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Recent data indicate that plants, in a manner similar to the situation found in mammalian phagocytotic cells, produce reactive oxygen species (ROS) in response to pathogen infection. This reaction could be very quick when using pre-existing, usually exocellular, components and/or, when biochemical machinery of the cell is activated, relatively late and long-lasting. The oxidative burst is defined as a rapid, transient production of high levels of ROS in response to external stimuli. Two major models depicting the origin of ROS in the oxidative burst are described, namely: the NADPH oxidase system and the pH-dependent generation of hydrogen peroxide by exocellular peroxidases. Additionally, the participation of exocellular ROS-generating enzymes, like germin-like oxalate oxidases and amine oxidases, in plant defence response is demonstrated. The involvement of protoplasmic ROS-generating systems is also indicated.
Low-temperature results in various physiological and metabolic disturbances in cells of plants which are sensitive to low-temperatures. Moringa is getting popularity as a field crop because of its multipurpose usage. There is no information available about effects of low-temperature (14-18℃) on moringa seedlings and its mitigation. The present study was conducted to test the performance of moringa seedling grown in wire house under low-temperature conditions in response to foliar application of moringa leaf extract (3% solution), hydrogen peroxide (5 ml L⁻¹), ascorbic acid (50 mg L⁻¹) and salicylic acid (50 mg L⁻¹). Seeds of six moringa accessions [Local landrace grown at Agronomic Research Area, Z.A Hashmi Hall, Firdous Colony; Exotic landrace grown at Lalazaar Colony, Department of Agronomy and Agronomic Research Area] were collected and grown in polythene bags filled with equal ratio of compost, sand, silt and clay. All foliar treatments were applied twice; the first round at the seedling age one month and the second round at the seedling age two months. Foliar application of moringa leaf extract significantly enhanced number of branches (92%) and leaves (39%), leaf total chlorophyll contents (73%), leaf phenolic contents (53%) and membrane stability index (57%) of moringa seedlings compared to control. Healthy and vigorous growth of moringa seedlings with higher concentration of antioxidants ensured the defensive potential of moringa leaf extract against low-temperature condition.
Two pot experiments were conducted during the two successive seasons of 2014 and 2015 to study the effect of propolis extract at the rates 0, 6000, 7000, 8000 and 9000 mg/L solution used as seed soaking to spinach seedlings on growth, yield and some chemical constituents of spinach plants (Spinacia oleracea L.) grown under calcareous saline soil conditions. The obtained results indicated that increasing the rates of propolis extract as seed soaking application increased the growth parameters of the treated plants. The best result was obtained by the middle rate (7000 mg/L) as seed soaking in both seasons of the study. The same trend was also observed regarding all studied chemical constituents, i.e. chlorophyll a, b and total caroteniods concentration, anthocyanine, total carbohydrates, total and reducing sugars, total free amino acid, free proline, crude protein, total indoles, total phenols, N, P and K in leaves. Moreover, soaking seeds in propolis extract before planting improved the metabolic activity of seeds through the increase in seed values in total and reducing sugars, total free amino acid, total indoles and total phenols as well as the lowest values of total carbohydrate. Thus, the coincident application of propolis extract at (7000 mg/L) as a seed soaking ingredient is recommended for improving growth, yield and chemical composition of spinach plants and for overcoming the adverse effect of saline conditions.
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