Influence of sudden and gradual drought stress (DS) and foliar-applied glycinebetaine (GB) on growth, water relations, osmolyte accumulation and antioxidant defence system were investigated in the plants of two maize (Zea mays L.) cultivars, that is, drought-tolerant Shaandan 9 (S 9 ) and drought-sensitive Shaandan 911 (S 911 ). Sudden DS caused less accumulation of GB and free proline, but a more accumulation of malondialdehyde (MDA), which resulted in a greater reduction in leaf relative water content (RWC) and dry matter (DM) in both cultivars compared with the gradual DS. Exogenous GB application caused a rise in DM, RWC, contents of GB and free proline as well as the activities of SOD, CAT and POD along with a decline in MDA content to various extent in both cultivars under both types of DS. A more pronounced effectiveness of GB application was observed in S 911 than that in S 9 under the same type of DS. It seemed that the more serious damage of DS was on maize plants, and the better positive role of GB was observed in terms of mitigating the adverse effects of DS. From this study, it was possible to propose that hardening for drought resistance by gradual DS treatment and GB application are effective to make plants robust to thrive under water-deficit conditions.

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Abiotic stresses, including nitrogen stress (NS), can hamper photosynthesis and cause oxidative damage to plants. Upregulation of the antioxidative defense system and photosynthesis induced by exogenous glycinebetaine (GB) and humic acid (HA) can mitigate the inhibitory effects of NS on plants. In the present investigation, the beneficial effects of exogenously applied GB and HA were examined on growth, leaf N status, photosynthesis, lipid peroxidation, and activities of some key antioxidant enzymes in the seedlings of maize cv. Zhengdan 958 (ZD958) exposed to NS. NS caused a significant reduction in total dry matter of seedlings of ZD958, but both GB and HA proved effective in mitigating this inhibition, hence, the beneficial effects of GB being more pronounced than those of HA. NS led to a considerable decrease in leaf total N and endogenous GB contents, stomatal conductance (g s ), net photosynthetic rate (P n ), intercellular CO 2 concentration (C i ), and activities of two key C 4 photosynthesis enzymes phosphoenolpyruvate carboxylase (PEPCase) and ribulose-1,5-bisphosphate carboxylase (RuBPCase) as well as of superoxide dismutase (SOD) and peroxidase (POD). This treatment caused an increase in lipid peroxidation, but showed no effect on POD activity. Exogenous application of varying doses of GB resulted in a decrease in lipid peroxidation and C i , and an increase in leaf total N and endogenous glycinebetaine (EGB) content, P n , and activities of RuBPCase, PEPCase, SOD, and catalase (CAT) under NS. In contrast, application of different doses of HA resulted in a decrease in lipid peroxidation, an increase in P n , g s , and C i as well as SOD, CAT, and POD activities without increasing leaf total N and EGB content, and enhanced RuBPCase and PEPCase activities. The present study suggests that exogenous application of GB and HA can induce tolerance in maize plants to NS, but through the regulation of different mechanisms.

Nano-fertilizer has been dubbed ‘the fertilizer of the 21st century’, and it is already being used extensively in agriculture. Zinc oxide nanoparticles (ZnO-NPs) have excellent biological properties and are expected to be an ideal choice for plant zinc fertilizer. Tea is one of the top three beverages in the world, and improving the quality of tea is a priority in its research field. In this study, different concentrations (0, 10, 50, 100, 150, and 200 mg·L−1) of ZnO-NPs were sprayed on tea leaves to investigate their effects on volatile aroma substances and biochemical aspects of tea leaves. The results revealed that various concentrations of ZnO-NPs had different effects on physiological indexes. The concentration of 150 mg·L−1 of ZnO-NPs enhanced chlorophyll content, while the 100 mg·L−1 concentration of ZnO-NPs promoted the accumulation of soluble proteins and the activity of antioxidant enzymes, including a decrease in the content of malondialdehyde. In addition, the ZnO-NPs spray reduced the content of tea polyphenols. A total of 27 volatiles were identified under six treatments, with benzene being the common compound with an average content of 45.97%. Ethanolamine and cis-3-hexenyl acetate were the other two major compounds. It was concluded that the presence of ZnO-NPs improved the antioxidant system of teas, increased soluble protein content and provided better reactive oxygen species protection for plants, especially in the case of ZnO-NPs at 100 mg·L−1. We highlighted that ZnO-NPs application was a favorable way to improve tea trees growth.