with SS, 0.3% PGA plus SS, respectively, increased wheat height and biomass by 27.4% and 41.7%. In the above ways, PGA mitigated salt toxicity in wheat seedlings. The current findings implied that there